Cryptophycins are secondary metabolites belonging to the class of depsipeptide macrocycles produced by cyanobacteria of the genus Nostoc. Their name refers to the fact that they are highly cytotoxic towards yeasts of the genus Cryptococcus. The first representative of this class of molecules, cryptophycin-1 (C-1), was isolated in 1990 from cyanobacterium Nostoc sp (ATCC 53789) (see Eiβler S., et al., Synthesis 2006, 22, 3747-3789). The structure, the general formula and the numbering of the carbon atoms of these compounds, as described in WO 98/08505, are recalled below:

Cryptophycins C1 and C-52, which are characterized by an epoxide function represented below, have anticancer properties. Phase II clinical trials in lung cancer were conducted with C-52 (LY 355073): see Edelman M. J., et al., Lung Cancer 2003, 39, 197-199; Sessa C., et al., Eur. J. Cancer 2002, 38, 2388-96. Cryptophycin C-55, a prodrug of C-52, is itself characterized by a chlorohydrin function instead of the epoxide function (Bionpally R. R., et al., Cancer Chemother Pharmacol 2003, 52, 25-33). C-55 proved to be very active, but is not stable in solution. Derivatives of chlorohydrin glycinate type such as the compound C-55 Gly have also been described as gaining in stability (Liang J., et al., Investigational New Drugs 2005, 23, 213-224).

Conjugate chemistry has been known for many years and has been applied to several families of cytotoxic agents, for instance the maytansinoids (WO 04/103 272), taxanes (WO 06/061 258), tomaymycins (WO 09/016,516), leptomycins (WO 07/144,709), CC-1065 and analogues thereof (WO 2007/102 069); see also, with regard to conjugates, Monneret C., et al., Bulletin du Cancer. 2000, 87(11), 829-38; Ricart A. D., et al., Nature Clinical Practice Oncology 2007, 4, 245-255. However, it has not been applied to cryptophycin derivatives conjugated to antibodies or to other targeting agents.
The technical problem that the present invention intends to solve is that of proposing novel conjugates based on cryptophycin derivatives, and also novel cryptophycin derivatives that are suitable for being conjugated.
EP 0 830 136 and WO 98/08505 describe cryptophycin derivatives but do not describe cryptophycin conjugates. WO 98/08505 describes cryptophycin derivatives of formula (A):
in which Ar may represent a group Ar′ of formula:
in which R54 represents H, a group (C1-C6)alkyl, (C1-C6)alkyl(R57, R57′, R57″), aryl, phenyl, heterocycloalkyl, a halogen atom, COOR57, PO3H, SO3H, SO2R58, NR59R60, NHOR61, NHOR61′, CN, NO2, OR62, CH2OR62′, CH2NR96R96′, (C1-C6)alkylOR100,
SR63; R55 and R56 represent H, a group (C1-C6)alkyl, C(R57R57′R57″), aryl, phenyl, heterocycloalkyl, a halogen atom, COOR57, PO3H, SO3H, SO2R58, NR59R60, NHOR61, NHCHR61′, CN, NO2, OR62, CH2OR62′, CH2OCOR95, CH2NR96R96′, (C1-C6)alkylOR100, (C1-C6)alkylNR59R60. WO 98/08505 especially describes the following compounds:
which are characterized by the end group —NHC(═O)Ot-Bu. WO 98/08505 does not specify that these compounds are suitable for or intended to be conjugated.
US 2007/0 213 511 describes calicheamicin immunoconjugates. Among these, mention is made of Mylotarg® (or CMA-676), which is a calicheamicin immunoconjugate used in the treatment of AML (anti-CD33-calicheamicin). See also in respect of conjugates: WO 2006/042 240.
Al-awar R. S., et al., J. Med. Chem. 2003, 46(14), 2985-3007 and Al-awar R. S., et al., Mol. Cancer Ther. 2004, 3(9), 1061-1067 describe cryptophycin derivatives, and also their in vivo evaluations.
WO 08/010,101 describes an anti-EphA2 monoclonal antibody and also the corresponding conjugates comprising one or more molecules of a cytotoxic compound attached to the monoclonal antibody. WO 08/047,242 describes an anti-CD38 monoclonal antibody and also the corresponding conjugates comprising one or more molecules of a cytotoxic compound attached to the monoclonal antibody. The cytotoxic compound may be chosen from maytansinoids, taxanes, tomaymycins, leptomycins and CC-1065 and analogues thereof.
WO 2009/126 934 describes anti-CD70 antibodies and their conjugates with cytotoxic compounds; cryptophycin is mentioned among the cytotoxic agents. WO 2009/134 976 describes conjugates with an optimized degree of substitution for delivering the required amount of cytotoxic agent into the cell; cryptophycin is mentioned among the cytotoxic agents.
WO 2005/116 255 describes conjugates of aptamers and of a cytotoxic agent that may be a cryptophycin (see [0037] and Table 2), the linker possibly comprising a PEG chain ([0038]). More particularly, the cryptophycin Cryp-NH2 is described:
and also its conjugates of aptamers with the following linkers: NHS-PEG-erythritol, pNP-PEG-erythritol, NHS-PEG-octaPEG, pNP-PEG-octaPEG and PEG-comb (Tables 3 and 4). The nature of the sequence on the phenyl ring (—CH2O—C(═O)—CMe2-CH2NH— . . . ) is different from that which is envisaged in the present invention. WO 2006/096 754 also describes conjugates of aptamers and of a cytotoxic agent that may also be a cryptophycin.
WO 2009/002 993 describes cytotoxic conjugates of formula B-L-A comprising hydrophilic linkers, for example the linker of formula:

The cytotoxic agent may be a cryptophycin (page 46), but the point of attachment of the linker is not specified. An example of a conjugate is EC0262:
whose linker and point of attachment are different from those envisaged in the present invention.