Human immune system is a complex system of different cells, tissues and organs. It responds appropriately to internal or external threats, one of which is the development of cancer cells. Many internal and external factors can affect the transformation of a normal cell to a cancerous one and among them is an intracellular cytosolic enzyme indoleamine 2,3-dioxygenase 1 (IDO1) has an important role in cancer metastasis. IDO1 is involved in the degradation pathway of the essential amino acid tryptophan (Trp), known as Kynurenine pathway (KP). IDO1 expression in cells regulates the ratio between Trp
concentration and concentration of metabolites of the KP, which have immunosuppressant activity, thus blocking the immune system response to cancer cells. The number of newly discovered IDO1 inhibitors is increasing every day
since big pharma companies are investing in their development, and many of them are already present in clinical trials.
In our Master thesis we synthesized 5 final compounds, which were evaluated for their inhibitory activity. All five synthesized compounds possess the same scaffold,
which is based on a virtual screening hit compound 3-(4-
fluorophenyl)[1,2]isoxazolo[5,4-d]pyrimidin-4(5H)-on. All compounds were confirmed by different analytical methods and their inhibitory activity was evaluated by biochemical assay based on fluorescence measurement. Among synthesized compounds, which differ in substitution on the phenyl ring, only two showed significant inhibitory activity. IC50 values for compounds 12 in 13 was determined in low micromolar range, thus we could assume that cyclohexyl ring or trifluoromethyl group fits into the pocket B in the enzyme’s active site, which was confirmed by molecular docking of compound 12 into the crystal structure of IDO1.With appropriate optimization compound 12 represents the important starting point for the development of potent IDO1 inhibitor, which could be used as potential antitumor agent.
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