WO2010012473A2

WO2010012473A2 - Hydrolase-specific nanosensors, methods for producing them and uses in molecular imaging

Info

Publication number: WO2010012473A2
Application number: PCT/EP2009/005539
Authority: WO
Inventors: Eyk Schellenberger
Original assignee: Charite - Universitätsmedizin Berlin
Priority date: 2008-07-30
Filing date: 2009-07-30
Publication date: 2010-02-04
Also published as: WO2010012473A3

Abstract

The present invention relates to hydrolase-specific sensor compounds which comprise a coated nanoparticle or core and a multimeric domain comprising a hydrolase-specific cleavage site. After cleavage by the hydrolase, the hydrolase-specific sensor compounds are transformed from a stable sensor compound to an aggregative compound, which allows in vivo detection and imaging of the aggregates. The present invention further relates to the uses of the hydrolase-specific sensor compounds as hydrolase reporter and as shuttles for therapeutic compounds, in particular as theranostics in magnetic thermotherapy.

Description

Hydrolase-specific nanosensors, methods for producing them and uses in molecular imaging

The present invention relates to hydrolase-specific sensor compounds which comprise a coated nanoparticle or core and a multimeric domain comprising a hydrolase-specific cleavage site. After cleavage by the hydrolase, the hydrolase-specific sensor compounds are transformed from a stable sensor compound to an aggregative compound, which allows in vivo detection and imaging of the aggregates. The present invention further relates to the uses of the hydrolase-specific sensor compounds as hydrolase reporter and as shuttles for therapeutic compounds, in particular as theranostics in magnetic thermotherapy.

BACKGROUND OF THE INVENTION

New technologies for imaging molecules, particularly optical technologies, are increasingly being used to understand the complexity, diversity and in vivo behaviour of diseases, in particular cancers. "Omic" approaches are providing comprehensive "snapshots" of biological indicators or biomarkers, of a disease, in particular cancer, but imaging can take this information a step further, showing the activity of these markers in vivo and how their location changes over time. Advances in experimental and clinical imaging are likely to improve how, for example, cancer is understood at a systems level and, ultimately, should enable doctors not only to locate rumours but also to assess the activity of the biological processes within these tumours and to provide "on the spot" treatment.

Molecular imaging can be broadly defined as the in vivo characterization and measurement of biological processes at the cellular and molecular level. In contrast to commonly used clinical imaging, it sets forth to probe the molecular abnormalities that are the basis of disease, rather than imaging the end effects of these molecular alterations. Specific imaging of disease targets will allow earlier detection and characterization of disease, as well as earlier and direct molecular assessment of treatment efficacy. A central goal of molecular imaging is the imaging of enzyme activity. The advent of fluorescent smart sensor probes which can be activated by proteases ignited the development of reporter probes (2) and instrumentation (3) establishing optical imaging as the modality of choice for in vivo detection of enzyme activity (1).

To take advantage of the high resolution and deep-tissue imaging capabilities of magnetic resonance imaging (MRI) as well as the absence of radiation exposure, several new probe designs were introduced. Meade and coworkers developed a reporter probe activatable by β- galactosidase on the basis of a paramagnetic contrast agent and demonstrated its successful use for the visualization of gene transfer by MRI (4).

A paramagnetic polymerization probe was presented by Bogdanov et al. which allowed imaging of tissue peroxidase activity by MRI (5). Josephson and coworkers introduced magnetic relaxation switches sensing enzymatic activity based on superparamagnetic high- relaxivity probes for in vitro MRI (6). Upon protease activation these sterically stabilized cross-linked iron oxide particles (CLIO) switch from large clustered high-relaxivity aggregates to smaller low-relaxivity single particles. This technique is not suitable for in vivo application, since the non-activated clustered particles are too large to have a favorable bioavailability and, more importantly, activation by elevated enzyme activity in the target tissue reduces the relaxivity and consequently the contrast effect.

Thus, there is a need for the improved means which allow a specific molecular imaging of protein and enzyme activity, in particular in vivo. The present invention, thus, aims to provide such means and their uses for the effective and specific diagnosis and treatment of diseases.

SUMMARY OF THE INVENTION

According to the present invention this object is solved by providing hydrolase-specific sensor compounds.

A hydrolase-specific sensor compound of the present invention comprises (a) a nanoparticle or core (P) which is coated with positively or negatively charged moieties (CM) or with hydrophobic moieties (HM), having a diameter of equal to or less than 30 run,

(b) a multimeric domain comprising

- at least one coupling domain (CO), which interacts with the positively or negatively charged or with the hydrophobic moieties (CM),

- at least one cleavage domain (CL) comprising at least one cleavage site or recognition motif of the hydrolase,

- a polymer envelope domain (E) wherein the domain CO and the domain CL are linked via a linker or spacer (L), and wherein the polymer envelope domain (E) is covalently coupled to the domain CL,

wherein the sensor compound has a diameter of equal to or less than 200 nm, preferably in the range of 10 to 80 nm, more preferably in the range of 15 to 40 nm,

wherein the nanoparticle or core (P) is detectable and is preferably a magnetic, fluorescent or radiant nanoparticle or core (P),

wherein the domain CO is preferably a peptide or wherein the domain HM is preferably a hydrophobic lipid,

wherein the at least one cleavage site or recognition motif of the hydrolase of the domain CL is preferably an amino acid sequence, a nucleotide sequence or a saccharide sequence or other covalent ester, ether, peptide, glycoside, acid anhydride or C-C-bonds,

wherein the sensor is stable in suspension and becomes aggregative or adhesive after cleavage of the at least one cleavage site or recognition motif by the hydrolase.

Preferably, the nanoparticle or core (P) is electrostatically stabilized by the positively or negatively charged moieties (CM) or is coated with hydrophobic moieties (HM) (such as lipophilic compounds) and the entire sensor compound is sterically stabilized by a sub- domain of the multimeric domain, namely the polymer envelope domain E. According to the present invention this object is furthermore solved by providing pharmaceutical compositions comprising at least one hydrolase-specific sensor compound of the present invention and optionally pharmaceutically acceptable carrier(s) and/or excipient(s).

According to the present invention this object is furthermore solved by providing methods of producing the hydrolase-specific sensor compounds of the present invention.

According to the present invention this object is furthermore solved by providing the hydrolase-specific sensor compound or the pharmaceutical composition of the present invention for detecting a hydrolase, in particular hydrolase activity.

According to the present invention this object is furthermore solved by providing the hydrolase-specific sensor compound or the pharmaceutical composition of the present invention as an in vivo imaging reporter for detecting a hydrolase, in particular hydrolase activity, wherein the detection is preferably via MRI, magnetic particle imaging (MPI), optical imaging, ultrasound or nuclear imaging.

According to the present invention this object is furthermore solved by providing the hydrolase-specific sensor compound or the pharmaceutical composition of the present invention for diagnosing and/or treating a disease or disorder, which involves the activity or dysregulation of a hydrolase.

According to the present invention this object is furthermore solved by providing the hydrolase-specific sensor compound of the present invention as a vehicle or shuttle for a therapeutic compound.

According to the present invention this object is furthermore solved by providing a method of detecting the presence or absence of a hydrolase in a sample.

The detection method of the present invention comprises the steps of

(i) providing a sample,

(ii) providing a hydrolase-specific sensor compound of the present invention, (iii) incubating the sample and the sensor compound,

(iv) detecting the aggregation or accumulation of nanoparticles or cores (P), wherein the aggregation or accumulation indicates the presence of the hydrolase in the sample and/or indicates the presence of the hydrolase in an active state in the sample.

DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

Before the present invention is described in more detail below, it is to be understood that this invention is not limited to the particular methodology, protocols and reagents described herein as these may vary. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to limit the scope of the present invention which will be limited only by the appended claims. Unless defined otherwise, all technical and scientific terms used herein have the same meanings as commonly understood by one of ordinary skill in the art. For the purpose of the present invention, all references cited herein are incorporated by reference in their entireties.

Hydrolase-specific sensor compounds

As outlined above, the present invention provides hydrolase-specific sensor compounds.

The hydrolase-specific sensor compounds of the present invention comprise (a) a nanoparticle or core (P) and (b) a multimeric domain, wherein multimeric domain refers to a domain comprising several sub-domains.

"Hydrolase" particularly refers to any protein or enzyme or cleaving protein that catalyzes the hydrolysis of a chemical bond or linkage, such as

• ester bonds (esterases: nucleases, phosphodiesterases, lipase, phosphatase),

• sugars, glycoside bonds (glycosidases, glycosylases, DNA glycosylases, glycoside hydrolase),

• ether bonds,

• peptide bonds (proteases, peptidases),

• carbon-nitrogen bonds, other than peptide bonds,

• acid anhydrides (acid anhydride hydrolases, including helicases and GTPase),

• C-C bonds,

• halide bonds, • P-N bonds,

• S-N bonds,

• C-P bonds,

• S-S bonds,

• C-S bonds.

