potentiation of cytotoxic chemotherapeutic agents by V158411. A. Comparison of potentiation factors in HT29 and Colo205 cancer cells grown anchorage dependently, anchorage independently or as multicellular tumor spheroids for cytotoxic chemotherapeutic agents with 400 nM V158411. Pf values were calculated from the average GI50 and combination GI50 (cGI50) of at least three determinations where Pf equals average GI50/average cGI50. *, P < 0.05; **, P < 0.01; ND, not determinable; #, Pf > 15. B. 72 hour HT29 dose response curves for gemcitabine, camptothecin and cisplatin in combination with DMSO or 400 nM V158411 demonstrating the calculation of the GI50 (square and dotted line) and cGI50 (circle and line). C. HT29 dose response curves for gemcitabine following 168 hour treatment with DMSO or 400 nM V158411. HT29 cells were grown either anchorage dependently (left graph) or as multi-cellular tumor spheroids (right graph). D. Comparison of the single agent GI50 and consequent potentiation factor (Pf, triangle and line) following either 72 hour (3 day) or 168 hour (7 day) incubation with gemcitabine, camptothecin or cisplatin with 0 or 400 nM V158411 in HT29 cells growing anchorage dependently. Values are the average of at least 3 determinations ± SD.