WO2013048811A1

WO2013048811A1 - Imaging and radiotherapy methods for tumour stem cells

Info

Publication number: WO2013048811A1
Application number: PCT/US2012/055845
Authority: WO
Inventors: Alan Cuthbertson; Magne Solbakken
Original assignee: Ge Healthcare Limited; Medi-Physics, Inc.
Priority date: 2011-09-30
Filing date: 2012-09-18
Publication date: 2013-04-04

Abstract

The present invention relates to in vivo imaging and radiotherapeutic methods and agents which target the enzyme aldehyde dehydrogenase (ALDH) and that are suitable for the in vivo imaging of tumours and treatment of cancer.

Description

IMAGING AND RADIOTHERAPY METHODS FOR TUMOUR STEM CELLS

Field of the Invention

The present invention relates to in vivo imaging and radiotherapeutic methods and agents suitable for the in vivo imaging of tumours and treatment of cancer. It further relates to methods and agents which target the enzyme aldehyde dehydrogenase (ALDH). The agents have utility for in vivo imaging by Positron Emission Tomography (PET), Single Photon Emission Computed Tomography (SPECT) imaging, and radiotherapy (RT).

Background of the Invention

Recently the stem cell model of cancer has emerged based on the principle that a sub-population of tumour initiating cells are present in the tumour which are distinct from the bulk cells of the tumour. The model predicts that eradication of the bulk of the tumour cells by chemotherapy or radiotherapy will at best result in temporary remission if cancer stem cells are left behind following treatment. It is also known that these stem cell-like populations are more resistant to many of the alkylating agents used in standard chemotherapy regimes [Gordon, M. Y., et al., Leuk. Res. 9, 1017, 1985]. For example, clinical studies have shown the benefit of purging samples with 4-hydroperoxycyclophosphamide (4-HC) before autologous bone marrow transplantation (ABMT) which removes committed progenitor cells but leaves the stem cell population largely intact [Kaizer, H., et al., Blood, 65, 1504-1510, 1985]. In addition, breast cancer studies have demonstrated correlation between ALDH expression in tumour tissue and poor clinical outcome and have also suggested ALDH as a marker of malignant mammary stem cells [Ginestier, C, et al., Cell Stem Cell, 1, 555, 2007].

Interestingly, the differential sensitivities of stem cells to 4-HC has been demonstrated to correlate with the intracellular activities of the enzyme aldehyde dehydrogenase [Sahovic, E.A. et al., Cancer Research, 48, 1223-1226, 1988]. Enzyme systems such as aldehyde dehydrogenase (ALDH) are ideal targets. The number of cancer stem cells is small in relation to the total tumour composition and more traditional approach employing 1:1 receptor targeting may therefore have limited value in molecular imaging and RT applications. However an imaging or therapeutic dose may be obtained within the stem cell population if the agent accumulates specifically within the stem cells. This signal amplification effect can be achieved by employing substrates for ALDH which freely diffuse through the tumour mass, are efficiently converted by the enzyme inside the cell from an aldehyde to a polar carboxylic acid which is trapped preferentially within the stem cell. Fluorescent substrates for ALDH are known and are typically used for the in vitro separation of stem cell populations from complex cellular mixtures. W096/36344 provides examples of dansylaminoacetaldehyde derivatives and WO2008/036419 teaches a method for detecting ALDH activity in cancer tissue samples using the BODIPY dye substrate ALDEFLUOR. In both cases the dyes are taken up by stem cells and processed by ALDH to give a negatively charged dye which accumulates intracellularly in the stem cell. The cells are then be sorted by flow cytometry. However, there still exists a need in oncology for in vivo imaging methods capable of distinguishing the cancer stem cell population to provide valuable prognostic, diagnostic and therapy monitoring information. In addition cancer stem cell targeted agents carrying therapeutic radionuclides such as iodine-131 may deliver a therapeutic payload directly to the stem cell, thus enhancing the benefit of therapy.

Summary of the Invention

The present invention relates to in vivo imaging and radiotherapeutic methods and agents which target the enzyme aldehyde dehydrogenase (ALDH) and that are suitable for the in vivo imaging of tumours and treatment of cancer.

In one embodiment, the invention provides a method for detection of tumour stem cells in a subject, comprising: (i) administrating a detectably labelled substrate for ALDH to the subject; (ii) detecting uptake of the detectably labelled substrate for ALDH by in vivo imaging; wherein the detectably labelled substrate for ALDH is a compound of formula (Id**):

or a salt or solvate thereof, wherein q, and r are each an integer independently selected from 0 and 1; A is a radioimaging moiety; X¹ is selected from -CR2- , -CR=CR- -C≡C- , -CR2CO2- , -CO2CR2- , -NRCO- , -CONR- , -NR(C=0)N R- -NR(C=S)N R-, -SO2NR- , -NRSO2- , -CR2OCR2- , -CR2SCR2- , and -CR2NRCR2-, wherein each R is independently selected from H, Ci-6 alkyl, C2-6 alkenyl, C2-6 alkynyl, Ci-6 alkoxyalkyl and Ci-6 hydroxyalkyl; and the compound of formula (Id**) has a molecular weight of below 800 Daltons. In an alternative embodiment, the method further comprises identifying ALDH expressing cells within a tumor.

In certain embodiments, A is a radioimaging moiety comprising a non-metal radiolabel suitable for imaging with PET or SPECT such as ¹²³> ¹²⁴> ¹²²l, ⁷⁵Br, ⁷⁶Br, ⁷⁷Br, ¹³N, ⁿC, or ¹⁸F.

In other embodiments, A comprises

In other embodiments, A com rises

In another embodiment, the invention provides a method for detection of tumour stem cells in a subject, comprising: (i) administrating to the subject a compound of formula (Id**) or a salt or solvate thereof; and (ii) detecting uptake of the compound by in vivo radioimaging. In still another embodiment, the invention provides a method of monitoring the effect of treatment of a tumour in a subject, comprising (i) administrating a detectably labelled substrate for ALDH to the subject; (ii) detecting uptake of the detectably labelled substrate for ALDH by in vivo imaging; wherein the detectably labelled substrate for ALDH is a compound of formula (Id**); and the method being effected optionally before, during and after treatment.

In yet another embodiment, the invention provides a method for radiotherapy of a cancer patient, comprising administration of an effective amount of radiotherapy-labelled substrate for ALDH to the cancer patient wherein the detectably labelled substrate for ALDH is a compound of formula (Id**).

In another embodiment, the invention provides a compound of formula (Id**):

or a salt or solvate thereof, for use in medicine, wherein q, and r are each an integer independently selected from 0 and 1; A is a radioimaging moiety; X¹ is selected from - CR₂- , -CR=CR- , -C≡C- , -CR2CO2- , -CO2CR2- , -N RCO- , -CON R- , -N R(C=0)N R- - NR(C=S)N R-, -SO2N R- , -N RSO2- , -CR2OCR2- , -CR2SCR2- , and -CR2N RCR2-, wherein each R is independently selected from H, Ci-6 alkyl, C2-6 alkenyl, C2-6 alkynyl, Ci-6 alkoxyalkyl and Ci-6 hydroxyalkyl; the compound of formula (Id**) has a molecular weight of below 800 Daltons.

In other embodiments, A comprises

In other embodiments, A comprises

In yet another embodiment, the invention provides a pharmaceutical formulation comprising the compound of formula (Id**) and a pharmaceutically acceptable excipient. Brief Description of the Drawings

Figure 1 shows the result from competition assay between ALDEFLUOR™ and 6-fluoro-/V-[2-(4-formyl-phenyl)-ethyl]-nicotinamide.

Detailed Description

Therefore, according to a first aspect of the invention, there is provided a method for detection of tumour stem cells in a subject, comprising:

(i) administrating a detectably labelled substrate for ALDH to said subject;

(ii) detecting uptake of said detectably labelled substrate for ALDH by in vivo imaging. The "detectably labelled substrate for ALDH" is a substrate for ALDH which preferably has no other known biological activity, and is suitably a compound of formula (I):

A-(B)n-C(0)H (I) or a salt or solvate thereof, wherein n is an integer 0 or 1;

A is a radioimaging moiety;

B is a carrier moiety; and

the compound of formula (I) has a molecular weight of below 800 Daltons,

The term "radioimaging moiety" means a group comprising a non-metal radiolabel suitable for imaging with PET or SPECT such as ¹²³> ^{124 122}l, ⁷⁵Br, ⁷⁶Br,⁷⁷Br, ¹³N, ⁿC, or ¹⁸F. In one aspect of the invention, the radioimaging moiety comprises a non- metal radiolabel suitable for imaging with PET or SPECT, suitably selected from ¹²³> ¹² > ¹²²l, ⁷⁵Br, ⁷⁶Br, ⁷⁷Br, ¹³N, ⁿC, and ¹⁸F, more suitably ¹²³> ^{124 122}l or ¹⁸F, and is preferably ¹⁸ F.