The term "hydrolase" further refers to any isoforms, precursors or zymogene or ribozyme forms.

Examples are proteases (or proteinases, peptidases), amidases, amylases, carboxypeptidases, desoxyribonucleases (DNAses), esterases, glycosidases, hemicellulases, lactase, peptidases, urease, lipases.

Thus, a hydrolase-specific sensor compound according to the invention is particularly suitable to detect the presence of a particular hydrolase, as described herein, in particular a hydrolase- specific sensor compound according to the invention is particularly suitable to detect the activity of a particular hydrolase, as described herein.

Briefly, in the hydrolase-specific sensor compounds the nanoparticle or core (P) is electrostatically stabilized or is coated with hydrophobic compounds/moieties and the entire sensor compound is sterically stabilized by a sub-domain of the multimeric domain, wherein "stabilization" refers to prevention of aggregation or accumulation. Thus, an intact sensor compound is stable in suspension, i.e. it does not aggregate with other sensor compounds or surrounding tissue, but after removal of the sub-domain of the multimeric domain, it will become aggregative or adsorptive, i.e. sensor compounds will aggregate or will accumulate in the biological tissue. The design of the hydrolase-specific sensor compounds can influence the parameters of stabilization and aggregation tendency, namely the stabilization strength, the aggregation rate, the blood circulation time (stealth properties). For further details, see Figure IB and below.

For example, the ratio of nanoparticle or core (P) and multimeric domain influences the stabilization and aggregation of the sensor compounds.

Preferably, the ratio between the nanoparticle or core (P) and the multimeric domain is in the range of 1 :2 to 1 :100, preferably in the range of 1 :3 and 1 :50, more preferably in the range of 1 :4 and 1 :15, even more preferably in the range of 1 :4 and 1 :12. - Coated nanoparticle or core (P)

The nanoparticle or core (P) is coated with positively or negatively charged moieties (CM) or with hydrophobic moieties (HM).

Thus, the positively or negatively charged moieties (CM) or hydrophobic moieties (HM) form a shell or coat around the nanoparticle or core (P). This shell or coat stabilizes the nanoparticle or core (P) in an electrostatic manner [(electrostatic stabilization) in the case of the charged moieties (CM)] or makes the cores suspendable in lipophilic compounds [in the case of hydrophobic moieties (HM)], thus, prevents or reduces aggregation and/or accumulation of the nanoparticles or cores. This shell or coat furthermore allows attachment of or interactions with further charged/hydrophobic components or moieties, such as a sub- domain of the multimeric domain, namely the coupling domain (CO).

The amount of positively or negatively charged moieties (CM) or hydrophobic moieties (HM) on the nanoparticle or core (P), i.e. the density and/or thickness of coating or the shell, influences the stabilization of the nanoparticle or core, which has to be selected depending on the respective nanoparticle or core (P) as well as the intended applications of the hydrolase- specific sensor compounds. The skilled artisan will be able to make these selections based on the disclosure of this application.

Preferably, the positively or negatively charged moieties (CM) are selected from

- ions,

- organic acids, such as carboxylic acids, monocarboxylic acids, dicarboxylic acids, polycarboxylic acids, amino acids, monoamino acids, diamino acids, polyamino acids, and derivatives and salts thereof;

- amines and polyamines;

- inorganic acids, such as phosphoric acid, sulfuric acid;

- phospholipids, glycerophosphate; or the salts or combinations thereof. More preferably, the positively charged moieties (pos CM) are selected from amino acids, amines, polyamines, and the negatively charged moieties (neg CM) are selected from citrate, phosphate, diphosphates, triphosphates, sulfate.

Preferably, the (uncharged) hydrophobic or lipophilic moieties (HM) are selected from

- fatty acids (such as oleic acid),

- hydrophobic cyclic compounds,

- hydrophobic amino acids.

The nanoparticle or core has a diameter of equal to or less than 30 run, preferably in the range of 2 to 20 nm, more preferably 3 to 15 nm.

The nanoparticle or core (P) is detectable, i.e. it can be detected by imaging and/or spectroscopic methods. Preferably, the nanoparticle or core (P) is detectable / can be detected in biological samples, in tissues and more preferably in vivo.

Preferably, the nanoparticle or core (P) is magnetic, fluorescent or radiant, i.e. it can be detected by means of nuclear imaging, fluorescence spectroscopy, fluorescence imaging, magnetic particle imaging (Gleich and Weizenecker, 2005) and magnetic resonance imaging.

In a preferred embodiment, the nanoparticle or core (P) is superparamagnetic.

In this embodiment, the nanoparticle or core (P) is selected from metal ions, metal oxides, metal salts, metal hydroxides, metal oxyhydroxides, mixtures of different metals and/or metal oxides as well as combinations thereof, wherein the metal ions are preferably selected from the group of ions of iron, manganese, copper, indium, gallium and lanthanides, such as gadolinium, europium, erbium, ytterbium, dysprosium, or preferably iron oxide, iron hydroxide and iron oxyhydroxide and/or mixtures thereof

In a further preferred embodiment, the nanoparticle or core (P) is a non-magnetic nanoparticle, preferably - a fluorescent quantum dot (Medintz et al. 2005),

- gas-filled microbubbles for ultrasound imaging (Klibanov 2009).

In a preferred embodiment, the coated nanoparticle is an electrostatically stabilized nanoparticle with an acidic coat, such as a citrate coat, more preferably the coated nanoparticle is an electrostatically stabilized, citrate coated Very Small iron Oxide Particle (VSOP) (Taupitz et al. 2004, Warmuth et al. 2007).

In a preferred embodiment, the coated nanoparticle is a lipophilic/hydrophobic nanoparticle with a lipid, such as a oleic acid (such as described in Sun et al., 2004).

- Multimeric domain

The multimeric domain comprises the following sub-domains:

- at least one coupling domain (CO), which interacts with the positively or negatively charged moieties (CM) or with the hydrophobic moieties (HM),

- a polymer envelope domain (E).

The multimeric domain comprises preferably the above three sub-domains or domains.

Preferably, the domain CO and the domain CL are comprised once (each one time) in the multimeric domain. However, in certain embodiments, the multineric domain can comprise several of the domain CO and/or the domain CL, such as 2, 3, 4 or more.

The domain CO and the domain CL are linked via a linker or spacer (L).

The polymer envelope domain (E) is covalently coupled to the domain CL.

- Coupling domain (CO)

The domain CO interacts with the positively or negatively charged moieties (CM) of the nanoparticle or core (P) or with the hydrophobic moieties (HM) of the nanoparticle or core

(P)- Thus, the domain CO is selected depending on the coat/shell of positively or negatively charged moieties (CM) of the nanoparticle or core (P), and comprises preferably charged moieties which are oppositely charged, or it is selected depending on the coat/shell of (uncharged) hydrophobic moieties (HM) of the nanoparticle or core (P)

The domain CO is preferably a peptide or comprises preferably a peptide or the domain CO is preferably a hydrophobic lipid chain or comprises preferably a hydrophobic lipid chain.

The at least one CO domain is preferably selected from / comprises preferably

- in case of negatively charged moieties (neg CM): a peptide sequence comprising several amino acids with positively charged side chains, preferably

Arg, Lys unnatural or synthetic amino acids with positively charged side chains;

- in case of positively charged moieties (pos CM): a peptide sequence comprising several amino acids with negatively charged side chains, preferably

GIu, Asp, unnatural or synthetic amino acids with negatively charged side chains,

- in case of hydrophobic moieties (HM): a peptide sequence comprising several amino acids with hydrophobic side chains, preferably

Tip, Phe, unnatural or synthetic amino acids with hydrophobic side chains, and/or a peptide sequence comprising several amino acids with hydrophobic side chains (preferably Trp, Phe, unnatural or synthetic amino acids with hydrophobic side chains) and/or a lipid sequence comprising hydrophobic lipid chains (preferably fatty acids) or other hydrophobic compounds (such as hydrophobic cyclic compounds) and/or combinations of the peptide and lipid sequence(s) (combinations thereof).

- Cleavage domain (CL)

The at least one cleavage domain (CL) comprises at least one cleavage site or recognition motif of the hydrolase to be sensed or detected by the hydrolase-specific sensor compound. The hydrolase is preferably selected from

- a protease or proteinase or peptidase, such as serine proteases, threonine proteases, cysteine proteases, aspartic acid proteases, metalloproteases, such as MMP-9 or MMP-2, glutamic acid proteases;

- an esterase such as a nuclease (such as a DNase or RNase, such as EcoRI, EcoRII), a phosphodiesterase, a lipase, a phosphatase;

- an amylase, such as alpha-amylase, beta-amylase.

