Structural effects on the phosphorylation of 3-substituted 1-beta-D-ribofuranosyl-1,2,4-triazoles by human adenosine kinase.

The conversion of ribavirin to the monophosphate by adenosine kinase is the rate-limiting step in activation of this broad spectrum antiviral drug. Variation of the 3-substituents in a series of bioisosteric and homologated 1-beta-D-ribofuranosyl-1,2,4-triazoles has marked effects on activity with the human adenosine kinase, and analysis of computational descriptors and binding models offers insight for the design of novel substrates.

In vitro and in vivo structure-activity relationships of novel androgen receptor ligands with multiple substituents in the B-ring.

We recently reported two nonsteroidal androgen receptor (AR) ligands that demonstrate tissue-selective pharmacological activity, identifying these S-3-(phenoxy)-2-hydroxy-2-methyl-N-(4-nitro-3-trifluoromethyl-phenyl)-propionamide analogs as the first members of a new class of drugs known as selective androgen receptor modulators. The purpose of these studies was to explore additional structure-activity relationships of selective androgen receptor modulators to enhance their AR binding affinity, AR-mediated transcriptional activation, and in vivo pharmacological activity. The AR binding affinity (K(i)) of 29 novel synthetic AR ligands was determined by a radioligand competitive binding assay and ranged from 1.0-51 nM. Compounds with electron-withdrawing substituents at the para- and meta-positions of the B-ring demonstrated the highest AR binding affinity. The AR-mediated transcriptional activation was determined using a cotransfection assay in CV-1 cells. Most compounds with two substituents in the B-ring maintained or improved their functional activity in vitro. However, compounds with three halogen substituents exhibited significant regioselectivity. Fifteen compounds were selected to examine their pharmacological activity in castrated rats. In vivo pharmacological activity and selectivity were significantly changed by structural modification in the B-ring. Compounds with halogen groups at the para- and meta-positions of the B-ring displayed the highest pharmacological activity. Incorporating substituents at the ortho-position of the B-ring resulted in poor pharmacological activity. In vitro and in vivo agonist activities were partially correlated. In conclusion, novel selective androgen receptor modulators with improved in vivo pharmacological activity can be designed and synthesized based on the structure-activity relationship identified in these studies.

Comparison of the pharmacological effects of a novel selective androgen receptor modulator, the 5alpha-reductase inhibitor finasteride, and the antiandrogen hydroxyflutamide in intact rats: new approach for benign prostate hyperplasia.

Tissue-selective androgen receptor modulators (SARMs) demonstrate tissue selectivity in both castrated and intact male rats, behaving as partial agonists in androgenic tissues (i.e. prostate and seminal vesicle), but full agonists in anabolic tissues (i.e. levator ani muscle). The partial agonist activity of SARMs (compounds S-1 and S-4) in the prostate of intact rats suggested that SARM could be used for androgen suppression in the treatment of benign prostate hyperplasia (BPH). This study was designed to explore the mechanisms of action of SARM and to characterize the tissue selectivity of S-1 in intact male rats compared with that of hydroxyflutamide (antiandrogen) and finasteride (5alpha-reductase inhibitor), two major drugs used for androgen suppression treatment of BPH. In intact male rats, S-1 (5, 10, and 25 mg/kg) selectively decreased the prostate weight with similar efficacy to finasteride (5 mg/kg), without affecting the levator ani muscle or increasing the plasma levels of testosterone, LH, and FSH. Hydroxyflutamide (0.5, 1, 5, 10, and 25 mg/kg), however, decreased both the prostate and levator ani muscle weights without any selectivity and increased plasma hormone levels in a dose-dependent manner. Furthermore, S-1 and S-4 showed very weak inhibitory effects toward transiently expressed type I and II human 5alpha-reductase (Ki, >20 microm) during in vitro assays. Therefore, although S-1 and finasteride showed very similar suppressive effects in the prostate of intact male rats, they decreased prostate size via different mechanisms of action. S-1 simply worked as androgen receptor partial agonist, whereas finasteride inhibited prostatic 5alpha-reductase. These studies indicate that SARMs may demonstrate clinical utility as single agent or combination therapy for BPH.

Design, synthesis, and biological characterization of metabolically stable selective androgen receptor modulators.

A series of nonsteroidal ligands were synthesized as second-generation agonists for the androgen receptor (AR). These ligands were designed to eliminate metabolic sites identified in one of our first-generation AR agonists, which was inactive in vivo due to its rapid metabolism to inactive constituents. The binding affinity of these compounds was evaluated using AR isolated from rat ventral prostate. These second-generation compounds bound the AR in a high affinity and stereoselective manner, with K(i) values ranging from about 4 to 130 nM. The ability of these ligands to stimulate AR-mediated transcriptional activation was examined in cells transfected with the human AR and a hormone-dependent luciferase reporter gene. Although some compounds were unable to stimulate AR-mediated transcription, several demonstrated activity similar to that of dihydrotestosterone (DHT, an endogenous steroidal ligand for the AR). We also evaluated the in vivo pharmacologic activity of selected compounds in castrated male rats. Three compounds were identified as selective androgen receptor modulators (SARMs), exhibiting significant anabolic activity while having only moderate to minimal androgenic activity in vivo.

Pharmacodynamics of selective androgen receptor modulators.

The present study aimed to identify selective androgen receptor modulators (SARMs) with in vivo pharmacological activity. We examined the in vitro and in vivo pharmacological activity of four chiral, nonsteroidal SARMs synthesized in our laboratories. In the in vitro assays, these compounds demonstrated moderate to high androgen receptor (AR) binding affinity, with K(i) values ranging from 4 to 37 nM, and three of the compounds efficaciously stimulated AR-mediated reporter gene expression. The compounds were then administered subcutaneously to castrated rats to appraise their in vivo pharmacological activity. Androgenic activity was evaluated by the ability of these compounds to maintain the weights of prostate and seminal vesicle, whereas levator ani muscle weight was used as a measure of anabolic activity. The maximal response (E(max)) and dose for half-maximal effect (ED(50)) were determined for each compound and compared with that observed for testosterone propionate (TP). Compounds S-1 and S-4 demonstrated in vivo androgenic and anabolic activity, whereas compounds S-2 and S-3 did not. The activities of S-1 and S-4 were tissue-selective in that both compounds stimulated the anabolic organs more than the androgenic organs. These two compounds were less potent and efficacious than TP in androgenic activity, but their anabolic activity was similar to or greater than that of TP. Neither S-1 nor S-4 caused significant luteinizing hormone or follicle stimulating hormone suppression at doses near the ED(50) value. Thus, compounds S-1 and S-4 were identified as SARMs with potent and tissue-selective in vivo pharmacological activity, and represent the first members of a new class of SARMs with selective anabolic effects.