WO2011133040A2

WO2011133040A2 - Replication-competent adenoviruses

Info

Publication number: WO2011133040A2
Application number: PCT/NL2011/050281
Authority: WO
Inventors: Christie Vermeulen; Victor Willem Van Beusechem; Nikki Tol
Original assignee: Orca Therapeutics B.V.
Priority date: 2010-04-23
Filing date: 2011-04-26
Publication date: 2011-10-27
Also published as: WO2011133040A3

Abstract

The invention provides a replication competent adenovirus, being capable of replicating and having lytic capacity in a host cell, the virus genome comprising at least one DNA sequence coding for a silencing factor functional in reducing expression and/or activity of a target gene in the host cell. The invention further provides a kit of parts comprising a silencing factor and a replication competent adenovirus and a cell comprising a silencing factor and a replication competent adenovirus. In addition, the invention provides use of the kit of parts and the cell according to the invention.

Description

Title: Replication-competent adenoviruses.

Field of the invention.

The present invention relates to the fields of genetic modification, biotechnology and medicine. In particular, the invention provides recombinant adenoviruses with a potency to suppress expression of one or more target genes in cells in which they replicate, thereby causing said viruses to more effectively replicate in said cells and to more effectively cause lysis of said cells. The invention thus provides efficient means to eradicate certain populations of cells.

The adenovirus replication process constitutes the following steps: (1) infection of the host cell by binding of the adenovirus particle to the cell surface, internalization and transport towards the cell nucleus, and import of the adenovirus DNA genome into the cell nucleus; (2) expression of adenovirus proteins encoded by the early regions in the adenovirus genome; (3) replication of the adenovirus genome, which marks the transition of the early replication phase to the late replication phase; (4) expression of adenovirus proteins encoded by the late regions in the adenovirus genome; (5) assembly of progeny adenovirus particles and inclusion of progeny adenovirus genomes into these particles; and (6) induction of cell death, leading to release of adenovirus progeny from the cell.

During their life cycle, adenoviruses modulate cell death pathways. In different cell lines, p53 dependent as well as p53 independent apoptosis has been documented after adenovirus infection (Teodoro and Branton, J. Virol.

71(1997):1739-1746; and references therein). During the early replication phase, cell death is suppressed to prevent premature cell death, thereby allowing the adenovirus to complete its life cycle in the cell. In contrast, at late stages of infection cell death and lysis are promoted to release the virus progeny from the cell.

Replication competent viruses, in particular adenoviruses, are finding increasing utility for the treatment of cancer and other diseases involving inappropriate cell survival. In particular, conditionally replicating adenoviruses (CRAds) have been developed to selectively replicate in and kill cancer cells. Such cancer-specific CRAds represent a novel and very promising class of anticancer agents (reviewed by Heise and Kirn, J. Clin. Invest. 105(2000):847-851; Alemany et al., Nat. Biotech. 18(2000):723-727; Gomez-Navarro and Curiel, Lancet Oncol. 1(2000):148-158). The tumor- selective replication of this type of CRAds is achieved through either of two alternative strategies. In the first strategy, the expression of an essential early adenovirus gene is controlled by a tumor- specific promoter (e.g., Rodriguez et al., Cancer Res. 57(1997):2559-2563; Hallenbeck et al., Hum. Gene Ther. 10(1999):1721-1733; Tsukuda et al., Cancer Res.

62(2002):3438-3447; Huang et al., Gene Ther. 10(2003):1241-1247; Cuevas et al., Cancer Res. 63(2003):6877-6884). The second strategy involves the introduction of mutations in viral genes to abrogate the interaction of the encoded RNA or protein products with cellular proteins, necessary to complete the viral life cycle in normal cells, but not in tumor cells (e.g., Bischoff et al., Science 274(1996):373- 376; Fueyo et al., Oncogene 19(2000):2-12; Heise et al., Clin. Cancer Res.

6(2000):4908-4914; Shen et al., J. Virol. 75(2001:4297-4307; Cascallo et al., Cancer Res. 63(2003):5544-5550). During their replication in tumor cells, CRAds destroy cancer cells by inducing lysis, a process that is further referred to as "oncolysis". The release of viral progeny from lysed cancer cells offers the potential to amplify CRAds in situ and to achieve lateral spread to neighboring cells in a solid tumor, thus expanding the oncolytic effect. The restriction of CRAd replication to cancer or hyperproliferative cells dictates the safety of the agent, by preventing lysis of normal tissue cells. Currently, CRAd-based cancer treatments are already being evaluated in clinical trials (e.g., Nemunaitis et al., Cancer Res. 60(2000):6359- 6366; Khuri et al., Nature Med. 6(2000):879-885; Habib et al., Hum. Gene Ther. 12(2001):219-226).

However, despite very encouraging results from in vitro and animal studies, the anti-cancer efficacy of replicative adenovirus as a therapeutic agent in humans has been limited. Thus, there is a clear need in the field of cancer treatment to increase the potency of replication- competent adenoviruses as oncolytic agents. This could be achieved by enhancing their replication and lysis capacities.

Therefore, the invention provides a replication competent adenovirus, being capable of replicating and having lytic capacity in a host cell, the virus genome comprising at least one DNA sequence coding for a silencing factor functional in reducing expression and/or activity of a target gene in the host cell, said virus further provided with one or more expression control sequences that mediate expression of the DNA sequence in the host cell, whereby the target gene is selected from the genes depicted in Table 1 or Table 6. The adenovirus according to the invention has enhanced capacity to kill the host cell by reduction of expression and/or activity of a target gene selected from Table 1 or Table 6. This enhanced capacity to kill the host cell is not mediated by modulation of p53 activity.

A replication competent adenovirus, as defined herein, is a virus which comprises, as part of its genome, the function to be replicated in the host cell, wherein replication is dependent on the replication functions provided by the virus, in combination with the endogenous cellular machinery of the host cells. The genome of the host cells does therefore not need to have exogenous sequences encoding factors that are necessary for viral replication. The term "endogenous" means in this respect that the cellular machinery (including the coding sequences therefore), necessary for virus replication, is the naturally present machinery, e.g. not introduced in the cells by manipulation techniques by man. The latter are defined as "exogenous". Replication functions, as defined, are factors such as proteins, encoded by the virus, necessary for replication of the virus in the host cells and are herein also referred to as viral replication factors. Said factors may be endogenous for the said virus, but may also be functional analogues, encoded by the viral genome, e.g. in cases for instance wherein the gene encoding the endogenous viral factor is deleted from the viral genome. It is important to note that these factors are encoded by the viral genome and need not be

complemented by exogenous factors. Thus, viruses, of which the replication is dependent on one or more replication functions, being deleted from the virus, but introduced in the host cell, are defined to be replication deficient, and are therefore not part of the present invention. The invention as claimed relates to replication competent viruses, i.e. wherein the viral genes encoding viral replication factors, essential for regulation of virus replication in the host cells are present on the viral genome. A replication competent adenovirus according to the invention is preferably generated from the genome of viruses through genetic engineering. This genetic engineering often involves insertion of heterologous DNA, including but not limited to DNA encoding a therapeutic product, into the adenovirus genome. It is to be understood, however, that the term replication competent adenovirus is also meant to include virus from which parts of the virus genome have been removed, besides the insertion of at least one DNA sequence coding for a silencing factor functional in reducing expression of a target gene in the host cells. Another example of a replication competent adenovirus is a chimeric virus containing parts of the genomes of different viruses or of different types of the same virus, such as e.g. different serotype adenoviruses or adenoviruses with different host animal species specificities.

The genes listed in Table 1 were selected because reducing the expression and/or activity of any one of these genes in a host cell that was infected with a replication competent adenovirus resulted in enhanced cell kill. This enhanced cell kill was significantly stronger in the presence of a replication competent adenovirus than in the absence of a virus that could replicate in the cell. The term "reducing expression and/or activity" is used to indicate a reduced functional presence of a protein product of a gene in a cell, which is due to either a reduced level of expression or a reduced level of activity of the protein. Said reduced functional presence preferably results in a reduction of more than 50% of the protein amount and/or activity, more preferred a reduction of more than 70% of the protein amount and/or activity, more preferred a reduction of more than 80% of the protein amount and/or activity, more preferred a reduction of more than 90% of the protein amount and/or activity, more preferred a reduction of more than 95% of the protein amount and/or activity, most preferred a reduction of more than 99% of the protein amount and/or activity, compared to the corresponding protein activity in a related cell not comprising the at least one silencing factor functional in reducing expression of a target gene.

In a preferred embodiment, a gene of which the expression and/or activity is reduced in a host cell has no residual activity and is equivalent to a knock-out gene. The term knock-out gene refers to a gene that has been made inoperative. The term gene includes enhancer/promoter regions, introns and exons. A gene can be made knock-out or functionally inactive by partial or complete alteration of at least one exon, or of the promoter region. Said alteration results in a deletion or the introduction of a premature translation stop through frame shift or nonsense mutations.

