Development of DNA-affinic aminoanthraquinones with alkylating potential that exhibit potent cytotoxicity against resistant ovarian carcinoma cell lines

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A novel series of chloroalkylaminoanthraquinones with alkylating potential, modelled on the non-symmetrical configuration of Alchemix, has been developed and is reported. The synthetic route to the target compounds involved preparation of heterocyclic (piperidinyl or pyrrolidinyl) alkylamino sidechains, by alkylating the heterocyclic moiety with halide-acetonitrile followed by reduction of the nitrile to the respective primary amine (R-CH₂CH₂-NH₂, R = heterocyclic). The heterocyclic alkylamino sidechains were then substituted onto anthraquinone chromophores to give a series of 1,4-disubstituted hydroxylalkylaminoanthraquinones. Conversion of the hydroxylated aminoanthraquinones to their chlorinated derivatives involved treatment with Ph₃P-CCl₄ complex. A novel route for the development of chloroalkylaminoanthraquinones was also devised in order to obtain target compounds containing secondary chlorides. This route comprised a 5-step procedure which involved (1) Boc-protection of hydroxylated heterocyclic alkylamino sidechains, (2) mesylation of the hydroxyl group, (3) conversion to the chloride with tetra-n-butylammonium chloride, (4) deprotection of the Boc group and (5) substitution onto either 1,4-difluoro-5,8-dihydroxyanthraquinone or 1-{2-[N,N-(dimethyl)amino]ethylamino]-4-fluoro-5,8-dihydroxy-anthraquinone. The novel chloroalkylaminoanthraquinones were shown to alkylate guanine residues of linearised pBR322 (1-20 μM) by using a DNA Taq-polymerase based footprinting assay, which was in good correlation to DNA-drug modelling studies. Two symmetrical chloroalkylaminoanthraquinones, 1,4-bis-{2-[(2-chloroethyl)-piperidinyl]-ethylamino}-5,8-dihydroxy-anthracene-9,10-dione KP190M and 1,4-bis-{2-[(2-chloroethyl)-pyrrolidinyl]-ethylamino}-5,8-dihydroxyanthracene-9,10-dione KP177M were found to interstrand crosslink pBR322 DNA at nM concentration by assessment in an in vitro gel based assay. Selected chloroalkylaminoanthraquinones and their non-covalent binding hydroxylated precursor anthraquinones were found to unwind supercoiled pBR322 DNA. The chloroalkylaminoanthraquinones with alkylating capacity were shown to be nM cytotoxic (IC₅₀ values: 9-428 nM) in the A2780 ovarian cancer cell line. Significantly, the chloroalkylaminoanthraquinones remained cytotoxic in doxorubicin (2780AD) and cisplatin (2780CP) resistant cell lines.