Suitable radioimaging moieties comprising a non-metal radiolabel are known in the art, and typically comprise a Ci-3ohydrocarbyl linker group optionally further containing 1 to 10 heteroatoms selected from nitrogen, oxygen, and sulphur and having the non-metal radiolabel covalently attached thereto or incorporated therein or alternatively, in the case of a radiohalo ¹²³> ¹² > ¹²²l, ⁷⁵Br, ⁷⁶Br, ⁷⁷Br, or ¹⁸F, such a radiolabel may be directly bonded to the rest of the compound of formula (I). Radiohalo radiolabels are commonly incorporated as radiohaloCi-6alkyl groups such as [¹⁸F]fluoroethyl or [¹⁸F]fluoropropyl, radiohaloCi-6alkoxy groups such as [¹⁸F]fluoroethoxy or [¹⁸F]fluoromethoxy. [ⁿC]carbon radiolabels are commonly incorporated as [ⁿC]Ci-6alkyl groups such as [ⁿC]nnethyl or [ⁿC]ethyl or as a [ⁿC]carbonyl group. Certain reagents are commonly used to introduce an ¹⁸F radiolabel which include N-succinimidyl-4-[¹⁸F]fluorobenzoate, m-maleimido-N-(p-

[¹⁸F]fluorobenzyl)benzamide, N-(p-[¹⁸F]fluorophenyl)maleimide, and 4- [¹⁸F]fluorophenacylbromide and are reviewed for example in Okarvi, European Journal of Nuclear Medicine 28, (7), 2001. Further description of prosthetic groups and methods for incorporating them into a ligand may be found in published international patent applications WO03/080544, WO2004/080492, WO2006/067376, and WO2010/114723. Suitable salts according to the invention include (i) physiologically acceptable acid addition salts such as those derived from mineral acids, for example hydrochloric, hydrobromic, phosphoric, metaphosphoric, nitric and sulphuric acids, and those derived from organic acids, for example tartaric, trifluoroacetic, citric, malic, lactic, fumaric, benzoic, glycollic, gluconic, succinic, methanesulphonic, and para-toluenesulphonic acids; and (ii) physiologically acceptable base salts such as ammonium salts, alkali metal salts (for example those of sodium and potassium), alkaline earth metal salts (for example those of calcium and magnesium), salts with organic bases such as triethanolamine, N-methyl-D-glucamine, piperidine, pyridine, piperazine, and morpholine, and salts with amino acids such as arginine and lysine.

Suitable solvates according to the invention include those formed with ethanol, water, saline, physiological buffer and glycol. The term "subject" means a mammal, preferably a human who has or is suspected of having a tumour, especially a solid tumour for example in the breast, colon, prostate, bone, bladder, ovary, pancreas, bowel, lung, kidney, adrenal glands, liver, or skin. Examples of solid tumours include sarcomas and carcinomas such as fibrosarcoma, myxosarcoma, liposarcoma, chondrosarcoma, osteogenic sarcoma, chordoma, angiosarcoma, endotheliosarcoma, lymphangiosarcoma, lymphangioendotheliosarcoma, synovioma, mesothelioma, Ewing's tumour, leiomyosarcoma, rhabdomyosarcoma, colon carcinoma, pancreatic cancer, breast cancer, ovarian cancer, prostate cancer, squamous cell carcinoma, basal cell carcinoma, adenocarcinoma, sweat gland carcinoma, sebaceous gland carcinoma, papillary carcinoma, papillary adenocarcinoma, cystadenocarcinoma, medullary carcinoma, bronchogenic carcinoma, renal cell carcinoma, hepatoma, bile duct carcinoma, choriocarcinoma, seminoma, embryonal carcinoma, Wilms' tumour, cervical cancer, testicular tumour, lung carcinoma, small cell lung carcinoma, bladder carcinoma, epithelial carcinoma, glioma, astrocytoma, medulloblastoma, craniopharyngioma, endymoma, pinealoma, hemangioblastoma, acoustic neuroma, oligiodendroglioma, meningioma, melanoma, neuroblastoma, and retinoblastoma.

Such a subject may have presented one or more symptoms indicative of a cancer such as a lump or mass, or may be being routinely screened for cancer, or screened for cancer due to presence of one or more risk factors, may have been identified as having cancer, or have had cancer in the past but being screened in remission.

The term "cancer patient" means a mammal, preferably a human, who is being treated for primary or metastatic cancer such as a solid tumour as defined above or a hematologic malignancy (for example acute or chronic myeloid leukaemia). Examples of such cancers include carcinoma, lymphoma, blastoma, sarcoma, and leukaemia.

As used herein the term "halo" either alone or as part of another term means iodo, bromo, chloro, or fluoro.

As used herein the term "alkyl" either alone or as part of another term means a straight, branched or cyclic alkyl group.

As used herein the term "aryl" either alone or as part of another term means a carbocyclic aromatic system, suitable examples being phenyl or naphthyl, more suitably phenyl.

As used herein the term "hydrocarbyl group" means an organic substituent consisting of carbon and hydrogen, such groups may include saturated, unsaturated, or aromatic portions.

As noted above, substrates for ALDH may also be used in radiotherapy, such that the accumulation of radiotherapeutic in the cancer stem cells effectively localises the therapeutic response. Cancer stem cells often show resistance to standard cancer therapeutic methods. Targeted destruction of these cells using an ALDH targeting radiotherapeutic may provide a more effective approach, either on its own or in combination with other cancer therapeutic methods. Cancer therapeutic methods which are conventionally used include chemotherapy, such as with alkylating agents (e.g., cyclophosphamide derivatives including 4- hydroperoxycyclophosphamide, and mafosphamide), hormonal therapy (e.g., with aromatase inhibitors, anti-androgens, or tamoxifen) and radiotherapy.

According to a further aspect of the invention, there is provided a method for radiotherapy of a cancer patient, comprising administration of an effective amount of radiotherapy-labelled substrate for ALDH to said cancer patient.

The "radiotherapy-labelled substrate for ALDH" is a compound of formula (II): R*-(B)m-C(0)H (I I) or a salt or solvate thereof, wherein

m is an integer 0 or 1;

R* is a radiotherapeutic moiety; and

B is a carrier moiety; and

the compound of formula (II) has a molecular weight of below 800 Daltons.

The term "radiotherapeutic moiety" means a group comprising a therapeutic radionuclide selected from the beta emitters ¹³¹l, ³³P, ¹⁶⁹Er, ¹⁷⁷Lu, ⁶⁷Cu, ¹⁵³Sm, ¹⁹⁸Au, ¹⁰⁹Pd, ¹⁸⁶Re, ¹⁶⁵Dy, ⁸⁹Sr, ³²P, ¹⁸⁸Re, and ⁹⁰Y; alpha emitters ²¹¹At, ²¹²Bi and ²¹³Bi; and Auger emitters ⁵¹Cr, ⁶⁷Ga, ⁷⁵Se, ⁷⁷Br, ¹²³l, ^mln, ^99mTc and ²⁰¹TI. Suitable radiotherapeutic moieties comprising a non-metal radiolabel are known in the art, and typically comprise a Ci-3ohydrocarbyl linker group optionally further containing 1 to 10 heteroatoms selected from nitrogen, oxygen, and sulphur and having the non- metal radiolabel covalently attached thereto or incorporated therein or alternatively, in the case of a radiohalo ¹³¹l or ⁷⁷Br, such a radiolabel may be directly bonded to the rest of the compound of formula (I I).

In a further aspect of the invention, there is provided a method for detection of tumour stem cells in a subject, comprising:

(i) administration of a compound of formula (la), to said subject:

A-(B)_n-C(0)H (la) or a salt or solvate thereof, wherein

n is an integer 0 or 1;

A is a radioimaging moiety;

B is a carrier moiety; and

the compound of formula (la) has a molecular weight of below 800 Daltons; and (ii) detecting uptake of the compound of formula (la) by in vivo radioimaging.

