Indoleamine 2,3-dioxygenase mediates immune-independent human tumor cell resistance to olaparib, gamma radiation, and cisplatin

// Saman Maleki Vareki 1,5 , Mateusz Rytelewski 1,5 , Rene Figueredo 5 , Di Chen 2 , Peter J. Ferguson 3,5 , Mark Vincent 3,5 , Weiping Min 2 , Xiufen Zheng 2 , and James Koropatnick 1,2,3,4,5 1 Department of Microbiology and Immunology, Western University, London, Ontario, Canada 2 Department of Pathology, Western University, London, Ontario, Canada 3 Department of Oncology, Western University, London, Ontario, Canada 4 Department of Physiology and Pharmacology, Western University, London, Ontario, Canada 5 Cancer Research Laboratory Program, Lawson Health Research Institute, London, Ontario, Canada Correspondence: James Koropatnick, email: // Keywords : IDO- PARP- OLAPARIB- RADIATION- CISPLATIN- BRCA2 Received : March 11, 2014 Accepted : April 16, 2014 Published : April 18, 2014 Abstract Indoleamine 2,3-dioxygenase-1 (IDO) is an immunosuppressive molecule expressed by most human tumors. IDO levels correlate with poor prognosis in cancer patients and IDO inhibitors are under investigation to enhance endogenous anticancer immunosurveillance. Little is known of immune-independent functions of IDO relevant to cancer therapy. We show, for the first time, that IDO mediates human tumor cell resistance to a PARP inhibitor (olaparib), gamma radiation, cisplatin, and combined treatment with olaparib and radiation, in the absence of immune cells. Antisense-mediated reduction of IDO, alone and (in a synthetic lethal approach) in combination with antisense to the DNA repair protein BRCA2 sensitizes human lung cancer cells to olaparib and cisplatin. Antisense reduction of IDO decreased NAD + in human tumor cells. NAD + is essential for PARP activity and these data suggest that IDO mediates treatment resistance independent of immunity and at least partially due to a previously unrecognized role for IDO in DNA repair. Furthermore, IDO levels correlated with accumulation of tumor cells in G 1 and depletion of cells in G 2 /M of the cell cycle, suggesting that IDO effects on cell cycle may also modulate sensitivity to radiation and chemotherapeutic agents. IDO is a potentially valuable therapeutic target in cancer treatment, independent of immune function and in combination with other therapies.