Effect of heat on the cytotoxicity and interaction with DNA of a series of platinum complexes.

The effect of elevated temperature on the cytotoxicity and interaction with DNA of a series of platinum(II) complexes was examined. CDDP showed greater enhancement in cell killing with heat than the other platinum(II) complexes. There were approximately 2 decades enhancement in cell killing by 10 microM CDDP at 42 degrees C compared to 37 degrees C. The other potential cross-linking agents also showed increasing cytotoxicity with increasing temperature. K2PtCl4 (500 microM) killed about 15 times more cells at 43 degrees C than at 37 degrees C and KPt(NH3)Cl3 (500 microM) killed about 18 times more cells at 43 degrees C than at 37 degrees C. The cytotoxicity of the triammine and tetraammine complexes was less influenced by temperature. There was no significant difference in the cytotoxicity of [Pt(NH3)3Cl]Cl at any of the temperatures examined. The cytotoxicity of [Pt(NH3)4]Cl2 (500 microM) was increased about 7-fold at 43 degrees C compared to 37 degrees C, but the total cell killing by this complex at 43 degrees C was less than 1 log. Carboplatin (250 microM) was about 5 times more toxic at 42 degrees C and killed about 2.5 decades more cells at 43 degrees C than at 37 degrees C. Although there was little enhancement in the cytotoxicity of trans-Pt(NH3)2Cl2 at 42 degrees C compared to 37 degrees C trans-Pt(NH3)2Cl2 (500 microM) was about 7 times more cytotoxic than at 37 degrees C. The interaction of the various drug/temperature treatments with supercoiled pBR322 plasmid DNA was examined to assess the effect of heat on the reaction of these agents with DNA. At 42 degrees C, CDDP was able to gradually alter the gel electrophoretic mobility of the plasmid DNA to near that of the linear form. This change also occurred at 37 degrees C but at a much slower rate. Carboplatin effected similar changes in the superhelical pBR322 DNA, and the effect of temperature appeared to increase the rate of the reaction. Trans-Pt(NH3)2Cl2 also interacted with the supercoiled DNA, but at a slower rate than CDDP even under hyperthermic conditions. These results indicate that neutral platinum complexes capable of cross-linking DNA interact positively with temperature elevation to increase cytotoxicity, and, that of the platinum complexes that meet these criteria, the effect of hyperthermia is greatest with CDDP.