In a further preferred embodiment, the target gene is selected from the genes depicted in Table 2. The genes depicted in Table 2 comprise a subset of the genes listed in Table 1. It was found that a reduced expression of any one of the genes listed in Table 2 in a cell resulted in enhanced adenovirus-induced cell death. Reduced expression of any of the genes depicted in Table 2 resulted in enhanced replication of the virus and/or enhanced lysis of the target cells. In an even further preferred embodiment, the target gene is selected from the genes depicted in Table 3, more preferably in Table 4. A particularly preferred target gene depicted in Tables 1 through 4 is POT1. Other preferred target genes are interaction partners of POT1, in particular those depicted in Table 6. Among these, particularly preferred target genes are TERF2IP and TNKS. An "interaction partner" of POT1 is a protein that interacts with POT1, where the interaction is not limited to a particular kind of interaction. Non- limiting examples of different kinds of interactions between two proteins include, e.g., a first protein that physically interacts with a second protein by binding with a certain affinity; a first protein that changes the activity of a second protein, e.g., through enzymatic modification; a first protein that changes the subcellular localization of a second protein; and a first protein that changes the expression of a second protein, e.g., via binding to the promoter of a gene encoding the second protein. In these examples, the interaction partner of POT1 can be the first or the second protein.

In a further preferred embodiment, the at least one DNA sequence coding for a silencing factor functional in reducing expression of a target gene in the host cells comprises at least two DNA sequences coding for a silencing factor functional in reducing expression of a target gene in the host cells such as at least three DNA sequences, at least four DNA sequences, at least five DNA sequences or at least six DNA sequences. The at least two DNA sequences coding for a silencing factor functional in reducing expression of a target gene may comprise different DNA sequences targeting the same target gene, or different DNA sequences targeting different target genes, or a combination thereof.

In one embodiment, the silencing factor is a protein that interferes with the product encoded by the target gene including, but is not limited to, an antibody or functionally active part or variant thereof such as a Fab fragment or a single chain Fv fragment that is directed against a protein encoded by a target gene. Intracellular expression of an antibody or functionally active part or variant thereof may sequester the protein encoded by a target gene such that the target is functionally inactivated. Alternatively, said protein is an altered protein encoded by a target gene, such as a truncated protein that acts in a dominant- negative way after expression in said cell or cell line and thereby functionally inactivates the target gene in said cell or cell line. In a preferred embodiment, the silencing factor is an antisense nucleic acid preferably comprising a stretch of more than 50 nucleic acid molecules that are antisense to and can base pair with an RNA transcript from a target gene. Expression of antisense RNA often leads to the formation of double stranded RNA molecules, comprising the antisense RNA and the endogenous sense mRNA. This double stranded RNA molecule prevents the mRNA from being translated into protein. As an alternative, the antisense nucleic acid may promote exon skipping of a target gene in a host cell such that a non-functional protein is produced in a substantial amount, thereby reducing functional expression of the target gene.

In a further preferred embodiment, the silencing factor is a ribozyme, preferably a full length hammerhead ribozyme, or a recombinant zinc finger protein that downmodulates expression from a target gene. Said zinc finger protein is capable of binding specifically to a promoter region or enhancer region of a target gene, thereby inhibiting or preventing transcriptional activation of said target gene, for example by competing with a positively acting transcription factor. Said zinc finger protein comprises a sequence-specific zinc finger DNA binding domain and preferably a negative acting transcription domain

(transcriptional repressor domain) which acts in a dominant way to inhibit or prevent transcription of a target gene such as, for example, a Kruppel-associated box domain.

In a further preferred embodiment, the silencing factor mediates reduced expression of a target gene through enhanced mRNA degradation or translation suppression employing RNA interference (RNAi). RNAi is based on the

generation of short, double-stranded RNA (dsRNA) which activates a cellular process leading to a highly specific RNA degradation (Zamore et al., 2000. Cell 101: 25-33) and/or suppression of translation. For the purpose of the invention, the dsRNA molecules that activate RNAi and their precursors that are processed in a cell to generate dsRNA molecules that activate RNAi are referred to as "RNAi molecules". Recent studies have demonstrated that RNA interference is mediated by the generation of 18-to 23-nucleotide dsRNA molecules with 2 nucleotide-long 3' overhangs termed small interfering RNA (siRNA) duplexes. RNAi allows silencing of a gene on the basis of its sequence. Preferably, an RNAi molecule is a molecule that can activate an RNAi process in a cell either directly or indirectly because it is a precursor of a molecule that can activate an RNAi process in a cell. Said precursor molecule is preferably an shRNA or a pre- or pri- miRNA or variants or analogues thereof.

The silencing factor preferably is an RNAi molecule, for example a short hairpin RNA (shRNA) or a miRNA precursor. A short hairpin RNA (shRNA) typically comprises a 50-100 nucleotide long RNA molecule comprising two stretches of nucleotides that are complementary and can base-pair, whereby the two stretches are interconnected through a hairpin turn. The shRNA hairpin structure is cleaved by the cellular machinery into 18-23 (typically 19) nucleotide- long double stranded siRNA molecules with 2 nucleotide-long 3' overhangs with one of the strands exhibiting extensive complementary homology to a part of a mRNA transcript from a target gene. Said siRNA activates the RNA interference (RNAi) pathway and interferes with the expression of said target gene by specific mRNA degradation. Expression of the shRNA can be driven by a polymerase II or polymerase III enhancer/promoter. Natural miRNA molecules are typically transcribed by polymerase II as pri-miRNA with a cap and poly-A tail and processed to short, 70-nucleotide stem-loop structures known as pre-miRNA in the cell nucleus. These pre-miRNAs are then processed to mature double stranded miRNAs of about 18-25 nucleotides in the cytoplasm which silence gene expression via RNA interference, partly by specific RNA degradation and partly by suppressing translation. Pri-miRNAs and pre-miRNA molecules are also useful silencing factors according to the invention. Artificial miRNAs can be transcribed from any promoter, for example a polIII promoter, in a format analogous to that of a shRNA. They then differ from a shRNA in that the double- stranded region is not completely complementary.

A preferred RNAi molecule according to the invention comprises a double stranded region of between 18 nucleotides and 25 nucleotides per strand, such as 18 nucleotides, 19 nucleotides, 20 nucleotides, 21 nucleotides. 22 nucleotides, 23 nucleotides, 24 nucleotides, or 25 nucleotides. A most preferred RNAi molecule according to the invention comprises a double stranded region that has a length of 19 nucleotides after processing into a mature siRNA.

In a preferred embodiment, said adenovirus is a replication-competent, oncolytic adenovirus that has been developed to specifically replicate in cancer cells. Said replication- competent adenovirus can be replicated and packaged in any suitable cell or cell line that sustains replication of the adenovirus.

Said adenovirus is preferably an adenovirus serotype 5, an adenovirus serotype 24 , an adenovirus serotype 35, or an adenovirus serotype 51 based virus, or a chimaeric adenovirus, for example based on a serotype 5 with serotype 35 tropism by replacing a part of the serotype 5 fiber with a part of the fiber of serotype 35. Said adenovirus may further provide expression of a therapeutic transgene such as, preferably, p53, a vaccine, or a secreted protein such as a growth factor. Said adenovirus is replication competent, in particular oncolytic. Said adenovirus is a human or primate adenovirus for infection of, and replication in, human and primate cells. Said adenovirus is another mammalian adenovirus, for example a canine or equine adenovirus for infection of, and replication in, dog cells or horse cells, respectively.

A preferred adenovirus according to the invention is a human adenovirus, preferably of serotype 5.

Replication competent adenoviruses can replicate in many different cells in an animal body, provided that they are derived from adenoviruses with the correct species tropism and that said cells express surface receptors for said adenoviruses. Specific cell surface recognition by recombinant adenoviruses including replication competent adenoviruses can be changed by pseudotyping or targeting, as is known to the skilled person.

In a further preferred embodiment, a replication competent adenovirus according to the invention is a conditionally replicating adenovirus (CRAd). A CRAd will only replicate in cells in which the particular conditions exist that are required for replication of the CRAd. CRAds are designed to meet the specific requirements for replication in a chosen type of cell and not in other types of cells. This property makes CRAds particularly useful for several embodiments of the present invention where the intend is to treat a disease by specific lytic replication of the recombinant adenovirus according to the invention in diseased cells in an animal or human body resulting in specific removal of said diseased cells from said body. A CRAd comprises an adenoviral genome from which one or more parts that are necessary for efficiently completing at least one step of the adenovirus infectious life cycle under certain physiological conditions (herein also "first conditions") but not under certain other physiological conditions (herein also "second conditions") have been modified, removed or have been otherwise engineered to be not expressed under the first conditions. Said first and second conditions could, e.g., be dictated by the physiological conditions that exist in a particular type of cells (herein also "first cells"), but not in another type of cells (herein also "second cells"). Such a first type of cell is e.g. a cell derived from a particular type of tissue, where said cell contains a protein that is not or much less present in cells from other tissues (second type of cells). An example of a second type of cell is a cell that has lost proper cell growth control, such as e.g. a cancer cell, where said cell either lacks a protein that is present in cells that have not lost proper cell growth control or where said cell has gained expression (or over-expression) of a protein that is not or much less present in cells that have not lost proper cell growth control. Another example of a second condition is a condition that exist in a particular stage of the cell cycle or in a particular developmental stage of the cell, where a certain protein is expressed specifically. Thus, CRAds can be designed such, that replication thereof is enabled in particular cells, such as cancer cells or a particular type of cancer cells, whereas in normal cells, replication of CRAds is not possible, or strongly reduced. A preferred CRAd is provided by an adenovirus according to the invention, wherein said adenovirus comprises at least one mutation in one or more genes from the group consisting of E1A, E1B, E4, and VA-RNAs, to achieve selective replication in tumors. An adenovirus according to the invention preferably carries a mutation in the E1A region encompassing at least a part of the CR2 domain of E1A, preferably a deletion encompassing amino acids 122 to 129 (LTCHEAGF) of E1A. The term gene, as used herein, comprises the complete genomic region that is required for expression of a gene including, for example, the enhancer/promoter region and intronic en exonic sequences.

