Inhibition of tryptophan 2,3-dioxygenase impairs DNA damage tolerance and repair in glioma cells

Aberrant expression of tryptophan 2,3-dioxygenase (TDO) is a determinant of malignancy and immune response in gliomas in part through kynurenine (KYN)-mediated activation of the aryl hydrocarbon receptor (AhR). In the current study, we investigated the hypothesis that TDO activation in gliomas has a broad impact upon genome maintenance - promoting tolerance of replication stress (RS) and repair of DNA damage. We report that inhibition of TDO activity attenuated recovery from hydroxyurea (HU)-induced RS and increased the genotoxic effects of bis-chloroethylnitrosourea (BCNU), as fork progress was impeded when TDO-deficient glioma cells were treated with BCNU. Activation of the Chk1 arm of the replication stress response (RSR) was reduced when TDO activity was blocked prior to treatment with BCNU, whereas phosphorylation of serine 33 (pS33) on replication protein A (RPA) was enhanced – indicative of increased fork collapse. Restoration of KYN levels protected against some replication-associated effects of BCNU. Inhibition of TDO activity had a strong anti-proliferative effect on glioma-derived cells – enhancing the cytotoxic effects of BCNU. Analysis of results obtained using quantitative proteomics revealed TDO-dependent changes in several signaling pathways – including down-regulation of DNA repair factors and sirtuin signaling. Consistent with these observations, inhibition of TDO diminished SIRT7 recruitment to chromatin, which increased histone H3K18 acetylation – a key mark involved in 53BP1 recruitment to sites of DNA damage. Cells lacking TDO activity exhibited defective recruitment of 53BP1 to gH2AX foci, which corresponded with delayed repair of BCNU-induced DNA breaks. Addition of exogenous KYN increased the rate of break repair. The discovery that TDO activity modulates sensitivity to DNA damage by fueling SIRT7/53BP1 localization to chromatin and repair of BCNU-induced DNA damage highlights the potential for tumor-specific metabolic changes to influence genome stability and may have implications for glioma biology and treatment strategies. ### Competing Interest Statement The authors have declared no competing interest.