Aberrant increases in
NMDA receptor (NMDAR) signaling contributes to central nervous system sensitization and
chronic pain by activating
neuronal nitric oxide synthase (nNOS) and generating
nitric oxide (NO). Because the scaffolding
protein postsynaptic density 95kDA (PSD95) tethers nNOS to NMDARs, the PSD95-nNOS complex represents a therapeutic target. Small molecule inhibitors
IC87201 (EC5O: 23.94 μM) and ZL006 (EC50: 12.88 μM) directly inhibited binding of purified PSD95 and nNOS
proteins in AlphaScreen without altering binding of PSD95 to ErbB4. Both PSD95-nNOS inhibitors suppressed
glutamate-induced cell death with efficacy comparable to
MK-801.
IC87201 and ZL006 preferentially suppressed phase 2A
pain behavior in the
formalin test and suppressed
allodynia induced by intraplantar complete
Freund's adjuvant administration.
IC87201 and ZL006 suppressed mechanical and cold
allodynia induced by the chemotherapeutic agent
paclitaxel (ED50s: 2.47 and 0.93 mg/kg i.p. for
IC87201 and ZL006, respectively). Efficacy of PSD95-nNOS disruptors was similar to
MK-801. Motor ataxic effects were induced by
MK-801 but not by ZL006 or
IC87201. Finally,
MK-801 produced
hyperalgesia in the tail-flick test whereas
IC87201 and ZL006 did not alter basal nociceptive thresholds. Our studies establish the utility of using AlphaScreen and purified
protein pairs to establish and quantify disruption of
protein-
protein interactions. Our results demonstrate previously unrecognized antinociceptive efficacy of ZL006 and establish, using two small molecules, a broad application for PSD95-nNOS inhibitors in treating neuropathic and inflammatory
pain. Collectively, our results demonstrate that disrupting PSD95-nNOS
protein-
protein interactions is effective in attenuating pathological
pain without producing unwanted side effects (i.e.
motor ataxia) associated with NMDAR antagonists.