The hepatic stellate cell (HSC) is the primary cell type in the liver responsible for excess collagen deposition during fibrosis. Following a fibrogenic stimulus the cell changes from a quiescent vitamin A-storing cell to an activated cell type associated with increased extracellular matrix synthesis and increased cell proliferation. The phosphatidylinositol 3-kinase (PI3K) signaling pathway has been shown to regulate several aspects of HSC activation in vitro, including collagen synthesis and cell proliferation. Using a targeted approach to inhibit PI3K signaling specifically in HSCs, we investigated the role of PI3K in HSCs using a rodent model of hepatic fibrosis. An adenovirus expressing a dominant negative form of PI3K under control of the smooth muscle ␣-actin (␣SMA) promoter was generated (AdSMAdnPI3K). Transducing HSCs with Ad-SMAdnPI3K resulted in decreased proliferation, migration, collagen expression, and several additional profibrogenic genes, while also promoting cell death. Inhibition of PI3K signaling was also associated with reduced activation of Akt, p70 S6 kinase, and extracellular regulated kinase signaling as well as reduced cyclin D1 expression. Administering Ad-SMAdnPI3K to mice following bile duct ligation resulted in reduced HSC activation and decreased extracellular matrix deposition, including collagen expression. A reduction in profibrogenic mediators, including transforming growth factor beta, tissue inhibitor of metalloproteinase 1, and connective tissue growth factor was also noted. However, liver damage, assessed by alanine aminotransferase levels, was not reduced. Conclusion: Inhibition of PI3K signaling in HSCs during active fibrogenesis inhibits extracellular matrix deposition, including synthesis of type I collagen, and reduces expression of profibrogenic factors. These data suggest that targeting PI3K signaling in HSCs may represent an effective therapeutic target for hepatic fibrosis. (HEPATOLOGY 2009;50:1512-1523

There are several independent metabolic steps that determine the level of a protein in eukaryotic cells. The steady-state level of the mRNA encoding the specific protein is determined by rate of transcription, percentage of transcripts that are ultimately processed and transported to the cytoplasm, and half-life of the mRNA in cytoplasm. The amount of protein that accumulates from a particular transcript is influenced not only by the amount of mRNA present in the cytoplasm but also by the rate of translation of the mRNA and stability of the protein product. There is compelling evidence that the steady-state level of many proteins is regulated at multiple steps, and when there is a large change in the amount of either mRNA or protein it is likely that multiple steps in the metabolism of the mRNA and protein have been altered. In the case of type I collagen production in the fibrotic liver, recent work has shown that there is regulation of multiple steps resulting in an approximately 70-fold increase in collagen production by the hepatic stellate cells. In addition to the well-documented relatively small effect on transcription, there are effects on processing/transport of the mRNA, translation of the mRNA, and stability of the mRNA. Large changes of protein levels are produced by altering the rates or efficiency of multiple steps. The molecular details of some of these posttranscriptional regulatory events are currently being elucidated. Here we review the various potential steps for regulation in the synthesis of a protein and discuss how the synthesis of type I collagen may be regulated in the fibrotic liver.

The TAXUS Express 2 Paclitaxel Eluting Coronary Stent System employs a coating consisting of the thermoplastic elastomer, poly(styrene-b-isobutylene-b-styrene; SIBS), selected for its drug-eluting characteristics, vascular compatibility, mechanical properties, and biostability. This study was conducted to evaluate the impact of different SIBS (17-51 mole % styrene) compositions on mechanical properties, chemical stability, and vascular compatibility. Mechanical property (stress-strain measurements) and stability studies were conducted on polymer films with five different styrene contents (17, 24, 32, 39, and 51 mole %). The ultimate tensile strength did not change significantly with composition, but the elongation at break decreased with increased styrene content. A pulsatile fatigue test further confirmed the mechanical stability of SIBS up to 39 mole % styrene. The vascular compatibility of five different SIBS compositions was assessed using SIBS-only coated stents, in the coronary and carotid arteries in a porcine model study. The stability of the vessel wall, rate/degree of endothelialization, inflammation, and thrombus at timepoints from 30 to 180 days were evaluated. The results confirm vascular compatibility over the range of 17-51 mole % styrene.

Kinases are known to regulate fundamental processes in cancer including tumor proliferation, metastasis, neovascularization, and chemoresistance. Accordingly, kinase inhibitors have been a major focus of drug development, and several kinase inhibitors are now approved for various cancer indications. Typically, kinase inhibitors are selected via high-throughput screening using catalytic kinase domains at low ATP concentration, and this process often yields ATP mimetics that lack specificity and/or function poorly in cells where ATP levels are high. Molecules targeting the allosteric site in the inactive kinase conformation (type II inhibitors) provide an alternative for developing selective inhibitors that are physiologically active. By applying a rational design approach using a constrained aminotriazole scaffold predicted to stabilize kinases in the inactive state, we generated a series of selective type II inhibitors of PDGFRβ and B-RAF, important targets for pericyte recruitment and endothelial cell survival, respectively. These molecules were designed in silico and screened for antivascular activity in both cell-based models and a Tg (fli1-EGFP) zebrafish embryogenesis model. Dual inhibition of PDGFRβ and B-RAF cellular signaling demonstrated synergistic antiangiogenic activity in both zebrafish and murine models of angiogenesis, and a combination of previously characterized PDGFRβ and RAF inhibitors validated the synergy. Our lead compound was selected as an orally active molecule with favorable pharmacokinetic properties which demonstrated target inhibition in vivo leading to suppression of murine orthotopic tumors in both the kidney and pancreas.R AF is an important convergent point downstream of FGFR and VEGFR2 signaling in endothelial cells and has previously been shown to play a critical role in endothelial cell survival during angiogenesis (1-3). PDGFRβ is a receptor tyrosine kinase that is essential for promoting proper pericyte function, which stabilizes blood vessels and enables vessel maturation (4-6). We rationalized that inhibition of both RAF and PDGFRβ would produce a potent antiangiogenic effect by targeting the two primary cell types involved in angiogenesis and vascular remodeling, endothelial cells and pericytes, respectively. As such, we designed compounds predicted to inhibit both RAF and PDGFRβ in a selective manner.The recent approval of imatinib (7, 8) (1) and sorafenib (9) (2), inhibitors which target PDGFRβ (10) and/or B-RAF (11, 12), has created much enthusiasm for small molecules that stabilize the inactive kinase conformation (13-15). These two molecules were cocrystallized with their respective targets, B-RAF (16) and Abl (17) kinase domains, and shown to interact in part with the allosteric site in the "DFG-out" conformation, referred to as type II inhibition. Based on the binding mode of sorafenib and imatinib, we synthesized an amino-triazole scaffold designed to target the allosteric site of both PDGFRβ and B-RAF using a combination of in silico screening and in vitro bioass...

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