The activity of cyclin-dependent kinase 2 (CDK2) is essential for progression of cells from G 1 to the S phase of the mammalian cell cycle. CVT-313 is a potent CDK2 inhibitor, which was identified from a purine analog library with an IC 50 of 0.5 M in vitro. Inhibition was competitive with respect to ATP (K i ‫؍‬ 95 nM), and selective CVT-313 had no effect on other, nonrelated ATP-dependent serine/threonine kinases. When added to CDK1 or CDK4, a 8.5-and 430-fold higher concentration of CVT-313 was required for half-maximal inhibition of the enzyme activity. In cells exposed to CVT-313, hyperphosphorylation of the retinoblastoma gene product was inhibited, and progression through the cell cycle was arrested at the G 1 /S boundary. The growth of mouse, rat, and human cells in culture was also inhibited by CVT-313 with the IC 50 for growth arrest ranging from 1.25 to 20 M. To evaluate the effects of CVT-313 in vivo, we tested this agent in a rat carotid artery model of restenosis. A brief intraluminal exposure of CVT-313 to a denuded rat carotid artery resulted in more than 80% inhibition of neointima formation. These observations suggest that CVT-313 is a promising candidate for evaluation in other disease models related to aberrant cell proliferation.Cell cycle progression in mammalian cells is regulated by a family of cyclin-dependent protein kinases (CDKs), 1 that include CDK1, CDK2, CDK3, CDK4, and CDK6 (1). CDK2 is a serine/threonine kinase whose activity is essential for the G 1 to S transition during cell division. A number of proteins have been shown to be substrates for CDK2 phosphorylation, and among them are the retinoblastoma gene product (Rb) and other related pocket proteins, members of the E2F transcription factor family, cyclin E, and members of the CDK inhibitory proteins. It is also postulated that CDK2 phosphorylates and regulates proteins involved in DNA replication (2, 3). Two lines of evidence suggest that CDK2 activity is essential for cell proliferation; microinjection of antibodies directed against CDK2 blocks the progression of human diploid fibroblasts into S phase (4, 5), and overexpression of a dominant negative mutant of CDK2 in human osteosarcoma cells has a similar effect (6). The crucial role of CDK2 in controlling cell cycle progression suggests that CDK2 is an attractive target for treatment of aberrant cell proliferation.Smooth muscle cell proliferation is largely responsible for restenosis following angioplasty (7). A recent study has shown that CDK2 is activated very early after endothelial denudation in the rat carotid artery model of restenosis (8); moreover, antisense oligonucleotides directed against CDK2 were shown to be effective in reducing neointima formation in this model (9, 10). Arguably, the restenosis model can be used as a "proof of principle" for developing CDK2 inhibitors as drug candidates for the treatment of diseases related to aberrant cell proliferation. Olomoucine is a purine analog of ATP and is a specific inhibitor of CDK1 and CDK2 (11). Its potency, ho...

Insulin resistance, an important feature of type 2 diabetes, is manifested as attenuated insulin receptor (IR) signaling in response to insulin binding. A drug that promotes the initiation of IR signaling by enhancing IR autophosphorylation should, therefore, be useful for treating type 2 diabetes. This report describes the effect of a small molecule IR sensitizer, TLK16998, on IR signaling. This compound activated the tyrosine kinase domain of the IR ␤-subunit at concentrations of 1 mol/l or less but had no effect on insulin binding to the IR ␣-subunit even at much higher concentrations. TLK16998 alone had no effect on IR signaling in mouse 3T3-L1 adipocytes but, at concentrations as low as 3.2 mol/l, enhanced the effects of insulin on the phosphorylation of the IR ␤-subunit and IR substrate 1, and on the amount of phosphatidylinositol 3-kinase that coimmunoprecipitated with IRS-1. Phosphopeptide mapping revealed that the effect of TLK16998 on the IR was associated with increased tyrosine phosphorylation of the activation loop of the ␤-subunit tyrosine kinase domain. TLK16998 also increased the potency of insulin in stimulating 2-deoxy-D-glucose uptake in 3T3-L1 adipocytes, with a detectable effect at 8 mol/l and a 10-fold increase at 40 mol/l. In contrast, only small effects were observed on IGF-1-stimulated 2-deoxy-D-glucose uptake. In diabetic mice, TLK16998, at a dose of 10 mg/kg, lowered blood glucose levels for up to 6 h. These results suggest, therefore, that small nonpeptide molecules that directly sensitize the IR may be useful for treating type 2 diabetes. Diabetes 50: 824 -830, 2001

In breast and certain other cancers, receptor tyrosine kinases, including the insulin-like growth factor I receptor (IGF-IR), play an important role in promoting the oncogenic process. The IGF-IR is therefore an important target for developing new anti–breast cancer therapies. An initial screening of a chemical library against the IGF-IR in breast cancer cells identified a diaryl urea compound as a potent inhibitor of IGF-IR signaling. This class of compounds has not been studied as inhibitors of the IGF-IR. We studied the effectiveness of one diaryl urea compound, PQ401, at antagonizing IGF-IR signaling and inhibiting breast cancer cell growth in culture and in vivo. PQ401 inhibited autophosphorylation of the IGF-IR in cultured human MCF-7 cells with an IC50 of 12 μmol/L and autophosphorylation of the isolated kinase domain of the IGF-IR with an IC50 <1 μmol/L. In addition, PQ401 inhibited the growth of cultured breast cancer cells in serum at 10 μmol/L. PQ401 was even more effective at inhibiting IGF-I-stimulated growth of MCF-7 cells (IC50, 6 μmol/L). Treatment of MCF-7 cells with PQ401 was associated with a decrease in IGF-I-mediated signaling through the Akt antiapoptotic pathway. Twenty-four hours of treatment with 15 μmol/L PQ401 induced caspase-mediated apoptosis. In vivo, treatment with PQ401 (i.p. injection thrice a week) reduced the growth rate of MCNeuA cells implanted into mice. These studies indicate that diaryl urea compounds are potential new agents to test in the treatment of breast and other IGF-I-sensitive cancers. [Mol Cancer Ther 2006;5(4):1079–86]

Milbemycin ß} (la), the simplest member of a family of some 13 architecturally novel macrolide antibiotics structurally related to the avermectins,2 was first isolated in 1975 by Mishima et al.3,4 from Streptomyces B-41-146. Subsequent screening demonstrated that this antibiotic complex possessed remarkably potent pesticidal activity4 against a host of agricultural pests, including aphids, la val forms of insects of the order fepidopera, mites, rice leaf beetles,

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