First bioconjugates in the role of highly effective human dihydroorotate dehydrogenase inhibitors: Synthesis, pharmacological, toxicological and hydrolytic stability studies of α-amino acid-modified pyrrolo[3,4-c]quinoline-1,3-dione scaffold.

Human dihydroorotate dehydrogenase (hDHODH) represents an attractive target for the treatment of cancer, diabetes, anti-infective and autoimmune diseases. In drug development, hDHODH inhibitors with great potency, good chemical stability and low toxicity open the broad therapeutic perspectives. Accordingly, this study identified the first bioconjugates as highly effective compounds in inhibition of hDHODH. Pyrrolo[3,4-c]quinoline-1,3-dione scaffold was modified with the selected α-amino acids in a new simple synthetic protocol giving the desired derivatives in good yields and high purity. Tyrosine bioconjugate 4g was found to be the most potent hDHODH inhibitor (IC50 = 32 nM) with an excellent cytotoxic profile on the healthy HaCaT cells and favorable lipophilicity. In the experiments with enzymes simulating oral, gastric and duodenal digestion, 4g demonstrated good resistance to degradation providing a sufficient level of bioavailability. In addition, the objective of the study was to evaluate the comparative differences in toxicological effects between the 4g and leflunomide on rat liver and kidney injury markers and parameters of redox homeostasis in erythrocytes. The bioactive conformation of 4g on the hDHODH, determined using molecular docking, highlighted key interactions within the hDHODH binding site and provides a rational basis for further optimization.