KATP Channel Prodrugs Reduce Inflammatory and Neuropathic Hypersensitivity, Morphine Induced Hypersensitivity, and Precipitated Withdrawal in Mice
Previous studies show ATP-sensitive potassium (KATP) channel openers can reduce hypersensitivity associated with chronic pain models in rodents, and reduce morphine tolerance. Many agonists of KATP channels are not soluble in physiologically relevant vehicles, requiring adaptation for clinical use. This study compared the antinociception activity of novel KATP channel targeting prodrugs, CKLP1, CKLP2, and CF3-CKLP. These prodrugs are activated by endogenous alkaline phosphatase enzymes present in the peripheral and central nervous systems. Analgesic capabilities of intrathecally injected prodrugs were tested in rodent models of spinal nerve ligation (SNL) and Complete Freunds Adjuvant (CFA) as models for neuropathic and inflammatory pain, respectively. CKLP1 and CKLP2 significantly increased mechanical paw withdrawal thresholds 1-2 hours after intrathecal administration in the SNL model, but all three prodrugs were able to attenuate hypersensitivity up to 7 days after CFA treatment. The reduction of opioid tolerance and opioid-induced hypersensitivity in mice treated chronically with morphine was significantly reduced in CKLP1 and CKLP2 treated animals. Prodrug cleavage was confirmed in mouse spinal cords using liquid chromatography. These studies may aid in the further development of KATP channel prodrugs for use in treatments of chronic pain, opioid tolerance, and withdrawal.