Novel Phenylene Lipids That Are Positive Allosteric Modulators of Glycine Receptors and Inhibitors of Glycine Transporter 2

Chronic pain is a complex condition that remains resistantto currenttherapeutics. We previously synthesized a series of N-acyl amino acids (NAAAs) that inhibit the glycine transporter, GlyT2,some of which are also positive allosteric modulators of glycine receptors(GlyRs). In this study, we have synthesized a library of NAAAs thatcontain a phenylene ring within the acyl tail with the objective ofimproving efficacy at both GlyT2 and GlyRs and also identifying compoundsthat are efficacious as dual-acting modulators to enhance glycineneurotransmission. The most efficacious positive allosteric modulatorof GlyRs was 2-[8-(2-octylphenyl)octanoylamino]acetic acid (8-8OPGly) which potentiates the EC5 for glycine activationof GlyR & alpha;(1) by 1500% with an EC50 of 664nM. Phenylene-containing NAAAs with a lysine headgroup were the mostpotent inhibitors of GlyT2 with (2S)-6-amino-2-[8-(3-octylphenyl)octanoylamino]hexanoicacid (8-8 MPLys) inhibiting GlyT2 with an IC50 of32 nM. The optimal modulator across both proteins was (2S)-6-amino-2-[8-(2-octylphenyl)octanoylamino]hexanoic acid (8-8OPLys), which inhibits GlyT2 with an IC50 of 192 nM andpotentiates GlyRs by up to 335% at 1 & mu;M. When tested in a dualGlyT2/GlyR & alpha;(1) expression system, 8-8 OPLyscaused the greatest reductions in the EC50 for glycine.This suggests that the synergistic effects of a dual-acting modulatorcause greater enhancements in glycinergic activity compared to single-targetmodulators and may provide an alternate approach to the developmentof new non-opioid analgesics for the treatment of chronic pain.