Preparation and characterization of platinum(II) and (M complexes of 1,3-diaminepropane and 1,4-diaminebutane:: Circumvention of cisplatin resistance and DNA interstrand cross-link formation in CH1cisR ovarian tumor cells

The reaction of Pt(dimethyl sulfoxide)(2)CBDCA (CBDCA = 1,1-cyclobutanedicarboxylate) with 1,4-diaminebutane and 1,3-diaminepropane ligands yields, under certain conditions, new [Pt(diamine)2]CBDCA complexes (1a,b), where the CBDCA ligand has been removed from the coordination sphere of the platinum atom by the diamine ligand, instead of forming the expected [Pt(diamine)CBDCA] complexes (1'a,b). The structure of complexes 1a and 1b was solved by X-ray diffraction. Complex 1a crystallizes in the orthorhombic system in the noncentrosymetric C222 space group with unit cell parameters: a = 20.053(2) Angstrom; b = 8.655(2) Angstrom, c = 5.711(3) Angstrom; V = 991.2(6) Angstrom(3); delta (calcd) = 1.627 mg/m(3); and R = 0.050. The Pt atom displays an unexpected distorted tetrahedral coordination with a N-Pt-N inner bond angle equal to 81(2)degrees for N atoms of the same 1,3-propanediamine ligand and a N-Pt-N bond angle for different ligands equal to 135.4(9)degrees. Complex 1b crystallizes in the monoclinic system, in the centrosymmetric P2(1)/c space group, with unit cell parameters: a = 6.007(2) Angstrom; b = 15.336(4) Angstrom, c = 13.232(5) Angstrom:beta = 101.90(3)degrees; V = 1192.8(7) Angstrom(3); delta (calcd) = 2.369 mg/m(3); and R = 0.067. Cytotoxicity data show that of all the synthesized compounds, only complexes 1'a and 1b exhibit remarkable cytotoxic properties. Thus, in contrast with carboplatin (cis-diammine-1,1-cyclobutane dicarboxilatoplatinum(II)), compounds 1'a and 1'b, which also contain the CBDCA ligand, are able to circumvent cisplatin (cis-diamminedichloroplatinum(II)) resistance in several tumor cells. Moreover, after 24 h of incubation of CH1cisR ovarian tumor cells with 10 muM of compounds 1'a and 1b, the level of DNA interstrand cross-links (ICLs) induced by compounds 1'a and 1'b is 3.3 and 3.8 times higher, respectively, than that of carboplatin and 3.5 and 4.0 times higher, respectively, than that of cisplatin. Interestingly, under the same conditions, the intracellular accumulation of compounds 1'a and 1b is similar to that of carboplatin and cisplatin. However, the extent of binding to DNA of compounds 1'a and 1b is similar to that of cisplatin but slightly higher than that of carboplatin. We propose that circumvention of cisplatin resistance in CH1cisR cells by compounds 1'a and 1'b might be related to its higher ability to form DNA ICLs relative to carboplatin and cisplatin.