Further preferred examples are amidases, carboxypeptidases, glycosidases, hemicellulases, lactase, urease, lipases.

Preferably, the hydrolase is tissue-specific and/or disease-specific, in particular tumor- specific, or is preferably localized in specific tissues or specific tumors.

Thus, a hydrolase which is to be sensed or detected is chosen, when the following is indicative for a certain disease or disease state, such as cancer:

- presence or activity increase OR absence or activity reduction of the hydrolase, and/or

- presence or activity increase OR absence or activity reduction of the hydrolase at a certain localization, such as in specific tissues or body regions/fluids and/or

- presence or activity increase OR absence or activity reduction of the hydrolase at certain time points, and/or presence or increase OR absence or reduction of the hydrolase in an active state (i.e. when it is able to cleave/hydrolize),

For example and as shown in the Examples and Figures, MMP-9 (matrix metalloproteinase 9) can be the hydrolase to be detected, which is an enzyme important in inflammation, atherosclerosis, and tumor progression. As cleavage motif the inventors chose a recognition site of the MMP-9, which was previously used to prepare a MMP-9-activatable fluorescent probe (8, 9). MMPs have been identified as important regulators of pathological remodeling of extracellular matrix in cancer and inflammation (10). Using fluorescent smart probes Bremer et al. developed a new concept to monitor the success of MMP inhibition by in vivo imaging, which may ultimately enable monitoring therapeutic responses in the large spectrum of diseases with alterations of the extracellular matrix (11). For further details, see Examples.

Depending on the hydrolase to be sensed or detected by the hydrolase-specific sensor compound of the invention, the at least one cleavage site or recognition motif of the hydrolase of the domain CL is preferably an amino acid sequence, a nucleotide sequence or a saccharide sequence or other covalent ester, ether, peptide, glycoside, acid anhydride or C-C-bonds.

In a preferred embodiment, the at least one cleavage domain (CL) comprises more than one cleavage sites or recognition motifs of the hydrolase, preferably of different hydrolases, more preferably two different cleavage sites or recognition motifs of two different hydrolases.

In this embodiment, the several cleavage sites or recognition motifs are arranged in a serial manner, such that the cleavage of only one of the several sites or motifs releases the domain E

(OR-switch), or the several cleavage sites or recognition motifs are arranged such that only the cleavage of all sites or motifs releases the domain E (AND-switch), wherein the CL domain preferably has a loop structure.

See Figure 5.

Thus, the sensor compound of the present invention can be used for the detection/sensing of several hydrolases, for example two hydrolases.

- Linker or Spacer (L)

The domain CO and the domain CL are linked via a linker or spacer (L).

Linker or spacer are known to the skilled artisan, such as polyalanine, polyglycin, carbohydrates, (CH₂)_n groups. The skilled artisan will, thus, be able to select the respective suitable linker(s) or spacer(s) depending on the respective application. The linker (L) is preferably a peptide sequence comprising several amino acids, wherein the amino acids are preferably selected from GIy, Ala or Pro. Linker and linker sequences are known in the art.

- Polymer envelope domain (E)

The polymer envelope domain (E) is covalently coupled to the domain CL.

The polymer envelope domain (E) is preferably selected from biocompatible polymer(s) and/or copolymers.

The domain E is preferably selected from: polyethylene glycol or derivatives thereof, like mPEG (such as mPEG-2000, mPEG- 5000, mPEG- 10000), polysaccharides, such as dextran, - polypeptides.

As discussed above, in the hydrolase-specific sensor compounds the nanoparticle or core (P) is electrically stabilized by the positively or negatively charged moieties (CM) (or is coated with hydrophobic moieties (HM)). The entire sensor compound is sterically stabilized by a sub-domain of the multimeric domain (namely the polymer envelope domain E).

"Stabilization" refers to prevention of aggregation. Thus, an intact sensor compound is stable in suspension, i.e. it does not aggregate with other sensor compounds or does not adsorb to surrounding tissue structures in case of in vivo application, but after removal of the domain E of the multimeric domain (which occurs after cleavage of the cleavage site or recognition motif of the hydrolase by the hydrolase), the sensor compounds will become aggregative or adsorptive, i.e. the sensor compounds will aggregate or will adsorb to surrounding tissue structures in case of in vivo application.

After cleavage of the cleavage site or recognition motif of the hydrolase which leads to a removal of domain E, the surface of the sensor compound(s) will be charged or hydrophobic, because the surface is now formed by the domains CO (which are charged or hydrophobic) and the positively or negatively charged moieties (CM) or the hydrophobic moieties (HM) of the nanoparticle/core, which leads to an aggregation of the compounds or to an adsorption to surrounding tissue structures.

Preferably, the sensor compound has a diameter of equal to or less than 200 nm, preferably in the range of 10 to 80 nm, more preferably in the range of 15 to 40 nm.

- Mode of operation

As described above, due to the sterical stabilization the hydrolase-specific sensor compounds of the present invention are stable in suspension and do not aggregate. They become aggregative and adsorptive after cleavage of the at least one cleavage site or recognition motif by the hydrolase, which removes the domain E from the sensor compounds. The aggregation or accumulation due to adsorption of the detectable cores/nanoparticles can then be detected and is indicative for the specific hydrolase or its activity/active state. The aggregation or adsorption of the compounds leads to an accumulation of even more compounds, which will ultimately increase the detected signal.

In an embodiment with a magnetic or superparamagnetic core/nanoparticle: The intact sensor has stable low R2-relaxivity which increases when the sensors aggregate after cleavage of the at least one cleavage site or recognition motif by the hydrolase, such that the sensor is stable in suspension and becomes aggregative with increasing R2-relaxivity.

This makes the hydrolase-specific sensor compounds of the present invention particularly suitable as hydrolase sensors or reporter probes, in particular in vivo.

The hydrolase-specific sensor compounds of the present invention can be transformed from state (i) to state (ii): wherein state (i) is the intact state of the sensor compound,

= long circulating, stealth compound, i.e. domain E-covered stable "stealth" particles/compounds, which are stable and can freely circulate in the body, wherein state (ii) is the cleaved state of the sensor compound,

= aggregative and therefore accumulating compound, i.e. particles/compounds without domain E with charged or hydrophobic surfaces which aggregate and also accumulate where the hydrolase is active and located. In an embodiment with a magnetic core/nanoparticle:

The hydrolase -specific sensor compounds of the present invention are the first high-relaxivity nanosensors to be used for in vivo imaging of hydrolase activity by magnetic resonance imaging. Upon specific hydrolase cleavage, the sensor compounds rapidly switch from a stable low-relaxivity stealth state (state (i)) to become highly adhesive, aggregating high- relaxivity particles (state (U)) with tunable activation kinetics.

The clustering of superparamagnetic nanoparticles causes a substantial increase in R2- relaxivity, called magnetic switch (6). Furthermore, the particles are converted from mPEG- covered stealth particles into highly aggregative particles with strongly charged surfaces (12). Consequently, once injected, the intact particles/compounds should remain for long time in the blood circulation until they reach a hydrolase- (e.g. MMP-9) expressing target tissue, where they are converted into aggregative particles and accumulate.

In certain embodiments, the sensor compounds of the present invention comprise at least one further component, preferably linked to the multimeric domain.

Such further component(s) are preferably selected from:

- label(s), such as chromophor(s), fluorophor(s), isotope(s),

- therapeutic compound(s), such as chemotherapeutic agent(s),

- (further) moiety/moieties for magnetic thermotherapy.

"Magnetic thermotherapy" or thermotherapy using magnetic nanoparticles is a technique for interstitial hyperthermia and thermoablation based on magnetic field-induced excitation of biocompatible superparamagnetic nanoparticles. It is used for direct cancer cell killing and as a radiosensitization technique for adjuvant therapy. The nanoparticles are directly injected into the tumors and exposed to magnetic field regimes, preferably combined with traditional external radiotherapy, which leads to a heating of the tumor cells and, thus, inhibiting of tumor growth and ultimately to killing of the tumor cells. See e.g. magforce^® (Thiesen and Jordan 2008). In a preferred embodiment, where the further component is a therapeutic compound, the hydrolase-specific sensor compounds of the present invention are suitable vectors or shuttles for the therapeutic compound. The therapeutic compound(s) can be specifically transported to the tissue/localization of the hydrolase.

Methods of producing the sensor compounds

The design of the multimeric domain is an important step for producing the hydrolase-specific sensor compounds of the invention.

