Targeting neuronal transport to ameliorate vincristine neurotoxicity

Microtubule-binding chemotherapeutics such as vincristine are among the most widely used anticancer agents in oncology for the treatment of multiple solid tumors and leukemias in children and adults. The clinical use of vincristine is associated with a debilitating, dose-limiting peripheral neurotoxicity for which no effective preventative treatments are presently available. In addition, the mechanism by which vincristine accumulates into dorsal root ganglion (DRG) neurons remains unclear to this day. Using a transporter screen of xenobiotic uptake carriers in heterologous overexpressed models, we recently found that the organic anion transporting polypeptide OATP1B3 (in mice, OATP1B2; collective referred to as OATP1B2/3) is an efficient transporter of vincristine that is expressed in human and mouse DRG neurons. Functional validation studies in OATP1B2deficient mice and secondary screens confirmed that vincristine is transported into DRG neurons by OATP1B2. Furthermore, deficiency of OATP1B2 protected mice from vincristine-related changes in various hallmarks of peripheral neurotoxicity without altering the plasma levels of vincristine. To provide proof-of-principle and demonstrate translational relevance of this transport mechanism, we found that several known pharmacological inhibitors of OATP1B, including rifampin and the tyrosine kinase inhibitor, nilotinib, can preserve DRG neuronal function following treatment with vincristine without affecting its plasma levels or its cytotoxic potential against multiple acute leukemia cell lines. Finally, we identified α-tocopherol (vintamin E) as a previously unrecognized biomarker of neuronal OATP1B2/3 function that can be measured in the systemic circulation, and we validated the translational utility of this biomarker in a mouse model receiving treatment with OATP1B inhibitors. Based on these preliminary findings, we now outline three sets of related studies that will further test and refine the validity of our central hypothesis that targeted modulation of OATP1B2/3 function with optimized doses and schedules of novel OATP1B2/3 inhibitors can specifically affect accumulation of vincristine in DRG neurons and affect downstream toxic events without negatively influencing its plasma pharmacokinetic profile or anti-leukemic properties: (i) mechanistic characterization of nilotinib as the proof-of principle OATP1B inhibitor, and identification and validation of additional modulators derived from a library screen that includes FDA-approved agents; (ii) biomarker-driven optimization using α-tocopherol as a companion diagnostic to guide dose selection of OATP1B modulators for in vivo testing; and (iii) safety and efficacy analyses of optimized combinatorial regimens of OATP1B inhibitors with vincristine, including simultaneous assessment of neuroprotection and anti-leukemic properties in established experimental models of acute leukemia. It is expected that these collective studies will not only shed light on the etiology of vincristine-induced peripheral neurotoxicity, but will be of translational relevance and provide a rationale for the future implementation of novel targeted intervention strategies to prevent this debilitating side effect.