CBIO-02KYNURENINE 3-MONOOXYGENASE INHIBITION SYNERGIZES WITH THE ALKYLATING CHEMOTHERAPY TEMOZOLOMIDE TO ATTENUATE PROLIFERATION IN HUMAN GLIOBLASTOMA CELLS

Abstract

BACKGROUND: Activation of the kynurenine pathway (KP) in cancer cells suppresses anti-tumor immunity, resulting partly from KP metabolite effects. The KP is the principal route of tryptophan metabolism leading to the production of metabolites, including kynurenine (KYN), anthralinic acid (AA) and nicotinamide adenine dinucleotide (NAD+). Kynurenine 3-monooxygenase (KMO) is a critical enzyme in the KP directly responsible for the production of the immunosuppressive metabolites, 3-hydroxyanthranilic acid (3-HAA) and 3-hydroxykynurenine (3-HK). Inhibition of one of the enzymes that degrades tryptophan in the KP, indoleamine 2,3-dioxygenase (IDO-1), suppresses cancer formation in animal models. However, no studies have evaluated the therapeutic potential of KMO inhibitors in brain cancer. METHODS: The effects of the KMO inhibitor, Ro 61-8048 (Ro), and the chemotherapeutic, temozolomide (TMZ), on glioblastoma (GBM) cell proliferation was evaluated using the MTS assay and GBM cell lines, U87, T98G and U138. KP metabolites were quantified using LC-MS/MS and KMO protein expression was evaluated using western blot. RESULTS: GBM cell lines expressed the KMO protein constitutively and following stimulation with the IDO-1 inducer, IFN-γ. GBM cell lines also produced the KP immunosuppressive metabolites, AA and 3-HK and increased KYN production concomitant with tryptophan catabolism following IFN-γ stimulation. KMO inhibition with Ro caused a dose-dependent decrease in GBM cell line proliferation. Ro also synergized with TMZ to decrease U87 cell proliferation more effectively than Ro treatment alone when cells were stimulated with IFN-γ. CONCLUSIONS: These findings suggest that KMO may play a significant role in GBM cell proliferation and highlight KMO inhibition as a potential new therapy for GBM. Clinically, KMO inhibition may shunt KP metabolism away from the immunosuppressive 3-HK and 3-HAA, restoring anti-tumor immunity while reducing the capacity for malignant cells to produce NAD + , which is necessary for cellular energy production, DNA repair and proliferation.