lllinois 60566 (F.W., J.P., R.C., C.S.)3-Hydroxy-3-methylglutaryl coenzyme A reductase (HMCR) catalyzes the irreversible conversion of 3-hydroxy-3-methylglutaryl coenzyme A to mevalonate and is considered a key regulatory step controlling isoprenoid metabolism in mammals and fungi. The ratelimiting nature of this enzyme for isoprenoid biosynthesis in plants remains controversial. To investigate whether HMCR activity could be limiting in plants, we introduced a constitutively expressing hamster HMCR gene into tobacco (Nicotiana tabacum L.) plants to obtain unregulated HMCR activity. The impact of the resulting enzyme activity on the biosynthesis and accumulation of particular isoprenoids was evaluated. Expression of the hamster HMCR gene led t o a 3-t o 6-fold increase in the total HMCR enzyme activity. Total sterol accumulation was consequently increased 3-to 1 O-fold, whereas end-product sterols such as sitosterol, campesterol, and stigmasterol were increased only 2-fold. l h e leve1 of cycloartenol, a sterol biosynthetic intermediate, was increased more than 100-fold. Although the synthesis of total sterols appears to be limited normally by HMCR activity, these results indicate that the activity of one or more later enzyme(s) i n the pathway must also be involved i n determining the relative accumulation of end-product sterols.The levels of other isoprenoids such as carotenoids, phytol chain of chlorophyll, and sesquiterpene phytoalexins were relatively unaltered in the transgenic plants. It appears from these results that compartmentation, channeling, or other rate-determining enzymes operate to control the accumulation of these other isoprenoid end products.

Members of the Wee family of kinases negatively regulate the cell cycle via phosphorylation of CDK1 and are considered potential drug targets. Herein, we investigated the structure–function relationship of human Wee1, Wee2, and Myt1 (PKMYT1). Purified recombinant full-length proteins and kinase domain constructs differed substantially in phosphorylation states and catalytic competency, suggesting complex mechanisms of activation. A series of crystal structures reveal unique features that distinguish Wee1 and Wee2 from Myt1 and establish the structural basis of differential inhibition by the widely used Wee1 inhibitor MK-1775. Kinome profiling and cellular studies demonstrate that, in addition to Wee1 and Wee2, MK-1775 is an equally potent inhibitor of the polo-like kinase PLK1. Several previously unrecognized inhibitors of Wee kinases were discovered and characterized. Combined, the data provide a comprehensive view on the catalytic and structural properties of Wee kinases and a framework for the rational design of novel inhibitors thereof.

A disodium phosphonooxymethyl prodrug of the antitumor agent triptolide was prepared from the natural product in three steps (39% yield) and displayed excellent aqueous solubility at pH 7.4 (61 mg/mL) compared to the natural product (17 μg/mL). The estimated shelf life (t90) for hydrolysis of the prodrug at 4 °C and pH 7.4 was found to be two years. In a mouse model of human colon adenocarcinoma (HT-29), the prodrug administered intraperitoneally was effective in reducing or eliminating xenograft tumors at dose levels as low as 0.3 mg/kg when given daily and at 0.9 mg/kg when given less frequently. When given via intraperitoneal and oral routes at daily doses of 0.6 and 0.9 mg/kg, the prodrug was also effective and well tolerated in a mouse model of human ovarian cancer (A2780).

Oral administration of a retinoic acid receptor (RAR) pan-antagonist reversibly inhibits spermatogenesis. Given the importance of RARα in regulating spermatogenesis, we identified two RARα-selective antagonists by transactivation and transactivation competition assays and asked whether they effectively inhibit spermatogenesis. Although these two antagonists were potent in vitro, they displayed poor in vivo activity in mice when administered orally. Testicular weights were normal and morphological analysis revealed normal spermatid alignment and sperm release. In vitro drug property analyses were performed with one of these antagonists and compared with the pan-antagonist. We showed that the discrepancies may be explained by several factors, including high plasma protein binding, faster hepatic metabolism relative to the pan-antagonist, and only moderate permeability. The conclusion of poor oral bioavailability was supported by more pronounced defects in mice when the antagonist was administered intravenously versus intraperitoneally. These results are crucial for designing new RARα-selective antagonists for pharmaceutical application.