Classifications

• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61K—PREPARATIONS FOR MEDICAL, DENTAL OR TOILETRY PURPOSES
  • A61K31/00—Medicinal preparations containing organic active ingredients
  • A61K31/33—Heterocyclic compounds
  • A61K31/395—Heterocyclic compounds having nitrogen as a ring hetero atom, e.g. guanethidine or rifamycins
  • A61K31/435—Heterocyclic compounds having nitrogen as a ring hetero atom, e.g. guanethidine or rifamycins having six-membered rings with one nitrogen as the only ring hetero atom
  • A61K31/47—Quinolines; Isoquinolines
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61K—PREPARATIONS FOR MEDICAL, DENTAL OR TOILETRY PURPOSES
  • A61K31/00—Medicinal preparations containing organic active ingredients
  • A61K31/33—Heterocyclic compounds
  • A61K31/395—Heterocyclic compounds having nitrogen as a ring hetero atom, e.g. guanethidine or rifamycins
  • A61K31/40—Heterocyclic compounds having nitrogen as a ring hetero atom, e.g. guanethidine or rifamycins having five-membered rings with one nitrogen as the only ring hetero atom, e.g. sulpiride, succinimide, tolmetin, buflomedil
  • A61K31/403—Heterocyclic compounds having nitrogen as a ring hetero atom, e.g. guanethidine or rifamycins having five-membered rings with one nitrogen as the only ring hetero atom, e.g. sulpiride, succinimide, tolmetin, buflomedil condensed with carbocyclic rings, e.g. carbazole
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61P—SPECIFIC THERAPEUTIC ACTIVITY OF CHEMICAL COMPOUNDS OR MEDICINAL PREPARATIONS
  • A61P35/00—Antineoplastic agents
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07D—HETEROCYCLIC COMPOUNDS
  • C07D209/00—Heterocyclic compounds containing five-membered rings, condensed with other rings, with one nitrogen atom as the only ring hetero atom
  • C07D209/56—Ring systems containing three or more rings
  • C07D209/58—[b]- or [c]-condensed
  • C07D209/60—Naphtho [b] pyrroles; Hydrogenated naphtho [b] pyrroles

Definitions

• the present invention concerns aromatic oxidation/hydroxylation activated prodrugs, particularly anti-tumour prodrugs and those which are specifically activated by the oxidation/hydroxylation activities of the cytochrome P450 family of enzymes.
• cytotoxic drugs are known that can be used for therapeutic purposes. However, they typically suffer from the problem that they are generally cytotoxic and therefore may affect cells other than those that are required to be destroyed. This can be alleviated to some extent by the use of targeted drug delivery systems, for example direct injection to a site of tumourous tissue or, e.g. binding the cytotoxic agent to an antibody that specifically recognises an antigen displayed only on the cancer cell surface. Alternatively, electromagnetic radiation may be used to cause chemical alteration in an agent at a desired site such that it becomes cytotoxic. However, all of these techniques have, to a greater or lesser extent, certain limitations and disadvantages.
• the compound (+)-CC-1065 and the duocarmycins are naturally occurring representatives of a class of DNA alkylating agents.
• the naturally occurring compounds consist of a DNA alkylating unit based upon a pyrrolo[3,2-e]indole core, with one or two sub units, conferring DNA binding capabilities.
• CC-1065 and duocarmycin A comprise a spirocyclic cyclopropane group responsible for the DNA alkylation properties.
• Duocarmycin B 2l C 2 and D 2 are believed to be precursors for cyclopropane actives, and comprise a substituted (by a leaving group) methyl group at the eight position on the dihydro pyrrole ring.
• CC-1065 has been synthesised by various routes, summarised by Boger ef a/ in Chem. Rev. 1997, 97, 787-828.
• the present invention relates to precursors of analogues CC-1065, which do not have the hydroxyl group in the B ring of the alkylating sub unit, and which are hence substantially inactive as DNA alkylating agents themselves.
