Pharmacogenetic variants in TPMT alter cellular responses to cisplatin in inner ear cell lines

Abstract

Cisplatin is a highly-effective and widely-used chemotherapeutic agent that causes ototoxicity in many patients. Pharmacogenomic studies of key genes controlling drug biotransformation identified variants in thiopurine methyltransferase (TPMT) as predictors of cisplatininduced ototoxicity, although the mechanistic basis of this interaction has not been reported. Expression constructs of TPMT∗3A, ∗3B and ∗3C variants were generated and monitored in cultured cells. Cellular TPMT∗3A levels were detected at >20-fold lower amounts than the wild type confirming the unstable nature of this variant. The expression of wild type TPMT (TPMT∗1) in two murine ear cell lines, HEI-OC1 and UB/OC-1, significantly mitigated their susceptibility to cisplatin toxicity. Cisplatin treatment induced Tlr4 gene expression in HEIOC1 cells and this response was blunted by the expression of wild type TPMT but not TPMT∗3A. In line with the significant mitigation of TPMT∗1-expressing cells to cisplatin cytotoxicity, these findings demonstrate a drug-gene interaction between increased TPMT activity and decreased susceptibility to cisplatin-induced toxicity of inner ear cells.