In vitro efficacy of carboplatin and hyperthermia in a murine retinoblastoma cell line.

OBJECTIVE

To determine the cell-killing activity of varying doses of carboplatin, graded hyperthermia, and the combination of carboplatin and hyperthermia in the treatment of a transgenic murine retinoblastoma cell line.

METHODS

Replicate cell wells (more than six wells per dose point) from an established transgenic murine retinoblastoma cell line (Rb-6) were exposed to a single application of hyperthermia for 15, 30, 60, and 120 minutes at temperatures of 37 degrees C (control), 40 degrees C, and 43 degrees C. Carboplatin dose response treatment was studied at doses of 2000, 1000, 500, 400, 300, 200, 100, and 50 ng per well. Combined treatment studies used these carboplatin dosages with each of the graded hyperthermia exposure temperatures at each exposure time. At 24 hours, all wells were pulsed with 3H-thymidine for 24 hours, washed three times, harvested, and counted. Raw counts (3H-thymidine) were fitted to a linear regression model to calculate the lethal dose for 50% (LD50) of cells.

RESULTS

The LD50 for carboplatin exposure at 37 degrees C occurred at 542 ng. The LD50 for hyperthermia at 40 degrees C occurred at 90 minutes and at 43 degrees C it occurred at 62 minutes. Combined hyperthermia and carboplatin exposure yielded a synergistic interaction with an LD50 of 327 ng at 43 degrees C for 30 minutes. Determination of a thermal enhancement ratio yielded an enhancement range of 1.1 to 25.8.

CONCLUSIONS

The synergistic cytocidal interaction of heat and carboplatin in a transgenic murine retinoblastoma cell line has been established in this study. The increased thermal enhancement ratio documents the potential utility of combined treatment applications in reducing treatment levels of single-modality therapy, potentially allowing for a decrease in treatment-related morbidity.