The role of the organic cation/carnitine transporters in the uptake and neurotoxicity of oxaliplatin

Abstract

Oxaliplatin is a platinum-based anticancer drug with treatment-limiting neurotoxicity. The role of the organic cation/carnitine transporters (OCTNs) in the transport and neurotoxicity of oxaliplatin is currently unknown. The expression and functional activities of OCTNs and organic cation transporters (OCTs) in rat dorsal root ganglion (DRG) tissue and cultures were determined using RT-PCR, Western blotting, and uptake of prototypical substrates including [3H]ergothioneine (OCTN1), [3H]L-carnitine (OCTN2), [3H]MPP+ (OCTs), and [14C]TEA+ (OCTNs/OCTs). Cellular [14C]oxaliplatin uptake, platinum accumulation, and sensitivity to oxaliplatin were determined using liquid scintillation counting, ICP-MS, and cytotoxicity assays in HEK293 cells over-expressing OCTNs and DRG neurons cultured from Wistar rats, C57BL wild type and Octn1 knockout mice. Daily oral administration of ergothioneine or acetyl-L-carnitine was investigated in a Wistar rat model of oxaliplatin neurotoxicity in vivo. OCTN1 and OCTN2 showed readily detectable mRNA expression levels and functional activities in rat DRG neurons, whereas the expression and activity of OCTs was low or absent. HEK293 cells over-expressing rOctn1, rOctn2, hOCTN1 and hOCTN2 demonstrated increased uptake and sensitivity to oxaliplatin compared with empty vector-transfected controls. Oxaliplatin growth inhibition was reduced by ergothioneine in HEK293 cells over-expressing rOctn1 and hOCTN1, and by L-carnitine in HEK293 cells over-expressing rOctn2. Oxaliplatin exposure decreased OCTN1- mediated ergothioneine uptake and OCTN2-mediated L-carnitine uptake. Oxaliplatin uptake, by cultured rat DRG neurons, was dependent on exposure concentration, time, temperature, and was inhibited by ergothioneine more so than by L-carnitine or MPP+. Oxaliplatin-induced loss of DRG neuronal viability was inhibited by ergothioneine, but not by Lcarnitine or MPP+. Daily oral administration of ergothioneine or acetyl-L-carnitine, an acetylated derivative of L-carnitine, was tolerated by oxaliplatin-treated Wistar rats. Trends towards protection against oxaliplatin-induced DRG neuronal cell body and nucleolus atrophy were found for ergothioneine. DRG neurons from C57BL Octn1 knockout mice showed lower neuronal accumulation of oxaliplatin compared with those from wild type mice. In conclusion, OCTN1 and OCTN2 both transport oxaliplatin and have functional activities in rat DRG neurons. OCTN1-mediated transport of oxaliplatin appeared to contribute to its neuronal accumulation and neurotoxicity. Targeting OCTN1 for the purpose of reducing o