Said design involves selection of a suitable cleavage site or recognition motif of the hydrolase to be sensed/detected, design of the linkage of cleavage domain (CL) with polymer envelope domain (E) (i.e. the linker or spacer (L)), wherein one criterion is that the hydrolase has to have enough space in order to reach the cleavage site or recognition motif, - design of a suitable coupling domain (C) which is compatible with the charged coat or the hydrophobic coat of the nanoparticle/core.

In case that the coupling domain, cleavage domain and/or linker are peptides:

Peptides can be prepared by a variety of procedures readily known to those skilled in the art, in general by synthetic chemical procedures and/or genetic engineering procedures.

Synthetic chemical procedures include more particularly the solid phase sequential and block synthesis (Erickson and Merrifield, 1976). The solid phase sequential procedure can be performed using established automated methods such as by use of an automated peptide synthesizer. The peptides of the present invention may also be obtained by coupling (poly)peptide fragments that are selectively protected, this coupling being effected e.g. in a solution.

Peptides can further be produced by genetic engineering techniques as known to the skilled artisan, in eukaryotic and/or prokaryotic expression systems. An example of a synthesis is given below and in the Examples. See also Figure IA.

In a preferred embodiment, the sensor compound of the present invention comprises a multimeric domain which comprises the CO domain and the CL domain (linked via a linker) which comprises a peptide with the amino acid sequence of SEQ ID NO. 1 or 2.

SEQ ID NO. 1

GGPRQJTAGKGGGG-RRRRRGRRRRR SEQIDNO.2 GGKGGPKQJTAGGGKGG-RRRRRGRRRRR

Pharmaceutical compositions

As outlined above, the present invention provides a pharmaceutical composition comprising at least one hydrolase-specifϊc sensor compound of the present invention as defined herein and optionally pharmaceutically acceptable carrier(s) and/or excipient(s).

The pharmaceutical compositions according to the present invention are very well suited for all the uses and methods described herein.

A "pharmaceutically acceptable carrier or excipient" refers to any vehicle wherein or with which the pharmaceutical compositions according to the invention may be formulated. It includes a saline solution such as phosphate buffer saline. In general, a diluent or carrier is selected on the basis of the mode and route of administration, and standard pharmaceutical practice.

The pharmaceutical composition are preferably formulated as injectable, oral formulation, dermal application form.

Uses of the sensor compounds

- Hydrolase sensor / reporter

As outlined above, the present invention provides the sensor compound(s) of the present invention or the pharmaceutical composition of the present invention for detecting a hydrolase, in particular hydrolase activity. The detection is preferably via MRI, magnetic particle imaging (MPI), optical imaging, ultrasound or nuclear imaging. The detection depends on the nanoparticle/core (P) chosen.

The sensor compound(s) can be used for in vitro as well as in vivo detection of the particular hydrolase or its activity.

Depending on the design of the domain CL (see above, e.g. as AND-switch or OR-switch, Figure 5), the sensor compound(s) can be used for detecting several hydrolases.

As outlined above, the present invention provides the sensor compound(s) of the present invention or the pharmaceutical composition of the present invention as an in vivo imaging reporter for detecting a hydrolase, in particular its activity or active state, wherein the detection is preferably via MRI, MPI, optical imaging, ultrasound or nuclear imaging.

- Shuttle / vectors

As outlined above, the present invention provides the sensor compound(s) of the present invention as a vehicle or shuttle for a therapeutic compound.

In this embodiment, the sensor compound(s) comprises a therapeutic compound.

The sensor compound(s) of the present invention then combine their hydrolase specificity, and, thus, local in vivo specificity (such as tissue, bodily fluid, tumor etc), with the capability to transport therapeutic compound(s) to that specific localization in vivo.

- Medical uses

As outlined above, the present invention provides the sensor compound(s) of the present invention or the pharmaceutical composition of the present invention for diagnosing and/or treating a disease or disorder, which involves the activity or dysregulation of a hydrolase.

The detection is preferably via MRI, MPI, optical imaging, ultrasound or nuclear imaging. The disease or disorder, which involves the activity or dysregulation of a hydrolase, is preferably selected from a tumor, atherosclerosis, inflammation, neurodegenerative diseases, diseases with remodelling of extracellular matrices.

The following is preferably indicative for the disease or disease state:

- presence or absence / up or down regulation of the hydrolase, and/or

- presence or absence / up or down regulation of the hydrolase at a certain localization, such as in specific tissues or body regions/fluids and/or

- presence or absence / up or down regulation of the hydrolase at certain time points, and/or

- presence or absence / up or down regulation of the hydrolase in an active state (i.e. when it is able to cleave/hydrolize).

As outlined above, the present invention also provides the sensor compound(s) of the present invention or the pharmaceutical composition of the present invention for diagnosing and/or treating a disease or disorder, which involves the activity or dysregulation of a hydrolase and/or which can be treated with the therapeutic compound,

In this embodiment, the sensor compound(s) comprises a therapeutic compound.

The detection is preferably via MRI, MPI, optical imaging, ultrasound or nuclear imaging.

The disease or disorder, which involves the activity or dysregulation of a hydrolase and/or which can be treated with the therapeutic compound, is preferably selected from a tumor, atherosclerosis, inflammation, neurodegenerative diseases, diseases with remodelling of extracellular matrices.

The following is preferably indicative for the disease or disease state: presence or absence / up or down regulation of the hydrolase, and/or presence or absence / up or down regulation of the hydrolase at a certain localization, such as in specific tissues or body regions/fluids and/or presence or absence / up or down regulation of the hydrolase at certain time points, and/or presence or absence / up or down regulation of the hydrolase in an active state (i.e. when it is able to cleave/hydrolize).

As outlined above, the present invention also provides the sensor compound(s) of the present invention or the pharmaceutical composition of the present invention as theranostic, preferably in magnetic thermotherapy of cancer.

In this embodiment, the sensor compound(s) preferably comprises a (further) moiety/moieties for magnetic thermotherapy and optionally a therapeutic compound.

A "theranostic" refers to compounds that comprise a moiety, which allows the detection or imaging of the compounds (such as the nanoparticle or core of the present sensor compounds) and comprise additionally a moiety that is acting as a therapeutic or can be used as therapeutic when activated by another device.

The sensor compound(s) of the invention can be used as theranostics since their specific accumulation can be exploited for particle delivery in magnetic thermotherapy of cancer (e.g. magforce^®), which currently requires magnetic nanoparticles to be injected directly into the target.

As discussed above, "magnetic thermotherapy" or thermotherapy using magnetic nanoparticles is a technique for interstitial hyperthermia and thermoablation based on magnetic field-induced excitation of biocompatible superparamagnetic nanoparticles. It is used for direct cancer cell killing and as a radiosensitization technique for adjuvant therapy. The nanoparticles are directly injected into the tumors and exposed to magnetic field regimes, preferably combined with traditional external radiotherapy, which leads to a heating of the tumor cells and, thus, inhibiting of tumor growth and ultimately to killing of the tumor cells. See e.g. magforce^® (Thiesen and Jordan, 2008).

The sensor compound(s) of the invention are very suitable as theranostic / for magnetic thermotherapy, because

- they do not have to be injected directly into the target tissue,

- they can be administered in a less invasive way, such as orally, intravenously, intraarterially, dermal application, - they will circulate in the system and specifically accumulate at the localization of the hydrolase they are specific for.

- Route of administration

Preferably, the route of administration of the sensor compounds or pharmaceutical compositions of the present invention is selected from subcutaneous, intravenous, intraarterially, oral, nasal, intramuscular, transdermal, inhalative, by suppository.

- Therapeutically effective amount

The sensor compounds or the pharmaceutical compositions of the invention are provided such that they comprise a therapeutically effective amount of said sensor compound(s) or said pharmaceutical composition(s).

A "therapeutically effective amount" of a sensor compound or a pharmaceutical composition of this invention refers to the amount that is sufficient to accomplish / achieve the desired therapeutic effect.

A preferred therapeutically effective amount is in the range of 10 μg to 10 mg per kg body weight, preferably 10 μg to 5 mg more preferably 10 μg to 1 mg.

The preferred therapeutically effective amount depends on the respective application and desired outcome of diagnosis and/or treatment. The skilled artisan will be able to determine suitable therapeutically effective amounts.

Hydrolase detection method

As outlined above, the present invention also provides a method of detecting the presence or absence of a hydrolase in a sample.

The detection method of the present invention comprises the steps of

(i) providing a sample,

(ii) providing a hydrolase-specific sensor compound of the present invention,

(iii) incubating the sample and the sensor compound, (iv) detecting the aggregation and/or accumulation of nanoparticles or cores (P), i.e. the aggregation and/or accumulation of the sensor compounds in the cleaved state / state (ii), see above.

