Design, synthesis, DNA binding, and biological evaluation of water-solublehybrid molecules containing two pyrazole analogues of the alkylating cyclopropylpyrroloindole (CPI) subunit of the antitumor agent CC-1065 and polypyrrole minor groove binders

We have synthesized and evaluated a series of hybrids, denoted 22-27, for i n vitro cytotoxic activity against a variety of cancer cell lines. These hy brids represent a molecular combination of polypyrrole minor groove binders structurally related to the natural antitumor agent distamycin A and two p yrazole analogues of the left-hand segment called cyclopropylpyrroloindole (CPI) of the potent antitumor antibiotic (+)-CC-1065. These novel water-sol uble hybrids have been designed to enhance the minor groove binding ability of alkylating units 20 and 21, which should increase their clinical appeal by overcoming the administration problems of (+)CC-1065 derivatives. The D NA alkylating and cytotoxic activities against several tumor cell lines are reported and discussed in terms of their structural differences in relatio n to both the number of N-methyl pyrrole rings and the type of the alkylati ng unit tethered to the oligopeptidic frame. It may be noted that, in gener al, and especially for 22-24, the cytotoxicity of the hybrids was much grea ter than that of the alkylating units alone. In only one case, compound 27, did the hybrid have cytotoxic activity comparable to that of the alkylatin g unit alone against FM3A/0 cells. The broadest spectrum of activity and gr eatest potency was shown by the hybrid 24, in which the alkylating unit 20 and the deformyl distamycin A are tethered by 1-methyl 2,5-dicarbonyl pyraz ole, with IC50 values for the different tumor cell lines ranging from 7 to 71 nM. For compounds 22-24, the increase of the length of the pseudopeptidi c moiety from one to three N-methylpyrrole residues led to an increased cyt otoxicity. Among the hybrids tested for their inhibitory effects on the pro liferation of murine L1210 leukemia cell line, compound 24 proved to be the most active (IC50 = 7.4 nM), and in the sequencing gel experiments, it sho wed the strongest and most highly sequence-specific DNA alkylation activity . For compounds 22-24, the sequence specificity of DNA alkylation appears t o be affected by the modification of the number of pyrrole rings, and the c orrelation between cytotoxicity and alkylation pattern suggests that 24 exe rts its cytotoxicity through DNA sequence-specific alkylation of the third adenine located in the sequence 5 ' -ACAAAAATCG-3 '. The two other hybrids 22 and 23 were slightly less active for tumor cell proliferation, with IC50 values of 58 and 19 nM, respectively. With only one exception, none of the compounds was endowed with antiviral activity at subtoxic concentrations. Compound 24 inhibited the effect of vaccinia virus at a concentration that was significantly lower than its minimum cytotoxic concentration for the E6 SM host cells. These compounds gave distinct patterns of alkylation in AT-r ich sequences, indicating that minor structural changes produced marked alt erations in sequence selectivity.