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Enhancement of cisplatin sensitivity and platinum uptake by 40 degrees C hyperthermia in resistant cells.

We studied the cytotoxic and pharmacological properties of 40 degrees C hyperthermia and CDDP in CDDP-sensitive (IMC-3) and CDDP-resistant (IMC-3-DDP) human maxillary carcinoma cells. Heating at 40 degrees C alone caused almost no cell killing to IMC-3 and IMC-3-DDP cells. In both cell lines, the dose-dependent cytotoxicity of 2-h exposures to CDDP was increased at 40 degrees C in comparison to 37 degrees C. Heating at 40 degrees C also potentiated CDDP cytotoxicity in both IMC-3 and IMC-3-DDP cells with thermal chemoenhancement ratios (CER) of 1.48 and 1.94, respectively. The intracellular CDDP uptake level of IMC-3-DDP at 37 degrees C was significantly reduced compared with IMC-3 cells. At 40 degrees C, however, hyperthermia increased platinum accumulation by factors of 1.4 and 1.8 in IMC-3 and IMC-3-DDP cells, respectively. These findings indicated that CDDP sensitivity was hyperthermically chemopotentiated in CDDP-resistant variants rather than in the control clones. Thus, clinical cancer chemotherapy with CDDP may be improved by an appropriate combination with hyperthermia even at 40 degrees C.