The aggregation/accumulation indicates the presence of the hydrolase in the sample and/or indicates the presence of the hydrolase in an active state (i.e. the hydrolase activity) in the sample.

Thus, if no aggregation/accumulation can be detected this indicates the absence of the hydrolase in the sample and/or indicates the absence of the hydrolase in an active state (i.e. absence of hydrolase activity) in the sample.

"Accumulation" refers to attachment of the activated particles to tissue structures in the target areas and therefore the increase of the number of nanoparticles or cores (P) in the target area. The accumulation preferably occurs due to adsorption to surrounding tissue.

"Aggregation" refers to the alignment of the activated particles with each other.

Accumulation of the particles in the target area allows detecting the particles. In case that ample particles accumulate in the target area, then they can align to/with each other (i.e. aggregate) and, thus, produce a magnetic switch effect, as discussed herein above.

The detection of the aggregation and/or accumulation depends on the nature of the nanoparticles or cores (P). The detection can be carried out by

- detecting increase in R2-relaxivity, preferably via MRI,

- detecting magnetic particle cores directly, preferably via MPI,

- detecting increase in fluorescence intensity,

- detecting increase in radiation,

- detecting increase of echoes in ultrasound.

Examples ofhydrolase-specific sensor compounds

Here the inventors present the first high-relaxivity nanosensor compound to be used for in vivo imaging of protease activity by magnetic resonance imaging. Upon specific protease cleavage, the nanoparticles/compounds rapidly switch from a stable low-relaxivity stealth state to become highly adhesive, aggregating high-relaxivity particles/compounds with tunable activation kinetics. As an example, the inventors chose a cleavage motif of matrix metalloproteinase 9, an enzyme important in inflammation, atherosclerosis, and tumor progression.

Here the inventors describe a new design of protease-sensitive nanosensors, which are based on electro-statically stabilized, citrate coated Very Small iron Oxide Particles (VSOP) with a hydrodynamic diameter of 7.7 ±2.1 nm (see Figure 2A) instead of larger sterically stabilized nanoparticles (over 20 nm). The inventors have previously developed a pharmacologically formulated variant of these super-paramagnetic particles (VSOP-C 184) for magnetic resonance angiography (7). To add protein/hydrolase-sensing capability, the inventors designed a construct shown in Figure IA consisting of a peptide and a methyl- polyethylenglycol polymer (mPEG, molecular weight 5,000). The peptide consists of a cleavage domain with the enzyme recognition motif and a highly positively charged, arginine- rich coupling domain, which are connected by a linker sequence. For analysis by fluorescence methods a fluorescine is coupled to the peptide. In a first step this peptide was reacted with NHS-mPEGs at the end of the cleavage domain. In a second step, after purification by gel filtration and HPLC control for purity, these peptide-mPEG copolymers were mixed in different ratios with the VSOP. The peptide-mPEGs absorb at the strongly negatively charged surface of the citrate-coated VSOP with their positively charged coupling domains. The resulting Protease-Specific iron Oxide Particles (PSOP) with the copolymers at the surface are no longer electrostatically but sterically stabilized, i.e., the natural tendency of superparamagnetic magnetite nanocores to aggregate is countered by the thick mPEG-coat and not by the negatively charged surface of the VSOP as before. Instead of PEG other macromolecules such as dextran can provide sterical stabilization as well. A ratio of 6 peptide-mPEGs per VSOP yielded 6x-MMP-9-PSOP with a hydrodynamic diameter of 24.9 ±7.0 nm (Figure 2B). Mixtures with ratios between 6 and 16 peptide-mPEGs consistently yielded particles with sizes around 24 nm whereas ratios below 6 resulted in particles over 30 nm in size, probably due to insufficient sterical stabilization (see Figure 3 and Table 1).

As cleavage motif, the inventors chose a recognition site of the MMP-9, which was previously used to prepare a MMP-9-activatable fluorescent probe (8,9). MMPs have been identified as important regulators of pathological remodeling of extracellular matrix in cancer and inflammation (10). Using fluorescent smart probes Bremer et al. developed a new concept to monitor the success of MMP inhibition by in vivo imaging, which may ultimately enable monitoring therapeutic responses in the large spectrum of diseases with alterations of the extracellular matrix (11).

For illustration a model of 6x-MMP-9-PSOP (6 peptide-mPEGs per particle), based on the sequence of the peptide-mPEG complexes and particle size measurements, is shown in Figure 2C.

The function of the particles is explained in Figure IB. When the sterically stabilized MMP-9- PSOPs (step 1) are exposed to MMP-9, the protease cleaves the peptide at the recognition site (step 2), resulting in loss of the sterically stabilizing mPEG shell. Due to the superparamagnetic properties of the iron oxide cores and the ambivalent surface of the remaining particles with positively (coupling domains) and negatively charged areas (citrate coat of VSOP) the particles aggregate driven by magnetic and electrostatic attraction (step 3).

This process has two important consequences: First, clustering of the superparamagnetic nanoparticles causes a substantial increase in R2-relaxivity, called magnetic switch (6). Second, the particles are converted from mPEG-covered stealth particles into highly aggregative particles with strongly charged surfaces (12). Conveniently, mPEG-5,000 has been shown to be optimal for achieving stealth properties for nanoparticles (13). Consequently, once injected, the intact PSOP's should remain for long time in the blood circulation until they reach a MMP-9 expressing target tissue, where they are converted into aggregative particles and accumulate.

Furthermore, the ratio of peptide-mPEG copolymers to VSOP cores determines the activation kinetics of the resulting PSOPs: the more copolymers on the particles, the more peptides have to be cleaved off to destroy the sterical stabilization.

The nanosensors presented here have several key characteristics making them a good candidate for an enzyme/hydrolase reporter probe for in vivo MRI and translation into the clinical setting:

Synthesis of the particles is fairly straightforward.

They can be adapted to any proteases or other cleaving proteins/enzymes (hydrolases). - Their sensitivity can be modulated by changing the ratio of peptide-mPEG copolymers to particle cores.

Polyethylene glycols have been proven to be biocompatible (listed in the pharmacopeia) and provide stealth properties, which is a prerequisite for a sufficiently long circulation time in vivo. Together with the nanosensors' small diameter of about 25 run, these properties ensure good bioavailability in the desired target tissues. PSOP become larger upon activation and relaxivity increases. This property allows the in vivo application of the nanoparticles. The parent VSOP has been shown to be safe in preclinical (15) and clinical trials (7).

- In contrast to near infrared fluorescence imaging, MRI with PSOP is a potential candidate for whole body imaging of protease/hydrolase activity in humans.

The particles have great potential as reporter probes for diagnostic imaging of enzyme/hydrolase activity by MRI. Moreover, the particles can be used as theranostics since their specific accumulation can be exploited for particle delivery in magnetic thermotherapy of cancer (e.g. mag/orce^®), which currently requires magnetic nanoparticles to be injected directly into the target.

The following examples and drawings illustrate the present invention without, however, limiting the same thereto.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 Synthesis and function ofMMP-9-PSOP.

(A) Synthesis. In step (1) the 25-amino acid peptides consisting of an arginine-rich coupling domain and a cleavage domain with the recognition site for MMP-9 linked by a glycine bridge are reacted with NHS-methyl-polyethylene glycol (NHS-mPEG). The resulting peptide-mPEG copolymers are purified by gel filtration to remove unreacted mPEG and NHS. In step (2) peptide-mPEGs are mixed with VSOPs, yielding MMP-9-PSOPs.

(B) Function. When sterically stabilized PSOPs with an intact mPEG shell (1) are exposed to a protease specific to the cleavage motif the peptide-mPEGs are cut at the cleavage domain, resulting in a loss of sterical stabilization (2). The remaining particles aggregate due to the magnetic attraction of the iron oxide cores and the electrostatic attraction of the positive (arginine-rich coupling domain) and negative charged surface areas (acid shell). Figure 2 Size and model ofMMP-9-PSOP.

The hydrodynamic size distribution of the parent VSOP with 7.7 ±2.1 nm is shown in (A). With the copolymers attached to the surface the PSOP are still small at 25 nm with a narrow size distribution (B). For illustration a model of 6x-MMP-9-PSOP based on the peptide sequence, the structure of mPEG, and the size measurements is shown in (C). The parent VSOP consists of a 5-nm magnetite core (gray) covered by a negatively charged citrate shell (red). The peptide-mPEG copolymers are electrostatically bound by the positively charged coupling domains (blue). The mPEG polymers (light blue) are linked to the coupling domain via the cleavage domain (yellow) and a linker peptide. Fluorescein dyes (green).

Figure 3 Dependence of size and fluorescence quenching on the ratio of peptide-mPEG copolymers to VSOP.

