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Cellular Pharmacology of Liposomal cis-Bis-neodecanoato-trans-R,R-1,2-diaminocyclohexaneplatinum(II) in A2780/S and A2780/PDD Cells¹

Departments of Thoracic/Head and Neck Medical Oncology [I. H., Y-H. L., R. P-S.] and Clinical Investigation [S. A-B., A. R. K.], The University of Texas M. D. Anderson Cancer Center, Houston, Texas 77030

We studied the cytotoxicity, cellular accumulation, and DNA interactions induced by liposome-entrapped NDDP (L-NDDP) and cisplatin in A2780 human ovarian carcinoma cells sensitive (A2780/S) and resistant (A2780/PDD) to cisplatin. L-NDDP was 2-fold more cytotoxic than cisplatin against A2780/S cells with 5-h or 24-h drug exposure. Both cell lines were equally sensitive to L-NDDP, while A2780/PDD cells were 4-fold resistant to cisplatin (resistance indexes, 1.30–1.85 and 4.02–4.50, respectively). Using a drug exposure time of 24 h, L-NDDP cytotoxicity was independent of the liposome composition used, whereas with shorter drug exposure (5 h), the cytotoxicity of L-NDDP was directly related to the relative content of DMPG in the liposome carrier. However, changes in liposome composition or drug exposure time did not alter the resistance index of L-NDDP in this cell system. The cellular accumulation of L-NDDP was similar in both cell lines and 2- to 5-fold higher than that of cisplatin in A2780/S cells, whereas the cellular accumulation of cisplatin was reduced by 2- to 3-fold in A2780/PDD cells. The presence of DMPG in the lipid bilayer enhanced by 2-fold the cellular accumulation of L-NDDP, in good correlation with the direct relation between cytotoxic potency of L-NDDP and the presence of DMPG in the liposome carrier.

Pt/DNA levels were determined at different time points after drug exposure for 1 h. Peak Pt/DNA levels were observed at 6 h for cisplatin and at 9 h for L-NDDP. Peak Pt/DNA levels and Pt/DNA over time of L-NDDP were about 1.5- and 3-fold higher than those of cisplatin in A2780/S and A2780/PDD cells, respectively, when equimolar concentrations of both drugs were used. Cisplatin induced significant DNA interstrand and DNA-protein cross-links in A2780/S cells, and a good correlation was observed between cytotoxicity against both cell lines and both types of lesions. In contrast, equimolar concentrations of L-NDDP induced only minimal DNA interstrand cross-links in either cell line. These results indicate that (a) L-NDDP is not cross-resistant to cisplatin against A2780/PDD ovarian carcinoma cells, (b) the cellular accumulation of L-NDDP is similar in both cells and severalfold higher than that of cisplatin, (c) the cytotoxicity of both drugs correlates with the extent of DNA platination over time, (d) the non-cross-resistance properties of L-NDDP are associated with its ability to induce similar Pt/DNA levels over time in sensitive and resistant cells, and (e) DNA interstrand cross-link formation does not seem to play a role in the cytotoxicity of L-NDDP.

¹ This work was supported in part by NIH Grants CA 41581, 45423, 50270, and 58342.

² To whom requests for reprints should be addressed, at Department of Thoracic/Head and Neck Medical Oncology, Box 80, M. D. Anderson Cancer Center, 1515 Holcombe Blvd., Houston, TX 77030.

Received 4/ 9/93. Accepted 8/ 9/93.