Development of TGF-beta antagonists for cancer therapy

基于有希望的临床前结果，各种转化生长因子-β途径拮抗剂正处于治疗晚期癌症的早期临床试验阶段。然而，考虑到转化生长因子-β的复杂生物学，成功开发用于癌症治疗的转化生长因子-β拮抗剂将取决于对这些药物如何发挥作用的清楚了解，以及如何选择将从这种治疗中受益的患者的相关问题。使用12个转移性乳腺癌小鼠同基因同种异体移植模型，以转移负荷为主要终点，我们揭示了对转化生长因子-β拮抗的异质性反应。在某些模型中，阻断转化生长因子-β途径可抑制肿瘤转移，而对其他模型则无影响。重要的是，在这个扩展的模型小组中，我们发现转化生长因子-β拮抗剂实际上在25%的模型中促进了转移，这表明良好的预测性生物标记物将对临床安全有效地应用转化生长因子-β拮抗剂至关重要。我们已经证明了许多符合逻辑的或文献建议的候选生物标记物(例如。在这个更大的小组中，转化生长因子-β表达水平、p53突变状态)不能可靠地预测治疗结果。对未经治疗的原发肿瘤的转录本进行分析，可以确定对转化生长因子-β拮抗的抑制和刺激反应具有特异性的基因特征。将这些信号应用于人类乳腺癌转录数据集表明，患有雌激素受体阴性疾病的患者，特别是基础类型和克拉丁低亚型的患者，可能最有可能对转化生长因子-β拮抗剂产生预期的治疗反应。通过分析小鼠模型组对转化生长因子-β的体外反应，我们假设转化生长因子-β拮抗的不良刺激作用是由于干扰转化生长因子-β对肿瘤干细胞亚群的抑制作用。我们正在利用我们的伙伴项目Zia BC 005785中开发的癌症干细胞报告以及其他正交技术，在体内测试这是否属实。目前，转化生长因子-β研究领域的一个主要障碍是相对缺乏关于转化生长因子-β在体内稳态和疾病中何时发出信号的信息。为了解决这个问题，我们已经产生并严格验证了一个转基因的转化生长因子-β途径报告鼠，在其中，具有活跃的转化生长因子-β信号的组织通过表达荧光蛋白而发出绿色光。令人惊讶的是，转化生长因子-β途径在正常成年小鼠的心脏瓣膜中高度活跃，与先前用转化生长因子-β信号的小分子抑制剂所显示的肿瘤外毒性一致。因此，这只小鼠对成年动物中转化生长因子-β途径的激活模式以及这些模式如何受到药物抑制的影响提供了重要的见解。

Based on promising preclinical results, a variety of TGF-beta pathway antagonists are in early phase clinical trials for the treatment of advanced cancer. However, given the complex biology of TGF-beta, the successful development of TGF-beta antagonists for cancer therapy will depend on a clear understanding of how these agents work, and the related question of how to select patients who will benefit from this type of treatment. Using a panel of 12 mouse syngeneic allograft models of metastatic breast cancer, with metastatic burden as the primary endpoint, we uncovered heterogeneous responses to TGF-beta antagonism. TGF-beta pathway blockade inhibited metastasis in some models, while having no effect on others. Importantly, in this expanded model panel, we found that TGF-beta antagonism actually stimulated metastasis in 25% of the models, suggesting that good predictive biomarkers will be crucial for safe and effective deployment of TGF-beta antagonists clinically. We have demonstrated that many of the logical or literature-suggested candidate biomarkers (eg. TGF-beta expression levels, p53 mutation status) do not reliably predict therapeutic outcome in this larger panel. Analysis of the transcriptomes of treatment-naive primary tumors allowed identification of gene signatures that were specific to the inhibitory vs the stimulatory response to TGF-beta antagonism. Applying these signatures to human breast cancer transcriptomic datasets suggested that patients with estrogen receptor-negative disease, particularly of the basal and claudin-low subtypes, might be most likely to have the desired therapeutic response to TGF-beta antagonists. Analysis of in vitro responses to TGF-beta across the mouse model panel led us to hypothesize that the undesirable stimulatory effect of TGF-beta antagonism is due to interference with inhibitory effects of TGF-beta on the cancer stem cell subpopulation. We are working to test whether this is true in vivo, using the cancer stem cell reporter developed in our companion project ZIA BC 005785, as well as other orthogonal techniques. Currently, a major barrier in the TGF-beta field is the relative lack of information about when an where TGF-beta signals in the adult organism in homeostasis and disease. To address this issue, we have generated and rigorously validated a transgenic TGF-beta pathway reporter mouse, in which tissues with active TGF-beta signaling light up green through expression of a fluorescent protein. Strikingly the TGF-beta pathway is highly active in the heart valves of normal adult mice, consistent with previously demonstrated off-tumor toxicities seen with small molecule inhibitors of TGF-beta signaling. Thus this mouse is giving important insights into patterns of TGF-beta pathway activation in the adult animal and how these are affected by pharmacologic inhibition.