Left axis: With an increasing number of peptide-mPEG copolymers per VSOP the hydrodynamic size (mean of distribution by number, SD) of MMP-9-PSOP decreases slightly up to a ratio of 6 peptide-mPEG per VSOP and stays constant around 24 nm up to a ratio of 16. An average ratio of 6 peptide-mPEG per VSOP seems to be necessary for good sterical stabilization. Below that ratio the particles most likely form more dimers or multimers. Right axis: Due to the proximity of the copolymer-coupled fluorescein dyes to each other and to the nanoparticle cores, strong quenching of fluorescence can be observed for PSOP with ratios up to 8, proving nearly complete binding of the copolymers to the VSOP. With higher ratios the quenching effect decreases, indicating incomplete coupling of copolymers due to saturation of the VSOP surface with peptide-mPEG copolymers.

Figure 4 Function of PSOP.

(A) Hydrodynamic size measurements. Time course of aggregation-induced size increase of the MMP-9-PS0P probe (0.125 nmol particles) induced by enzyme activation with 7.4 U of MMP-9. The aggregation of 12x-MMP-9-PSOP (12 peptide-mPEG copolymers per VSOP) was delayed by a factor of approximately two compared with 6x-MMP-9-PSOP (6 peptide- mPEGs per VSOP), proving that the activation kinetic of PSOP can be tuned by changing the ratio of peptide-mPEG per iron oxide core. There was no probe activation when the experiments were done in the presence of 30 μM MMP-9-inhibitor. (B-C) MRI experiments.

(B) Time course of activation of 6x-MMP-9-PSOP at four different particle concentrations. As aggregates form, the T2*-relaxivity of these particles increases, causing a drop in signal intensities on the gradient echo sequences to a minimum until no further decrease occurs because continuing aggregation and precipitation reduce the amount of water protons affected. MR image obtained at the time point indicated by the arrow. (C) Time course of signal intensities of 6x-MMP-9-PSOP (300 nM particle concentration) incubated with different concentrations of a MMP-9-inhibitor. (D) Inhibition of the T2* -time-shortening at the time point indicated by the arrow in (C). The 50% inhibitory concentration in this assay is approximately 10 nM. MR experiments were done with 1.3 U MMP-9 in 200 μl buffer.

Figure 5 The cleavage domain can be designed as AND-switch or as OR-switch.

Figure 6 Ex vivo immunohistology of MMP-9 and MMP -2.

Antibody staining against MMP-9 and MMP-2 in ex vivo samples confirm low expression of MMP-9 (A) and MMP-2 (C) in the BT-20 tumor. In contrast the HT-1080 tumors express high levels of MMP-9 (B) and MMP-2 (D). The MMP's are preferentially expressed in the tumor rim.

Figure 7 Prussian blue staining for iron oxide cores of the PSOP. The explanted sample tumors were stained with Prussian blue staining (see arrows) to reveal the accumulation of the PSOP. In contrast to the MMP-2/9-low expressing BT-20 tumor (A) the MMP-2/9-high expressing HT- 1080 tumor demonstrated a strong PSOP accumulation, indicating correct MMP activation of the PSOP.

EXAMPLES Example 1

Experimental procedures Synthesis.

(1) The synthesized fluorescein-labeled MMP-9 peptide ^Ii₂-GGPRQITA G-K(FITC)- GGGG-RRRRR-G-RRRRR-amide [SEQ ID NO. 1] (the italicized amino acids correspond to the MMP-9 substrate (16)) was confirmed by MALDI-TOF (MALDI 2, Shimadzu). The molecular weight was within 1 Da of the expected value. One mg of the MMP-9 peptide (in 100 μl DMSO) was reacted with 31 mg NHS-mPEG (O-[(N-Succinimidyl)succinyl- aminoethyl]-O'-methyl-polyethylene glycol 5'00O, Fluka) in 300 μl 0.1 M HEPES, pH 7.5, overnight at 4°C. The resulting MMP-9-peptide-mPEG copolymer was purified by gel filtration with BioGel P6 (BioRad, in 10 mM HEPES, 140 niM NaCl, pH 7.5). The absence of unreacted MMP-9 peptide was confirmed by HPLC using a reverse phase Cl 8 column with acetonitrile/water gradient. The concentration of the peptide-mPEG copolymers was determined spectrophotometrically by measuring peptide-bound fluorescein absorption (absorption at 494 run, extinction coefficient of 72,000 M^-1Cm^"1).

(2) VSOP (VSOP-C200) was purchased from Ferropharm GmbH. To prepare 6x-MMP-9- PSOP (with six MMP-9-peptides per VSOP) 1.25 nmol VSOP (3.25 μmol Fe assuming 2600 iron atoms per particle, data from Ferropharm GmbH) in 250 μl HEPES buffer (10 mM HEPES, 140 mM NaCl, pH 7.5) were mixed with 7.5 nmol MMP-9-peptide-mPEG in 250 μl HEPES buffer and stirred immediately. Other ratios (3 to 16) were prepared accordingly. Hydrodynamic diameters of MMP-9-PSOPs were determined by dynamic light scattering (Zetasizer Nano ZS, Malvern Instruments) in the same buffer. Relaxivities were measured with a MR spectrometer at 0.94 T (Bruker, Minispec MQ 40) according to the manufacturer's instructions.

For quenching experiments (Figure 3) 50 pmol VSOP was mixed with different amounts of the peptide-mPEG copolymers (150 pmol to 800 pmol) in 200 μl and subjected to fluorescence measurements (excitation/emission 494 / 521 nm, Hitachi Fluorescence Spectrophotometer F-7000). Ratios of these quenched fluorescences and corresponding unquenched fluorescences of equal copolymer concentrations without VSOP addition were calculated and compared with the fluorescence of free fluorescein dye mixed with VSOP accordingly.

Enzyme activation.

To demonstrate the ability of MMP-9 to activate MMP-9-PSOP (0.125 nmol particles in 50 μl) hydrodynamic size measurements were carried out before and after adding MMP-9 (7.4 U MMP-9, human, Calbiochem) at 37°C. For experiments with enzyme inhibition, MMP- 2/MMP-9 Inhibitor II (30 μM final concentration, Calbiochem) was added before the addition of MMP-9 enzyme. The hydrodynamic diameters (Zetasizer) were monitored for two hours. The incubation buffer for enzyme experiments was 10 mM HEPES, 140 mM NaCl, 1.3 mM CaCl₂, and 50 μM ZnCl₂, pH 7.5. MR imaging.

For the MR experiments (Fig. 4B) four different particle concentrations of 6x-MMP-9-PSOP (30O nM, 150 nM, 75 nM, and 38 nM particle concentration) were incubated with 1.3 U MMP-9 in 200 μl incubation buffer (see above) at 37°C. All inhibitor experiments (Fig. 4C and D) were done under identical conditions using a particle concentration of 300 nM. All enzyme reactions were imaged with a clinical 1.5-T MR scanner (Siemens Sonata). The gradient echo sequence with 12 echo times (TR = 100 ms, TE = 3.1-44.8 ms) was repeated 200 times over 50 min. The images were analyzed with OsiriX DICOM viewer, ImageJ (National Institutes of Health, USA), and Prism 5 (GraphPad Software). Curve fits for T2 calculation and enzyme inhibition (logarithmic inhibitor response curve, standard slope) were done with Prism 5.

Molecular modeling.

The 5-nm octahedral magnetite core of VSOP-C200 with approximately 2,600 iron atoms and 75 citrate shell molecules per core (data provided by Ferropharm GmbH) was generated with CrystalMaker (CrystalMaker Software). Molecular modeling of MMP-9-PSOP was done based on the size measurements and the sequence of the MMP-9 peptide and NHS-mPEG (MW 5,000) using the PyMOL Molecular Graphics System (17).

Results Synthesis

Here the inventors describe a new design of protease-sensitive nanosensors, which are based on electro-statically stabilized, citrate coated Very Small iron Oxide Particles (VSOP) with a hydrodynamic diameter of 7.7 ±2.1 nm (see Figure 2A) instead of larger sterically stabilized nanoparticles (over 20 nm).