Preferred methods of in vivo radioimaging are PET and SPECT. These imaging methods are well known in the art, and may be used to provide useful information in the management of subjects having or suspected of having a tumour. The properties of the compound of formula (I) or (la) allow for selective imaging of ALDH expression during imaging, i.e. identification or quantitative assessment of ALDH expressing cells within a tumour that also contains non-ALDH expressing cells. Analysis of imaging data, for example by comparison of data from ALDH expressing area with adjacent or background areas, will allow estimation of levels of ALDH expression.

The data and images obtained from the imaging methods of the invention may contribute to improved clinical patient management, for example they may provide valuable prognostic information, assist with selection of the most suitable therapy for the subject, or provide a measure of therapy efficacy.

According to a further aspect, the invention provides a method of monitoring the effect of treatment of a tumor in a subject (for example treatment with a cytotoxic agent or radiotherapy), said method comprising:

(i) administration of a compound of formula (I), to said subject:

A-(B)n-C(0)H (I) or a salt or solvate thereof, wherein

n is an integer 0 or 1;

A is a radioimaging moiety;

B is a carrier moiety; and

the compound of formula (I) has a molecular weight of below 800 Daltons (ii) detecting uptake of said compound of formula (I) by in vivo imaging,

the administration and detection steps (i) and (ii) optionally but preferably being effected repeatedly, for example before, during and after treatment.

The compounds of formula (I), (la), and (II) are substrates for ALDH, having an aldehyde functionality which is converted to a carboxylic acid in vivo, and most preferably selectively by the highly expressed intracellular levels of the enzyme in the cancer stem cell population of the tumour. The negatively charged product of enzyme conversion is trapped within the cell allowing the signal to accumulate over time in vivo.

The optional carrier moiety B is designed to modify the hydrophobicity of the compound of formula (I) or (II) so as to optimize cell permeability, and is suitably of formula:

-(Ar)p-(Xⁱ)_q-(Ci-₅alkyl) _r - wherein:

p, q, and r are each an integer independently selected from 0 and 1 with the proviso that at least one of p, q, and r is 1;

Ar is a 1, 2, or 3 member aromatic ring system, either fused or unfused, and optionally comprising 1 to 3 heteroatoms selected from nitrogen, oxygen, sulphur, and boron and optionally having from 1 to 5 substituents selected from Ci-6alkyl, Ci- 6haloalkyl, Ci-6alkoxy, Ci-6haloalkoxy, halo, cyano, nitro, hydroxy, hydroxyCi-6alkyl, and -N R!R² , wherein R¹ and R² are independently selected from hydrogen, Ci-6alkyl, and Ci-ehaloalkyl; X¹ is selected from -CR₂-, -CR=CR-, -OC-, -CR₂C0₂-, -C0₂CR₂-, - NRCO-, -CONR-, -NR(C=0)NR- -NR(C=S)NR- -S0₂NR-, -NRS0₂-, -CR₂OCR₂-, -CR₂SCR₂-, and -CR₂NRCR₂-, wherein each R is independently selected from H, Ci-6 alkyl, C₂-6 alkenyl, C₂-6 alkynyl, Ci-6 alkoxyalkyl and Ci-6 hydroxyalkyl.

Preferred groups Ar include phenyl, naphthyl, biphenyl, quinoline, isoquinoline, and indole.

In certain embodiments, the compounds of formula (I), (II) and (la) also includes one or more PEG containing moieties. The PEG containing moiety of the compound according to the invention may be a straight chain PEG containing moiety comprising one or more PEG units, the units may or may not be interrupted by a spacer group or functional group or a dendrimeric PEG containing moiety comprising more than one PEG unit. In a preferred embodiment, the PEG containing is a straight chain PEG containing moiety comprising two or more ethylene glycol units.

The PEG containing moiety has a molecular weight of less than 3000 Da, preferably a molecular weight of less than 2000 Da, more preferably a molecular weight of from 600 to 1000 Da and most preferably a molecular weight of from 120 to 360 Da. It comprises 2 to 50 ethylene glycol units, preferably, 10 to 30 ethylene glycol units and particularly preferably 2 to 6 ethylene glycol units.

In a preferred embodiment, the PEG containing moiety forms part of the linker group of the radioimaging moiety A. If serving as part of the linker, the PEG containing moiety preferably comprises two identical or different functional groups which allow the covalent binding of the PEG containing moiety to the radiolabel and the carrier moiety. Suitable functional groups are for instance amino, hydroxyl, sulfhydryl, carboxyl and carbonyl groups, carbohydrate groups, phenolic and active halogen containing groups. In a preferred embodiment, the PEG containing moiety comprises two different functional groups (heterobifunctional PEG containing moieties).

In another preferred embodiment, the PEG containing moiety is covalently linked to either the radioimaging moiety A or carrier moiety B. In this case, the PEG containing moiety comprises a functional group which allows the covalent binding of the PEG containing moiety to the radioimaging moiety or the carrier moiety. Suitable functional groups are those mentioned in the preceding paragraph. Preferably, the PEG containing moiety is linked to the radioimaging moiety A and/or the carrier moiety B in such a way that the function of the radioimaging and the carrier moiety is not affected by this linkage. PEG containing moieties that comprise one or more functional groups which may be used for the synthesis of the compounds according to the invention are known in the art and are commercially available. Alternatively, PEG containing moieties can be synthesised by methods known in the art. Briefly, PEG containing moieties can be synthesised from PEG, which may be produced by based catalysed polymerisation of ethylene oxide, giving a distribution of chain lengths and end group modifications depending on the conditions chosen. From the product mixture, low molecular components, like tetraethylene glycol, can be purified by fractional distillation giving homogeneous products. The PEG end groups can be subjected to chemical modifications introducing functional groups like amino, mercaptol, halo, carboxyl and the like suitable for conjugation to other molecules by well-known synthetic methods (see for instance S. Zaiipsky, Adv. Drug Del. Rev. 16 (1995), 157 and references cited therein).

In one aspect, the compound of formula (I) as used in the imaging methods of the invention is a compound of formulae (Id):

wherein A, X¹, q and r are as defined above and each aryl group optionally has 1 to 5 substituents selected from Ci-6alkyl, Ci-6haloalkyl , Ci-6alkoxy, Ci-6haloalkoxy, halo, cyano, nitro, hydroxy, hydroxyCi-6alkyl , and -NR!R² , wherein R¹ and R² are independently selected from hydrogen, Ci-6alkyl, and Ci-6haloalkyl.

In formulae (Id), the group A is as defined for formula (I) or (la) above. In one aspect of the invention, the group A is selected from Ci-6radiohaloalkyl such as [¹⁸F]fluoro Ci-₆alkyl or [¹²²> ¹²³> ¹²⁴l]iodo Ci-₆alkyl, Ci-₆radiohaloalkoxy such as [¹⁸F]fluoro Ci-6dlkoxy or [¹²²> ¹²³> ¹² l]iodo Ci-6alkoxy, Ci-6radiohaloalkylamine such as [¹⁸F]fluoro Ci-ealkylNH-, [¹²²> ¹²³> ¹²⁴l]iodo Ci-₆alkylNH-, [¹⁸F]fluoro Ci-₆alkylN(Ci-₆alkyl)-, [¹²²> ¹²³> ¹²⁴l]iodo Ci-₆alkylN(Ci-₆alkyl)- , [¹⁸F]fluoro , and [¹²²' ¹²³> ¹²⁴l]iodo.

In one aspect of the invention, X¹ is -CONH- or -SO2NH-.

In one aspect, the compound of formula (Id) is of formula (Id*)

or a salt or solvate thereof wherein:

A^d is selected from [¹⁸F]fluoro Ci-₆alkyl, [^{122> 123> 124}l]iodo Ci-₆alkyl, [¹⁸F]fluoro Ci-₆alkoxy,

[122, 123, i2 |]i₀do Ci-₆alkoxy, [¹⁸F]fluoro Ci-₆alkylNH-, [¹²²> ¹²³> ¹²⁴l]iodo Ci-₆alkylN H- [¹⁸F]fluoro Ci-₆alkylN(Ci-₆alkyl)-, [¹²²> ¹²³> ¹²⁴l]iodo Ci-₆alkylN(Ci-₆alkyl)- , [¹⁸F]fluoro , and

q and r are each independently an integer 0 or 1 provided that if r is 0 then q is also 0.

In the compound of formula (Id*), A^d is suitably selected from [¹⁸F]fl Ikoxy, [¹⁸F]fluoro , and [^{122 123 124}l]iodo, and q is suitably 1.

