AKR1C3 inhibitors should not inhibit the related isoforms, AKR1C1 and AKR1C2 that are involved in 5-dihydrotestosterone inactivation in the prostate. androgen biosynthesis and its localization within the tumor make AKR1C3 an important target for the treatment of CRPC. However, the presence of the closely related AKR1C isoforms AKR1C1 and AKR1C2, both of which are involved in DHT inactivation in the prostate, makes it imperative that AKR1C3 be inhibited selectively.15C17 The high sequence identity (> 86%) between the AKR1C isoforms makes the discovery of selective AKR1C3 inhibitors challenging. Non-steroidal anti-inflammatory drugs (NSAIDs) used clinically for their cyclooxygenase (COX) inhibitory properties are known to inhibit AKR1C3 at therapeutically relevant concentrations.18, 19 In particular, the = 81.58, = 70.2647.17 49.00 83.56= 87.37, = 70.18?Unique reflections measured22331 (2242)b56673 (5206)b?(is the observed intensity and ?= (|screen are directly comparable to IC50 values generated in the cell-based assays. Regardless, compound 2 will require optimization for AR antagonism. The AKR1C3 structure with the bifunctional analog bound shows a unique double-decker structure that can be exploited in the design and optimization of second generation AKR1C3 inhibitors. The development of a bifunctional agent that inhibits AKR1C3 and AR should provide therapeutic benefit in CRPC. Such compounds could be superior to drugs that act on a single target e.g., CYP17A1 (abiraterone) or AR (MDV3100) and may have less adverse effects. These compounds are interesting leads for drug development CRPC. Supplementary GSK591 Material 01Click here to view.(38K, docx) Acknowledgments Supported by R01-CA90744, P30-ES013508, a Prostate Cancer Foundation Challenge grant, and UL1RR024134 from the National Center for GSK591 Research Resources (NCRR) from the National Institute of Health awarded to T.M.P. Grant GM-056838 awarded to D.W.C., and Grant F32DK089827 awarded to M.C, from the National Rabbit polyclonal to PDK4 Institutes of Health. The crystallography studies are based upon research conducted at beamline X25 and X29 of the National Synchrotron Light Source. Financial support for the National Synchrotron Light Source comes principally from the Offices of Biological and GSK591 Environmental Research and of Basic Energy Sciences of the US Department of Energy, and from the NCRR of the National Institutes of Health grant number P41RR012408. We thank Ms. Ling Duan for help with the metabolism studies. ABBREVIATIONS AKRaldo-keto reductaseAKR1C3type 5 17-hydroxysteroid dehydrogenaseARandrogen receptorCOXcyclooxygenaseCRPCcastrate resistant prostate cancerDHT5-dihydrotestosteroneFLUflufenamic acidNSAIDsnon-steroidal anti-inflammatory drugsN-PAN-phenylanthranilic acidsSARstructure activity relationship Footnotes The steroid/inhibitor binding cavity of AKR1C3 is composed of five compartments as defined by Byrns et al. in GSK591 reference 15: oxyanion site (OS; formed by Tyr55, His117, and NADP+), steroid channel (SC; Trp227 and Leu54), and three subpockets, SP1 (Ser118, Asn167, Phe306, Phe311, and Tyr319), SP2 (Trp86, Leu122, Ser129, and Phe311), and SP3 (Tyr24, Glu192, Ser221, and Tyr305). Atomic coordinates and structure factors for the AKR1C3?NADP+?2 complex (code 4DBS) and the AKR1C3?NADP+?BMT-1 complex (code 4DBU) have been deposited with the RCSB Protein Data Bank. CONFLICT OF INTEREST The authors declare no conflict of interest EDITORS NOTE A provisional patent application based on these compounds has been submitted to the US patent office. US provisional patent applications no 61/4,754,091 filed April 13, 2011. Publisher’s Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form..