An adenovirus according to the invention may further comprise mutations that increase its replication potential, such as e.g. retention of the E3 region (Suzuki et al., Clin. Cancer Res. 8(2002):3348-3359) or deletion of the E1B-19K gene (Sauthoff et al. Hum. Gene Ther. ll(2000):379-388), or that increase the replication selectivity for a certain type of cells, including but not limited to the modifications to make CRAds (supra), or that reduce the immunogenicity (i.e., their potency to induce an immune response when introduced into an animal body), such as e.g. retention of the E3B region (Wang et al., Nature Biotechnol. 21(2003):1328-1335).

An adenovirus according to the invention may further be modified to express one or more transgenes, such as e.g. a gene encoding a cytokine, a pro- apoptotic protein, an anti- angiogenic protein, a membrane fusogenic protein or a prodrug converting enzyme; or such as e.g. a gene encoding a cytokine, a pro- apoptotic protein, an anti- angiogenic protein, a membrane fusogenic protein or a prodrug converting enzyme.

Methods to select an RNAi molecule useful in the invention, preferably a short hairpin RNA (shRNA) or a miRNA precursor, that is capable of reducing expression of a target gene in a host cell are known in the art. Criteria that can be used to select one or more sequences of a target gene (the targeted region) for incorporation into the double- stranded part of the RNAi molecule are known in the art. For example, the targeted region is preferably located 50-100 nucleotides downstream of the start codon (ATG); is selected from an exon sequence since RNAi only works in the cytoplasm; sequences with > 50% G+C content or sequences with stretches of 4 or more nucleotide repeats are avoided as are sequences that share a certain degree of homology with another related or unrelated gene. Based on these or similar criteria, the skilled person is able to select one or more targeted regions of a target gene for generating the

corresponding RNAi molecule. Testing one or more, preferably at least four, of the selected potential RNAi molecules for reducing expression of the

corresponding target gene in a host cell, will provide the skilled person with one or more RNAi molecules that reduce expression of a target gene in a host cell.

In a specific embodiment, the at least one DNA sequence coding for a silencing factor in an adenovirus according to the invention comprises at least one of the sequences listed in Table 5 or in Table 7.

Expression control sequences for expression of a silencing factor in a target cell preferably comprise a polymerase II or polymerase III enhancer/promoter. A preferred polymerase II promoter for expression of a pri-miRNA is a selective RNA polymerase II promoter, such as a tissue-specific or a cell-specific promoter that directs expression of the silencing factor specifically or exclusively in the target cell. Expression control sequences for expression of a silencing factor preferably also comprise transcriptional stop sequences such as a poly(A) signal for polymerase II-mediated expression, and a termination signal such as a stretch of at least 4 consecutive thymidine nucleotides for polymerase Ill- mediated expression.

A preferred polymerase II promoter is selected from a CMV promoter, the immediate early gene of human cytomegalovirus, the SV40 promoter, and the long terminal repeat of Rous sarcoma virus. Another preferred promoter comprises regulatable elements, such as tetracycline, radiation or hormone regulated elements allowing control of the timing and level of transcription driven by the promoter. Preferred expression control sequences according to the invention comprise a selective RNA polymerase II promoter.

In another embodiment, the one or more expression control sequences in an adenovirus according to the invention comprise a RNA polymerase III promoter. Preferred polymerase III promoter sequences are selected from the group consisting of 5S rRNA, tRNAs, VA RNAs, Alu RNAs, HI, and U6 small nuclear RNA promoter sequences. A preferred host cell for an adenovirus according to the invention, is a cancer cell. The term cancer refers to malignant primary and/or metastasized cancers. Examples of a cancer include, but are not limited to, a carcinoma; a sarcoma, a lymphoma, a leukemia, or a myeloma. A cancer can be present in any tissue or part of a body, including but not limited to bone, brain, eye, breast, skin, bladder, lung, ureter, urethra, thyroid, parathyroid, salivary gland, kidney, prostate, genital system including ovary and testis, endometrium,

blood/hematologic system, or in a gastrointestinal tissue. In a preferred embodiment said cancer is a prostate cancer. The invention further provides an adenovirus according to the invention for use as a medicament. The invention further provides an adenovirus according to the invention for use as a medicament for the treatment of cancer, preferably prostate cancer. Adenoviruses are propagated according to standard methods in the fields of adenovirology and adenoviral vectors. The preferred method of propagation is by infecting a suitable cell line that allows replication of adenoviruses. An example of a method for generating adenoviruses may further comprise the steps of collecting the cells when they show cytopathic effect, indicative of virus production and freeze-thawing of the cells to generate a cellular extract. The virus is purified from the cellular extract using standard techniques, e.g. banding on a cesium chloride gradient and dialysis, for example against Phosphate-Buffered Saline- 10% glycerol. The dialyzed virus may be aliquoted and stored at -80 °C. The quantification of the number of plaque- forming adenovirus particles and units is performed according to standard protocol. A saline phosphate buffer with 10% glycerol is a standard formulation for the storage of adenovirus

The adenovirus can be administered to an animal or human body to infect cells in vivo. Administration can be done via several routes including, but not limited to, locoregional injection into the tumor or into a body cavity where the tumor is located, injection into the blood circulation, inhalation and application to the surface of a certain body area. Following infection, the replication competent adenovirus can replicate and spread to other cells, provided that the infected cells support replication of said recombinant adenovirus. The replication competent adenovirus can thus be used to re-infect new cells to further propagate and expand said replication competent adenovirus.

The adenovirus preferably is formulated into an aqueous or solution medium for the preservation of viral particles which can directly be administered to an organism. The formulation preferably comprises pharmaceutical acceptable salts and excipients such as, for example, human serum albumin, sugars such as sucrose and mannitol, and/or a surfactant such as, for example, a difunctional block copolymer surfactant terminating in primary hydroxyl groups (Pluronic ¥68™).

In one embodiment, a replication competent adenovirus according to the invention further comprises an expression cassette that mediates expression of one or more RNAi-mediating molecules that are specific for one or more p53 antagonists and/or inhibitors of the p53 pathway or a combination thereof in a cell.

Cancer cells and cell lines are the result of neoplastic transformation. The genetic events underlying neoplastic transformation include activation of proto- oncogenes and inactivation of tumor-suppressor genes. A major player in this respect is the gene encoding the tumor-suppressor protein p53. The p53 protein is the central coordinator of damage-induced cell-cycle checkpoint control. In a perturbed cell, p53 can induce growth arrest and cell death. p53 exerts these effects by functioning as a specific transcription factor that controls the expression of a large panel of genes involved in growth control, DNA repair, cell- cycle arrest, apoptosis promotion, redox regulation, nitric oxide production, and protein degradation (Polyak et al., Nature 389(1997):237-238; El-Deiry, Sem. Cancer. Biol. 8(1998):345-357; Yu et al., Proc. Natl. Acad. Sci. USA

96(1999):14517-14522; Hupp et al., Biochem. J. 352(2000):1-17; and references therein). The induction of cell death by p53 is mediated at least in part by activation of pro-apoptotic death genes of the bcl-2 family, such as bax, bak, bad, bid, bik, bim, bok, blk, hrk, puma, noxa and bcl-xS (Miyashita and Reed, Cell 80(1995):293-299; Han et al., Genes Dev. 10(1996):461-477; Zoernig et al., Biochim. Biophys. Acta 1551(2001):F1-F37). On the other hand, anti- apoptotic members of the bcl-2 family, such as bcl-2 itself and bcl-xL, bcl-w, bfl-1, brag-1 and mcl-1 inhibit p53-dependent cell death (Zoernig et al., supra). The anti- apoptotic protein Bax Inhibitor- 1 (BI-1) suppresses apoptosis through interacting with bcl-2 and bcl-xL (Xu and Reed, Mol. Cell l(1998):337-346). The immediate effector proteins of p53 as well as p53 itself target mitochondria, thereby releasing cytochrome c into the cytosol to activate the caspase cascade via the initiator caspase- 9/Apaf-l complex (Juergensmeier et al., Proc. Natl. Acad. Sci. USA 95(1998):4997-5002; Fearnhead et al., Proc. Natl. Acad. Sci. USA

95(1998):13664-13669; Soengas et al., Science 284(1999):156-159; Marchenko et al., J. Biol. Chem. 275(2000):16202-16212). Negative regulators of the caspase cascade include but are not limited to members of the Inhibitor of Apoptosis Protein (IAP) family of proteins, such as cIAPl, cIAP2, cIAP3, XIAP and survivin (Zoernig et al., supra).