In one aspect, the compound of formula (Id) is of formula (Id**):

or a salt or solvate thereof, wherein A, X¹, q and r are as defined above.

In one embodiment, A comprises

wherein one or two of Z -Z⁵ is a nitrogen atom and one of Z -Z⁵ is C-¹⁸F and the remaining Z1-Z5 are CH.

n a particular embodiment in the compound of formula (Id**), A is

, preferably, A is

Particular compounds of formula (Id*) or (Id**) include:

In one aspect, the compound of formula (II) as used in the radiotherapy methods of the invention is a compound of formula (lid):

H

wherein R*, X¹, q and r are as defined above and each aryl group optionally has 1 to 5 substituents selected from Ci-6alkyl, Ci-6haloalkyl, Ci-6alkoxy, Ci-6haloalkoxy, halo, cyano, nitro, hydroxy, hydroxyCi-6alkyl, and -NR^!R², wherein R¹ and R² are independently selected from hydrogen, Ci-6alkyl, and Ci-6haloalkyl .

Certain compounds of formula (Id), (Id*), (Id**), and (lid) are novel and therefore form a further aspect of the invention.

The compounds of formula (I) and (II) as well as the more specific aspects thereof, may be prepared by conventional techniques, for example as described below and in the examples. Incorporation of the radioimaging moiety into a compound of formula (I) or of a radiotherapeutic moiety into a compound of formula (II) is suitably effected as close to the end of synthesis as possible, so as to avoid unnecessary decay or loss of thereof.

A ⁿC label may be incorporated into a compound of the invention by way of a ⁿC-labelling agent, i.e. a small reactive molecule capable of reacting with a functional group in a precursor to the compound of the invention. Examples of such labelling agents include [ⁿC]carbon dioxide, [ⁿC]carbon monoxide, [ⁿC]nnethane, [ⁿC]nnethyl iodide, [ⁿC]phosgene, [ⁿC]cyanide, [ⁿC]cyanannide, and [ⁿC]guanidine. Of these, the most commonly used are [ⁿC]carbon dioxide and [ⁿC]nnethyl iodide. A thorough review of such ^1]-C-labelling techniques may be found in Antoni et ol "Aspects on the the Synthesis of ⁿC-Labelled Compounds" in Handbook of Radiopharmaceuticals, Ed. M.J. Welch and C.S. Redvanly (2003, John Wiley and Sons). nC is produced as ⁿCC>2 or ⁿCH , from N2 target gas with a trace of O2 or H2 respectively, via the ¹ N(p,a)^1:LC nuclear reaction (Bida et o!, Radiochim. Acta., 27 91979) 181). Either of ⁿC0₂ or ⁿCH4 may be converted to useful ⁿC-labelling agents such as [ⁿC]nnethyl iodide.

[ⁿC]nnethyl iodide is commonly used to effect [ⁿC]nnethylation of a carbon, nitrogen, oxygen, or sulphur nucleophile, for example an amine or hydroxy group. The reactivity of the electrophilic carbon in [ⁿC]nnethyl iodide may be increased by conversion to, for example, [ⁿC]nnethyl triflate (Holschbach and Schuller, Appl. Radiat. I sot, 44 (1993), 897). Alternatively, [ⁿC]nnethyl iodide may be converted to nucleophilic [ⁿC]nnethyl lithium or a lithium [^1:LC]methyl(2-thienyl)cuprate which broadens the spectrum of functionalities which can be labelled by [ⁿC]nnethylation. [ⁿC]nnethyl iodide may also be converted to further labelling agents such as

[ⁿC]nnethylhypofluorite, triphenylarsonium [ⁿC]nnethylide, or [^1]-C]methylmagnesium iodide. [ⁿC]nnethylation may be carried out in solution phase, dissolving the appropriate precursor in a solvent such as dimethylsulphoxide, dimethylformamide, acetonitrile, or acetone, and in the presence of a base, for example potassium carbonate, sodium hydroxide, or sodium hydride. Alternatively, [ⁿC]nnethylation may be performed using a solid support such as an HPLC loop or a solid phase extraction cartridge to first immobilise the precursor before passing through the [ⁿC]nnethylation agent. Higher [ⁿC]alkyl halides, such as [ⁿC]ethyliodide or benzyl halides may be prepared from [ⁿC]carbon dioxide by reaction with a Grignard reagent followed by reduction with lithium aluminium hydride and halogenation, for example, iodination with hydroiodic acid. These halides are used in a similar way to [ⁿC]nnethyl iodide for alkylation of a carbon, nitrogen, oxygen, or sulphur nucleophile.

[ⁿC]acyl chlorides such as acetyl chloride, cyclohexanecarbonyl chloride and furoyi chloride may be used for labelling of carbonyl positions, as described for example in McCarron et al, J. Labelled Compd. Radiopharm, 38, 941-953. Carbonyl positions may also be labelled using [ⁿC]phosgene or [ⁿC]carbon monoxide.

[ⁿC] cyanogen bromide may be used for unspecific labelling of macromolecules and for chemoselective labelling of cyanamides, cyanates, and thiocyanates by reaction with amines, alcohols, and thiols respectively.

Incorporation of a [ⁿC]label in an aromatic ring may be achieved by the methods of Mading et al (2000) J. Labelled Compd. Radiopharm. 39, 585-600, and in a heterocyclic ring by the methods of Thorell et al (1998), J. Labelled Compd. Radiopharm. 41, 345-353.

¹⁸F may be incorporated into a compound of the invention either by nucleophilic or electrophilic fluorination methods. The fluorine may be incorporated directly, for example, by nucleophilic displacement of a leaving group by [¹⁸F]fluoride, or by way of a ¹⁸F-fluorinated labelling agent which is prepared and then attached to the target molecule by a second reaction, such as an alkylation.

[¹⁸F]fluoride is conveniently prepared from ¹⁸0-enriched water using the (p,n)- nuclear reaction, (Guillaume et al, Appl. Radiat. Isot. 42 (1991) 749-762) and generally isolated as the potassium salt which is dried and solubilised with a phase transfer agent such as a tetraalkylammonium salt or an aminopolyether (for example, Kryptofix 2.2.2). Nucleophilic displacement of a leaving group, often a sulphonate ester, such as a p-toluenesulphonate, trifluoromethanesulphonate, or methanesulphonate, nitro, triCi-4alkylammonium group, or a halo group such as iodo or bromo, may typically be effected by heating for 10 to 30 minutes at elevated temperatures, for example 80 to 160°C, suitably 60 to 120°C, or by microwave heating, in a polar aprotic solvent such as acetonitrile, dimethylsulphoxide, or dimethylformamide.

Useful [¹⁸F]labelling agents include the [¹⁸F]fluoroalkylhalides, such as [¹⁸F]fluoropropylbromide. These are routinely prepared by nucleophilic displacement of a suitable leaving group by [¹⁸F]fluoride before being coupled to a suitable precursor.

Electrophilic [¹⁸F]fluorination may be performed using ¹⁸F2, alternatively the ¹⁸F2 may be converted to [¹⁸F]acetylhypofluorite (Lerman et al, Appl. Radiat. Isot. 49 (1984), 806-813) or to a N-[18F]fluoropyridinium salt (Oberdorfer et al, Appl. Radiat. Isot. 39 (1988), 806-813). These electrophilic reagents may be used to incorporate ¹⁸F by performing double bond addition, aromatic substitution reactions, for example substitution of a trialkyl tin or mercury group, or fluorination of carbanions.

⁷⁶Br is usually produced by the reaction ⁷⁶Se[p,n]⁷⁶Br (Friedman et al, J Label Compd Radiopharm, 1982, 19, 1427-8) and used as a bromide salt such as ammonium bromide or sodium bromide. ¹² l is commonly obtained by the reaction ¹² Te (p,n)¹² l and used as an iodide salt such as sodium iodide. Other isotopes of bromine and iodine may be prepared by analogy. Radiobromo and radioiodo are commonly introduced to an organic molecule by electrophilic bromination or iodination of a trialkyltin precursor, such as a tributylstannyl compound, in the presence of an oxidising agent such as peracetic acid, N-chlorosuccinimide, and N- chlorotolylsulphonamide (for example chloramine-T or lodogen) or by indirect methods such as use of Bolton Hunter reagent at non-extreme temperature and in a suitable solvent such as an aqueous buffer. Radiohalogenation methods are reviewed in detail in Bolton, J Label. Compd Radiopharm 2002, 45, 485-528.

