RESUMEN
The cytotoxic activity of cisplatin and/or L-histidinol was studied on Ehrlich ascites carcinoma [EAC] cell line. Cisplatin in concentration ranged from 1-20 microM reduced cell survival of cultured EAC cells in a concentration-related manner. The concentration of cisplatin that inhibited the survival of 50% of cells [IC50] was 16 micro M. L-Histidionl [0.5-4 mM] per se did not affect the survival tumor cells, however, it significantly potentiated the cytotoxicity of cisplatin. An important observation is that with the use of L-histidinol [4 mM] in combination with cisplatin, the IC50 of cisplatin was shifted to be 4 micro M only. By means of tritiated thymidine incorporation into the cellular acid-insolube material, cisplatin [8 and 16 micro M] inhibited DNA synthesis [41% and 51% respectively] in cultured tumor cells. Also, a marked inhibition of DNA synthesis [31% and 42%] was observed with L-histidinol [2 and 4 mM respectively]. In conclusion, L-histidinol, a structural analog of the essential amino acid L-histidine, enhances cisplatin cytotoxic activity against EAC cells. These findings may reflect a potential of L-histidinol to improve the therapeutic index of cisplatin. Further studies should thoroughly investigate the mechanism[s] of enhancement of therapeutic efficacy of cisplatin by L-histidinol