Inhibition of CaVα-β interaction with orally available small organic molecules for chronic pain

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ABSTRACT Revisions noted in blue font Chemotherapy-induced peripheral neuropathy (CIPN) is a common (prevalence 30–70%) and potentially dose- limiting side effect of many cancer chemotherapy drug treatment regimens. Clinically, CIPN presents with pain that is burning, shooting or electric-shock-like. The increase in prevalence of cancer coupled with an increase in the cancer survival rates due to chemotherapy regimens is transforming cancer pain into a large, unmet medical problem. Neurotoxic chemotherapeutic agents (e.g., antimicrotubule agents like paclitaxel) may cause structural damage to peripheral nerves (small fibers), resulting in aberrant somatosensory processing in the peripheral and/or central nervous system. Dorsal root ganglia (DRG) sensory neurons as well as neuronal cells in the spinal cord are the preferential sites in which chemotherapy induced neurotoxicity occurs. Pathogenesis is complex but includes alterations in ion channels. For example, the taxane paclitaxel (Taxol®) increases N-type (CaV2.2) voltage-gated Ca2+ currents in rat dorsal root ganglion (DRG) neurons; these neurons are responsible for conveying noxious sensory stimuli, suggesting these channels are important mediators of specific sensory abnormalities associated with CIPN. CaV2.2 channels are critical determinants of increased neuronal excitability and neurotransmission accompanying persistent neuropathic pain. Though CaV2.2 has been targeted clinically with Prialt® and Gabapentin, both drugs are encumbered with serious side effects. This proposal aims to develop potent, orally available, and selective CaV2.2 channel antagonists, building on the seminal discovery of a quinazoline CaV2.2 antagonist (IPPQ) developed in the laboratory of Dr. Rajesh Khanna (University of Arizona (UA)), as potential candidates for the management of CIPN. IPPQ represents a new class of compounds targeting CaV2.2 via a completely unique mechanism – that of targeting the CaVα-CaVβ interface. For this work, we have partnered with Regulonix, LLC for characterizing select CaV2.2-targeted compounds and their analogs in in vitro and in vivo efficacy assays as well as early ADME profiling. The work proposed here is the first step in developing non-opioid pain treatments for CIPN. We anticipate success against paclitaxel-induced chronic pain to translate into other chronic pain types as well, but CIPN provides focus for early stage proof-of-concept. Regulonix’s specific aims are: (1) Design (Dr. Marcel Patek, Medicinal chemistry consultant, former Vice President of Chemistry at Icagen, Inc.) and synthesis (Dr. Wei Wang, Director of the Drug Discovery Center, UA or CROs) and optimization of drug-like lead series (IPPQ) and elucidation of channel specificity and biophysical properties of select IPPQ analogs to gain mechanistic and safety information and to document the unique pathway for function in relevant neuronal cells; (2) Profile IPPQ analogs for their in vitro cellular cytotoxicity, physico-chemical, early ADME, and for off-target effects on GPCRs, kinases, ion channels and alternative known pain targets; (3) Characterize the best three IPPQ analogs from Aim 2 for preclinical studies using a phenotypic screen for motor impairment (rotarod assay) and then test the two best IPPQ analogs in an acute pain model (paw incision) and an aggressive clinically-relevant neuropathic pain model (paclitaxel) to provide information about oral efficacy; behavioral studies will be registered at a preclinical trials website prior to the start. An operant method of pain testing with rodents that complements reflexive methods by addressing cognitive and motivational processing will also be used. At the conclusion of our study, we expect to have a validated IPPQ analog and several worthy backup compounds.