Type 5 17β-hydroxysteroid dehydrogenase/prostaglandin F synthase (AKR1C3): Role in breast cancer and inhibition by non-steroidal anti-inflammatory drug analogs

Aldo-keto reductase (AKR) 1C3 catalyzes the NADPH-dependent reduction of Delta(4)-androstene-3,17-dione to yield testosterone, reduction or estrone to yield 17 beta-estradiol and reduction of progesterone to yield 20 alpha-hydroxyprogesterone. In addition, it functions as a prostaglandin (PG) F synthase and reduces PGH(2) to PGF(2)alpha and PGD(2) to 11 beta-PGF(2). Immunohistochemistry showed that AKR1C3 is over-expressed in invasive ductal carcinoma of the breast. Retroviral expression of AKR1C3 in MCF-7 breast carcinoma cells shows that each of the assigned reactions occur in a breast cell microenvironment. Steroid and prostaglandin conversions were monitored by radiochromatography. Prostaglandin conversion was validated by a second method using HPLC coupled to APCI-MRM/MS. The combined effect of the AKR1C3 catalyzed 17- and 20-ketosteroid reductions will be to increase the 17 beta-estradiol:progesterane ratio in the breast. In addition, formation of PGF(2) epimers would activate F prostanoid receptors and deprive PPAR gamma of its putative anti-proliferative PGJ(2) ligands. Thus, AKR1C3 is a source of proliferative signals and a potential therapeutic target for hormone-dependent and -independent breast cancer. Two strategies for AKR1C3 inhibition based on non-steroidal anti-inflammatory drugs were developed. The first strategy uses the Ullmann coupling reaction to generate N-phenylanthranilate derivatives that inhibit AKR1C enzymes without affecting PGH2 synthase (PGHS) 1 or PGHS-2. The second strategy exploits the selective inhibition of AKR1C3 by indomethacin, which did not inhibit highly related AKR1C1 or AKR1C2. Using known structure-activity relationships for the inhibition of PGHS-1 and PGHS-2 by indole acetic acids we obtained N-(4-chlorobenzoyl)-melatonin as a specific AKR1C3 inhibitor (K-1 = 6.0 mu M) that does not inhibit PGHS-1, PGHS-2, AKR1C1, or AKR1C2. Both strategies are informed by crystal structures of ternary AKR1C3 center dot NADP(+center dot)NSAID complexes, The identification of NSAID analogs as specific inhibitors of AKR1C3 will help validate its role in the proliferation of breast cancer cells. (C) 2008 Elsevier Ireland Ltd. All rights reserved.