Cancer research
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Three homologous alicyclic mixed amine cis-(NH3)(R-NH2)Cl2Pt(II) complexes, in which R = C3H5, C6H11, and C8H15 (complexes abbreviated C3, C6, and C8, respectively), were evaluated with reference compounds cisplatin and tetraplatin for antitumor activities and biochemical pharmacology in wild-type (murine leukemia L1210/0 and human ovarian A2780) and corresponding variant cell lines resistant to cisplatin (L1210/DDP and 2780CP) and tetraplatin (L1210/DACH and 2780TP). Cytotoxicities, measured by either a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide or a clonogenic assay, were maximal for the C6 complex, which was up to 12-, 40-, and 6-fold more potent than C3 against wild-type, cisplatin-resistant, and tetraplatin-resistant models, respectively, and up to 2-fold more potent than C8 against these cell lines. In general, cross-resistance to mixed amine analogues was partial in cisplatin- and tetraplatin-resistant cells and decreased (in L1210/DDP and 2780CP) or increased (in L1210/DACH and 2780TP) with increase in the alicyclic ring size. ⋯ For instance, complex C8, which accumulated to the greatest extent in any given cell line, produced adduct levels that were similar to or lower than those produced by C6. A partial explanation for this observation was the demonstrated reduced rate of binding of C8 to DNA. This study has highlighted the significance of alicyclic ring size in modulating the potency, cross-resistance profile, and biochemical pharmacology of mixed amine platinum(II) complexes in sensitive and cisplatin- or tetraplatin-resistant tumor cells.
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Previous investigations have revealed that the human TE-671 MR human rhabdomyosarcoma xenograft selected in vivo for melphalan resistance (M. C. Rosenberg, et al., Cancer Res., 49: 6917-6922, 1989) is cross-resistant to a wide variety of alkylating agents and to bleomycin, but is collaterally sensitive to etoposide. ⋯ Measurement of additional enzyme activities that might be involved in DNA repair revealed significant elevations in DNA polymerase alpha (46 +/- 8 (SD) units/mg protein in TE-671, 69 +/- 6 units/mg protein in TE-671 MR, P < 0.05) and DNA polymerase beta (0.43 +/- 0.01 units/mg protein in TE-671, 0.78 +/- 0.12 units/mg protein in TE-671 MR, P < 0.05) but not DNA polymerase delta or total DNA ligase. Examination of topoisomerases by activity assays and Western blotting revealed a 2-fold increase in topoisomerase II and a 2-fold decrease in topoisomerase I in the TE-671 MR xenograft compared to the parental xenograft, apparently explaining the collateral sensitivity to etoposide and cross-resistance to topotecan. These results suggest that TE-671 MR xenografts contain multiple changes in activities of DNA repair-related proteins and other nuclear proteins that could contribute to alkylating agent resistance.
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Apoptosis in the androgen-sensitive Dunning R3327 PAP prostatic adenocarcinoma was studied during the post castration period of 14 days and compared with the ventral prostate. The mRNA expression of testosterone repressed prostatic message-2 and tissue-type plasminogen activator in the Dunning tumor and in the ventral prostate was analyzed by Northern blot experiments and immunohistochemical procedures. The degree of endonuclease-degraded genomic DNA was examined by gel electrophoresis. ⋯ BrdUrd immunodetection showed that castration induced an initial increase in the number of BrdUrd-positive epithelial cells in the ventral prostate. In the tumors, castration resulted in a decrease in BrdUrd-positive epithelial cells. It was concluded that in the androgen-sensitive prostatic Dunning R3327 PAP adenocarcinoma, the biochemical cascade leading to apoptosis is not activated by androgen withdrawal, as in the ventral prostate.