• cytochrome P450 isoforms in tumour cells provides a molecular target for the development of new antitumour drugs that could be selectively activated by the CYP enzymes in tumour cells, although no drug examples were given.
• a number of other CYP isoforms have been shown to be expressed in various tumours. Many of the CYP's expressed in tumours are mentioned in Patterson, LH et al, (1999) Anticancer Drug Des. 14(6), 473-486.
• prodrugs of styrene- and chalcone-derivatives are described.
• the respective hydroxylated forms of the prodrugs, formed in situ, are potent tyrosine kinase (TK) inhibitors. Inhibition of TK activity contributes to tumour inhibition and cell destruction.
• the prodrugs were shown to be activated by microsomal preparations expressing CYP1 B1 enzyme, and to have cytotoxic activity against cell lines expressing the same enzyme, whilst having much lower cytotoxic activity against cell lines not expressing the enzyme.
• the present invention is directed to a new class of prodrugs which are expected to be hydroxylated in situ by CYP enzymes, in particular enzymes expressed at high levels in tumours.
• the prodrugs are believed to be metabolisable by CYP1 B1 enzyme.
• Some of the compounds are new.
• the present invention relates to the first therapeutic use of a broad range of compounds, and their synthesis as well as intermediates used therein.
• R 1 is -Ar, NH 2 , OR 7 or R 7 ;
• R 2 , R 3 , R 4 R 5 and R 6 are each independently selected from H, C alkyl, -OH, C M alkoxy, -CN, Cl, Br, I, -NO 2l -NH 2 , -NHR 16 , -NR 16 2 , -N + R 6 3 , • NHCOR 8 , -COOH, CONHR 9 , -NHCOOR 9 and -COOR 9 ;
• R 7 , R 8 and R 9 are independently selected from C,- 4 alkyl, optionally substituted phenyl, C 7 _ 12 ⁇ aralkyl, optionally substituted heteroaryl and a ligand;
• Ar is selected from
• B is N or CR 10 ;
• R 10 is selected from OH, C M alkoxy, C ⁇ alkyl, -NO 2 , -NH 2 , -CN, Cl, Br, I, -NHCOR 14 , -COOH, -CONHR 15 , -NHCOOR 15 and -COOR 15 and H;
• the or each R 11 is selected from OH, C alkoxy, C, ⁇ alkyl, -NO 2 , - NH 2 , -NHR 16 , -NR 16 2 , -N + R 16 3 , -CN, Cl, Br, 1,-NHCOR 14 , -COOH, -CONHR 15 , - NHCOOR 15 and -COOR 15 ;
• n is an integer in the range 0 to 4;
• R 12 is H, -COAr 1 , -CONH 2 , -COOH, -COOR 15 or -COR 15 ; the or each R 13 is selected from OH, C,_ 4 alkoxy, O, ⁇ alkyl, -NO 2 , - NH 2 , -NHR 16 , -NR 16 2 , -N + R 16 3 , -CN, Cl, Br, I, -NHCOR 14 , -COOH, -CONHR 15 , -NHCOOR 15 and -COOR 15 ; m is 0, 1 or 2;
• R 14 is selected from C ⁇ alkyl, optionally substituted phenyl, optionally substituted heteroaryl, C 7 . 12 aralkyl, Ar 1 and ligands;
• R 15 is selected from C M alkyl, optionally substituted phenyl, C 7 . 12 - aralkyl optionally substituted heteroaryl and ligands;
• the or each R 16 is independently selected from C,. 4 alkyl, optionally substituted phenyl, C 7 . 12 -aralkyl and optionally substituted heteroaryl;
• Ar 1 is selected from the same groups as Ar; provided that no more than one group R 11 or R 3 in any one ring includes a group Ar 1 .
• Ar 1 is preferably
• the animal which is treated is generally a human, although the compounds may also have veternary use.
