Targeting the human Dihydroorotate Dehydrogenase (hDHODH) by a Scaffold Hopping Bioisosteric approach using Hydroxylated Pentatomic Heterocycles

The human isoform of the dihydroorotate dehydrogenase enzyme (hDHODH) catalyzes the fourth step of the de novo pyrimidine synthesis, a biosynthetic pathway enhanced in proliferating cells such as activated T-lymphocytes, and cancer cells. The efficacy of hDHODH inhibitors in the treatment of rheumatoid arthritis and multiple sclerosis has been evaluated, and leflunomide (Arava®) and its active metabolite teriflunomide (Aubagio®) have been already approved for therapy. Brequinar is another well-studied hDHODH inhibitor, but it was unsuccessfully evaluated against a number of tumor categories due to several drug-related side effects.1 Inside the inhibitor-binding site, conventionally divided into five subsites, two different binding-modes have been described in literature.2 In recent years our group at DSTF has directed its efforts towards the investigation of a general tool able to mimic the carboxyl group. We focused our attention on a pool of over ten acidic hydroxylated pentatomic heterocyclic systems. The result of such work was the development of a flexible tool capable of adapting to the requirements of different targets, both in terms of acidity as well as general chemio-physical profiles. Starting from structural information from both brequinar and teriflunomide, a scaffold hopping approach was applied using our heterocyclic panel affording a new series of products able to establish additional interactions with subsites 3 and 4. The general model of these compounds (1) is a hydroxylated heterocycle linked to a biphenyl system through an amide bond.3 According to molecular modeling studies, the deprotonated acidic moiety should interact with residues Arg136 and Gln47 of subsite 2 (Brequinar-like binding-mode2), while the biphenyl system may establish lipophilic interactions with residues of subsites 1 and 5 (Figure a). New compounds showed inhibitory activity on recombinant hDHODH with IC50 values in the nanomolar range and inhibition of human T-cell proliferation comparable to brequinar and teriflunomide. Our theoretical design, modeling, synthesis, SAR and biological assays, as well as cell viability, proliferation, cytotoxicity and immunosuppression results are presented in detail. Fig.