Withanolide Compounds as Inhibitors of Fibrosis and Identification of Molecular Targets for Anti-Fibrotic Drug Development

Provided are methods for screening for drugs effective for treating fibrotic conditions. One screening method comprises exposing a cell to a test compound, monitoring the effect of the test compound on the amount or form of a cell molecule, comparing the amount or form of the cell molecule with the result obtained by treatment of the cell with an anti-fibrotic -effective amount of a withanolide compound, and selecting a drug effective for treating a fibrotic disease based on the ability of the test compound to provide the effect obtained by the withanolide compound on the cell molecule. Also provided is a method of treating a fibrotic disease comprising administering an anti-fibrotic effective amount of a withanolide compound to a mammal in need of treatment for fibrosis

Withanolides, Probes and Binding Targets and Methods of Use Thereof

Novel withanolide chemical genetic probes identify the in vivo binding target of withaferin A, which is the intermediate filament type III protein vimentin. In addition, a withanolide-based small molecule screening method screens drug candidates that target intermediate filament type III proteins. The method includes introducing a tagged linker covalently bonded to the withanolide molecule to form a withanolide probe. Better or alternative small molecule compounds as potential drug candidates can be generated based on their likely affinity for the determined binding site in vimentin. The affinity labeled withanolide can also be used to find intermediate filament-associated proteins using chemical proteomics by extracting proteins from cells that were exposed to withanolide-biotin analog. The withanolide probes can be used to monitor expression of vimentin, in tumor samples or other diseased tissues. Withaferin analogs can be used as a treatment for diverse vimentin-associated disorders, such as cancers, angiofibrotic diseases, and chronic inflammation

Withaferin A Effectively Targets Soluble Vimentin in the Glaucoma Filtration Surgical Model of Fibrosis

Withaferin A (WFA) is a natural product that binds to soluble forms of the type III intermediate filament (IF) vimentin. Currently, it is unknown under what pathophysiological contexts vimentin is druggable, as cytoskeltal vimentin-IFs are abundantly expressed. To investigate druggability of vimentin, we exploited rabbit Tenon\u27s capsule fibroblast (RbTCF) cell cultures and the rabbit glaucoma filtration surgical (GFS) model of fibrosis. WFA potently caused G₀/G₁ cell cycle inhibition (IC₅₀ 25 nM) in RbTCFs, downregulating ubiquitin E3 ligase skp2 and inducing p27(Kip1) expression. Transforming growth factor (TGF)-ß-induced myofibroblast transformation caused development of cell spheroids with numerous elongated invadopodia, which WFA blocked potently by downregulating soluble vimentin and α-smooth muscle actin (SMA) expression. In the pilot proof-of-concept study using the GFS model, subconjunctival injections of a low WFA dose reduced skp2 expression in Tenon\u27s capsule and increased p27(Kip1) expression without significant alteration to vimentin-IFs. This treatment maintains significant nanomolar WFA concentrations in anterior segment tissues that correspond to WFA\u27s cell cycle targeting activity. A ten-fold higher WFA dose caused potent downregulation of soluble vimentin and skp2 expression, but as found in cell cultures, no further increase in p27(Kip1) expression was observed. Instead, this high WFA dose potently induced vimentin-IF disruption and downregulated α-SMA expression that mimicked WFA activity in TGF-ß-treated RbTCFs that blocked cell contractile activity at submicromolar concentrations. These findings illuminate that localized WFA injection to ocular tissues exerts pharmacological control over the skp2-p27(Kip1) pathway by targeting of soluble vimentin in a model of surgical fibrosis

Small molecule antiangiogenic probes of the ubiquitin proteasome pathway: potential application to choroidal neovascularization. Invest Ophthalmol Vis Sci 47

PURPOSE. To characterize the angiogenic and inflammatory responses of human choroidal endothelial cells (HCECs) to stimulators and inhibitors of the ubiquitin proteasome pathway (UPP). METHODS. The regulation of the UPP by the inhibitor withaferin A and its congener, withanolide D, two natural products derived from the medicinal plant Withania somnifera was assessed in the three-dimensional endothelial cell sprouting assay (3D-ECSA), by using HCEC-and human umbilical vein endothelial cell (HUVEC)-derived spheroids embedded in a collagen I matrix. Western blot analysis was used to investigate the effect of withanolides on IB-␣, polyubiquitination, and heme oxygenase (HO)-1 regulation in HCEC and HUVEC cultures. RESULTS. HCECs, like HUVECs, responded to fibroblast growth factor-2, vascular endothelial growth factor, and tumor necrosis factor (TNF)-␣ stimulation and sprouted vessel-like structures in collagen I matrix. However, HCECs were slower to generate these sprouting vessels, when compared with HUVECs. The extent of inhibition of endothelial cell sprouting in 3D matrix, the blockade of TNF-␣-induced IB-␣ degradation, levels of global polyubiquitinated proteins, and induced production of HO-1 in response to treatment by the withanolides in cultured endothelial cells was similarly regulated between HCECs and HUVECs. CONCLUSIONS. HCECs share with HUVECs a similar response to UPP inhibitors, suggesting that this well-conserved pathway that regulates angioinflammatory mechanisms could be exploited for drug-targeting in the development of novel agents for CNV treatment. (Invest Ophthalmol Vis Sci. 2006;47: 4138 -4145