During incorporation of the radioimaging moiety into a compound of formula (I) or of a radiotherapeutic moiety into a compound of formula (II) the aldehyde function is optionally blocked as a protecting group to avoid unwanted side-reaction. Suitable protecting groups for this purpose include an acetal such as -CH(-0-Ci-4alkyl- 0-) (for example -CH(-OCH₂CH₂0-); or -CH(OCi-₄alkyl)₂ (for example -CH(OCH₃)₂). Subsequent deprotection to form the free aldehyde may be effected using standard methods such as treatment with acid. In one embodiment the aldehyde is present in the free form with no protection during incorporation of the radioimaging moiety into a compound of formula (I) or of a radiotherapeutic moiety into a compound of formula (II). Compounds of formula (Id*) may be prepared according to scheme 1 or 2, or by methods analogous thereto.

Scheme 1.

Boc=t-butoxycarbonyl

n= 1 to 6

Scheme 2

Compounds of formula (Id**), as exemplified by compound 15:

may be prepared according to scheme 3 or 4, or by methods analogous thereto. Scheme 3

In Scheme 3, R represents free aldehyde or an protecting group, for example an acetal; n is 0-6; m is 0-6, preferably 1-2. The radiosynthesis of the nicotinic acid derivatised prosthetic group is described, for example, in Olberg, DE et al, J. Med. Chem. 5 , 1732-1740 (2010).

In Scheme 4, R represents free aldehyde or an protecting group, for example acetal; n is 0-6; m is 0-6, preferably 1-2.

A compound of formula (I), (la), (Id), (Id*), (Id**) (II), (lid), or a salt or solvate thereof is preferably administered for in vivo use in a pharmaceutical formulation comprising the compound of the invention and a pharmaceutically acceptable excipient, such formulations thus form a further aspect of the invention. A "pharmaceutical formulation" is defined in the present invention as a formulation comprising an effective amount of a compound of formula (I), (la), (Id), (Id*), (Id**), (II), (lid), or a salt or solvate thereof in a form suitable for administration to a mammal, suitably a human. The "pharmaceutically acceptable excipient" is a fluid, especially a liquid, in which the compound of the invention can be suspended or dissolved, such that the formulation is physiologically tolerable, ie. can be administered to the mammalian body without toxicity or undue discomfort. The pharmaceutically acceptable excipient is suitably an injectable carrier liquid such as sterile, pyrogen- free water for injection; an aqueous solution such as saline (which may advantageously be balanced so that the final formulation for injection is isotonic); an aqueous solution of one or more tonicity-adjusting substances (for example, salts of plasma cations with biocompatible counterions), sugars (for example, glucose or sucrose), sugar alcohols (for example, sorbitol or mannitol), glycols (for example, glycerol), or other non-ionic polyol materials (for example, polyethyleneglycols, propylene glycols and the like). Preferably the pharmaceutically acceptable excipient is pyrogen-free water for injection or isotonic saline.

The pharmaceutical formulation may optionally contain additional excipients such as an antimicrobial preservative, pH-adjusting agent, filler, stabiliser or osmolality adjusting agent. By the term "antimicrobial preservative" is meant an agent which inhibits the growth of potentially harmful micro-organisms such as bacteria, yeasts or moulds. The antimicrobial preservative may also exhibit some bactericidal properties, depending on the dosage employed. The main role of the antimicrobial preservative(s) of the present invention is to inhibit the growth of any such micro-organism in the pharmaceutical formulation. The antimicrobial preservative may, however, also optionally be used to inhibit the growth of potentially harmful micro-organisms in one or more components of kits used to prepare said pharmaceutical formulation prior to administration. Suitable antimicrobial preservative(s) include: the parabens, ie. methyl, ethyl, propyl or butyl paraben or mixtures thereof; benzyl alcohol; phenol; cresol; cetrimide and thiomersal. Preferred antimicrobial preservative(s) are the parabens.

The term "pH-adjusting agent" means a compound or mixture of compounds useful to ensure that the pH of the pharmaceutical formulation is within acceptable limits (approximately pH 4.0 to 10.5) for human or mammalian administration. Suitable such pH-adjusting agents include pharmaceutically acceptable buffers, such as tricine, phosphate or TRIS [ie. ins(hydroxymethyl)aminomethane], and pharmaceutically acceptable bases such as sodium carbonate, sodium bicarbonate or mixtures thereof. When the pharmaceutical formulation is employed in kit form, the pH adjusting agent may optionally be provided in a separate vial or container, so that the user of the kit can adjust the pH as part of a multi-step procedure.

By the term "filler" is meant a pharmaceutically acceptable bulking agent which may facilitate material handling during production and lyophilisation. Suitable fillers include inorganic salts such as sodium chloride, and water soluble sugars or sugar alcohols such as sucrose, maltose, mannitol or trehalose.

Administration for radioimaging or radiotherapy methods is preferably carried out by injection of the pharmaceutical formulation as an aqueous solution. Such a formulation may optionally contain further excipients as described above, more typically including one or more excipient such as buffers; pharmaceutically acceptable solubilisers (e.g. cyclodextrins or surfactants such as Pluronic, Tween or phospholipids); pharmaceutically acceptable stabilisers or antioxidants (such as ascorbic acid, gentisic acid or para-aminobenzoic acid).

The pharmaceutical formulations of the invention are typically supplied in suitable vials or vessels which comprise a sealed container which permits maintenance of sterile integrity and/or radioactive safety, plus optionally an inert headspace gas (eg. nitrogen or argon), whilst permitting addition and withdrawal of solutions by syringe or cannula. A preferred such container is a septum-sealed vial, wherein the gas-tight closure is crimped on with an overseal (typically of aluminium). The closure is suitable for single or multiple puncturing with a hypodermic needle (e.g. a crimped-on septum seal closure) whilst maintaining sterile integrity. Such containers have the additional advantage that the closure can withstand vacuum if desired (eg. to change the headspace gas or degas solutions), and withstand pressure changes such as reductions in pressure without permitting ingress of external atmospheric gases, such as oxygen or water vapour.

Preferred multiple dose containers comprise a single bulk vial (e.g. of 10 to 30 cm³ volume) which contains multiple patient doses, whereby single patient doses can thus be withdrawn into clinical grade syringes at various time intervals during the viable lifetime of the preparation to suit the clinical situation. Pre-filled syringes are designed to contain a single human dose, or "unit dose" and are therefore preferably a disposable or other syringe suitable for clinical use. The pharmaceutical formulations of the present invention preferably have a dosage suitable for a single patient and are provided in a suitable syringe or container, as described above. The pharmaceutical formulations of the invention may be prepared under aseptic manufacture (ie. clean room) conditions to give the desired sterile, non- pyrogenic product. It is preferred that the key components, especially the excipients plus those parts of the apparatus which come into contact with the pharmaceutical formulation (for example, vials) are sterile. The components of the pharmaceutical formulation can be sterilised by methods known in the art, including: sterile filtration, terminal sterilisation using, for example, gamma-irradiation, autoclaving, dry heat or chemical treatment (for example, with ethylene oxide). It is preferred to sterilise some components in advance, so that the minimum number of manipulations needs to be carried out. As a precaution, however, it is preferred to include at least a sterile filtration step as the final step in the preparation of the pharmaceutical formulation.

An "effective amount" of a compound of formula (I), (ia), (Id), (Id*), (Id**) or (II), (lid) or a salt or solvate thereof means an amount which is effective for use in in vivo imaging (PET, SPECT) or for use in radiotherapy and will vary depending on the exact compound to be administered, the weight of the subject or patient, and other variables as would be apparent to a physician skilled in the art. The radiolabelled compounds of this invention may be administered to a subject for PET or SPECT imaging in amounts sufficient to yield the desired signal, typical radionuclide dosages of 0.01 to 100 mCi, preferably 0.1 to 50 mCi will normally be sufficient per 70kg bodyweight. Likewise for radiotherapy an acceptable dose not exceeding the maximum tolerated dose for the bone marrow (typically 200-300 cGy) is employed. In a further aspect of the invention, there is provided a compound of formula

(I), (la), (Id) (Id*), (Id**) or (II), (lid) or a salt or solvate of any thereof, for use in medicine.