• the indication treated is generally cancer including adenocarcinoma, leukemia, . lymphoma, melanoma, myeloma, sarcoma, teratocarcinoma, and, in particular, cancers of the adrenal gland, bladder, bone, bone marrow, brain, breast, cervix, gall bladder, ganglia, gastrointestinal tract, heart, kidney, liver, lung, muscle, ovary, pancreas, parathyroid, penis, prostate, salivary glands, skin, spleen, testis, thymus, thyroid, and uterus.
• the tumour may, for instance, be defined as a tumour expressing high levels of CYP1 B1.
• the leaving group Y is, for instance, in a group which has utility in nucleophilic substitution reactions. Suitable examples of leaving groups are -OCOOR 17 , -OCONHR 18 Cl, Br, I, or -OSOOR 19 , in which R 17 , R 18 and R 19 are selected from C,. 4 alkyl, optionally substituted phenyl, C 7 _ 12 -aralkyl and optionally substituted heteroaryl. Most preferably the leaving group is a halogen atom, preferably chlorine.
• Optional substituents in phenyl, aralkyl and heteroaryl groups are, for instance, C ⁇ -alky!, halogen, hydroxyl, C.,_ 4 -alkoxy, -NH 2 , -NHR 16 , -NR 16 2 , -N + R 16 3 , -NO 2l -CN, -COOH, -NHCOR 14 , -CONHR 15 , -NHCOOR 15 , -COOR 15 etc.
• ligand includes a group having specific targeting characteristics, useful for instance in antibody or gene- directed enzyme prodrug-type environments.
• a ligand may be an oligopeptide, biotin, avidin or streptavidin, a polymeric group, an oligonucleotide or a protein .
• it has specific binding characteristics such as an antibody or fragment, an antigen, a sense or anti- sense oligo-nucleotide, or one of avidin, streptavidin and biotin, that is it is one component of a specific binding pair.
• it may be a group designed for passive targeting, such as a polymeric group, or a group designed to prolong the stability or reduce immunogenicity such as a hydrophilic group.
• US-A-5843937 discloses suitable ligands for conjugating to these types of actives and methods for carrying out the conjugation.
• R 1 is other than OR 7 .
• the group R 1 in a compound of the general formula I is a group Ar.
• the compound may include two aromatic groups joined to one another.
• one of the groups R 11 of the Ar group, or the group R 12 is a group Ar 1 .
• the group R 12 should be other than a group -COAr 1 .
• a group Ar 1 which is one of the other types of group there should preferably either be no substituents R 11 or R 13 , as the case may be, or, if there are any substituents, no such substituents should include a group Ar 1 .
• the substituent Ar is a group
• B is preferably CR 10 .
• R 10 is preferably H.
• the groups B and Z are selected amongst the same preferable groups.
• n is at least 1 and one of the groups R 11 is -NHCOAr 1 .
• Ar 1 is preferably a group
• R 12 in Ar is other than -COOR 15 , more preferably it is a group -COAr 1 in which Ar 1 preferably is the same type of group.
• m in the indole type group is preferably zero.
• substituents R 11 there may be several substituents R 11 . Most preferably such substituents are selected amongst C,_ 4 -alkoxy groups.
• the core indole ring of the DNA alkylating sub-unit is preferably unsubstituted in the benzene ring (R 2 is hydrogen), whilst the benz ring may be unsubstituted (R 3 , R 4 , R 5 and R 6 are all hydrogen), or one or more of R 3 to R 6 represents a cyano group, an alkoxy group, a group -COOR 10 , or a C.,- 4 -alkyl group (preferably methyl).
• R 5 is a alkoxy, preferably methoxy and R 2 , R 3 , R 4 , R 6 are all H.
• R 5 is cyano and R 2 , R 3 , R 4 and R 6 are H.
• X is H. It is believed that, hydroxylation of the compound will occur in situ at the carbon atom to which X is attached, thereby activating the compound enabling it to act as a DNA alkylating agent.
