Neural Mechanisms of Cancer Pain

ABSTRACT The management of cancer pain remains a major challenge. Cancer pain is a complex pain state that includes inflammatory, neuropathic components and a unique set of cancer-specific components. Exosomes secreted by cancer cells is one of those cancer-specific factors. In preliminary studies, exosomes confirmed by size and expression of protein markers, induced acute mechanical and heat hyperalgesia following injection into the hind paw of both sexes of naïve C3H/HeN mice. This project will test the hypothesis that exosomes secreted by fibrosarcoma cells produce pain by sensitizing nociceptive primary afferent neurons via the autotaxin (ATX)-lysophosphatidic acid (LPA)-LPA1 receptor (R) pathway. Exosomes isolated from fibrosarcoma cell-conditioned media will be verified by size (Nanoparticle tracking analysis), expression of the exosome-specific markers, and activity of ATX. Electrophysiological studies in vivo will determine the contribution of ATX-LPA-LPA1R signaling to exosome-specific sensitization of nociceptors. At the cellular level, acute sensitization of small dorsal root ganglion (DRG) neurons from adult mice will be defined in a bioassay that measures the occurrence of a calcium transient in response to depolarization with 25 mM KCl in vitro with Indo-1. Whether the exosome-bound ATX-LPA complex released from fibrosarcoma cells sensitizes DRG neurons through activation of LPA1 receptors will be determined using pharmacological and molecular (siRNA) approaches. Resolvin D1 is proposed to attenuate exosome-evoked sensitization of nociceptors and hyperalgesia by interfering with ATX-LPA- LPA1R signaling. If exosome-mediated ATX-LPA-LPA1R signaling underlies hyperalgesia, it will provide insight into a new strategy for managing bone cancer pain. Future studies will further investigate the molecular, biochemical and electrophysiological mechanisms by which exosomes released from cancer cells contribute to cancer pain.