CypA: A Potential Target of Tumor Radiotherapy and/or Chemotherapy

Cyclophilin A (CypA) is a ubiquitous and highly conserved protein. CypA, the intracellular target protein for the immunosuppressant cyclosporine A (CsA), plays important cellular roles through peptidyl-prolyl cis-trans isomerase (PPIase). Increasing evidence shows that CypA is up-regulated in a variety of human cancers. In addition to being involved in the occurrence and development of multiple tumors, overexpression of CypA has also been shown to be strongly associated with malignant transformation. Surgery, chemotherapy and radiotherapy are the three main treatments for cancer. Che-motherapy and radiotherapy are often used as direct or adjuvant treatments for cancer. However, various side effects and resistance to both chemotherapy and radiotherapy bring great challenges to these two forms of treatment. According to recent reports, Cy-pA can improve the chemosensitivity and/or radiosensitivity of cancers, possibly by af-fecting the expression of drug-resistant related proteins, cell cycle arrest and activation of the mitogen-activated protein kinase (MAPK) signaling pathways. In this review, we fo-cus on the role of CypA in cancer, its impact on cancer chemotherapeutic and radiothera-py sensitivity, and the mechanism of action. It is suggested that CypA may be a novel po-tential therapeutic target for cancer chemotherapy and/or radiotherapy.