TGFBeta receptor antagonists as anticancer agents

转化生长因子-β是一种由多种癌症结构性分泌和激活的多肽。它们有助于肿瘤的侵袭和转移、诱导血管生成和逃避免疫破坏。出于同样的原因，癌细胞本身通常对转化生长因子β介导的生长抑制是无效的。这种特殊的情况提出了一个问题，即阻断肿瘤来源的TGFbeta对正常组织(间质细胞、微血管内皮细胞和免疫细胞)的影响是否可能构成癌症治疗的新方法。在过去，有几种不同的策略被用来抵消肿瘤生长因子β在癌症和其他疾病中的生物效应。这些措施包括使用转化生长因子β中和抗体、转化生长因子β结合蛋白，如核心蛋白，以及转化生长因子β1反义RNA寡核苷酸。使用这些方法的动物实验和小规模临床研究都提供了概念上的证据，即灭活TGFbeta具有预期的抗肿瘤效果。然而，这些化合物中任何一种的更大规模的测试和进一步的临床开发都受到技术困难和可获得性有限的影响。我们现在提出了一种替代策略，通过靶向TGFbeta信号中的关键分子，即I型TGFbeta受体(TbetaR-I)丝氨酸-苏氨酸激酶来阻断TGFbeta的作用。小分子选择性TbetaR-I拮抗剂可能比上述方法更有效，在生产和生物利用度方面不应受到同样的限制。我们在Scios，Inc.的合作者已经确定了几种有希望的先导化合物，它们在体外细胞系统和细胞系统中抑制TbetaR-I激酶的活性。此外，我们已经开发了在体内测量TbetaR-I激酶抑制剂的效果的能力，使用一种专有的高度敏感的抗体，选择性地检测磷酸化的Smad2。我们打算在体外使用多种不同的方法来检测铅化合物对正常细胞的影响，以检测转化生长因子β的生物学效应。然后将测试最好的TbetaR-I拮抗剂对小鼠可移植肿瘤的抗肿瘤活性，特别关注它们对转移、血管生成和抗肿瘤免疫的影响。最后，将从效力、选择性和生物利用度方面对这些化合物进行优化，以获得具有良好毒性特征的类似物，这些类似物可以进一步开发用于临床。

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.