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 (androgen,
estrogen, and
progesterone receptors) and the orphan
peroxisome proliferator-activated receptor (
PPARgamma). In human
myeloid leukemia (HL-60) cells,
ligand access to
PPARgamma is regulated by AKR1C3, which diverts
PGD(2) metabolism away from J-series
prostanoids (Desmond et al., 2003). Inhibition of AKR1C3 by
indomethacin, a nonsteroidal anti-inflammatory drug (
NSAID), caused
PPARgamma-mediated terminal differentiation of the HL-60 cells. To discriminate between
antineoplastic effects of
NSAIDs that are mediated by either AKR1C or
cyclooxygenase (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 but do not inhibit recombinant COX-1 or COX-2. The inhibition constants, IC(50), K(I) values, and inhibition patterns were determined for the
NSAID analogs and
steroid carboxylates against 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 IC(50) values that had greater than 500-fold selectivity for AKR1C
isozymes compared with 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-
OH(2)(+) 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.