TGFBeta receptor antagonists as anticancer agents

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Transforming Growth Factor-betas are polypeptides that are constitutively secreted and activated by many carcinomas. They contribute to the tumor's ability to invade and metastasize, to induce angiogenesis and to escape from immune destruction. By the same token, cancer cells themselves are generally refractory to TGFbeta-mediated growth arrest. This particular set of circumstances raises the question whether blocking the effects of tumor-derived TGFbeta on normal tissue (stromal cells, microvascular endothelial cells and immune cells) might constitute a novel approach to cancer treatment. In the past, several different strategies have been employed to counteract the biological effects of TGFbeta in cancer and other diseases. These have included the use of TGFbeta neutralizing antibodies, of TGFbeta- binding proteins, such as decorin, and of TGFbeta1 antisense RNA oligonucleotides. Animal experiments and small-scale clinical studies using each of these approaches have provided proof of concept that inactivation of TGFbeta has the predicted anti-tumor effect. However, larger scale testing and further clinical development of any of these compounds has been marred by technical difficulties and limited availability. We now propose an alternative strategy to blocking TGFbeta action by targeting the key molecule in TGFbeta signaling, i.e. the type I TGFbeta receptor (TbetaR-I) serine-threonine kinase. Small molecular selective TbetaR-I antagonists are likely to be more effective than the approaches mentioned above, and should not be subject to the same limitations in terms of production and bioavailability. Our collaborators at SCIOS, Inc. have identified several promising lead compounds that inhibit TbetaR-I kinase activity in cell-free as well as in cellular systems in vitro. In addition, we have developed the capability to measure effects of TbetaR-I kinase inhibitors in vivo, using a proprietary highly sensitive antibody that selectively detects phosphorylated Smad2. We intend to examine the effects of lead compounds against normal cells in vitro using a number of different assays for TGFbeta's biological effects. The best TbetaR-I antagonists will then be tested for their antitumor activity against transplantable tumors in mice, with particular attention to their effects on metastasis, angiogenesis and anti-tumor immunity. Finally, optimization of the compounds in terms of potency, selectivity and bioavailability will be carried out to derive analogs with a favorable toxicity profile that can be developed further for clinical use.