Targeting intrinsically disordered regions facilitates discovery of CaV3.2 inhibitory peptides for AAV-mediated peripheral analgesia.

ABSTRACT: Ample data support a prominent role of peripheral T-type calcium channels 3.2 (CaV3.2) in generating pain states. Development of primary sensory neuron-specific inhibitors of CaV3.2 channels is an opportunity for achieving effective analgesic therapeutics, but success has been elusive. Small peptides, especially those derived from the natural proteins as inhibitory peptide aptamers (iPAs), can produce highly effective and selective blockade of specific nociceptive molecular pathways to reduce pain with minimal off-target effects. Here, we report the engineering of the potent and selective iPAs of CaV3.2 from the intrinsically disordered regions (IDR) of CaV3.2 intracellular segments. Using established prediction algorithms, we localized the IDRs in CaV3.2 protein and identified several CaV3.2iPA candidates that significantly reduced CaV3.2 current in HEK293 cells stably expressing human wide-type CaV3.2. Two prototype CaV3.2iPAs (iPA1 and iPA2) derived from the IDRs of CaV3.2 intracellular loop 2 and 3 respectively were expressed selectively in the primary sensory neurons of dorsal root ganglia in vivo using recombinant adeno-associated virus (AAV), which produced sustained inhibition of calcium current conducted by CaV3.2/T-type channels and significantly attenuated both evoked and spontaneous pain behavior in rats with neuropathic pain following tibial nerve injury. Recordings from dissociated sensory neurons showed that AAV-mediated CaV3.2iPA expression suppressed neuronal excitability, suggesting that CaV3.2iPA treatment attenuated pain by reversal of injury-induced neuronal hypersensitivity. Collectively, our results indicate that CaV3.2iPAs are promising analgesic leads that, combined with AAV-mediated delivery in anatomically targeted sensory ganglia, have the potential to be a selective peripheral CaV3.2-targeting strategy for clinical treatment of pain.