Abstract
Phospholipase A2 (PLA2) forms are expressed in spinal cord, and inhibiting spinal PLA2 induces a potent antihyperalgesia. Here, we examined the antihyperalgesic effects after systemic and i.t. delivery of four compounds constructed with a common motif consisting of a 2-oxoamide with a hydrocarbon tail and a four-carbon tether. These molecules were characterized for their ability to block group IVA calcium-dependent PLA2 (cPLA2) and group VIA calcium-independent PLA2 (iPLA2) in inhibition assays using human recombinant enzyme. The rank ordering of potency in blocking group IVA cPLA2 was AX048 (ethyl 4-[(2-oxohexadecanoyl)amino]butanoate), AX006 (4-[(2-oxohexadecanoyl)amino]butanoic acid), and AX057 (tert-butyl 4-[(2-oxohexadecanoyl)amino]butanoate) > AX010 (methyl 4-[(2-oxohexadecanoyl)amino]butanoate) and for inhibiting group VIA iPLA2 was AX048, AX057 > AX006, and AX010. No agent altered recombinant cyclooxygenase activity. In vivo, i.t. (30 μg) and systemic (0.2-3 mg/kg i.p.) AX048 blocked carrageenan hyperalgesia and after systemic delivery in a model of spinally mediated hyperalgesia induced by i.t. substance P (SP). The other agents were without activity. In rats prepared with lumbar i.t. loop dialysis catheters, SP evoked spinal prostaglandin E2 (PGE2) release. AX048 alone inhibited PGE2 release. Intrathecal SR141617, a cannabinoid CB1 inhibitor at doses that blocked the effects of i.t. anandamide had no effect upon i.t. AX048. These results suggest that AX048 is the first systemically bioavailable compound with a significant affinity for group IVA cPLA2, which produces a potent antihyperalgesia. The other agents, although demonstrating enzymatic activity in cell-free assays, appear unable to gain access to the intracellular PLA2 toward which their action is targeted.
Footnotes
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This work was supported by AnalgesiX/University of California Biotechnology Grant B1002-10303. The Regents of the University of California (G.K., E.A.D., and T.L.Y.) hold equity in AnalgesiX.
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Article, publication date, and citation information can be found at http://jpet.aspetjournals.org.
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doi:10.1124/jpet.105.091686.
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ABBREVIATIONS: COX, cyclooxygenase; PG, prostaglandin; PLA2, phospholipase A2; cPLA2, calcium-dependent PLA2; iPLA2, calcium-independent PLA2; AX006, 4-[(2-oxohexadecanoyl)amino]butanoic acid; AX010, methyl 4-[(2-oxohexadecanoyl)amino]butanoate; AX048, ethyl 4-[(2-oxohexadecanoyl)amino]butanoate; AX057, tert-butyl 4-[(2-oxohexadecanoyl)amino]butanoate; SP, substance P; NMDA, N-methyl-d-aspartate; DMSO, dimethyl sulfoxide; SR141716A, N-(piperidin-1-yl)-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboximide hydrochloride; ANOVA, analysis of variance; AACOCF3, arachidonyl trifluoromethylketone; BMS-229724, 4-[4-[2-[2-[bis(4-chlorophenyl)methoxy]ethylsulfonyl]ethoxy]phenyl]-1,1,1-trifluoro-2-butanone.
- Received June 28, 2005.
- Accepted September 30, 2005.
- The American Society for Pharmacology and Experimental Therapeutics
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