CELLULAR PHARMACOLOGY OF NOVEL C8-LINKED ANTHRAMYCIN-BASED SEQUENCE-SELECTIVE DNA MINOR-GROOVE CROSS-LINKING AGENTS

The cellular pharmacology of a series of C8-linked pyrrolobenzodiazepi ne dimers with polymethylene linkers of n = 3-6 (compounds 1-4) has be en studied in a range of human tumour cell lines. The four compounds s howed the same pattern of relative activity in five ovarian carcinoma cell lines and one cervical carcinoma cell line with the order of IC50 values of 1 less than or equal to 3 < 4 < 2, which correlated with th e previously demonstrated DNA interstrand cross-linking ability of the compounds in plasmid DNA. In human leukaemic K562 cells the agents pr oduced a block in the G(2)/M phase of the cell cycle characteristic of cross-linking drugs, and extensive interstrand cross-linking was obse rved in cells by alkaline elution with no evidence of single-strand br eaks. Cross-links continued to increase up to 24 h following a 1 h exp osure to drug, and no repair was evident by 48 h. In a series of ovari an and cervical carcinoma cell lines with acquired resistance to cispl atin no cross-resistance to the most potent compound 1 was observed in two lines whose major mechanism of resistance to cisplatin was reduce d platinum transport. Cross-resistance to 1 was observed in a cell lin e (A2780cisR) possessing elevated glutathione, and depletion of intrac ellular glutathione using D,L-buthionine-S,R-sulphoximine (BSO) from 1 0.25 nmol to 2.8 nmol 10(-6) cells reduced the level of resistance fro m 11-fold to 2-fold compared with sensitive cells. Cross-linking in th e resistant cells was restored to 80% of the level in the parent line by BSO pretreatment. There was also a correlation between glutathione levels and sensitivity to 1 measured in several other ovarian cell lin es. Compound 1 also showed cross-resistance in the doxorubicin-resista nt cell line 41MdoxR and partial cross-resistance in CH1doxR cells. Bo th these lines possess elevated levels of p170 glycoprotein. Following treatment with 6 mu M verapamil, the resistance in these lines decrea sed almost 2-fold and 8-fold respectively.