BACKGROUNDWhile the androgens of testicular origin (representing about 50% of total androgens in men over 50 years) can be completely eliminated by surgical or medical castration with GnRH (gonadotropin-releasing hormone) agonists or antagonists, the antiandrogens currently available as blockers of androgen binding to the androgen receptor (AR), namely bicalutamide (BICA), flutamide (FLU) and nilutamide have too weak affinity to completely neutralize the other 50% of androgens made locally from dehydroepiandrosterone (DHEA) in the prostate cancer tissue by the mechanisms of intracrinology.MATERIALS AND METHODSSeries of steroid derivatives having pure and potent antagonistic activity on the human and rodent AR were synthesized. Assays of AR binding and activity in carcinoma mouse Shionogi and human LNCaP cells as well as in vivo bioavailability measurements and in vivo prostate weight assays in the rat were used.RESULTSThe chosen lead steroidal compound, namely EM-5854, has a 3.7-fold higher affinity than BICA for the human AR while EM-5855, an important metabolite of EM-5854, has a 94-fold higher affinity for the human AR compared to BICA. EM-5854 and EM-5855 are 14 times more potent than BICA in inhibiting androgen (R1881)-stimulated prostatic specific antigen (PSA) secretion in human prostatic carcinoma LNCaP cells in vitro. MDV3100 has a potency comparable to bicalutamide in these assays. Depending upon the oral formulation, EM-5854 is 5- to 10-times more potent than BICA to inhibit dihydrotestosterone (DHT)-stimulated ventral prostatic weight in vivo in the rat while MDV3100 has lower activity than BICA in this in vivo model. These data are supported by respective 40-fold and 105-fold higher potencies of EM-5854 and EM-5855 compared to BICA to inhibit cell proliferation in the androgen-sensitive Shionogi carcinoma cell model.CONCLUSIONSAlthough the present preclinical results data need evaluation in clinical trials in men, combination of the data obtained in vitro in human LNCaP cells as indicator of potency in the human prostate and the data on metabolism evaluated in vivo on ventral prostate weight in the rat, could suggest the possibility of a 70- to 140-fold higher potency of EM-5854 compared to bicalutamide (Casodex) for the treatment of prostate cancer in men.

01 Feb 2006·SLAS Discovery

A Radioligand Binding Assay for Antitubulin Activity in Tumor Cells

Article

Author: David H. Young ; Paul O. Danis ; Fernando M. Rubio

The benzamide RH-5854 is shown to be highly potent toward tumor cells and to arrest nuclear division by a highly specific covalent binding to the beta-subunit of tubulin in the colchicine binding region. Binding of 3H-RH-5854 to beta-tubulin in HCT-116 colon cancer cells is saturable and has been exploited in the development of a cell-based competitive binding assay, which allows antitubulin effects to be detected in whole cells. 3H-RH-5854 binding is strongly inhibited by preincubating the cells with compounds that bind to the colchicine site and with paclitaxel. Binding of 3H-RH-5854 is enhanced by preincubating the cells with vinblastine but not by other agents that bind at or near the vinblastine site (ansamitocin P-3 and phomopsin A). Various cytotoxic agents that do not act on tubulin do not affect binding of 3H-RH-5854 in HCT-116 cells, demonstrating specificity of the assay for detection of antitubulin activity. As an alternative to traditional assays that employ isolated brain tubulin, the 3HRH-5854 binding assay enables screening for antitubulin effects directly in tumor cells, providing an assay that accounts for cell-specific criteria that influence sensitivity such as different tubulin isotypes, tubulin mutations, drug metabolism, and efflux mechanisms.

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Indication	Highest Phase	Country/Location	Organization	Date
Prostatic Cancer	Phase 2	CA	Endoceutics, Inc.	-

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