The goal of cancer immunotherapy is to restore the balance of immune system that is being used by cancer cells in order to improve their survival and cancer growth in a process called immunoediting. One of mechanisms of immunoediting is increased expression of inhibitory receptors named checkpoint inhibitors, which control peripheral tolerance and regulate intensity of immune response. Their increased expression allows tumor cells to achieve immune escape. Indolamine 2,3-dioxygenase 1 (IDO1) is a cytosolic heme containing oxidoreductase, which is involved in kynurenine pathway catabolism of tryptophane into kynurenine and other metabolites. Lowered tryptophane levels and increased kynurenine levels induce immunotolerance and tumor growth. That makes IDO1 a suitable target for cancer therapy research, that aims to restore the balance of immune system.
The aim of this thesis was to synthesize new potential IDO1 inhibitors, based on 2-(4-oxo-3-phenylisoxazolo[5,4-d]pyrimidin-5(4H)-yl)-N-phenylacetamide structure. The main synthetic pathway consisted of five steps and the synthesis of alkylating agents used for N-alkylation reaction was performed in only one step. Various analytical methods were used to determine the physicochemical properties of intermediates and final products and confirm their identity and purity. Fluorescence-based biochemical assay was used to determine the inhibitory activity of final products on IDO1.
All final products, apart from N-(4-nitrophenyl)-2-(4-oxo-3-(p-tolyl)isoxazolo[5,4-d] pyrimidin-5(4H)-yl)-N-phenylacetamide (14), were found as weak inhibitors of enzyme activity. The latter showed 45 % inhibition at 100 μM concentration, therefore being the only suitable product for further determination of IC50 value of 145 μM. We were able to synthesize one micromolar IDO1 inhibitor and gain new data about the effects of substitution on the phenyl ring attached to isoxazolo and acetamide moiety, that can be used for future work and development of IDO1 inhibitors.
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