HYPOXIA-SELECTIVE ANTITUMOR AGENTS .9. STRUCTURE-ACTIVITY-RELATIONSHIPS FOR HYPOXIA-SELECTIVE CYTOTOXICITY AMONG ANALOGS OF [N,N-BIS(2-CHLOROETHYL)AMINO]-2,4-DINITROBENZAMIDE

A series of analogues of the novel hypoxia-selective cytotoxin 5-[N,N- bis(2-chloroethyl)amino] 2,4-dinitrobenzamide (6) have been prepared a nd evaluated, in a search for compounds which retain high hypoxic sele ctivity but have increased potency and/or aqueous solubility. Several analogues with ionizable or dipolar carboxamide side chains showed imp roved solubility but generally had reduced cytotoxic potency and hypox ic selectivity. Modification of the mustard leaving groups or replacem ent of the carboxamide moiety provided some compounds with superior po tency, but only the mixed chloro/mesylate mustard 20 provided a gain i n potency relative to solubility while retaining the hypoxic selectivi ty of 6. These nitrogen mustards did not show the remarkable activity demonstrated by the related aziridine 7 [CB 1954, 5-(N-aziridinyl)-2,4 -dinitrobenzamide] in Walker 256 adenocarcinoma cells and are not effi cient substrates for the DT-diaphorase which activates the latter comp ound by aerobic nitroreduction in Walker cells. Variations in hypoxic selectivity within the dinitrobenzamide mustards appear not to be due to differences in sensitivity to activation by this enzyme. Walker cel ls showed intermediate sensitivity to the mono(2-chloroethyl) analogue 26 but not to the related half-mustard 27, suggesting that the inhibi tion of DT-diaphorase activity is due to steric effects in the 5-posit ion. The preferred compound overall with respect to solubility, potenc y, and in vitro hypoxic cell selectivity was the (dimethylamino)ethyl derivative 11. DNA elution studies and comparison of the sensitivity o f AA8 and UV4 cells to this compound indicated reductive activation to form a DNA cross-linking agent under hypoxia. Radiobiological studies indicated 11 to be equally active against both aerobic and hypoxic ce lls in KHT tumors. It is not clear whether this reflects efficient kil ling of aerobic cells as a result of diffusion of reduced metabolites from hypoxic regions or whether cytotoxicity in tumors is independent of hypoxia.