Scheduling effects of 5-(3,3-Dimethyl-1-triazeno)imidazole-4-carboxamide (DTIC) and 1,3-Bis-chloroethyl-1-nitrosourea (BCNU) on mouse melanoma cells B16CL5

Abstract

DTIC and BCNU have been demonstrated to have enhanced chemotherapeutic effects in mice bearing Bl6 mouse melanoma cells. The order of administration seems to be important in maintaining optimum effects. This was shown is a study by Hill et al. (unpublished). In the present study, mouse melanoma cells, Bl6CL4, were treated with either DTIC or BCNU. The drug was allowed to remain on the cells for 2, 3, or 4 days. The drug-containing media were then removed, the cells were washed and fresh medium was added. The cells were incubated in an atmosphere of 5% CO2 and 95% air at 37 °C. In combination experiments, dishes of B16CL4 cells were treated with DTIC on day 0. BCNU was then added on days 0, 1, or 2 of exposure. At the end of the allotted time the drug-containing media were removed and replaced with fresh medium. The dishes were incubated under the same conditions as those used for the controls. This procedure was repeated except that BCNU was added first and DTIC was added on day 0, 1, or 2 of exposure. The dishes were incubated for 15 days and the colonies were then fixed and stained. All colonies containing 50 cells or more were counted. The results showed that DTIC alone enhanced cell death the longer it remained in contact with the cells. BCNU alone had no effect at the concentration used. The results for the dose schedule when DTIC was added on day 0, followed by BCNU on day 2, showed a 60% decrease in the observed surviving fraction of cells from the expected surviving fraction of cells. This indicated that melanoma cell death was enhanced and these results are in agreement with the previous study conducted by Hill et al. (unpublished). The results for the dose schedule when BCNU was added on day 0, followed by DTIC on day 1, showed a 66% decrease in the observed surviving fraction of cells from the expected surviving fraction of cells. But then, the decrease in observed surviving fraction of cells from the expected surviving fraction of cells rose from 66% to 26%. These results were similar to the in vivo results seen in the study conducted by Hill et al. (21). However, these in vivo effects were not as dramatic as the effects seen when DTIC was added first