Interaction of novel bis(platinum) complexes with DNA.

Bis(platinum) complexes cis-PtCl2(NH3)]2H2N(CH2)nNH2] are a novel series of potential anticancer agents in which two cis-diamine(platinum) groups are linked by an alkyldiamine of variable length. These complexes are potentially tetrafunctional, a unique feature in comparison with known anticancer agents. Studies of DNA interactions of bis(platinum) complexes in comparison with cisplatin demonstrate significant differences. Investigations of interstrand crosslink formation in which crosslinking of a short DNA fragment is detected by gel electrophoresis under denaturing conditions demonstrate that interstrand crosslinks are 250 fold more frequent among bis(platinum) adducts than among cisplatin-derived adducts under the conditions examined. These investigations indicate that bis(platinum) adducts contain a high frequency of structurally novel interstrand crosslinks formed through binding of the two platinum centers to opposite DNA strands. Unlike cisplatin, bis(platinum) complex binding does not unwind supercoiled DNA. Studies with the E. coli UvrABC nuclease complex demonstrate that both linear and supercoiled DNA containing bis(platinum) adducts are subject to incision by the repair enzyme complex. Initial studies using UvrABC nuclease as a probe to define the base and sequence specificity for bis(platinum) complex binding suggest that the specificity of the bis(platinum)s is similar, but not identical, to that of cisplatin.