Received for publication August 26, 2004.
Revised October 5, 2004.
Accepted for publication October 5, 2004.

Development of non-steroidal anti-inflammatory drug (NSAID) analogs and steroid carboxylates selective for human aldo-keto reductase isoforms: Potential antineoplastic agents that work independently of cyclooxygenase isozymes*

Abstract

Human aldo-keto reductases (AKRs) regulate nuclear receptors by controlling ligand availability. Enzymes implicated in regulating ligand occupancy and trans-activation of the nuclear receptors belong to the AKR1C family (AKR1C1-AKR1C3). Nuclear receptors regulated by AKR1C members include the steroid-hormone receptors (AR, ER, and PR) and the orphan receptor, PPAR. In human myeloid leukemia (HL-60) cells ligand access to PPAR is regulated by AKR1C3, which diverts PGD₂ metabolism away from J-series prostanoids (Desmond, 2003). Inhibition of AKR1C3 by indomethacin, an NSAID, caused PPAR mediated terminal differentiation of the HL-60 cells. To discriminate between anti-neoplastic effects of NSAIDs that are mediated by either AKR1C or COX isozymes, selective inhibitors are required. We report a structural series of N-phenylanthranilic acid derivatives and steroid carboxylates that selectively inhibit recombinant AKR1C isoforms while not inhibiting recombinant COX-1 or COX-2. The inhibition constants, IC₅₀, K_I values and inhibition patterns were determined for the NSAID analogs and steroid carboxylates against the AKR1C and COX isozymes. Lead compounds, 4-chloro-N-phenylanthranilic acid and 4-benzoyl-benzoic acid for the N-phenylanthranilic acid analogs and most steroid carboxylates, exhibited IC₅₀ values that had greater than 500-fold selectivity for AKR1C isozymes as compared to COX-1 and COX-2. Crystallographic and molecular modeling studies showed that the carboxylic acid of the inhibitor ligand was tethered by the catalytic Tyr55-OH₂⁺ and explained why A-ring substituted N-phenylanthranilates inhibited only AKR1C enzymes. These compounds can be used to dissect the role of the AKR1C isozymes in neoplastic diseases and may have cancer chemopreventive roles independent of COX inhibition.

Key words: Prostanoid, Sex hormones, PPARs, Structure-activity relationships and modeling, Enzymology, Regulation - transcriptional, Structure/function/mechanism, Cyclooxygenases, Eicosanoids