Radiation reprograms fibroblasts to drive prostate cancer therapy resistance.

Radiotherapy is a mainstay treatment for localized prostate cancer (PCa). Yet, radiation resistance remains a major clinical obstacle. Here, radiation induced a BMP/CD105-dependent metabolic shift in the tumor microenvironment that facilitates PCa cell survival. Using prostate tumor models and fibroblast cultures, we show that radiation enhances epithelial BMP ligand production, which promotes fibroblastic CD105 signaling. Metabolomic analysis upon radiation revealed that fibroblastic CD105 signaling elevated key enzymes involved in mitochondrial biogenesis (PGC1α) and ketogenesis (HMGCS2). The increased production of β-hydroxybutyrate in the tumor microenvironment sustained PCa cell energy metabolism and enhanced DNA repair upon radiation stress. Blocking BMP signaling through carotuximab (ENV105), a CD105-targeting antibody, disrupted epithelial-fibroblast crosstalk, resulting in decreased β-hydroxybutyrate within the tumor microenvironment. This attenuation of fibroblast-mediated metabolic support increased DNA damage and apoptosis, sensitizing PCa cells to radiation. In subcutaneous mouse models, grafting PCa cells with CD105-KO or HMGCS2-KO fibroblasts yielded smaller tumors following radiation compared with wild-type fibroblast controls. Across subcutaneous and orthotopic models, combined treatment with carotuximab and irradiation reproducibly achieved superior tumor volume reduction relative to single-agent therapy. This study identified the BMP/CD105 axis as a key pathway in radiation resistance, highlighting the potential of targeting fibroblastic CD105 with carotuximab to enhance radiation sensitivity.