Persistent <i>in vitro</i> nociceptor hyperexcitability and axonal retraction produced by repeated paclitaxel doses

Paclitaxel-induced peripheral neuropathy is a common, clinically relevant sensory side effect that may lead to chemotherapy dose reduction or cessation, compromising patient survival. The neuropathy may persist for more than 6 months, suggesting lasting effects on peripheral nociceptor endings. The mechanisms underlying these persistent nociceptive alterations remain poorly explored. Here, we developed a nociceptor primary culture from adult mice to assess the effects of two 24 h (h) paclitaxel incubations separated by a 96 h recovery period, mimicking chemotherapy cycles. Repeated dosing of paclitaxel produced persistent, spontaneous and evoked hyperexcitability, and axonal retraction. The first paclitaxel incubation promoted a reversible axonopathy with increased spontaneous and evoked electrogenicity that peaked 48-h post-treatment and resolved 96 h after treatment. Notably, the second paclitaxel instillation produced severe and persistent axonal degeneration. In addition, it promoted strong, long-lasting, spontaneous and evoked excitability, particularly in IB4 (-) sensory neurons. Enhanced neuronal excitability was ascribed to increased depolarization spontaneous fluctuations (DFSs) of the membrane potential and elevated somal input resistance. These changes are likely mediated by the upregulation of Na_V1.8 and TRPV1 channels following paclitaxel administration. Furthermore, repeated exposure to the drug resulted in additional upregulation of TRPM8, TRPA1, and K_V3.4 channels. Therefore, our findings support Na_V1.8 and TRPV1 as important therapeutic targets for alleviating or preventing neuropathic symptoms induced by paclitaxel. Additionally, these results validate the application of long-term nociceptor primary cultures as preclinical models to investigate the cumulative neurotoxicity of chemotherapeutic agents, as well as to evaluate interventions that promote axonal regeneration and decrease hyperexcitability.