EXAMPLES:

The invention is illustrated by way of examples in which the following abbreviations are used:

DM F: N, N'-dimethylformamide;

TFA: trifluoroacetic acid;

min(s): minute(s);

HPLC: high performance liquid chromatography;

THF: tetrahydrofuran;

NMR: nuclear magnetic resonance Example 1. Preparation of 2-[2-(2-fluoromethyl-phenylsulfanyl)-ethyl]-aldehyde

la) Synthesis of [2-(2-[l,3]dioxolan-2-ylethylsulfanyl)phenyl]methanol

2-(2-Bromoethyl)-l,3-dioxolane (223 μΙ, 1.86 mmol) was added to 2- mercaptobenzyl alcohol (52.3 mg, 0.37 mmol) and potassium carbonate (102.3, 0.74 mmol) in DMF. The mixture was stirred at room temperature over night before DMF was evaporated under reduced pressure and the crude product purified by reverse phase preparative chromatography (Vydac 218TP1022 column; solvents A= water / 0.1% TFA and B= CH₃CN / 0.1% TFA; gradient 10-50 % B over 40 min; flow 10 ml / min; detection at 214 nm). A yield of 65.1 mg of purified material was obtained (Analytical HPLC: Vydac 218TP54 column; solvents: A= water / 0.1% TFA and B= CH₃CN / 0.1% TFA; gradient 10-50 % B over 20 min; flow 1.0 ml /minute; retention time 15.017 minutes detected at 214 and 254 nm). lb) Synthesis of 2-[2-(2-chloromethyl-phenylsulfanyl)-ethyl]-[l,3]dioxolane

Mesyl chloride (65 μΙ, 0.83 mmol) was added to a solution of [2-(2-

[l,3]dioxolan-2-yl-ethylsulfanyl)-phenyl]-methanol (40 mg, 0.17 mmol) and triethyl amine (116 μΙ, 0.83 mmol) in THF. After 5 days the precipitate was filtered of and THF evaporated under reduced pressure and the crude product purified by reverse phase preparative chromatography (Vydac 218TP1022 column; solvents A= water / 0.1% TFA and B= CH₃CN / 0.1% TFA; gradient 40-80 % B over 40 min; flow 10 ml / minute; detection at 254 nm). The fractions were left in the fridge overnight and to the acetonitrile phase was added diethyl ether, dried (Na2S0 ) and evaporated under reduced pressure. A yield of 24.5 mg of purified material was obtained (Analytical HPLC: Vydac 218TP54 column; solvents: A= water / 0.1% TFA and B= CH₃CN / 0.1% TFA; gradient 40-80 % B over 20 min; flow 1.0 ml /minute; retention time 10.4 minutes detected at 214 and 254 nm). Structure verified by NMR. lc) Synthesis of 2-[2-(2-fluoromethyl-phenylsulfanyl)-ethyl]-[l,3]dioxolane

Potassium fluoride (3.5 mg, 0.060 mmol) and kryptofix 222 (22.5 mg, 0.060 mmol) were dissolved in acetonitrile (1 ml) and added to 2-[2-(2-chloromethyl- phenylsulfanyl)-ethyl]-[l,3]dioxolane (7.7 mg, 0.030 mmol) in acetonitrile (1 ml). The reaction mixture was heated to 70 degrees for 30 minutes. The crude product was purified by reverse phase preparative chromatography (Vydac 218TP1022 column; solvents A= water / 0.1% TFA and B= CH₃CN / 0.1% TFA; gradient 40-80 % B over 40 min; flow 10 ml / minute; detection at 254 nm). The fractions were left in the fridge overnight and to the acetonitrile phase was added diethyl ether, dried (Na2SC¼) and evaporated under reduced pressure. (Analytical HPLC: Vydac 218TP54 column; solvents: A= water / 0.1% TFA and B= CH₃CN / 0.1% TFA; gradient 40-80 % B over 20 min; flow 1.0 ml /minute; retention time 9.200 minutes detected at 214 and 254 nm). Structure verified by NMR.

The protecting group on 3-(2-fluoromethyl-phenylsulfanyl)-propionaldehyde (0.81 mg, 0.0034 mmol) was removed using IN HCI in acetonitrile (1:1) 0.1 ml for 30 minutes.

Example 2. Synthesis of (2-formylethyl)-4-fluorobenzamide

2a. Preparation of (3-hydroxypropyl)-4-fluorobenzamide

To a dry 100ml 3 necked round bottomed flask (RBF) provided with nitrogen, 5.68g ( 0.07562 mole) of 3-amino-l-propanol, 12.68g of TEA in 100ml dry ethyl acetate was added and cooled to 0-5°C. 4-fluorobenzoyl chloride (lOg, 0.0630mole) in ethyl acetate was then added drop-wise over a period of 30min and allowed stir overnight. Progress of the reaction was monitored by thin layer chromatography (TLC). After the completion of the reaction, ethyl acetate was distilled out completely and the residue extracted again with ethylacetate/ washed with water dilute sodium bicarbonate solution and dried. Ethyl acetate layer was then distilled and the residue was purified by silica column using methanol dichloromethane ( 5-20%) as eluent. Yield: 5.86g (50%); Purity: 93.9%; iH-NMR(CDCl₃): 3.6(d, 2H, CH₂), 3.8(d, 2H, CH₂), 7.01(s, 1H, NH), 7.1(d, 2H, ArH), 7.8(d, 2H, ArH); MS: 198(M+1)

2b. Preparation of (2-formylethyl)-4-fluorobenzamide

To a dry 50ml 3 necked RBF provided with nitrogen, 3.2g of PCC ( 0.0148mole) and 2.0g of silica gel in 32 ml dry dicloromethane was added and cooled to -5 to - 10°C. 2.0g ( 0.01014 mole ) of (3-hydroxypropyl)-4-fluorobenzamide in dicloromethane was then added drop-wise over a period of 30min and allowed stir overnight at RT. Progress of the reaction was monitored TLC. After the completion of the reaction, dicloromethane was distilled out completely and the residue residue was purified by combiflash using silica column twice. Eluent used was 0-10% methanol in dichloromethane. Yield: 0.2g (10%); Purity: 89%; ⁱH-NMRlCDCb): 2.8 (d, 2H, CH₂), 3.8(d, 2H, CH₂), 6.81s, 1H, NH), 7.1(d, 2H, ArH), 7.8(d, 2H, ArH);, 10.0 (s, 1H, CHO) MS: 314 (M+l)

Example 3. Preparation of 6-fluoro-/\/-[2-(4-formyl-phenyl)-ethyl]-nicotinamide

To a solution of nicotinic acid (Aldrich, 100 mg, 0.71 mmol) in DMF (Sigma Aldrich, 5 mL). were added diisopropylethylamine (Fluka, 371 μΙ_, 2.13 mmol) and Λ/,Λ/,Λ/',Λ/'-tetramethyl (succinimido)uronium tetrafluoroborate (TSTU) (Fluka, 278 mg, 0.92 mmol). The mixture was stirred at ambient temperature for 2 h. The mixture turned red but remained clear. 4-(2-Aminoethyl)benzaldehyde (Fluorochem, 200 mg, 1.08 mmol) was added followed by a second aliquot of diisopropylethylamine (371 mL) and the mixture was stirred at ambient temperature. After 24 h reaction time DMF was evaporated off. The residue was purified by flash chromatography

(acetone/dichloromethane, 3:2). After concentration the residue was taken up in dichloromethane (20 mL), washed with water (4x15 mL) and dried (Na₂SC¼). The solution was filtered and evaporated affording the product as yellow solid. Yield 132 mg (68%).LC-MS (ESI, column Phenomenex Luna C18 (2) column 20 x 2.0 mm, 3 μιτη, flow 0.6 mL/min, gradient 5 to 50% B over 5 min, solvent A: water/0.1% TFA, solvent B: acetonitrile/0.1% TFA, UV detection at 214 and 254 nm), . =5.3 min, m/z expected

273.1 (MH⁺), found 273.2. ⁱH NMR (500 MHz, CDCI₃): δ 3.05 (2H, tr, CH₂Ph), 3.77 (2H, q, NCH₂), 6.19 (1H, tr, NH) , 7.00 (1H, m, CHCF), 7.40 (2H, m, Ph), 7.84 (2H, m, Ph), 8.19 (1H, m, Nic), 8.51 (1H, m, Nic), 9.98 (1H, s, CHO). ¹³C NMR (125 MHz, CDCI₃): δ 35.88 (CH₂Ph), 40.95 (NHCH₂), 109.89 (d,²J_Fc = 37.5 Hz, Nic), 129.50 (Ph), 130.25 (Ph), 135.22 (CCH(O)), 140.77 (d, ³JFC = 9.0 Hz, Nic), 145.82 (Ph-CCH₂), 146.45 (d, ³J_Fc = 16.0 Hz, Nic), 164.53 (C(O)N), 165.07, (d,U_Fc = 243.0 Hz, CF), 191.74 (CHO).