Previously, we found that oncolysis and release of adenovirus progeny from infected cancer cells can be accelerated by restoring p53 functions in said cancer cells (van Beusechem et al., Cancer Res. 62(2002):6165-6171; WO 03/057892, incorporated by reference herein). Said restoring of p53 functions is done by expressing in said cancer cells a restoring factor, i.e. a functional factor of the p53-dependent apoptosis pathway, the function whereof is not or insufficiently expressed in said cancer cells, wherein said restoring factor preferably comprises a protein (WO 03/057892). Hence, said restoring factor is an essential positive component of the p53-dependent apoptosis pathway.

A loss of normal function of p53 is associated with resistance to

programmed cell death, cell transformation in vitro and development of cancers in vivo. In approximately 50% of human cancers the gene encoding p53 is nonfunctional through deletion or mutation (Levine et al, Nature 351(1991):453-456; Hollstein et al, Science 253(1991):49-53; Chang et al, J. Clin. Oncol.

13(1995):1009-1022). In many of the other 50% cancer cells that do express wild- type p53 protein, p53 function is still hampered by the action of a p53 antagonist. An example of a p53 antagonist is MDM2. Loss of the tumor-suppressor protein pl4ARF or overexpression of MDM2 protein can lead to functional inactivation of p53 by binding to the MDM2 protein and subsequent degradation. In addition, even if p53 function itself is intact, p53-dependent cell death can be hampered due to overexpression of anti-apoptotic proteins acting on the p53 pathway downstream from p53, such as the anti-apoptotic bcl-2 and IAP family members and BI-1. Another example is p73DeltaN, which binds to p53-responsive promoters competing with p53, thereby antagonizing p53- dependent cell death (Kartasheva et al, Oncogene 21(2002):4715-4727). The expression of one or more RNAi- mediating molecules that are specific for one or more p53 antagonists and/or inhibitors of the p53 pathway or a combination thereof in a cell will enhance the lysogenic activity in a target cell that comprises functional p53.

Said antagonists and/or inhibitors of the p53 pathway are preferably selected from synoviolin, MDM2, Pirh2, COP1, Bruce, HPV-E6, herpesvirus-8 LANA, Pare, Mortalin, Plk-1, BI-1, p73DeltaN, bcl-2, bcl-xL, bcl-w, bfl-1, brag-1, mcl-1, cIAPl, cIAP2, cIAP3, XIAP and survivin. The expression cassette further comprises one or more expression control sequences, functional in the said host cells such as an enhancer/promoter and a terminator that are operably linked to the one or more RNAi-mediating molecules. As an alternative, the expression of the one or more p53 antagonists and/or inhibitors of the p53 pathway or a combination thereof is operably linked to the control elements that mediate expression of the at least one DNA sequence coding for a silencing factor functional in reducing expression of a target gene in the host cells. It has been found that a cancer cell can contain more than one p53 antagonists and/or inhibitors of the p53 pathway. Such cells are more effectively lysed when they are provided by RNAi against at least two of those p53 antagonists and/or inhibitors of the p53 pathway. In a further embodiment, a replication competent adenovirus according to the invention further comprises a DNA sequence that encodes at least one restoring factor functional in restoring the p53 dependent apoptosis pathway in the host cells, operably linked to one or more expression control elements, functional in the host cells. Said restoring factor preferably is selected from the pro-apoptotic death genes of the bcl-2 family, such as bax, bak, bad, bid, bik, bim, bok, blk, hrk, puma, noxa and bcl-xS (Miyashita and Reed, Cell 80(1995):293-299; Han et al., Genes Dev. 10(1996):461-477; Zoernig et al., Biochim. Biophys. Acta 1551(2001):F1-F37), and/or p53, or a functional part or derivative thereof. A preferred restoring factor functional in restoring the p53 dependent apoptosis pathway is p53.

In a further embodiment, the invention provides a kit of parts comprising at least a silencing factor functional in reducing expression and/or activity of a target gene in a host cell and a replication competent adenovirus, whereby the target gene is selected from the genes depicted in Table 1, Table 2, Table 3, Table 4, or Table 6.

Further provided is a kit of parts according to the invention for use as a medicament. Said medicament preferably is for treatment of cancer, preferably a prostate cancer. In a preferred embodiment, a kit of parts comprises at least one DNA sequence encoding a silencing factor functional in reducing expression and/or activity of a target gene depicted in Table 1, Table 2, Table 3, Table 4, or Table 6. Also provided is a silencing factor functional in reducing expression and/or activity of a target gene selected from the genes depicted in Table 1, Table 2, Table 3, Table 4, or Table 6, for use as a medicament for the treatment of a disease, wherein the disease is further treated with a replication competent adenovirus. Said silencing factor is preferably selected from a protein that interferes with the product encoded by the target gene including, but is not limited to, a recombinant zinc finger protein that downmodulates expression from a target gene and an antibody or functionally active part or variant thereof such as a Fab fragment or a single chain Fv fragment; an antisense nucleic acid preferably comprising a stretch of more than 50 nucleic acid molecules that are antisense to and can base pair with an RNA transcript from a target gene; a ribozyme, preferably a full length hammerhead ribozyme; a short, double- stranded RNA that induces RNAi-mediated silencing of a target gene such as an siRNA or a miRNA; or a small molecule.

In one embodiment, the invention provides a cell comprising an adenovirus according to the invention. In a further embodiment, the invention provides a cell comprising at least one silencing factor functional in reducing expression and/or activity of at least one target gene in the cell and a replication competent adenovirus, whereby the at least one target gene is selected from the genes depicted in Table 1, Table 2, Table 3, Table 4, or Table 6. The invention further provides the use of a cell comprising at least one silencing factor functional in reducing expression and/or activity of at least one target gene selected from Table 1, Table 2, Table 3, Table 4, or Table 6 and a replication competent adenovirus for propagation of said replication competent adenovirus. In a preferred embodiment, said adenovirus is a conditionally replicating adenovirus (CRAD).

In one embodiment, a silencing factor in a kit of parts according to the invention or a cell according to the invention is selected from a protein that interferes with the product encoded by the target gene including, but is not limited to, a recombinant zinc finger protein that downmodulates expression from a target gene and an antibody or functionally active part or variant thereof such as a Fab fragment or a single chain Fv fragment, an antisense nucleic acid preferably comprising a stretch of more than 50 nucleic acid molecules that are antisense to and can base pair with an RNA transcript from a target gene, a ribozyme, preferably a full length hammerhead ribozyme, and a short, double- stranded RNA that induces RNAi-mediated silencing of a target gene such as an siRNA or a miRNA.

The silencing factor in a kit of parts according to the invention or a cell according to the invention is preferably a small molecule that inhibits the activity of a product of one or more of the target genes depicted in Table 1, Table 2, Table 3, Table 4, or Table 6. Examples of small molecules are provided in Tables 1-4 and comprise digoxin, omeprazole, ethacrynic acid, and/or perphenazine for inhibition of ATP1A2; abiraterone acetate, and/or ketoconazole for inhibition of CYP17A1; aliskiren, and/or aliskiren/valsartan for inhibition of renin; epothilone B, ixabepilone, colchicine/probenecid, XRP9881, E7389, AL 108, EC145, NPI-

2358, milataxel, TPI 287, TTI-237, docetaxel, vinflunine, vinorelbine, vincristine, vinblastine, paclitaxel, podophyllotoxin, and/or colchicine for inhibition of tubulin alpha 8; allopurinol and/or febuxostat for inhibition of xanthine dehydrogenase. Another example is telomestatin that decreases the binding of POT1 and TERF2 to telomeres (Tahara et al., Oncogene 25(2006):1955-1966; Gomez et al., J. Biol. Chem. 281(2006):38721-38729; Gomez et al., Cancer Res. 66(2006):6908-6912).

In a further embodiment, the silencing factor in a kit of parts according to the invention or a cell according to the invention is transduced by a virus, preferably a retrovirus, more preferably a lentivirus. Said silencing factor is preferably selected from a protein that interferes with the product encoded by the target gene including, but is not limited to, a recombinant zinc finger protein that downmodulates expression from a target gene and an antibody or functionally active part or variant thereof such as a Fab fragment or a single chain Fv fragment; an antisense nucleic acid preferably comprising a stretch of more than 50 nucleic acid molecules that are antisense to and can base pair with an RNA transcript from a target gene; a ribozyme, preferably a full length hammerhead ribozyme; a short, double- stranded RNA that induces RNAi-mediated silencing of a target gene such as an siRNA or a miRNA.

The invention further provides a method of lysing a cancer cell comprising the step of providing the cancer cell with a virus according to invention, or a kit of parts according the invention, thereby inducing lysis of the cancer cell. The cancer cell is preferably present in an animal body, preferably a human body. A preferred cancer cell is a prostate cancer cell. The invention further provides a method for treatment of a subject suffering from a cancer, preferably a prostate cancer, the method comprising the step of administering to the said subject an effective amount of the replication competent virus according to the invention or a kit of parts according to the invention.

Table 1 depicts the genes POTl, A4GALT, AARS, ABHD6, ADH6, ADMR, ALOX12, AMPD2, ARFGEF1, ARHGEF15, ARHGEF6, AS3MT, ATP1A2, BCL2L13, CHD8, COR02B, CYP17A1, DAPP1, DGAT1, EIF3S4, EPHX2, FDFT1, FKBP6, GLI, IFITM3, LPAL2, MSC, OMD, OR51E2, ORC5L, ORC6L, PBX2, PECI, PPARA, RBBP8, REN, RFX4, RNASET2, RPS13, RRAS, RUNX1, RUVBL1, SERPINIl, SFRSl, SFRS5, SH3BP2, SLC9A3R2, SQSTM1, TPCN2, TUBA8, TUSC3, TWIST2, WWP2, and XDH.