• X 1 is H
• Y 1 is a leaving group
• R 20 is -R 7 , -OR 7 , -NH 2 or Ar 2 ;
• B 1 is N or CR 22 ;
• R 21 is an amine protecting group; the or each R 22 is selected from OH, C . 4 alkoxy C,. 4 alkyl, NO 2 ,
• R 23 is H, COAr 3 , -CONH 2 , -COOH, -CONHR 7 or -COR 7 or is an amine protecting group; the or each R 24 is selected from OH, C ⁇ alkoxy C.,.. 4 alkyl, NO 2 , -NHR 21 , -NHR 26 , -NR 26 2 , -N + R 26 3 , -CN, Cl, Br, I, -NHCOR 25 , -COOH, - CONHR 7 and -COOR 7 ; q is 0, 1 or 2; R 25 is selected from C,. 4 alkyl, optionally substituted phenyl, optionally substituted heteroalkyl, C 7 . 12 aralkyl Ar 3 and a ligand.
• R 26 is selected from C M alkyl, optionally substituted phenyl, C 7 . 12 - aralkyl and optionally substituted heteroaryl;
• Ar 3 is selected from the same groups as Ar 2 provided that no more than one R 22 or R 24 in any one ring includes a group Ar 3 .
• Ar 3 is preferably
• amine protecting groups R 21 or R 23 are benzyl, benzyloxycarbonyl, tertiary butyloxycarbonyl (BOC), fluorenyl-N-methoxy-carbonyl (FMOC) and 2-[biphenylyl-(4)]-propyl-2- oxycarbonyl. Where more than one amine group is protected in the molecule, the protecting groups may be the same or different.
• R 20 is OR 7 and R 7 is an amine protecting group different to R 1 CO.
• R 20 is other than OR 7 .
• R 20 is preferably Ar 2
• Y 1 is preferably selected from -OCOOR 17 , -OCONHR 18 , Cl, Br, I, or - OSOOR 19 , in which R 17 , R 18 and R 19 are selected from C,. 4 alkyl, optionally substituted phenyl, C 7 . 12 -aralkyl and optionally substituted heteroaryl.
• the leaving group is a halogen atom, preferably chlorine.
• compositions comprising compounds of the formula I or IA and a pharmaceutically acceptable excipient.
• Pharmaceutical compositions may be suitable for intramuscular, intraperitoneal, intrapulmonary, oral or, most preferably, intravenous administration.
• the compositions contain suitable matrixes, for example for controlled or delayed release.
• the compositions may be in the form of solutions, solids, for instance powders, tablets or implants, and may comprise the compound of the formula I in solid or dissolved form.
• the compound may be incorporated in a particulate drug delivery system, for instance in a liquid formulation.
• excipients include lactose, sucrose, mannitol, and sorbitol; starch from corn, wheat, rice, potato, or other plants; cellulose, such as methyl cellulose, hydroxypropylmethyl-cellulose, or sodium carboxymethylcellulose; gums, including arabic and tragacanth; and proteins, such as gelatin and collagen.
• disintegrating or solubilizing agents may be added, such as the cross-linked polyvinyl pyrrolidone, agar, and alginic acid or a salt thereof, such as sodium alginate.
• Solid compositions may take the form of powders and gels but are more conveniently of a formed type, for example as tablets, cachets or capsules (including spansules).
