We evaluated the in vitro cytotoxicity of topotecan (TPT), versus cisplatin, etoposide (VP-16) and paclitaxel (PTX) in four squamous cell cancer cell lines ol the cervix uteri and vulva. Four established human squamous cancer cell lines from the cervix uteri (A-431, Ca Ski and (C-33) and vulva (CAL-39) were used. The cytotoxic effects of the agents were examined using the ATP-Tumor Chemosensitivity Assay (ATP-TCA). In addition to the single agents, the following combinations were tested: TPT+cisplatin, TPT+VP-16 and TPT+PTX. Three cell lines (C-33, Ca Ski and CAL-39) were highly sensitive to TPT, but one cell line (A-431) was less sensitive. Furthermore, the cytotoxic activity of TPT was superior to that of cisplatin in Ca Ski and C-33 cells, but inferior in CAL-39 and A-431. TPT was also more active than VP-16 in CAL-39 and Ca Ski. On the other hand, the cytotoxic activity of TPT was weaker than PTX in C-33, CAL-39 and A-431.TPT increased the cytotoxic activity of cisplatin and VP-16 in C-33, Ca Ski and A-431. However, synergistic features were observed only in A-431 cells. TPT also enhanced the cytotoxic activity of PTX in A-431 and Ca Ski. In CAL-39 and C-33, however, increased cytotoxic activity occurred only at higher drug concentrations, whereas antagonism was observed at lower drug concentrations. In conclusion, our results suggest that TPT has a significant cytotoxic effect on most squamous cell cancer cell lines which may be superior to cisplatin, VP-16 and PTX in some instances. Furthermore, TPT is likely to potentiate the cytotoxic activity of these agents in individual cell lines tested. [(C) 2000 Lippincott Williams & Wilkins.].
