Inhibition of the complete set of mammalian secreted phospholipases A2 by indole analogues: a structure-guided study Original Research Article

Structure-guided design was employed in a search for potent and selective inhibitors of mammalian secreted phospholipases A2 (sPLA2s). Using the X-ray structures of human groups IIA and X sPLA2s (hGIIA and hGX) as templates, homology structural models were made for the other human and mouse sPLA2s (hGIB, mGIB, mGIIA, mGIIC, hGIID, mGIID, hGIIE, mGIIE, hGIIF, mGIIF, hGV, mGV, and mGX). Me-Indoxam is a previously discovered indole analogue that binds tightly to many sPLA2s, and the X-ray structure of the hGX-Me-Indoxam complex was determined at a resolution of 2.0 Å. Modeling suggests that the residues near the N1-substituent of Me-Indoxam vary significantly among the mammalian sPLA2s, and therefore a library of 83 N1-variants was prepared by parallel synthesis. Several Me-Indoxam analogues bearing a 4-(2-oxy-ethanoic acid) side chain were potent inhibitors (IC50 <0.05 μM) of hGIIA, mGIIA, mGIIC, hGIIE, mGIIE, hGV, and mGV, while they displayed intermediate potency (0.05–5 μM) against hGIB, mGIB, hGX, and mGX, and poorly inhibited (>5 μM) hGIID, mGIID, hGIIF, and mGIIF. Me-Indoxam analogues bearing a 5-(4-oxy-butanoic acid) side chain were generally less potent inhibitors. Although no compounds were found to be highly specific for a single human or mouse sPLA2, combinations of Me-Indoxam analogues were discovered that could be used to distinguish the action of various sPLA2s in cellular events. For example, Me-Indoxam and compound 5 are approximately 5-fold more potent on hGIIA than on hGV, and compound 21 is 10-fold more potent on hGV versus hGIIA.