Goins, Aleyah E.

Chronic pain affects nearly 100 million adults in the U.S., yet few novel therapeutics have emerged in recent decades. P2X4 receptor (P2X4R), implicated in pain signaling, represents a promising target. We evaluated a humanized single-chain variable fragment (hscFv) targeting P2X4R for its ability to reduce ATP-induced currents and modulate excitability in human dorsal root ganglion (hDRG) neurons. Voltage-clamp recordings confirmed that human P2X4R (hP2X4R) hscFv significantly reduced ATP-evoked currents in HEK-293T cells expressing human P2X4, likely by relocalization of the receptor to the perinuclear region after hscFv treatment. Immunohistochemistry and transcriptomic analyses demonstrated widespread P2X4R ( P2RX4 ) expression across hDRG neuronal subtypes in both male and female donors. Current-clamp recordings revealed that hP2X4R hscFv selectively increased action potential (AP) threshold in multi-firing hDRG neurons, without affecting single-firing neurons. Spontaneous activity at rest and depolarizing spontaneous fluctuation (DSF) amplitude were also reduced. Analysis confirmed consistent effects of hP2X4R hscFv on excitability parameters. These findings suggest that hP2X4 hscFv exerts modest but targeted effects on human sensory neurons, supporting its potential as a novel therapeutic for chronic pain.

Non-opioid single-chain variable fragment (scFv) small antibodies were generated as pain-reducing block of P2X4R receptor (P2X4R). A panel of scFvs targeting an extracellular peptide sequence of P2X4R was generated followed by cell-free ribosome display for recombinant antibody selection. After three rounds of bio-panning, a panel of recombinant antibodies was isolated and characterized by ELISA, cross-reactivity analysis, and immunoblotting/immunostaining. Generated scFv antibodies feature binding activity similar to monoclonal antibodies but with stronger affinity and increased tissue penetrability due to their ~30% smaller size. Two anti-P2X4R scFv clones (95, 12) with high specificity and affinity binding were selected for in vivo testing in male and female mice with trigeminal nerve chronic neuropathic pain (FRICT-ION model) persisting for several months in untreated BALBc mice. A single dose of P2X4R scFv (4 mg/kg, i.p.) successfully, completely, and permanently reversed chronic neuropathic pain-like measures in male mice only, providing retention of baseline behaviors indefinitely. Untreated mice retained hypersensitivity, and developed anxiety- and depression-like behaviors within 5 weeks. In vitro P2X4R scFv 95 treatment significantly increased the rheobase of larger-diameter (>25 µm) trigeminal ganglia (TG) neurons from FRICT-ION mice compared to controls. The data support use of engineered scFv antibodies as non-opioid biotherapeutic interventions for chronic pain.