Example 4. General Preparation of internal carboxylic acid standards

Internal standards such as carboxylic acids are synthesized using Oxone.

4a. General procedure: Aldehyde ( 0.002mole) is taken in dimethylformamide (DM F) and Oxone ( 0.24mole) was added to it and the reaction mixture was stirred overnight. Progress of the reaction was monitored using TLC. Distilled water was then added and the solid obtained was filtered.

4b. Purification: The solid was then purified by dissolving first bicarbonate, extracting out the organic impurities and then re-precipitating with dilute

hydrochloric acid at pH 2.0-3.0. All the compounds are isolated with a purity of 95+% by HPLC analysis.

Example 5. Screening for ALDH activity

5a. ALDH Assay

Aldehyde Dehydrogenase is an enzyme that acts on aldehydes as substrates and converts them to acid (products).

Principle:

Aldehyde + 6-NAD⁺ Aldehyde Dehydrogenase Acid + β-NADH

►

Abbreviations used:

β-ΝΑϋ⁺ = β-Nicotinamide Adenine Dinucleotide, Oxidized Form

β-NADH = β-Nicotinamide Adenine Dinucleotide, Reduced Form

• Designing and Standardization of ALDH assay: following the conversion of NAD+ to NADH typically one does the ALDH assays. Substrate + NAD⁺ ALDH ^ Product + NADH

The formation of NADH is monitored by measuring the absorbance at 340nm. However, before employing this method, the compounds were screened for their spectral properties, especially to avoid any interference in absorbance either from the substrate or the product.

• Spectral Studies of the compounds:

o Absorbance Spectra: The compounds were initially screened for their absorbance from 200nm to 800nm.

o Fluorescence Spectra: In some cases, the studies indicated that the compounds (Substrate or products) had interfering absorbance at 340nm. Such compounds were further screened for their fluorescence properties by recording their excitation/emission wavelengths.

· ALDH Assay by spectroscopic method: The ALDH assay is designed to measure either the utilization of the substrate or formation of product by measuring at their unique wavelengths (Absorbance or Fluorescence).

5b. Spectral Studies

All the spectral studies for the compounds were carried out in 0.1M Tris HCI pH

8.0 buffer. CSCT Compounds were initially dissolved in Methanol (~2.0mg/mL). The compounds were further diluted in 0.1M Tris HCI pH 8.0 buffer (concentration ranging from -20 to 50μg/mL). The Spectra was recorded using Spectramax M5. The ALDH activity can be followed either by monitoring the conversion of β-

NAD⁺ to β-NADH or by directly monitoring the product/substrate. The conversion of β- NAD⁺ to β-NADH yields increasing in absorbance at 340nm. If either the substrate/products have any spectral interference at this wavelength then unique absorbance /fluorescence wavelength of either product/substrate are used. The measurements were taken on Spectromax M5.

5c. ALDH Assay Reagents

1. Reggent 1: 1 M Tris HCI Buffer, pH 8.0 at 25°C(Prepare 50 ml in deionized water using Trizma Base, Sigma Prod. No. T-1503. Adjust to pH 8.0 at 25°C with 1 M HCI.)

2. Reagent 2: 20 mM β-Nicotinamide Adenine Dinucleotide, Oxidized Form, Solution (B-NAD⁺) (Prepare 1 ml in deionized water using β-Nicotinamide Adenine Dinucleotide, PREPARE FRESH). 3. Reagent 3: 3 M Potassium Chloride Solution (KCI) (Prepare 1 ml in deionized water using Potassium Chloride).

4. Reagent 4: 1 M 2-Mercaptoethanol Solution (2-ME) (Prepare 1 ml in deionized water using 2-Mercaptoethanol. PREPARE FRESH.)

5. Reagent 5: 100 mM Tris HCI Buffer with 0.02% (w/v) Bovine Serum Albumin, pH 8.0 at 25°C (for Enzyme Dilution).

6. Reagent 6: Aldehyde Dehydrogenase Enzyme Solution (Yeast ALDH).

Immediately before use, prepare a solution containing 0.5-1 unit/ml of

Aldehyde Dehydrogenase in cold Reagent 5).

5d. ALDH Assay Method

Pipette (in milliliters) the following reagents into vial:

Test Blank

Deionized Water 2.32 2.32

Reagent 1 (Buffer) 0.30 0.30

Reagent 2 (β-NAD) 0.10 0.10

Reagent 3 (KCI) 0.10 0.10

Reagent 7 (Substrate) 0.05 0.05

Reagent 4 (2-M E) 0.03 0.03

Mix by inversion and equilibrate to 25°C.

Reagent 5 (Enz Dil) 0.10

Reagent 6 (Enzyme Solution) 0.10

**Reagent 7 (Substrate): 50μΜ concentration of Substrate in 0.1M TrisHCl pH 8.0 buffer.

5e. Final assay concentration:

In a 3.00 ml reaction mix, the final concentrations are 103 mM Tris HCI Buffer (Reagent 1), 0.67 mM β-nicotinamide adenine dinucleotide (Reagent 2), 100 mM potassium chloride (Reagent 3), 10 mM 2-mercaptoethanol (Reagent 4), 0.0007% (w/v) bovine serum albumin (Reagent 5) and 0.05 - 0.1 unit aldehyde dehydrogenase (Reagent 6). Table 1 : Substrates selected for ALDH assay

RESU LTS

The results of the ALDH assay are summarized in Table 2. Table 2: Screening results:

Active: Compounds for which enzymatic activity was observed spectroscopically either by change in absorbance or fluorescence as a function of time.

Non active: Compounds for which no enzymatic activity was observed

spectroscopically either by change in absorbance or fluorescence as a function of time.

Example 6.General Radiosynthesis Method for preparation of ¹⁸F-compounds

¹⁸F-fluoride (up to 370MBq) is azeotropically dried in the presence of Kryptofix 222 (12-14mg in 0.5ml MeCN) and potassium carbonate (ΙΟΟμΙ 0.1M solution in water) by heating under N2 to 125°C for 15mins. During this time 2xlml MeCN are added and evaporated. After cooling to <40°C, a solution of precursor compound such as trimethylammonium benzaldehyde triflate (3-7mg in 0.7ml DMSO) is added. The reaction vessel is sealed and heated to 120°C for 15mins to effect labelling. The crude reaction mixture is cooled to room temperature and diluted by addition to 10ml water. The mixture is passed sequentially through a Sep-pak CM-plus cartridge (conditioned with 10ml water) and a SepPak C18-plus cartridge (conditioned with 20ml EtOH and 20ml H2O). The cartridges are flushed with water (10 ml), and the product, such as ¹⁸F-fluorobenzaldehyde is eluted from the SepPak C18-plus cartridge with MeOH (1ml).

Example 7. Cell based ALDH assay for 6-fluoro-/V-[2-(4-formyl-phenyl)-ethyl]- nicotinamide (GEH 120688)

Summary - Briefly, the compound was dissolved in DMSO and competed against ALDEFLUOR™, a BODIPY-conjugated ALDH substrate, in a cell-based assay using SK-BR-3 cells. The BODIPY fluorescence in the cell samples were measured using FACS at 488 nm. The median fluorescence of each sample was measured and fitted to a sigmoidal dose-response curve for calculation of IC50 using Prism Graphpad. The results demonstrate a decrease in fluorescence of the samples with increasing concentrations of the tested compound, this suggests that the compound is ALDH substrates and can displace ALDEFLUOR™. The IC50 value was 3.23 μΜ. Method and material

Test compounds - 6-fluoro-/V-[2-(4-formyl-phenyl)-ethyl]-nicotinamide was dissolved and diluted in DMSO prior to use.

Cell line - SK-BR-3 cells, a cell line reported to have a high expression of ALDH+ cells, was used for all experiments. The cells were cultured in RPM I media supplemented with 10% fetal bovine serum and 2 mM L-glutamine, in 37°C, 5% CO2. On the day of assay, cells were harvested by trypsination, centrifuged, and re- suspended in ALDEFLUOR™ assay buffer to a concentration of 1 x 10⁶ cells.

