Marked synergism of cytotoxic agents with either a prenylation inhibitor or M-TOR inhibitor in acute leukemia cell lines: Potential clinical implications
13103 Background: The most combinations of anticancer drugs are based upon empiricism. The potential permutations of drugs overwhelm the clinical trials system. Acute leukemia is sensitive to a variety of agents but relapses are common. Targeted agents are attractive new venues of therapy both as single agents and in combination with older agents. Isobologram median effect analysis allows up to three agents to be studied together in vitro to identify interesting combinations. We evaluated a commercially available statin, fluvastatin, to block prenylation which affects a variety of pathways, rapamycin and its experimental analogue RAD001 as M-TOR inhibitors to block downstream of the AKT pathway, and cytotoxic agents. Methods: The human leukemia cell lines AML-193 and KG-1 were obtained from ATTC (Rockville, MD), fluvastatin and RAD001 from Novartis Pharma, and the other agents from Sigma-Aldrich (St. Louis, MO). The IC50 of the single agent was determined by a 72 hr incubation of log growth cells using a MTT assay and the EZ-ED50 program (Perrella Scientific, Conyers, CA). The dosages of all agents were at clinically achievable concentrations. All reported values were the means of at least 3 experiments with each study using 4 wells per point. For isobologram analysis, a minimum of 8 concentrations of drug mixtures were studied above and below the IC50. Median effect CI values less than 1 are synergistic. Results: Doublets of fluvastatin with Ara-C (0.7), daunomycin (0.4), idarubicin (0.7), RAD001 (0.5), or rapamycin (0.3) demonstrated synergy. Doublets of RAD001 with Ara-C (0.3), daunomycin (0.7), or idarubicin (0.5) demonstrated synergy. Triplets of RAD001/daunorubicin/Ara-C, RAD001/daunomycin/fluvastatin, and RAD001/Ara-C/idarubicin all demonstrated marked synergy in both cell lines. Conclusion: A new potential non classical combination for further investigation is RAD001 or rapamycin with an inhibitor of prenylation such as fluvastatin. Additional potential combinations include cytotoxics with either fluvastatin or RAD001, and triplet combinations. No significant financial relationships to disclose.