Organic cation transporters and cisplatin-induced peripheral neurotoxicity in dorsal root ganglia neurons

Organic cation transporters (OCTs) are critical in drug absorption, targeting, and disposition. It has become increasingly clear that multiple mechanisms are involved in organic cation transport in the key tissues responsible for drug absorption and disposition: the kidney, liver and intestine. However, only limited information is available regarding their distribution and activity in the central and peripheral nervous system. Cisplatin (CDDP), a widely used chemotherapeutic agent for the treatment of several solid tumors induces a severe and dose-limiting sensory neuropathy, due to damage of the primary sensory neurons of the dorsal root ganglia (DRG) where it forms DNA adducts. Previous in vivo and in vitro studies demonstrated that OCTs are implicated in CDDP nephrotoxicity. The present study was aimed to investigate (1) the presence of different OCTs (OCT-1, OCT-2, OCTN-1 and OCTN-2) in embryonic and adult rat DRG neurons and (2) their putative role in CDDP induced neurotoxicity. To examine the functional role of OCT-2, an in vivo study investigated the correlation existing between the neurophysiologic/morphometric parameters and the OCT-2 mRNA levels when rats were treated with CDDP. This analysis evidenced that the reduction of OCT-2 expression correlated with the decrease of NCV as well as with the reduction of soma, nucleus and nucleolus size in treated animals. Finally, to obtain mechanistic information about the role of OCT-2 in CDDP neurotoxicity we used an in vitro model of DRG neurons obtained from embryonic rats E15. The OCTs expression in rat DRG was studied by TaqMan Real Time PCR and it was demonstrated that CDDP administration reduced OCT-2 mRNA levels with respect to the control. In order to verify the involvement of OCT2 in the neuronal uptake of CDDP, nerve growth factor (NGF) differentiated neurons were exposed to CDDP alone or in combination with the OCT-2 inhibitor cimetidine (CMT). After 24 and 48 hours of co-treatment with CDDP and CMT 100 M we observed a significant increase of neuronal survival with respect to CDDP treated cells. Based on these results, a pilot in vivo study was performed that also confirmed a partial neuroprotective effect of CMT. Our data demonstrate that OCT-2 are present and are functionally active in rats. Moreover, it is likely that they are implicated in the pathogenesis of CDDP-induced DRG neuron damage, thus suggesting that they can be a target for future neuroprotective attempts. Supported in part by an unrestricted research grant from the Fondazione Banca del Monte di Lombardia