• Y 2 is a leaving group or a hydroxyl or protected hydroxyl group; is reacted with a compound of the general formula IV R 27 COY 3 IV in which R 27 is selected from C ⁇ -alkyl, optionally substituted phenyl, C 7 . 12 -aralkyl, optionally substituted heteroaryl and Ar 4 ; Ar 4 is selected from
• B 2 is N or CR 32 ;
• R 29 is an amine protecting group
• R 30 is an amine protecting group, -CONH 2 , -COOH, -COR 36 or -COAr 5 ; the or each R 31 is selected from C ⁇ -alkoxy, C ⁇ -alkyl, NO 2 , CN, Cl, Br, I, -NHR 33 , -NHR 35 , -NR 35 2 , -N + R 5 3 -, NHCOR 34 , -COOH, -CONHR 36 and -COOR 36 ; s is 0, 1 or 2;
• R 32 is selected from H, C,_ 4 -alkoxy, C 1 . 4 -alkyl, NO 2 , CN, Cl, Br, I, - NHR 53 , -NHR 35 , -NHR 35 2 , -N T R 35 3 , NHCOR 34 , COOH, -CONHR 36 and COOR 36 ;
• R 33 is an amine protecting group
• R 34 is selected from Ar 5 , C 1 . 4 -alkyl, optionally substituted phenyl, C 7 . 12 - aralkyl, optionally substituted heteroaryl and a ligand;
• R 35 is selected from C ⁇ -alkyl, optionally substituted phenyl, C 7 . 12 - aralkyl and optionally substituted heteroaryl;
• R 36 is selected from C.,- 4 -alkyl, optionally substituted phenyl, C 7 . 12 - aralkyl optionally substituted heteroaryl and a ligand;
• Ar 5 is selected from the same groups as Ar 4 and
• Y 3 is a leaving group provided that no more than one R 28 or R 31 in any one ring includes a group Ar 5 .
• a 5 is preferably
• Y 3 is, for instance, selected amongst the preferred leaving groups listed above for Y. Most suitably the definition of Y 3 is Cl. Alternatively, the group Y 3 may be OH. In this case, it may be necessary to include a coupling agent to assist in the coupling reaction.
• reaction between the compound of the general formula III or IIIA and the carboxylic acid or derivative of the general formula IV is carried out under conditions allowing such coupling to take place.
• Such conditions are similar to those generally used for formation of peptide bonds, for instance as used in peptide synthetic methods.
• Y 2 is a hydroxy or protected hydroxyl group or a leaving group, which may be the same as Y, or may be converted to Y in a subsequent step.
• it may be desirable to deprotect one or more of the protected amine groups. If further reaction, for instance with other derivatising agents such as glycosyl compounds, peptides, polymers etc is desired through any such amine groups, it may be desirable to deprotect only those to which subsequent reaction to to take place, whilst retaining the other amine groups in a protected form. Selection of suitable amine protecting groups and protection and deprotection protocols may be made using techniques commonly utilised in peptide chemistry.
• a novel compound may have the general formula V or VA
• R 38 , R 39 , R 40 , R 41 and R 42 are selected from H, C ⁇ -alkyl, -OH, C ⁇ - alkoxy, -CN, Cl, Br, I, NO 2 , NHR 43 , -NHCOR 44 , -NR 45 2 , -N + R 45 3 , -COOH, - CONHR 46 and -COOR 46
• X 2 is H
• Y 2 is a leaving group or a hydroxyl or protected hydroxyl group
• R 37 is H or an amine protecting group
• R 43 is selected from H, C alkyl, optionally substituted phenyl, C 7 . 12 - aralkyl, and optionally substituted heteroaryl an amine protecting group;
• R 44 is selected from C.,. 4 alkyl, optionally substituted phenyl, C 7 . 12 - aralkyl, optionally substituted heteroaryl and a ligand; each R 45 is selected from C,. 4 alkyl, optionally substituted phenyl, C 7 . 12 -aralkyl and optionally substituted heteroaryl; and
• R 46 is selected from C,,. 4 alkyl, optionally substituted phenyl, C 7 . 12 " aralkyl, optionally substituted heteroaryl and a ligand.
• R 24 is H.
• Precursors for such compounds have the ring nitrogen atom in rntected form, that is in which R 37 represents a protecting group.
• the group Y 2 may be selected amongst those defined above for leaving group Y.
• the nature of the group Y 2 should be selected having regard to the nature of the reagent with which the compound of the formula lll/V is to react in a subsequent step, for instance with a compound of the general formula IV, such that the group Y 2 is not deactivated and does not form a dimer of compounds of the formula III or V.
• Suitable examples of leaving group Y 2 are Cl and Br.
