Repurposing Sulfasalazine as a Radiosensitizer in Hypoxic Human Colorectal Cancer

Abstract

xCT overexpression in cancer cells has been linked to tumor growth, metastasis and treatment resistance. Sulfasalazine (SSZ), an FDA-approved drug for the treatment of rheumatoid sarthritis, and inflammatory bowel diseases, has anticancer properties via inhibition of xCT, leading to the disruption of redox homeostasis. Since reactive oxygen species (ROS) are pivotal for the efficacy of radiotherapy (RT), elevated levels of ROS are associated with improved RT outcomes. In this study, the influence of SSZ treatment on the radiosensitivity of human colorectal cancer (CRC) cells was investigated. Our principal finding in human HCT116 and DLD-1 cells was that SSZ enhances the radiosensitivity of hypoxic CRC cells but does not alter the intrinsic radiosensitivity. The radiosensitizing effect was attributed to the depletion of glutathione and thioredoxin reductase levels. In turn, the reduction leads to excessive levels of ROS, increased DNA damage, and ferroptosis induction. Confirmation of these findings was performed in 3D models and in DLD-1 xenografts. Taken together, this study is a stepping stone for applying SSZ as a radiosensitizer in the clinic and confirms that xCT in cancer cells is a valid radiobiological target.

Ferroptosis: Frenemy of Radiotherapy

“…Lately, the role of ferroptosis in RT efficacy has been under intensive investigation. This association has been observed in multiple cancer cell lines, including lung cancer, oesophageal cancer, breast cancer, fibrosarcoma, colorectal cancer, and melanoma [56][57][58][59]. Increased quantity of lipid peroxidation and enhanced prostaglandin-endoperoxide synthase 2 (PTGS2-a ferroptosis marker gene) or malondialdehyde (MDA) levels were observed in different cell lines after single dose ionizing radiation (IR).…”

“…The interplay between ferroptosis inducers (FINs) and RT has been established. A multitude of FINs, including erastin, sulfasalazine, sorafenib, RSL3, ML162, IKE, and FIN56, can synergize with RT in vitro and in vivo [56][57][58][59]. Moreover, the first clinical link between ferroptosis and radiotherapy was elucidated by Lei et al The degree of ferroptosis induction in samples of oesophageal cancer patients showed a correlation with disease-free survival in response to RT [58].…”

“…The radiomodulatory properties of SSZ have been established in various cancer cells under normoxic conditions, including melanoma cells, glioma cells, osteosarcoma cells, ovarian cancer cells, and non-small cell lung cancer cells (NSCLC) [56,58,81,82]. Additionally, SSZ had radiosensitizing effects on hypoxic colorectal cancer cells [59]. In melanoma and glioma cells, the mechanisms responsible for the observed effects were attributed to increased DNA damage following enhanced ROS levels and cell cycle arrest [81,82].…”

“…Nevertheless, the link with ferroptosis induction was not studied. More recent papers have established ferroptosis induction as an underlying mechanism for radiosensitization by SSZ [56,58,59]. Exploration of SSZ as a radiosensitizer in clinical trials is limited.…”