Targeting oncogenic TβRI signaling inhibits androgen-independent prostate cancer growth and metastasis.

Metastatic castration-resistant prostate cancer (mCRPC) remains the primary cause of prostate cancer-related mortality. Despite the availability of treatments, the molecular mechanisms underlying tumor invasion and metastasis are not fully understood, highlighting the need for novel therapeutic strategies. In this study, we developed fully human monoclonal antibodies (mAbs) that prevent the proteolytic cleavage of the transforming growth factor-beta (TGFβ) type I receptor (TβRI) by steric hindrance. This cleavage, mediated by the metalloprotease ADAM17 (a disintegrin and metalloprotease domain 17; also known as TACE), results in the generation of a soluble intracellular domain (TβRI-ICD) that is translocated to the nucleus of castration-resistant prostate cancer (CRPC) cells and promotes epithelial-to-mesenchymal transition (EMT), invasion, and metastasis. High levels of TGFBR1 correlated with poor survival in two independent clinical cohorts of patients with mCRPC, and a strong positive correlation between TGFBR1 and ADAM17 expression was observed. In a preclinical human orthotopic mCRPC mouse model, treatment with therapeutic mAbs effectively prevented the nuclear accumulation of TβRI-ICD, inhibited EMT, and suppressed tumor growth, invasion, and metastasis. Notably, the therapeutic effect was comparable to that of docetaxel, a current standard-of-care chemotherapy, without noticeable side effects on body weight, proximal aorta or heart function detected in immune-deficient mice. These findings suggest that targeting TβRI cleavage using specific mAbs is a novel precision medicine approach for the treatment of mCRPC. By selectively blocking the prometastatic activity of TβRI-ICD without disrupting physiological TGFβ signaling, this strategy may provide a safer and more effective alternative to existing therapies for advanced prostate cancer.