a-134974 and Disease-Models--Animal

There is a major clinical need for new therapies for the treatment of chronic itch. Many of the molecular components involved in itch neurotransmission are known, including the neuropeptide NPPB, a transmitter required for normal itch responses to multiple pruritogens in mice. Here, we investigated the potential for a novel strategy for the treatment of itch that involves the inhibition of the NPPB receptor NPR1 (natriuretic peptide receptor 1). Because there are no available effective human NPR1 (hNPR1) antagonists, we performed a high-throughput cell-based screen and identified 15 small-molecule hNPR1 inhibitors. Using in vitro assays, we demonstrated that these compounds specifically inhibit hNPR1 and murine NPR1 (mNPR1). In vivo, NPR1 antagonism attenuated behavioral responses to both acute itch- and chronic itch-challenged mice. Together, our results suggest that inhibiting NPR1 might be an effective strategy for treating acute and chronic itch.

Topics: Animals; Behavior, Animal; Cell-Free System; Dermatitis, Contact; Disease Models, Animal; Ganglia, Spinal; Humans; Mice, Inbred C57BL; Mice, Knockout; Neurons; Pruritus; Receptors, Atrial Natriuretic Factor; Reproducibility of Results; Signal Transduction; Small Molecule Libraries

Extracellular levels of adenosine (ADO) can be raised through inhibition of adenosine kinase (AK), a primary metabolic enzyme for ADO. AK inhibitors have shown antinociceptive activity in a variety of animal models of nociception. The present study investigated the antinociceptive actions of a novel and selective AK inhibitor, A-134974 (IC(50)=60 pM), in a rat model of neuropathic pain (ligations of the L5/L6 spinal nerves) and explored the relative contributions of supraspinal, spinal and peripheral sites to the actions of A-134974. Systemic A-134974 dose-dependently reduced tactile allodynia (ED(50)=5 micromol/kg, i.p.) for up to 2 h. Fall latencies in the rotorod test of motor coordination were unaffected by systemic administration of A-134974 (at doses up to 30 micromol/kg, i.p.). Administration of A-134974 intrathecally (i.t.) was more potent (ED(50)=10 nmol) in relieving tactile allodynia than delivering the compound by intracerebroventricular (ED(50)>100 nmol, i.c.v.) or intraplantar (ED(50)>500 nmol) routes suggesting that spinal sites of action are the primary contributors to the anti-allodynic action of A-134974. The anti-allodynic effects of systemic A-134974 (10 micromol/kg, i.p.) were antagonized by the non-selective ADO receptor antagonist, theophylline (30-500 nmol) administered i.t. These data demonstrate that the novel AK inhibitor A-134974 potently reduces tactile allodynia through interactions with spinal sites and adds to the growing evidence that AK inhibitors may be useful as analgesic agents in a broad spectrum of pain states.

Topics: Adenosine Kinase; Animals; Disease Models, Animal; Dose-Response Relationship, Drug; Enzyme Inhibitors; Hyperalgesia; Male; Nerve Crush; Nociceptors; Nucleosides; Pain; Pain Measurement; Peripheral Nervous System Diseases; Phosphodiesterase Inhibitors; Physical Stimulation; Posterior Horn Cells; Rats; Rats, Sprague-Dawley; Theophylline