The inventors have previously developed a pharmacologically formulated variant of these super-paramagnetic particles (VSOP-C 184) for magnetic resonance angiography (7). To add protein/hydrolase-sensing capability, the inventors designed a construct shown in Figure IA consisting of a peptide and a methyl-polyethylenglycol polymer (mPEG, molecular weight 5,000). The peptide consists of a cleavage domain with the enzyme recognition motif and a highly positively charged, arginine-rich coupling domain, which are connected by a linker sequence. For analysis by fluorescence methods a fluorescine is coupled to the peptide. In a first step this peptide was reacted with NHS-mPEGs at the end of the cleavage domain. In a second step, after purification by gel filtration and HPLC control for purity, these peptide- mPEG copolymers were mixed in different ratios with the VSOP. The peptide-mPEGs absorb at the strongly negatively charged surface of the citrate-coated VSOP with their positively charged coupling domains. The resulting Protease-Specific iron Oxide Particles (PSOP) with the copolymers at the surface are no longer electrostatically but sterically stabilized, i.e., the natural tendency of superparamagnetic magnetite nanocores to aggregate is countered by the thick mPEG-coat and not by the negatively charged surface of the VSOP as before. Instead of PEG other macromolecules such as dextran can provide sterical stabilization as well.

A ratio of 6 peptide-mPEGs per VSOP yielded 6x-MMP-9-PSOP with a hydrodynamic diameter of 24.9 ±7.0 nm (Figure 2B). Mixtures with ratios between 6 and 16 peptide-mPEGs consistently yielded particles with sizes around 24 nm whereas ratios below 6 resulted in particles over 30 nm in size, probably due to insufficient sterical stabilization (see Figure 3 and Table 1).

Table 1: Properties of 6x- and 12x-MMP-9-VSOP

6x-MMP-9-VSOP 12x-MMP-9-VSOP

Size [nm] 24.9 ±7.0 23.7 ±6.2

Peptide-mPEG copolymers per particle 6 12

Rl relaxivity [mM Fe^-1S^'1] 8.9 9.5

R2 relaxivity [mM Fe^-1S^"1] 41 47

Fe atoms per particle* 2600 2600

*Data provided by Ferropharm GmbH. Relaxivities at 0.94 T

To evaluate the level of copolymer coupling to the VSOP surface we measured the fluorescence quenching effect of the peptide-bound fluorescein, which is caused by non- radiative energy transfer due to the proximity of the dyes to each other and to the iron oxide cores. Compared with the fluorescence of the peptide-mPEG complexes without the particles, the fluorescence was strongly quenched up to ratios of 8 complexes per VSOP (Fig. 3). PSOP with 6 complexes per VSOP had a quenched relative fluorescence of 0.02, indicating nearly complete coupling of the complexes to the VSOP surface. Higher ratios of complexes to particle cores showed a decreasing quenching effect, revealing incomplete coupling, most likely due to saturation of the VSOP surface. When free fluorescein was mixed with the particles (6 fluorescein dyes per VSOP) as control, the fluorescence was only reduced to 0.78, confirming that the reduction of copolymer fluorescence was not only caused by light absorption by the particles. Therefore, 6 peptide-mPEG copolymers per particle was considered a good ratio for further experiments.

Function and activation of MMP-9-PSOP

To demonstrate the function of MMP-9-PSOP the inventors measured the changes in size and T2* contrast in MRI following activation by MMP-9. Results are shown in Figure 4.

First, the inventors tested the activation of MMP-9-PSOP by monitoring hydrodynamic diameters (Figure 4A). Incubation of 6x-MMP-9-PSOP (6 peptide-mPEGs per particle) with MMP-9 caused dramatic aggregation already after few minutes leading to particles sizes exceeding the micrometer range. In contrast the activation of 12x-MMP-9-PSOP under the same conditions was delayed by a factor of approximately two demonstrating the ability to tune the activation kinetics of MMP-9-PSOP. When both experiments were repeated in the presence of a MMP-9 inhibitor the size remained almost unchanged over a period of two hours.

To monitor the activation using MRI, the inventors prepared 200 μl reactions with different concentrations of 6x-MMP-9-PSOP (300 nM, 150 nM, 75 nM, and 38 nM) and 1.3 U MMP-9 each. Approximately every 15 sec T2*-weighted images (gradient echo sequences with 12 echo times (TE) between 3.1 and 44.8 ms and a repetition time (TR) of 100 ms) were acquired over a period of 50 min. Figure 4B shows the time course of the signal intensities (for a TE of 10.6 ms). Depending on the concentration the signal intensities decrease and reach a minimum at about 15 min for a concentration of 75 nM concentration and at about 27 min for 300 nM. The signal decrease was about 79% for 300 nM and 24% for 38 nM. The differences in the time it took to reach the signal minimum can be explained by the different amounts of peptide substrates to be cleaved by the MMP-9. The MR image in Figure 4B represents a snapshot taken at 17.6 min. Figure 4C shows the time course of signal intensities measured under the same conditions for 300-μM 6x-MMP-9-PSOP incubated with different concentrations of a MMP-9-inhibitor. The signal drop is delayed at a concentration of 10 nM and nearly completely suppressed for the observation period of 50 min at a MMP-9-inhibitor concentration of 1 μM. T2* relaxation times for the different inhibitor concentrations were calculated from the MR images obtained at 32 min and analyzed using an inhibition function of Prism 5 software (log(inhibitor) vs. response curve with standard slope, R² = 0.996). The 50% inhibitory concentration in this assay was 9.3 nM (95% confidence interval 4.2 nM to 21 nM).

These experiments demonstrate the activation of the particles by specific enzyme cleavage. Noteworthy is that the size measurements yield meaningful results only until the aggregates start to precipitate, thereby dropping out of the measurement field of the zetasizer. In the MR experiments one can observe that the T2* contrast effect also starts to decrease at a certain time point, which is partially attributable to precipitation as well. Additionally, the fraction of water protons influenced by the magnetic field of the particles adecrease from a certain time onwards as a result of a continuing size increase but decrease in the number of aggregates (14). Although precipitation due to aggregation is problematic for these in vitro measurements, it is intended and important mode of function for the in vivo application.

Example 2

Synthesis.

(1) The synthesized 5-ROX-labeled MMP-9 peptide NH₂-GGKGGP7?O./7MGGG-K(5-ROX)- GG-RRRRRGRRRRR-amide [SEQ ID NO. 2] (the italicized amino acids correspond to the MMP-9 substrate (16)), which is less effectively also cleavable by MMP-2 (slightly less effectively) was confirmed by MALDI-TOF (MALDI 2, Shimadzu). This sequence resulted in a copolymer with 2 mPEG chains per peptide due to the additionally lysine in position 3 of the peptide. The molecular weight was within 1 Da of the expected value. One mg of the MMP-9 peptide (in 100 μl DMSO) was reacted with 31 mg NHS-mPEG (O-[(N- Succinimidyl)succinyl-aminoethyl]-O'-methyl-polyethylene glycol 5'00O, Rapp) in 300 μl 0.1 M HEPES, pH 7.5, overnight at 4°C. The resulting MMP-9-peptide-mPEG copolymer was purified by gel filtration with BioGel P6 (BioRad, in 10 mM HEPES, 140 mM NaCl, pH 7.5). The absence of unreacted MMP-9 peptide was confirmed by HPLC using a reverse phase Cl 8 column with acetonitrile/water gradient. The concentration of the peptide-mPEG copolymers was determined spectrophotometrically by measuring peptide-bound 5-carboy-x-rhodamine (5-ROX) absoφtion (absoφtion at 576 nm, extinction coefficient of 92,000 M^-1Cm^"1).

(2) VSOP (VSOP-C200) was purchased from Ferropharm GmbH. To prepare 6x-MMP-9- PSOP (with six MMP-9-peptides per VSOP) 1.25 nmol VSOP (3.25 μmol Fe assuming 2600 iron atoms per particle, data from Ferropharm GmbH) in 250 μl in water were mixed with 7.5 nmol MMP-9-peptide-mPEG and stirred immediately. The procedure resulted in nanoparticles with about 6 peptides and 12 mPEG chains per core. Other ratios (3 to 10) were prepared accordingly. Hydrodynamic diameters of MMP-9-PSOPs were determined by dynamic light scattering (Zetasizer Nano ZS, Malvern Instruments) in the same buffer. Relaxivities were measured with a MR spectrometer at 0.94 T (Bruker, Minispec MQ 40) according to the manufacturer's instructions.

Immunocompromised athymic nude mice were implanted with tumor xenografts from a MMP-2 and MMP-9-expressing cell line (HT- 1080) in one flank and a cell line with minimal expression of these proteases as control in the other flank. The quantification with PCR (polymerase chain reaction) proved that the expression difference was over 40-fold for both proteases between both cell lines. The tumors were grown to a size over 5 mm before they were injected with PSOP with a dose of 30 μmol Fe per kg body weight. After about 10 hours the tumors were explanted and subjected to histology.

The MMP expression difference of the xenografts was confirmed by immunohistology with MMP-2 and MMP-9 antibodies (see Figure 6) and matched the expected distribution preferentially in the border zones of the tumors.

