Abstract A147: Novel fluorinated taxane SB-T-12854 active in drug-resistant and sensitive cell lines: Human, pig, rat metabolism, cell transport, and effects on cell cycle

Abstract

Abstract SB-T-12854 is a novel taxane where fluorine in the molecule could decrease metabolism and increase activity over paclitaxel with efficiency limited by multidrug resistance due to ABCB1 transport, metabolism, and other factors. Purposes of the study: this study investigated metabolism of SB-T-12854 by human, pig and rat CYP enzymes, cytotoxicity of the drug and isolated metabolites, transport in drug-resistant NCI/ADR-RES cells and sensitive MDA-MB-435, and effects on the cell cycle. Experimental procedures: Metabolism of SB-T-12854 was studied in human, pig, rat and CYP3A1/2-induced rat microsomes and human cDNA-expressed CYP enzymes in vitro. The metabolites were determined by HPLC and MS analyses. Human tumor lines MDA-MB-435 and NCI-ADR-RES (NCI, Frederick MD) were kept in standard conditions. Viability was assessed by the MTT assay. Transport of SB-T-12854 by tumor cells was determined by measuring their cellular levels by HPLC. Progress in the cell cycle was determined by FACS. Summary of new and unpublished data: In human, pig and rat microsomes SB-T-12854 formed the same four products at similar rates, but CYP3A1/2-induced rat microsomes formed 13 metabolites at 16-fold higher rate indicating very high activity of CYP3A, the main human CYP form of varied expression. The cDNA-expressed CYP3A4 formed the same products, but CYP1A2, 1B1, 2A6, 2C9, or 2E1 were inactive. The time course of metabolism and further metabolism of isolated metabolites showed their mutual conversion and identified primary and secondary products. In rat microsomes, Km values for metabolites M5-6 and M9-12 were 14.01 and 6.89 (M), respectively, and Vmax (pmol/min/mg protein) were 70.4 (M5-6) and 370.4 (M9-12). In MDA-MB-435 cells some metabolites were inactive, but others were considerably more cytotoxic than SB-T-12854 itself in contrast to paclitaxel whose metabolites are less active. SB-T-12854 was 6-fold more cytotoxic than paclitaxel in MDA-MB-435 cells and 30-fold more potent in NCI/ADRRES cells. In both cell lines SB-T-12854 caused G2/M block in the same way as paclitaxel. Conclusions: SB-T-12854 is metabolized by human, pig and rat CYP3A enzymes to identical and to some markedly more active products in contrast to paclitaxel, which is only inactivated. SB-T-12854 is 30-fold more cytotoxic than paclitaxel in ABCB1 highly expressing NCI/ADR-RES cells, partly because SB-T-12854 is not transported by ABCB1 in contrast to paclitaxel. SB-T-12854 influenced the cell cycle of NCI/ADR-RES and MDA-MB-435 cells in the same way as paclitaxel causing G2/M block, but at substantially lower concentrations. Lack of ABCB1 transport and higher cytotoxicity suggest a potential advantage of this taxane over paclitaxel, which is ineffective against certain tumors, due to high ABCB1 expression. Citation Information: Mol Cancer Ther 2009;8(12 Suppl):A147.