Competition ossoy - The compound was competed against ALDEFLUOR™, a BODIPY-conjugated ALDH substrate. Two series of cell samples with a fixed concentration of ALDEFLUOR™ were prepared according to the manufacturers protocol (ALDEFLUOR™ kit #01700, Stem Cell Technologies), either with or without addition of the inhibitor DEAB. The compound was added to the cell samples for a final concentration of 0.005-50 μΜ. Following incubation at 37°C, the fluorescence was measured in each sample by FACS at 488 nm. The assay was repeated in triplicate.

The median fluorescence of each sample was calculated, and the values were then normalized and fitted to a dose-response curve for calculation of IC50 using Prism Graphpad. Results

6-fluoro-N-[2-(4-formyl-phenyl)-ethyl]-nicotinamide displaced ALDEFLUOR™, as is demonstrated by the decrease in fluorescence of the samples with increasing compound concentration. Calculation of IC50 values result in an IC50 of 3.23 μΜ (Figure 1). The results suggest that the compound is a potent ALDH substrate, and can efficiently displace ALDEFLUOR™ in vitro.

While the particular embodiment of the present invention has been shown and described, it will be obvious to those skilled in the art that changes and modifications may be made without departing from the teachings of the invention. The matter set forth in the foregoing description and accompanying drawings is offered by way of illustration only and not as a limitation. The actual scope of the invention is intended to be defined in the following claims when viewed in their proper perspective based on the prior art.

Claims

1. A method for detection of tumour stem cells in a subject, comprising:

(i) administrating a detectably labelled substrate for ALDH to said subject;

(ii) detecting uptake of said detectably labelled substrate for ALDH by in vivo imaging;

wherein the detectably labelled substrate for ALDH is a compound of formula (Id**):

or a salt or solvate thereof, wherein

q, and r are each an integer independently selected from 0 and 1;

A is a radioimaging moiety;

X¹ is selected from -CR₂- , -CR=CR- , -C≡C- , -CR₂C0₂- , -C0₂CR₂- , -NRCO- , -CONR- , -NR(C=0)NR- -NR(C=S)NR- -S0₂NR- , -NRS0₂- , -CR₂OCR₂- , -CR₂SCR₂- , and -CR₂NRCR₂-, wherein each R is independently selected from H, Ci-6 alkyl, C₂-6 alkenyl, C₂-6 alkynyl, Ci-6 alkoxyalkyl and Ci-6 hydroxyalkyl; and

the compound of formula (Id**) has a molecular weight of below 800 Daltons.

2. The method according to claim 1, wherein A is a radioimaging moiety comprising a non-metal radiolabel suitable for imaging with PET or SPECT such as ¹²³> ¹²⁴> ¹²²l, ⁷⁵Br, ⁷⁶Br, ⁷⁷Br, ¹³N, ⁿC, or ¹⁸F.

3. The method according to claim 1, wherein A comprises

4. The method according to claim 1, wherein A comprises

5. The method according to claim 1, wherein the detectably labelled substrate for ALDH is

6. The method of claim 1, further comprising identifying ALDH expressing cells within a tumor.

7. A method for detection of tumour stem cells in a subject, comprising

(i) administrating to said subject a compound of formula (Id**):

or a salt or solvate thereof, wherein

q, and r are each an integer independently selected from 0 and 1;

A is a radioimaging moiety;

X¹ is selected from -CR₂- , -CR=CR- , -C≡C- , -CR2CO2- , -CO2CR2- , -N RCO- , -CON R- , -NR(C=0)NR- -NR(C=S)NR- -SO2N R- , -N RSO2- , -CR2OCR2- , -CR2SCR2- , and -CR2NRCR2-, wherein each R is independently selected from H, Ci-6 alkyl, C2-6 alkenyl, C2-6 alkynyl, Ci-6 alkoxyalkyl and Ci-6 hydroxyalkyl; and

the compound of formula (Id**) has a molecular weight of below 800 Daltons; and (ii) detecting uptake of said compound by in vivo radioimaging.

8. The method according to claim 7, wherein A is a radioimaging moiety comprising a non-metal radiolabel suitable for imaging with PET or SPECT such as ¹²³> ¹²⁴> ¹²²l, ⁷⁵Br, ⁷⁶Br, ⁷⁷Br, ¹³N, ⁿC, or ¹⁸F.

9. The method according to claim 7, wherein A comprises

10. The method according to claim 7 wherein A com rises

11. The method according to claim 7, wherein the compound is

12. A method of monitoring the effect of treatment of a tumour in a subject, said method comprising

(i) administrating a detectably labelled substrate for ALDH to said subject;

or a salt or solvate thereof, wherein

q, and r are each an integer independently selected from 0 and 1;

A is a radioimaging moiety;

X¹ is selected from -CR₂- , -CR=CR- , -C≡C- , -CR₂C0₂- , -C0₂CR₂- , -NRCO- , -CONR- , -NR(C=0)NR- -NR(C=S)NR- -S0₂NR- , -NRS0₂- , -CR₂OCR₂- , -CR₂SCR₂- , and -CR2NRCR2-, wherein each R is independently selected from H, Ci-6 alkyl, C2-6 alkenyl, C2-6 alkynyl, Ci-6 alkoxyalkyl and Ci-6 hydroxyalkyl;

the compound of formula (Id**) has a molecular weight of below 800 Daltons; and said method being effected optionally before, during and after treatment.

13. The method according to claim 12, wherein A is a radioimaging moiety comprising a non-metal radiolabel suitable for imaging with PET or SPECT such as ¹²³>

124, 122|_ 75Br, 76β_Γ, ^Br, ^N, ⁿC, ΟΓ ¹⁸F. 14. The method according to claim 12, wherein A comprises

15. The method according to claim 12, wherein A com rises

16. The method according to claim 12, wherein the detectably labelled substrate for ALDH is

17. A method for radiotherapy of a cancer patient, comprising administration of an effective amount of radiotherapy-labelled substrate for ALDH to said cancer patient wherein the detectably labelled substrate for ALDH is a compound of formula (Id**):

or a salt or solvate thereof, wherein

q, and r are each an integer independently selected from 0 and 1;

A is a radioimaging moiety;

X¹ is selected from -CR₂- , -CR=CR- , -C≡C- , -CR₂C0₂- , -C0₂CR₂- , -NRCO- , -CONR- , -NR(C=0)NR-, -NR(C=S)NR-, -S0₂NR- , -NRS0₂- , -CR₂OCR₂- , -CR₂SCR₂- , and -CR₂NRCR₂-, wherein each R is independently selected from H, Ci-6 alkyl, C₂-6 alkenyl, C₂-6 alkynyl, Ci-6 alkoxyalkyl and Ci-6 hydroxyalkyl; and

the compound of formula (Id**) has a molecular weight of below 800 Daltons.

18. The method according to claim 17, wherein A is a radioimaging moiety comprising a non-metal radiolabel suitable for imaging with PET or SPECT such as ¹²³> 12 , i₂₂|_i 75β_Γι 76Br, ⁷⁷Br, ¹³N, ⁿC, or ¹⁸F.

19. The method according to claim 17, wherein A comprises

20. The method according to claim 17, wherein A com rises

method according to claim 17, wherein the detectably labelled substrate for

22. A compound of formula (Id**):

,aikvi

or a salt or solvate thereof, for use in medicine, wherein

q, and r are each an integer independently selected from 0 and 1;

A is a radioimaging moiety;

X¹ is selected from -CR₂- , -CR=CR- , -C≡C- , -CR₂C0₂- , -C0₂CR₂- , -NRCO- , -CONR- , -NR(C=0)NR- -NR(C=S)NR-, -S0₂NR- , -NRS0₂- , -CR₂OCR₂- , -CR₂SCR₂- , and -CR₂NRCR₂-, wherein each R is independently selected from H, Ci-6 alkyl, C₂-6 alkenyl, C₂-6 alkynyl, Ci-6 alkoxyalkyl and Ci-6 hydroxyalkyl;

the compound of formula (Id**) has a molecular weight of below 800 Daltons. 23. The compound according to claim 22, wherein A is a radioimaging moiety comprising a non-metal radiolabel suitable for imaging with PET or SPECT such as ¹²³>

124, 122 \_t 75Br, 76β_Γ, ^Br, ^N, ⁿC, ΟΓ ¹⁸F.

24. The compound according to claim 22, wherein A comprises

25. The compound according to claim 22, wherein A comprises

26. The compound according to claim 22, having the structure of

27. A pharmaceutical formulation comprising the compound of claim 22 and a pharmaceutically acceptable excipient.