Histological slices of these tumors were additionally stained with Prussian blue dye, a technique that reveals iron deposits in histological slices and therefore the iron oxide cores of the PSOP. Figure 7 shows the PSOP distribution in a MMP-2/9 negative and MMP-2/9 positive tumor.

In concordance with the immunohistology in Figure 6 the accumulation of the particles was substantially higher in the MMP-2/9 positive tumors (HT- 1080) compared with the control tumor (BT-20). For both tumors the PSOP accumulation was primarily in the border zone of the tumors matching the MMP distribution. The results demonstrate the correct activation of the PSOP by the activity MMP-2 and MMP-9.

The features disclosed in the foregoing description, in the claims and/or in the accompanying drawings may, both separately and in any combination thereof, be material for realizing the invention in diverse forms thereof.

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Claims

Charite - Universitatsmedidizin Berlin,,Hydrolase-specific nanosensors, methods for producing them and uses in molecular imaging"U30223PCTClaims

1. Hydrolase-specific sensor compound comprising

(a) a nanoparticle or core (P) which is coated with positively or negatively charged moieties (CM) or with hydrophobic moieties (HM), having a diameter of equal to or less than 30 run, preferably in the range of 2 to 20 nm, more preferably 3 to 15 nm,

(b) a multimeric domain comprising

wherein the at least one cleavage site or recognition motif of the hydrolase of the domain CL is preferably an amino acid sequence, a nucleotide sequence or a saccharide sequence, wherein the sensor is stable in suspension and becomes aggregative or adhesive after cleavage of the at least one cleavage site or recognition motif by the hydrolase.

2. The sensor compound of claim 1, further comprising at least one further component, preferably linked to the multimeric domain, selected from a label, a therapeutic compound and/or moieties for magnetic thermotherapy.

3. The sensor compound of claim 1 or 2, wherein the nanoparticle or core (P) is superparamagnetic and selected from metal ions, metal oxides, metal salts, metal hydroxides, metal oxyhydroxides, mixtures of different metals and/or metal oxides as well as combinations thereof, wherein the metal ions are preferably selected from the group of ions of iron, manganese, copper, indium, gallium and lanthanides, such as gadolinium, europium, erbium, ytterbium, dysprosium, or preferably iron oxide, iron hydroxide and iron oxyhydroxide and/or mixtures thereof.

4. The sensor compound of claim 1 or 2, wherein the nanoparticle or core (P) is a nonmagnetic nanoparticle, preferably a fluorescent quantum dot or gas-filled microbubbles.

5. The sensor compound of any of the preceding claims, wherein the positively or negatively charged moieties (CM) are selected from

- ions,

- organic acids, such as carboxylic acids, monocarboxylic acids, dicarboxylic acids, polycarboxylic acids, amino acids, monoamino acids, diamino acids, polyamino acids, and derivatives thereof;

- amines and polyamines;

- inorganic acids, such as phosphoric acid, sulfuric acid;

- phospholipids, glycerophosphate; or the salts or combinations thereof, wherein the positively charged moieties (pos CM) are preferably selected from amino acids, amines, polyamines, and wherein the negatively charged moieties (neg CM) are preferably selected from citrate, phosphate, diphosphates, triphosphates, sulfate, or wherein the hydrophobic moieties (HM) are selected from

- fatty acids,

- hydrophobic cyclic compounds,

- hydrophobic amino acids.

6. The sensor compound of any of the preceding claims, wherein the at least one coupling domain (CO), which interacts with the positively or negatively charged moieties (CM) or with the hydrophobic moieties (HM), is selected from

- a peptide sequence comprising several amino acids with positively charged side chains, in case of negatively charged moieties (neg CM),

- a peptide sequence comprising several amino acids with negatively charged side chains, in case of positively charged moieties (pos CM),

- a peptide sequence comprising several amino acids with hydrophobic side chains, in case of hydrophobic moieties (HM), and/or a peptide sequence comprising several amino acids with hydrophobic side chains and/or a lipid sequence comprising hydrophobic lipid chains or hydrophobic (cyclic) compounds and/or combinations thereof, in case of hydrophobic moieties (HM).

7. The sensor compound of any of the preceding claims, wherein the at least one cleavage domain (CL) comprises more than one cleavage site or recognition motif of the hydrolase, preferably of different hydrolases, more preferably two different cleavage sites or recognition motifs of two different hydrolases.

8. The sensor compound of claim 7, wherein the several cleavage sites or recognition motifs are arranged in a serial manner, such that the cleavage of only one of the several sites or motifs releases the domain E (OR-switch), or the several cleavage sites or recognition motifs are arranged such that only the cleavage of all sites or motifs releases the domain E (AND-switch), wherein the CL domain preferably has a loop structure.

9. The sensor compound of any of the preceding claims, wherein the hydrolase is selected from proteases or proteinases or peptidases, such as serine proteases, threonine proteases, cysteine proteases, aspartic acid proteases, metalloproteases, such as MMP-9 or MMP-2, glutamic acid proteases; esterases, such as nucleases, (such as DNases or RNases, such as EcoRI, EcoRII), phosphodiesterases, lipases, phosphatases; amylases, such as alpha-amylase, beta-amylase; preferably from a hydrolase that is tissue-specific and/or disease-specific or preferably localized in specific tissues or specific tumors.

10. The sensor compound of any of the preceding claims, wherein the linker or spacer (L) is a peptide sequence comprising several amino acids, wherein the amino acids are preferably selected from GIy, Pro and Ala, or wherein L is polyalanine, polyglycine, carbohydrates and/or (CH₂)_n groups.

11. The sensor compound of any of the preceding claims, wherein the polymer envelope domain (E) is selected from a biocompatible polymer, and is preferably selected from polyethylene glycol or derivatives thereof, like mPEG (such as mPEG-2000, mPEG-5000, mPEG- 10000), polysaccharides (such as dextran) and polypeptides,

12. The sensor compound of any of the preceding claims, wherein the ratio between the nanoparticle or core (P) and the multimeric domain is in the range of 1 :2 to 1:100, preferably 1 :3 and 1:50, more preferably 1 :4 and 1:15.

13. The sensor compound of any of the preceding claims, wherein the multimeric domain comprises a peptide with the amino acid sequence of SEQ ID NO. 1 or 2.

14. Pharmaceutical composition comprising at least one sensor compound of any of claims 1 to 13, optionally pharmaceutically acceptable carrier(s) and/or excipient(s), preferably as injectable, oral formulation.

15. The sensor compound of any of claims 1 to 13 or the pharmaceutical composition of claim 14 for detecting a hydrolase, in particular hydrolase activity, wherein the detection is preferably via MRI, magnetic particle imaging (MPI), optical imaging, ultrasound or nuclear imaging.

16. The sensor compound of any of claims 1 to 13 or the pharmaceutical composition of claim 14 as an in vivo imaging reporter for detecting a hydrolase, in particular hydrolase activity wherein the detection is preferably via MRI, optical imaging, ultrasound or nuclear imaging.

17. The sensor compound of any of claims 2 to 13 as a vehicle or shuttle for a therapeutic compound.

18. The sensor compound of any of claims 1 to 13 or the pharmaceutical composition of claim 14 for diagnosing and/or treating a disease or disorder, which involves the activity or dysregulation of a hydrolase, wherein the detection is preferably via MRI, MPI, optical imaging, ultrasound or nuclear imaging. wherein the disease or disorder, which involves the activity or dysregulation of a hydrolase is selected from a tumor, atherosclerosis, inflammation, neurodegenerative disease, disease with remodelling of extracellular matrices.

19. The sensor compound or the pharmaceutical composition of claim 17 for diagnosing and/or treating a disease or disorder, which involves the activity or dysregulation of a hydrolase and/or which can be treated with a therapeutic compound, wherein the detection is preferably via MRI, optical imaging, ultrasound or nuclear imaging, wherein the disease or disorder, which involves the activity or dysregulation of a hydrolase and/or which can be treated with the therapeutic compound is selected from a tumor, atherosclerosis, inflammation, neurodegenerative disease, disease with remodelling of extracellular matrices.

20. The sensor compound or the pharmaceutical composition of claim 18 or 19 as theranostic, preferably in magnetic thermotherapy of cancer.

21. Method of detecting the presence or absence of a hydrolase in a sample, comprising the steps of (i) providing a sample,

(ii) providing a hydrolase-specific sensor compound of any of claims 1 to 13,

(iii) incubating the sample and the sensor compound,

22. The method of claim 21, wherein the detection of the aggregation or accumulation of nanoparticles or cores (P) is carried out by

- detecting increase in R2-relaxivity, preferably via MRI,

- detecting magnetic particle cores directly, preferably via MPI,

- detecting increase in fluorescence intensity,

- detecting increase in radiation,

- detecting increase of echoes in ultrasound