Cancer is a disease caused by uncontrolled and abnormal cell growth. There are quite a few ways of treatment with immunotherapy being the most recent one, which is based on the restoration of the immune system's balance. Indoleamine 2,3-dioxygenase 1 (IDO1) is a heme-containing oxidoreductase that catalyzes the breakdown of L-tryptophan to L-kynurenine and later toxic kynurenine derivates, which can lead to the suppresion of the immune response and tumor spread. With new discoveries of immunosuppressive functions and the role of IDO1 in the immune escape of cancer cells, the scientists identified the activity of the enzyme in favor of cancer. For this reason, IDO1 represents an interesting target for anticancer drug development. IDO1 inhibition is thus an innovative and promising strategy for the treatment of many types of cancer. There are quite a few inhibitors in clinical studies that could be used in the future to support cancer treatment.
In this Master's thesis, we synthesized seven final compounds using five-step synthetic procedure, on the basis of a known IDO1 inhibitor 5-(2-(3,4-dihydroquinolin-1(2H)-yl)-2-oxoethyl)-3-(4-fluorophenyl)isoxazolo[5,4-d]pyrimidin-4(5H)-one, previously discovered by virtual screening. All final compounds are structurally similar to each other as they are based on the same basic scaffold 3-(4-fluorophenyl)isoxazolo[5,4-d]pyrimidin-4(5H)-one, to which various substituents were attached via the amide nitrogen. The identity and purity of the final compounds were confirmed by analytical methods, and their inhibitory activity on the IDO1, indolamine 2,3-dioxygenase 2 (IDO2) and tryptophan 2,3-dioxygenase (TDO) enzymes was evaluated by the biochemical assay.
None of the final compounds exhibited a sufficient inhibitory activity that it would make sense to determine IC50 values. The compound 3-(4-fluorophenyl)-5-(4-nitrobenzyl)isoxazolo[5,4-d]pyrimidin-4(5H)-one compound (8) showed the most potent inhibitory effect on IDO1 with 24 % inhibiton at the concentration of 100 µM. With our study we proved that the presence of an amide moiety in substituents attached to isoxazolo[5,4-d]pyrimidin-4(5H)-one is essential for potent IDO1 inhibitory activity.
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