Table 2 depicts the genes A4GALT, AARS, ABHD6, ADH6, ADMR, AMPD2, ARFGEFl. ARHGEF15, ATP1A2, CYP17A1, FKBP6, IFITM3, LPAL2, MSC, OMD, ORC6L, PECI, POTl, PPARA, RBBP8, REN, RFX4, RNASET2, RRAS, SERPINIl, SFRSl, SFRS5, SH3BP2, SLC9A3R2, SQSTM1, TUBA8, and XDH.

Table 3 depicts the genes AARS, ADH6, BIGl, ATP1A2, CYP17A1, IFITM3, MSC, ORC6L, PECI, POTl, RBBP8, REN, RFX4, RNASET2, RRAS, SERPINIl, SFRSl, TUBA8, and XDH. Table 4 depicts the genes AARS, BIGl, ATP1A2, CYP17A1, MSC, PECI, POTl, RBBP8, RRAS, and SERPINI1.

Table 5 depicts sequences of short hairpin RNAs directed against the target genes listed in Table 4 useful for the invention.

Table 6 depicts the genes TERF1, TERF2, TERF2IP, TINF2, ACD, PINX1, TNKS, and WRN, which encode interaction partners of POTl and include components of the multiprotein complex shelterin and telomere-associated proteins.

Table 7 depicts sequences of short hairpin RNAs directed against the target genes listed in Table 6 useful for the invention. Hereinafter, the invention will be further exemplified in examples and figures. The examples show a number of ways to provide said replication competent adenoviruses according to the invention. It is to be clearly understood that the description is not meant in any way to limit the scope of the invention as was explained in general terms above. Skilled artisans will be able to transfer the teachings of the present invention to other replication competent adenoviruses, silencing factors, formulations, methods, compositions, and uses without departing from the present invention.

Figure legends

Figure 1. Results of screens of the siRNA pools against 170 genes with and without addition of replication competent adenoviruses. Shown are the mean scores of three independent experiments. Figure 1A shows cell death induced by the siRNA pools (X-axis) versus cell death induced by the siRNA pools in combination with replication competent adenovirus (Y-axis). The open symbols represent the scores of the 170 genes, the closed symbols are negative controls (irrelevant siRNA). A downwards shift indicates sensitization to adenovirus- induced cell death, a leftwards shift indicates that the siRNA pool itself is toxic. Figure IB shows the log2 of the ratio with/without a virus. On the right are provided the mean scores for the negative controls +/- standard deviation (SD). The dotted line depicts the mean of the negative controls minus 3SD. Figure 2. Analysis of the genes depicted in Table 3 for each of the four individual siRNAs. Figure 2A shows the mean scores of three independent experiments +/- SD. Figure 2B shows the log2 of the ratio with/without a virus, with on the right the mean scores for the negative controls +/- SD (NT-1). The dotted line depicts the mean of the negative controls minus 3SD.

Figure 3. Correlation between phenotype (A) and efficiency of downregulation of the target gene (B), for one of the target genes (POTl). mRNA expression levels of POTl were determined by quantitative RT-PCR. Two of the siRNAs (numbers 1 en 3) show good silencing in combination with enhanced cell lysis after Ad5 infection. (C) Relative cell viability in the presence and absence of Ad5 infection (x-axis) plotted against relative POTl expression (y-axis) for the four siRNAs. Correlation coefficient R(2)=0.90.

Figure 4. Effect of silencing genes encoding POTl interaction partners on adenovirus-induced cell death. Interaction partners of POTl were silenced using siRNA and subsequently infected with Ad5 at MOI 30 IU/cell or not. Non- targeting siRNA (NT#1) was used as control. Five days later cell viability was measured by BCA protein assay. The figure shows the mean percent cell viability after Ad5 infection compared to the cell viability without Ad5 infection of three independent experiments +/- SD.

Examples

Example 1. Identification of genes that inhibit death of PC-3 prostate cancer cells infected with Ad5.

We used high-throughput RNAi loss-of-function screens to identify modulators of Ad5-induced oncolysis in cancer cells. We followed a two-step screening procedure using PC-3 prostate cancer cells and the Dharmacon siARRAY whole human genome siRNA library. PC-3 cells were grown at 37°C and 5% C02 in a humidified incubator in Dulbecco's modified Eagle's medium F12 (DMEM-F12) supplemented with 10% fetal bovine serum and antibiotics (100 U/ml penicillin and 100 μg/ml streptomycin). The siRNA library consists of approximately 21,000 arrayed pools of 4 siRNAs, each directed against a different human gene. In the first step, three independent replicate genome- wide screens were performed in which cell viability was measured using Cell-Titer Blue reagent three days after infecting siRNA-transfected PC-3 cells with Ad5. To this end, 1 x 104 cells were seeded per well in 96-well plates. The next day, cells were transfected with 25nM siRNA using 0.2 μΐ/well Dharmafect 2 (Dharmacon).

Twenty-four hours post transfection, cells were infected with Ad5 at 100 IU/cell. Three days post infection, 30μ1 CellTiter-Blue reagent (Promega) was added to the culture medium and plates were placed at 37°C in a 5% C02 incubator for two hours. After two hours, 50μ1 3% SDS was added and cell viability was determined by measuring fluorescence at 540 nm excitation and 590 nm emission wave lengths using a Tecan Infinite F200 reader. Data analysis was done using CellHTS2 software and primary hits were selected on the basis of robust B- scoring. The primary hit selection threshold was set at a B- score above 3 or below -3. Hits were selected when they met the B-score selection criteria in at least 2 out of the 3 screens. We found 193 siRNA pools that protected Ad5-infected PC-3 cells against death, suggesting that the genes that are silenced by these siRNAs are supporting adenovirus-induced cell death. We also found 170 siRNA pools that promoted death of Ad5-infected PC-3 cells, suggesting that the genes that are silenced by these siRNAs are genes inhibiting death of Ad5-infected cells.

In the second step, the 170 potential cell death inhibitors were reexamined in three independent replicate cell viability screens, each with and without adenovirus infection. Negative control transfections with irrelevant siRNA siGENOME Non-Targeting siRNA-1 were included. The same methods were used as in the primary screens, with the following modifications: cells were transfected two days after seeding 0.5 x 104 cells per well; and replicate plates were not infected with Ad5. Figure 1A shows the mean results from the three secondary screens for each siRNA pool. As can be seen, 56 primary hits were confirmed in the secondary screens to cause increased death of Ad5-infected PC-3 cells. The confirmed hits were selected because viability of Ad5-infected PC-3 cells transfected with the siRNA pools was less than the mean viability minus 2 standard deviations of Ad5-infected PC-3 cells transfected with irrelevant control siRNA. The 56 secondary hits are therefore considered to represent genes encoding proteins that inhibit death of Ad5-infected PC-3 cells. These genes are listed in Table 1. Example 2. Identification of genes that inhibit Ad5-induced death of PC-3 prostate cancer cells.

The secondary screens described in example 1 were also used to identify genes encoding proteins that selectively inhibit Ad5-induced PC-3 cell death. Silencing of these genes causes a stronger increase in cell death of Ad5-infected PC-3 cells than of uninfected PC-3 cells. For each siRNA pool, the cell viability ratio with/without Ad5 was calculated and log2 transformed. This was also done for the irrelevant siRNA controls. Selective sensitization to Ad5-induced cell death was assessed by comparing to the mean result for the negative controls. To stratify hits, two stringencies of hit selection were used, i.e., a log2 ratio lower than the mean log2 ratio minus 2 or minus 3 standard deviations for the negative controls. Figure IB shows that 32 hits met the first criterion and 19 genes met the most stringent second criterion. The 32 and 19 selective inhibitors of Ad5- induced cell death are listed in Tables 2 and 3, respectively.

To discriminate between true targets and possible off-target-effects, another three independent screens were done with the four individual siRNAs from the pools against each of the 19 genes identified by the most stringent selection criterion. Figure 2A shows the cell viability expressed as mean fluorescence SD (arbitrary units), after subtraction of CellTiter-Blue conversion in the absence of cells. Figure 2B shows selective sensitization to Ad5 infection (log2 ratio with/without Ad5). According to the same stringent hit selection criterion on which the siRNA pools were selected (less cell viability than the mean minus 3SD of irrelevant control siRNA), ten candidate inhibitor genes were identified as reproducible hits with at least 2 of the 4 siRNAs. It is highly unlikely that two or more independent siRNA molecules directed against a target gene exhibit off- target activity. The 10 genes are thus identified as selective inhibitors of Ad5- induced cell death with high-confidence. These 10 genes are listed in Table 4.

Example 3. Correlation of gene silencing efficiency and selective sensitization to Ad5-induced cell death.