• the starting compound for such a reaction may be represented by the general formula VI
• R 47 is an amine protecting group, one of Z 1 and Z 2 is Y 5 and the other is H;
• Y 5 is a leaving group which is different from or the same as Y 2 ;
• Y 4 is the radical leaving group.
• the group Z 1 is Y 5 and Y 5 is either H or a leaving group, preferably the same group. as Y 2 wherein the group Y 5 is not effective as a leaving group in this step of the synthesis.
• the reaction is conducted in the presence of a suitable catalyst, optionally in the presence of a free radical trap.
• the group Y 4 should be a radical leaving group, such as halogen, preferably Br or I.
• Suitable radicals for carrying out the cyclisation reaction using a compound VI in which Y 5 is H are nitroxy compounds such as 2,2,6,6-tetramethylpiperidinyloxy (TEMPO).
• Y 5 is a leaving group
• cyclisation may be carried out in the presence of a radical derived from azoisobutyronitrile (AIBN).
• AIBN azoisobutyronitrile
• Suitable catalysts for such a radical cyclisation step are tin hydride compounds such as tributyl tin hydride. Such a synthetic route is illustrated in Examples 1 and 3.
• a compound VI for cyclisation to form a 6-membered ring it is preferred to use a compound VI in which Z 2 is Y 5 and Y 5 is a leaving group, preferably a trialkyl stannyl group, and to carry out the reaction in the presence of a suitable catalyst palladium complexes such as tetrakis (triphenylphosphine) palladium (0), bis(triphenyl phosphine) palladium (II) chloride or palladium (II) acetate.
• the dihydroquinoline intermediate is oxidised to form a further intermediate which is an epoxide, for instance using a peroxide reagent.
• the epoxide intermediate is reduced using a suitable selective reducing agent such as a dialkyl aluminium hydride to produce the corresponding tetrahydroquinoline alcohol which is subsequently halogenated, for instance using carbon tetrachloride/triphenyl phosphine.
• a suitable selective reducing agent such as a dialkyl aluminium hydride to produce the corresponding tetrahydroquinoline alcohol which is subsequently halogenated, for instance using carbon tetrachloride/triphenyl phosphine.
• the compound of the general formula VI may be produced by alkylation of the sodium salt of the corresponding aniline derivative with a 1 ,3-dihalo propene compound.
• the carboxylic acid derivative of the general formula V may be synthesised using the methods generally described in Boger ef al, 1997 op.cit. for instance PDE-I and PDE-II may be synthesised using the Umezawa synthesis, the Rees-Moody synthesis, the Magnus synthesis, the Cava-Rawal synthesis, the Boger-Coleman synthesis, the Sundberg synthesis, the Martin synthesis, the Tojo synthesis, lndole-2-carboxylic acid is commercially available.
• Other analogues of the DNA binding sub-units of the duocarmycins, and reactive carboxylic acid derivatives thereof are described by Boger et al, op.cit.
• the present invention relates to the creation of a range of prodrugs that have little or no cytotoxic effects when in their normal state, but are highly cytotoxic (i.e. have a substantially increased cytotoxicity) when activated by oxidation or hydroxylation by CYP enzymes.
• This provides for a 5 self-targeting drug delivery system in which a non cytotoxic (or negligibly cytotoxic) compound can be administered to a patient, for example in a systemic manner, the compound then being activated at the site of the tumour cells (intratumoural activation) to form a highly cytotoxic compound which acts to kill the tumour cells.
• CYP isoforms are not 0 expressed by normal cells mean that the activation of the compound only occurs at the site of the tumour cells and therefore only tumour cells are affected, thus providing a self-targeting system.
• the prodrugs of the present invention have the distinct advantage of being useful in the treatment of tumours at any site in the body, meaning that 5 even tumours that have undergone metastasis (which are normally not susceptible to site specific therapies) may be treated.
• the prodrug may be an antitumour prodrug.
• tumours include cancers (malignant neoplasms) as well as other neoplasms e.g. innocent tumours.
