The Development and Application of a Human Stem Cell-Based Model of Chemotherapy-Induced Neuropathy

Abstract

Chemotherapy-induced peripheral neuropathy (CIPN) is a devastating side effect of multiple classes of antineoplastic drugs used to treat cancer. These agents cause degeneration of the peripheral axons of sensory, motor and autonomic system neurons, leading to symptoms like loss of sensation, spontaneous pain, muscle weakness and incontinence. Developing treatments for CIPN has been difficult because the mechanisms by which antineoplastic agents cause degeneration of post-mitotic neurons are unknown. In recent years, some mechanistic details of CIPN have begun to be uncovered using animal models. However, there is little evidence to support these same processes occurring in humans. Therefore, I set out to develop and characterize a human cellular surrogate model for CIPN using induced pluripotent stem cell (iPSC)-derived neurons. I examined phenotypic changes induced in sensory, motor and cortical neurons by treatment with the common neuropathy-causing chemotherapeutic agents paclitaxel, vincristine and bortezomib. Despite their distinct mechanisms of antineoplastic actions, all three drugs caused axonal toxicity in the iPSC-derived neurons. By developing a spot culture method for examining neurite degeneration over time using iPSC-derived neurons, I was able to conclusively demonstrate that these chemotherapeutics disrupt axons through two distinct effects; growth cone stalling and axon degeneration. Utilizing this novel culture system, I examined whether the mechanism of chemotherapy induced neurotoxicity proposed in animal studies could be demonstrated in this humanized model. I found evidence of post-translation modifications in tubulin and of mitochondrial dysfunction congruent with those previously reported, although the timing of the mitochondrial alterations indicates it is likely secondary to axon degeneration. I also found clear evidence of caspase activation, but this does not appear to be necessary for the degeneration to occur since its inhibition did not rescue the phenotype. Instead, my findings that exogenous nicotinamide adenine dinucleotide or inhibition of the kinase DLK can both reduce the observed neurotoxicity in human neurons treated with chemotherapeutic agents indicates that the axonal degeneration is Wallerian-like. These findings in human cells further our understanding of the pathobiology of CIPN and provide a humanized preclinical model that may be suitable for the identification and development of CIPN modifying therapies in the future.