In one of the experiments with individual siRNAs against POT1 in which PC-3 cell death with and without Ad5 infection was determined, POT1 target gene knockdown for the four individual siRNAs was determined in parallel. To this end, cells were collected by centrifugation 96 hours after siRNA transfection. RNA was prepared by using the RNeasy kit (Qiagen) according to the

manufacturer's protocol. Total RNA (^g) was reversely transcribed using the SuperScript III reverse transcriptase (Invitrogen) after priming with random hexamers (Applied Biosystems). Real-time quantitative PCR was carried out on a Roche LS480 instrument in a 20μ1 reaction containing ΙΟμΙ of SYBR Green PCR mix (Roche), diluted cDNA and primers. QuantiTect Primers for human POT1 (QT00008148) and GAPD (QT01192646) were purchased from Qiagen. Relative quantification analysis compared the levels of POT1 and GAPD in a single sample and final results were expressed as a difference of these targets using the 2-ΔΔΟΤ method. For the comparison between the different samples we

normalized to the untreated control. We found a direct correlation between the knockdown efficiencies of the four individual siRNAs targeting POT1 and their capacity to increase Ad5-induced cell death (Figure 3). This further confirmed that POT1 is a genuine target to increase the oncolytic potency of replication competent adenovirus.

Example 4. General methods to construct replication competent adenoviruses expressing shRNA molecules.

First, adenovirus shuttle vectors carrying a Gateway recombination destination cassette are made.

To construct a shuttle vector carrying a Gateway recombination

destination cassette between the adenovirus E4 region and the right-hand ITR, the construct pEndK/Spel (generously provided by Dr. R. Alemany, Institut Catala d'Oncologia, Barcelona, Spain) was used. pEndK/Spel was made by first digesting pTG3602 (Chartier et al., J. Virol, 70(1996):4805-4810) with Kpnl and religating the vector fragment comprising Ad5 map units 0-7 and 93-100 to create pEndK. Next, a unique Spel site was introduced into pEndK by changing Ad5 nucleotide 35813 from A to T by site directed mutagenesis to create pEndK/Spel. PEndK/Spel carries Pad restriction sites flanking the two Ad5 ITRs. pEndK/Spel was made compatible with the Gateway system by ligating the Gateway destination cassette rfa (Gateway Vector Conversion System;

Invitrogen, Carlsbad, CA) as a blunt fragment into the Spel site (filled in with Klenow polymerase). Plasmids were selected that contained the Gateway destination cassette with the coding sequence of the ccdB gene on the adenovirus R or L strand and were designated pEndK/DEST-R and pEndK/DEST-L, respectively.

To construct a shuttle vector carrying a Gateway recombination

destination cassette in place of the adenovirus E3 region, the GATEWAY destination cassette rfa (from the Gateway Vector Conversion System) was first cloned into pBluescript SK(-)(Stratagene) digested with EcoRV to obtain pBSK- DEST. From this template, the DEST cassette was PCR amplified using primers 5'-GAGGTCGACGCGATCGATAAGCTTGATATC-3' (SEQ ID NO 1) and 5'- TAGAACTAGTCGATCGCCCGGGCTGCAG-3'(SEQ ID NO 2) with overhanging Pvul sites and digested with Pvul. This fragment was ligated in pBHGll (Microbix) digested with Pad to obtain pBHGll-DEST_R.

To construct a shuttle vector carrying the full-length genome of a CRAd with a Gateway recombination destination cassette in place of the adenovirus E3 region, first pEndK/Spel (supra) was digested with EcoRV and the EcoRV- fragment comprising the fiber gene from pBHGll was inserted to create pEndK- Fiber. Next, the Hpal-fragment containing DEST_R from pBHGll-DEST_R was inserted into Hpal-digested pEndK- Fiber to create pEndK-Fiber_DEST_R.

Linear dsDNA was isolated from Ad5-A24E3(Suzuki et al., Clin. Cancer Res. 8(2002):3348-3359) virions and recombined with Kpnl -linearized pEndK/Spe (supra) in BJ5183 bacteria to obtain plasmid clone pAdA24E3. Finally, the Fiber_DEST_R containing Spel fragment from pEndK-Fiber_DEST_R was inserted into pAdA24E3 digested with Spel to replace the E3 region and fiber gene with the DEST_R_Fiber fragment from pEndK-Fiber_DEST_R. The resulting plasmid is pAdA24-DEST_R.

Second, plasmids are made with an shRNA expression cassette that can be transported into an adenovirus shuttle vector by Gateway recombination.

The plasmid pSHAG-1 (Paddison et al., Genes Dev. 16(2002)948-958; generously provided by Dr. G.J. Hannon, Cold Spring Harbor Laboratory, NY) is used as entry clone for the GATEWAY system (Invitrogen, Carlsbad, CA).

pSHAG-1 contains a U6 promoter- driven expression cassette flanked by the attLl and attL2 recombination sites such that the expression cassette can be transported into destination plasmid vectors including pEndK/DEST-R, pEndK/DEST-L, pBHGll-DEST_R and pAdA24-DEST_R of example 1 using the Gateway system. shRNA-encoding sequences can be introduced by ligation of pSHAG-1 digested with BseRI and BamHI with two annealed synthetic oligonucleotides with compatible overhanging DNA sequences. The first of the two oligonucleotides should be designed to contain in the 5' to 3' order: a first stretch of at least 19 and preferably no more than 29 nucleotides complementary to the target mRNA (i.e., antisense), a loop sequence, a second stretch of nucleotides of the same length and of reverse complementary sequence to the first stretch of nucleotides, and a stretch of at least 4 thymidines. The second oligonucleotide should be reverse complementary to the first oligonucleotide. Furthermore, when annealed the then double- stranded oligonucleotides should form overhanging sites compatible with BseRI and BamHI restriction sites. Depending on the choice of the sequence of 19 to 29 nucleotides a useful shRNA for the invention directed against a target of choice can be made. Annealing of the two oligonucleotides followed by ligation into pSHAG-1 digested with BseRI and BamHI results in the formation of pSHAG- shRNA.

Third, adenovirus shuttle vectors carrying an shRNA expression cassette are made using the adenovirus shuttle vectors carrying a Gateway recombination destination cassette and the plasmids with an shRNA expression cassette that can be transported into an adenovirus shuttle vector by Gateway recombination.

To construct an adenoviral shuttle vector carrying an shRNA-expression cassette inserted between the E4 region and the right-hand ITR, the shRNA expression cassette is transferred from the pSHAG-shRNA construct to the pEndK/DEST-R or pEndK/DEST-L plasmid via an in vitro GATEWAY LR recombination reaction using the GATEWAY LR Clonase enzyme mix

(Invitrogen) according to manufacturer's protocol. This results in pEndK/shRNA- R or pEndK/shRNA-L.

To construct an adenoviral shuttle vector carrying an shRNA-expression cassette inserted in place of the E3 region, the shRNA expression cassette is transferred from the pSHAG-shRNA construct to the pBHGll-DEST_R plasmid via the same in vitro GATEWAY LR recombination reaction to create pBHGll- shRNA. To construct a plasmid carrying the full-length genome of an AdA24-type CRAd (Fueyo et al., Oncogene 19(2000):2-12) with an shRNA-expression cassette inserted in place of the adenovirus E3 region, the shRNA expression cassette is transferred from the pSHAG- shRNA construct to the pAdA24-DEST_R plasmid via the same in vitro GATEWAY LR recombination reaction to create pAdA24- shRNA.

Finally, replication competent adenoviruses expressing shRNA molecules are generated using the adenovirus shuttle vectors carrying an shRNA expression cassette.

The plasmids pEndK/shRNA-R and pEndK/shRNA-L can be linearized with Kpnl and/or EcoRV. This separates the Ad5 map units 0-7 from Ad5 map units 93-100 with the inserted shRNA expression cassette. These linearized molecules can be recombined in bacteria, for example in E. coli BJ5183, with full- length replication competent adenovirus DNA. Said full-length replication competent adenovirus DNA can be isolated from adenovirus particles or, alternatively can be released by digestion from a plasmid carrying a full-length replication competent adenovirus DNA insert. Double homologous recombination then creates a plasmid with a full-length replication competent adenovirus genome insert, in which the shRNA expression cassette is inserted between the E4 region and the right-hand ITR. It should be noted that any full-length replication competent adenovirus can be used to insert shRNA expression cassettes according to this method, including recombinant adenoviruses with additional modifications, such as e.g. enhanced tumor-selectivity or oncolytic potential, a changed tropism or transgene insertion. It is preferred, however, that said full-length replication competent adenovirus does not include a Pad restriction site in its genome. The complete replication competent adenovirus genome with inserted shRNA expression cassette is subsequently released from the plasmid by Pad digestion. This DNA is transfected into human cells using, e.g., lipofectamine reagent. The resulting recombinant replication competent adenovirus according to the invention is isolated and further propagated and purified according to standard cell culture and virology methods known in the art.

pBHGll-shRNA plasmids are transfected into human cells together with pXCl (Microbix Biosystems) or pXCl-derived plasmids with modifications of choice, e.g., in the El region to create CRAds including but not limited to the A24-mutation (infra), to allow homologous recombination reconstituting a complete replication competent adenovirus genome with the shRNA expression cassette inserted in place of the E3 region. This virus can then be isolated, propagated, purified and used according to methods known in the art. The pAdA24- shRNA plasmid can be digested with Pad and transfected into human cells to isolate a A24-type CRAd with the shRNA expression cassette inserted in place of the E3 region. This virus can then also be isolated, propagated, purified and used according to methods known in the art. Example 5: Construction of oncolytic adenoviruses expressing short hairpin RNAs directed against genes that inhibit Ad5-induced cell death.