• the prodrug may be activated by hydroxylation by o isoforms of cytochrome P450's.
• tumour tissue and normal tissue can be enhanced in a two part procedure.
• infecting tumor 5 cells with a viral vector carrying a cytochrome P450 gene and a cytochrome P450 reductase gene wherein expression of cytochrome P450 gene and cytochrome P450 reductase gene by tumor cells enables the enzymatic conversion of a chemotherapeutic agent to its cytotoxic form within the tumor, whereby the tumor cells become selectively sensitized to the prodrug o chemotherapeutic agent
• prodrugs are benz(e)dihydroindole or benz-tetrahydroquinoline derivatives. Their specific use as antitumour prodrugs has not been previously suggested or disclosed, nor has the suggestion that they are prodrugs having an activated hydroxylated form. Where compounds of formula (I) have been previously identified and made, they have not been identified as anti-tumour agents due to their poor (or negligible) cytotoxicity. Thus the intratumoural hydroxylation of the prodrugs of the present invention provides them with a surprising and unexpected efficacy.
• Hydroxylated forms of the prodrugs are potent DNA alkylating agents that bind in the minor groove of DNA and alkylate the purine bases at the N3 position. As such, they are potent cytotoxic agents whose exact biological mechanism of action is unknown but involves the disruption of template and other functions of DNA.
• General inhibition of template function of DNA will affect and be generally cytotoxic to all dividing cells in the body and lead to unacceptable side effects in a therapeutic setting.
• the targetted production of hydroxylated forms only in tumour cells that overexpress particular isoforms of cytochrome P450's will lead to a specific cytotoxic effect only in those cells.
• the non-hydroxylated forms are essentially non- toxic to all cells. The following examples illustrate the invention.
• FABMS (NBA/Nal): 318 (M + H + expected 318), 340 (M + Na + expected 340).
• the product may subsequently be deprotected and 0 conjugated to a DNA-binding subunit such as 5-methoxyindole-2-carboxylic acid by process steps analogous to example 1.8.
• Test compound activation by CYP enzymes was carried out using NADPH supplemented rat liver microsomes.
• Incubation mixtures comprised microsomal protein (1 mg/ml), reduced-nicotinamide adenine dinucleotide phosphate (NADPH, 10mM) and phosphate buffer (pH7.4, 100mM).
• Test 0 compound (0.01- 100 ⁇ M final concentration) in DMSO (20 ⁇ l) was added to the microsomal incubation mixtures (0.5ml) and incubated for 60 min at 37C.
• Control incubates contained test compound and microsomal incubation mixture terminated at 0 time. All incubations were terminated by addition of an equal volume of ice-cold acetonitrile and microfuged for 3 min. Aliquots of 5 the supernatant were added to cells in culture and cytotoxicity determined as described below.
• CHO Chinese Hamster Ovary (CHO) cell were grown in MEM supplemented with 10% dialysed FBS and G418 (400 ⁇ g/ml). All cells were seeded at an initial o density of 1000 cells/well in 96-well-plates, incubation at 37°C for 24 hours. Aliquots (0.1 ml) of the test compound/microsomal/acetonitrile supematnant was then added to the CHO cells. Cells were then incubated for 24 hours at 37°C, 5% CO 2 . After this time period MTT (50 ⁇ l; 2mg/ml stock solution) was added to each well and cells were incubated for a further 4 hours.
• MTT 50 ⁇ l; 2mg/ml stock solution
• a hydrogen acceptor tetrazolium salt is reduced to formazan dye by mitochondrial dehydrogenase of viable cells.
• the media was aspirated from cells and DMSO (100 ⁇ l/well) added to solubilise the coloured formazan dye. Absorbance of the formazan dye in the 96-well- plates was then determined at 550nm. The effect of microsomal activation by the test compound on the arrest of CHO cell growth could be determined by comparing the IC 50 (concentration that inhibited cell growth by 50%) with and without microsomal incubation.
• * represents significance at p>0.05.

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