Proline Intake Dampens Radiosensitivity in Prostate Cancer Cells by Targeting PRODH/MAPK Pathway

Radiotherapy remains a standard treatment for prostate cancer (PCa), inducing tumor cell death and apoptosis. However, its efficacy depends on various factors, including tumor cell metabolism. In this study, we investigated whether alterations in proline metabolism influence the response of prostate cancer cells to radiation. The radiosensitivity of LNCaP and C4-2 cells after X-ray irradiation was assessed using colony formation and tumor-sphere assays, while Matrigel invasion assays evaluated in vitro cell invasion. We then examined the effect of radiation on proline dehydrogenase (PRODH) expression and MAPK/p-MAPK signaling via Western blotting. To further explore the role of proline metabolism in radiation response, we tested the impact of exogenous proline supplementation and PRODH knockdown on radiation efficacy in LNCaP and C4-2 cells using the same assays. Finally, in vivo validation was performed using xenograft tumor models in nude mice to determine how proline and PRODH modulation influences radiation outcomes. Our results demonstrated that X-ray irradiation significantly inhibited prostate cancer cell growth and invasion. However, this effect was attenuated by exogenous proline supplementation. Following irradiation, proline dehydrogenase (PRODH) expression was upregulated, while phosphorylated MAPK (p-MAPK) levels were downregulated. Notably, the suppressive effect of proline on radiation efficacy was abolished upon PRODH knockdown, suggesting a key role for proline metabolism in radiation response. In vivo studies further supported these findings: X-ray irradiation effectively suppressed tumor growth in xenograft mouse models, but this therapeutic effect was diminished when mice were treated with proline solution. These observations align with our in vitro data, reinforcing the modulatory role of proline metabolism in radiosensitivity. While radiotherapy demonstrates robust antitumor effects in prostate cancer, our findings reveal that proline metabolism significantly impairs radiation efficacy in both cellular and animal models.