Example 4 provides ways to construct conditionally replication competent adenoviruses with shRNA expression cassettes inserted in place of the

adenovirus E3 region or between the adenovirus E4 region and the right-hand ITR, using Gateway recombination methods. Here, these teachings were followed to construct conditionally replication competent adenoviruses expressing shRNAs directed against the 10 genes that inhibit Ad5-induced death of PC-3 prostate cancer cells listed in Table 4 inserted between the adenovirus E4 region and the right-hand ITR in a replication competent adenovirus with the Ε1Α-Δ24 mutation that confers tumor- selective replication.

First, a shuttle vector was made carrying a full length adenovirus genome flanked with Pad sites, comprising the ElAA24-mutation (Fueyo et al., Oncogene 19(2000):2-12) and the Gateway recombination destination cassette between the adenovirus E4 region and the right-hand ITR. To this end, the constructs pEndK/DEST-R and pAdA24E3 (supra) were used. Full length AdA24E3 DNA was released by Pad digestion. This DNA was recombined in BJ5183 bacteria with Kpnl-digested pEndK/DEST-R to obtain pAdA24E3-DEST-R. pAdA24E3- DEST-R is propagated in the E.coli STBL2-DB3.1 strain, which contains a gyrase mutation that renders it resistant to the lethal effects of the CcdB protein thereby allowing propagation of plasmids carrying the ccdB gene in the DEST cassette.

Second, shRNA-encoding sequences directed against the selected target genes are introduced into entry clone pSHAG-1 (supra). pSHAG-1 contains a U6 promoter- driven expression cassette flanked by the Gateway attLl and attL2

recombination sites such that the expression cassette can be transported into destination plasmid vectors including pAdA24E3-DEST-R using the Gateway system. shRNA-encoding sequences are introduced by ligation of pSHAG-1 digested with BseRI and BamHI with two annealed synthetic oligonucleotides with compatible overhanging DNA sequences. The first of the two

oligonucleotides contains in the 5' to 3' order: a first stretch of nucleotides complementary to the target gene mRNA (i.e., antisense), a loop sequence, a second stretch of nucleotides of the same length and of reverse complementary sequence to the first stretch of nucleotides, and a stretch of at least 4 thymidines. The second oligonucleotide is reverse complementary to the first oligonucleotide. Furthermore, when annealed the then double- stranded oligonucleotides form overhanging sites compatible with BseRI and BamHI restriction sites. Sequences of shRNAs directed against the 10 selected target genes listed in Table 4 are given in Table 5.

Third, the shRNA expression cassettes obtained in the second step are

transferred from pSHAG constructs into pAdA24E3-DEST-R via an LR

GATEWAY in vitro recombination reaction using the GATEWAY LR Clonase enzyme mix (Invitrogen) according to manufacturer's protocol, to create pAdA24E3- shRNA oncolytic adenovirus constructs.

Finally, full-length AdA24 CRAd genomes with inserted shRNA expression cassettes are released from pAdA24E3- shRNA contructs by Pad digestion and transfected using lipofectamine reagent in 911 cells or A549 cells to obtain the different AdA24E3- derived shRNA- expressing replication competent

adenoviruses, which are further propagated on A549 cells according to standard cell culture and virology methods known in the art. The Ε1Δ24 deletion and the U6-shRNA insertion and orientation are confirmed by PCR on the final products, shRNA sequences are confirmed by sequencing and functional virus titers are determined by limiting- dilution titration according to standard techniques.

Example 6. Validation of enhanced Ad5-induced cell death upon POTl silencing using a short hairpin expression construct. We validated the effect of POTl silencing independently using a using a human pLKO.l lentiviral vector (Thermo scientific, Open Biosystems) expressing a shRNA directed against POTl. The sequence of the shRNA expressed by this vector is the first POTl sequence given in table 5. PC-3 cells were transfected with the POTl shRNA expression vector and as a negative control with an empty pLKO.l vector. Stable transfected cells were selected using puromycin. Silencing efficiencies were determined by qRT-PCR, as described in Example 3. The shRNA was found to silence POTl expression 34%. Stable transfected PC-3 cells were subjected to Ad5 infection at an MOI of 100 and 3 days later cell viability was determined by measuring total protein content of the adherent cell fraction using the BCA protein assay (Thermo scientific, Pierce), according to the

manufacturer's protocol. Briefly, culture medium was replaced by 25μ1 lysis buffer after washing with PBS. Cell lysates were mixed with BCA reagent and plates were placed at 37°C in a 5% C02 incubator. After 30 minutes, 50μ1 3% SDS was added and absorbance was measured at 595nm using a Bio-Rad model microplate reader. Protein concentration ^g/ml) of each sample was calculated using a BSA standard curve. Three individual experiments were done in triplicate. Ad5 infection reduced cell viability of empty control pLKO.l vector transduced cells 87+/-4%. Cells transduced with the POTl shRNAmir-expressing pLKO.l vector were killed more effectively (62+/- 11%; difference significant, p<0.02). Example 7. Identification of POT1 interaction partners by STRING protein interaction analysis.

The database and web resource STRING (Jensen et al., Nucl. Acids Res.

37(2009):D412-416) was used to identify interaction partners of POT1. This revealed direct interactions with TERFl, TERF2, TERF2IP, TINF2, ACD (TPPl), PINX1, TNKS and WRN. These genes are listed in Table 6. POT1, TERFl, TERF2, TERF2IP, TINF2 and ACD collectively form the multi-protein complex shelterin that binds to the TTAGGG repeats of telomeres, regulating telomere length and protecting chromosome ends from illegitimate recombination, catastrophic chromosome instability, and abnormal chromosome segregation (reviewed in Palm and De Lange, Annu. Rev. Genet. 42(2008):301-334).

Inhibition or deletion of individual shelterin components leads to a robust DNA damage response (DDR) signal mediated by ATM, phosphorylation of Chk2 and H2AX, the formation of 53BPl-associated telomere induced DNA damage foci, and NHEJ-mediated chromosome fusion. In addition, inhibiting POT1 leads to a cell cycle arrest in late S/G2 phase (Denchi and De Lange, Nature

448(2007):1068-1071; Churikov and Price, Nat. Struct. Mol. Biol. 15(2008):79-84; Pitt and Cooper, Nucl. Acids Res. 38(2010):6968-6975; Veldman et al., Curr. Biol. 14(2004):2264-2270). The RecQ helicase WRN is proposed to function in dissociating alternative DNA structures during recombination and/or replication at telomeric ends (Monnat, Semin. Cancer Biol. 20(2010):329-339). A defect in WRN is responsible for the cancer prone disorder Werner syndrome. The cellular phenotype of Werner syndrome, including genomic instability and premature senescence, is consistent with telomere dysfunction. Evidence indicates that WRN and POT1 may cooperate in common pathways at telomeric ends, where POT1 strongly stimulates WRN to unwind long telomeric forked duplexes and D- loop structures (Mao et al., Cancer Res. 70(2010):6548-6555; Crabbe et al., Science 306(2004):1951-1953; Sowd et al., Nucl. Acids Res. 36(2008):4242-4256.) Examples of sequences of shRNAs directed against the target genes listed in Table 6 are given in Table 7. Example 8. Silencing of genes encoding POT1 interaction partners sensitizes PC- 3 prostate cancer cells to Ad5-induced cell death.

To investigate if the promoting effect on Ad5-induced cell death that was observed upon POT1 silencing could also be accomplished by silencing any of its interaction partners, we silenced their expression in the PC-3 cells in which the effect of POT1 silencing on adenovirus-induced cell death was established using siRNA. Cells were transfected with SMARTpool siRNA duplexes from

Dharmacon according to the manufacturer's protocol using 50nM siRNA and 500- times diluted Dharmafect 2 (Dharmacon), in 96-well plates. The SMARTpool siRNA reagents used were directed against the following human target genes (SMARTpool catalog number): irrelevant non- targeting control siCONTROL-1 (D- 001210-01), TERF1 (M-010542-01), TERF2 (M-003546-00), TERF2IP (M-021219- 01), TINF2 (M-019951-01), ACD, (M-014237-02), TNKS (M-004740-01), and WRN (M-010378-01). Knockdown efficiencies of the targeted genes were measured by quantitative reverse transcription PCR, as described in Example 3, using

QuantiTect Primers purchased from Qiagen. Relative mRNA levels compared to GAPDH controls were calculated using the AACt method. Silencing efficiencies ranged from approximately 70% to approximately 95%. Subsequently, we tested the response to adenovirus infection by measuring cell viability 5 days after infection using the BCA protein assay, as described in Example 6. As can be seen in Figure 4, Ad5 infection caused approximately 50% cell death. Silencing of several interaction partners of POT1 caused an increase in Ad5-induced cell death. In particular silencing of TERF2IP and TNKS was very effective, increasing cell death to 78 and 86%, respectively. Hence, not only silencing of POT1 that was identified in our high throughput screening procedure, but also silencing of interaction partners of POT1, sensitized cancer cells to adenovirus- induced cell death. Table 1

Table 2

Table 3

Table 4

Table 6.

Table 7.

