Correlation between Cell Killing by m-Diamminedichloroplatinum(II) in Six Mammalian Cell Lines and Binding of a cw-Diamminedichloroplatinum(II)- DNA Antiserum1

The relationship between cell killing and the binding of the anticancer drug m-diamminedichloroplatinum(II) (c/'s-DDP) to DNA was studied in six mammalian cell lines. Two of the human cell lines (COV413B) were of the same origin, comprising one sensitive to m-DDP and the other with induced resistance to the drug. The four other lines, two rodent (RIF-1, Chinese hamster ovary) and two human (A2780, A1847), were unrelated. The cell lines differed in their sensitivity to c/i-DDP, as tested in a clonogenic assay. c/î-DDP-DNAbinding was determined by quanti tative immunocytochemistry using an antiserum against c/s-DDP-modified DNA. The resistance factors relative to RIF-1, calculated from full survival curves for c/s-DDP, were 3.8 ±0.4 for Chinese hamster ovary cells and 8.8 ±0.7 for both A2780 and A1847 lines. Using quantitative immunocytochemistry, the levels of the adduct-specific nuclear staining density compared with RIF-1 cells were 4.8 ±0.2 for Chinese hamster ovary cells, 9.1 ±0.2 for A2780, and 10.0 ±0.1 for A1847 cells, i.e., in good agreement with the resistance factors. In studies with the COV413B cells and their c/î-DDP-resistantcounterpart COV413B-PtR, immunologically detected adduct levels again correlated closely with resistance factors (correlation coefficient = 0.97). The kinetics of c/î-DDP-DNA adduct formation and loss was investigated in RIF-1, A2780, and A1847 cells by the immunocytochemistry technique. Adduct levels after a 1-h incubation with approximately equitoxic doses of m-l)1 )!' increased by 18 to 32% (average, 27%) between 0 and 6.5 h after treatment and then declined. Adduct half-lives in this latter phase did not correlate with the sensitivities of the cells for c/s-DDP. These results indicate that the initial level of cis-DDP-DNA binding measured by quantitative inuminocytochemistry may be a reasonable predictor of sensitivity to this chemotherapeutic drug.