Human Sequence

Gene

Symbols

TERF1 CCGGGATGGCAGAAACAGAGAGAAACTCGAGTTTCTCTCTGTTTCTGCCATCTTTTTG

CCGGCCCAGCAACAAGACCTTAATACTCGAGTATTAAGGTCTTGTTGCTGGGTTTTTG

CCGGCCCTTGATGCACAGTTTGAAACTCGAGTTTCAAACTGTGCATCAAGGGTTTTTG

TERF2 CCGGCCCTCTCTTATGTGAAATTATCTCGAGATAATTTCACATAAGAGAGGGTTTTTG

CCGGCGGCAGCATCATCATCTGTTACTCGAGTAACAGATGATGATGCTGCCGTTTTTG

CCGGCCTGATGAATTTGTGGGTTTACTCGAGTAAACCCACAAATTCATCAGGTTTTTG

CCGGCCAGAACAACAGACAGAGAAACTCGAGTTTCTCTGTCTGTTGTTCTGGTTTTTG

CCGGGCCTGGACTAACTTACTGCTTCTCGAGAAGCAGTAAGTTAGTCCAGGCTTTTTG

TERF2I P CCGGCGGCAGTTAATGGAGAAGTTTCTCGAGAAACTTCTCCATTAACTGCCGTTTTTG

CCGGCGGACGACGTAGCCATCCTTACTCGAGTAAGGATGGCTACGTCGTCCGTTTTTG

CCGGAGAGTATGTGAAGGAAGAAATCTCGAGATTTCTTCCTTCACATACTCTTTTTTG

CCGGCATCCTTACCTACGTGAAGGACTCGAGTCCTTCACGTAGGTAAGGATGTTTTTG

CCGGCAGAATAAGAGAACTCCAGATCTCGAGATCTGGAGTTCTCTTATTCTGTTTTTG

CCGGAGAGTTCTTGCATTGGAACTCTCGAGAGTTCCAATGCAAGAACTCTCTTTTTG

TINF2 CCGGGCAAGGAAGAACATGCGATATCTCGAGATATCGCATGTTCTTCCTTGCTTTTTG

CCGGACGCCTTTGTATGGGCCTAAACTCGAGTTTAGGCCCATACAAAGGCGTTTTTTG

CCGGGAGACAATATGGTGTGGACATCTCGAGATGTCCACACCATATTGTCTCTTTTTG

CCGGGCAGGAACTTGAACAAGAGTACTCGAGTACTCTTGTTCAAGTTCCTGCTTTTTG

CCGGAGACAATATGGTGTGGACATCTCGAGATGTCCACACCATATTGTCTCTTTTTG

ACD CCGGCTCGTCCAATGCAGGCCTACTCGAGTAGGCCTGCATTGGACGAGTTTTTG

CCGGCGTTGCATCCGCTGGGTGTCTCGAGACACCCAGCGGATGCAACGTTTTTG

CCGGGGGTGCCTGGTTGCAACCACTCGAGTGGTTGCAACCAGGCACCCTTTTTG

CCGGTGGAGTTCAAGGAGTTTGTCTCGAGACAAACTCCTTGAACTCCATTTTTG

CCGGAGACTTAGATGTTCAGAAACTCGAGTTTCTGAACATCTAAGTCTTTTTTG

CCGGAGCTAATTCTGAGCTCTCTCTCGAGAGAGAGCTCAGAATTAGCTTTTTTG

CCGGGACTTAGATGTTCAGAAAACTCGAGTTTTCTGAACATCTAAGTCTTTTTG

PINX1 CCGGCAGGTAAAGATGTGGAAAGTTCTCGAGAACTTTCCACATCTTTACCTGTTTTTTG

CCGGGCTACACTAGAAGAAACGCTACTCGAGTAGCGTTTCTTCTAGTGTAGCTTTTTTG

CCGGGCAAGGAGCCACAGATCATATCTCGAGATATGATCTGTGGCTCCTTGCTTTTTTG

CCGGCACAGATTCCTCGGACAAGAACTCGAGTTCTTGTCCGAGGAATCTGTGTTTTTTG

TNKS CCGGCGCTTCATAATGCCTGTTCTTCTCGAGAAGAACAGGCATTATGAAGCGTTTTTG

CCGGCGACTCTTAGAGGCATCTAAACTCGAGTTTAGATGCCTCTAAGAGTCGTTTTTG

CCGGGCTCCAGAAGATAAAGAATATCTCGAGATATTCTTTATCTTCTGGAGCTTTTTG

CCGGGCCAGGGATAACTGGAACTATCTCGAGATAGTTCCAGTTATCCCTGGCTTTTTG

CCGGGCCCATAATGATGTCATGGAACTCGAGTTCCATGACATCATTATGGGCTTTTTG

CCGGAACTATACACCTCTGCATGACTCGAGTCATGCAGAGGTGTATAGTTCTTTTTG

CCGGCATCACAATGAGCGCATGTTGCTCGAGCAACATGCGCTCATTGTGATGTTTTTG

CCGGAGAACAGGCATACCCAGAGTCTCGAGACTCTGGGTATGCCTGTTCTCTTTTTG WRN CCGGCCTGTAAGATTGCTTTAAGAACTCGAGTTCTTAAAGCAATCTTACAGGTTTTT

CCGGCGTTGCTTAAATCTGAGAAATCTCGAGATTTCTCAGATTTAAGCAACGTTTTT

CCGGCCATTATACAATAGAGGGAAACTCGAGTTTCCCTCTATTGTATAATGGTTTTT

CCGGCCTGTTTATGTAGGCAAGATTCTCGAGAATCTTGCCTACATAAACAGGTTTTT

CCGGGCTGGCAATTACCAGAACAATCTCGAGATTGTTCTGGTAATTGCCAGCTTTTT

Claims

1. Replication competent adenovirus, being capable of replicating and having lytic capacity in a host cell, the virus genome comprising at least one DNA sequence coding for a silencing factor functional in reducing expression and/or activity of a target gene in the host cell, said virus further provided with one or more expression control sequences that mediate expression of the DNA sequence in the host cell, whereby the target gene is selected from the genes depicted in Table I.

2. Replication competent adenovirus, being capable of replicating and having lytic capacity in a host cell, the virus genome comprising at least one DNA sequence coding for a silencing factor functional in reducing expression and/or activity of a target gene in the host cell, said virus further provided with one or more expression control sequences that mediate expression of the DNA sequence in the host cell, whereby the target gene is selected from the genes depicted in Table 6.

3. Replication competent adenovirus, being capable of replicating and having lytic capacity in a host cell, the virus genome comprising at least one DNA sequence coding for a silencing factor functional in reducing expression and/or activity of a target gene in the host cell, said virus further provided with one or more expression control sequences that mediate expression of the DNA sequence in the host cell, whereby the target gene is POT-1 or an interaction partner of POT1.

4. The adenovirus according to claim 1 or 3, whereby the target gene is POT1.

5. The adenovirus according to claim 2 or 3, whereby the target gene is selected from the genes TERF2IP and TNKS.

6. The adenovirus according to any of claims 1-5, wherein the silencing factor comprises an RNAi molecule comprising a region with double stranded RNA.

7. The adenovirus according to any of claims 1-6, wherein the adenovirus is a human adenovirus, preferably of serotype 5.

8. The adenovirus according to claim 1-7, wherein the adenovirus is a conditionally replicating virus.

9. The adenovirus according to claim 8, wherein said adenovirus comprises a mutation in one or more genes from the group consisting of Ela, Elb, E4, and VA-RNAs, to achieve selective replication in tumors.

10. The adenovirus according to any of the previous claims, wherein the at least one DNA sequence coding for a silencing factor comprises at least one of the sequences listed in Table 5 or Table 7.

11. The adenovirus according to any of claims 1-10, for use as a medicament.

12. The adenovirus according to any of claims 1-11, for use as a medicament for the treatment of cancer.

13. The adenovirus according to any of claims 1-12, for use as a medicament for the treatment of prostate cancer.

14. A kit of parts, comprising a silencing factor functional in reducing expression of a target gene in a host cell, and a replication competent adenovirus being capable of replicating in and having lytic capacity in said host cell, whereby the target gene is selected from the genes depicted in Table 1 or Table 6, preferably said kit of parts comprises a DNA sequence encoding the silencing factor.

15. A method of lysing a cell comprising the step of providing the cancer cell with a virus according to any of claims 1-13, or the kit of parts according to claim 14, thereby inducing lysis of the cancer cell.

16. The method according to claim 15, wherein the cancer cell is present in an animal body, preferably a human body.

17. A method for treatment of a subject suffering from a cancer, preferably a prostate cancer, the method comprising the step of administering to the said subject an effective amount of the replication competent virus according to any of claims 1-13 or the kit of parts according to claim 14.

18. A cell comprising an adenovirus according to any of claims 1-13.

19. A cell comprising a silencing factor functional in reducing expression and/or activity of a target gene in the cell and a replication competent

adenovirus, whereby the target gene is selected from the genes listed in Table 1 or Table 6.

20. Use of a silencing factor functional in reducing expression and/or activity of a target gene in the cell, whereby the target gene is selected from the genes listed in Table 1 or Table 6, for enhancing replication and/or lytic capacity of a replication competent adenovirus in a host cell.