Targeting Myeloid Leukemias Using human Dihydroorotate Dehydrogenase Inhibitors Based on 2-Hydroxypyrazolo[1,5-a]pyridine Scaffold: Overcoming of Metabolic Issues

Human Dihydroorotate Dehydrogenase (hDHODH), a mitochondrial enzyme that plays a pivotal role in the de novo pyrimidine biosynthesis, has been associated to Acute Myelogenous Leukemia (AML), as hDHODH inhibitors are able to restore myeloid differentiation (1). In recent years, we designed potent hDHODH inhibitors applying a scaffold-hopping approach to brequinar’s structure (2). By investigating the lead compound’s SAR, we recently discovered compound 1 (Figure), a candidate superior to brequinar in terms of in vitro potency. Unfortunately, compound 1 showed in vitro metabolic instability, as it soon undergoes to hydroxylation on alkoxy side chain by microsomal enzymes (3). In this occasion, we investigated on the metabolic hydroxylation site through the synthesis of the possible products of microsomal metabolism according to literature (4) and their comparison to compound 1’ s own metabolite in high resolution mass spectrometry (HR-MS); then we designed a new generation of hDHODH inhibitors protected from metabolic oxidation on the alkoxy side chain. Design, synthesis, in vitro metabolism and biological characterization of the new developed compounds are here described and discussed. 1. Sykes, D. B. et al. Inhibition of Dihydroorotate Dehydrogenase Overcomes Differentiation Blockade in Acute Myeloid Leukemia. Cell. 2016, 167(1), 171-186 2. Sainas, S. et al. Targeting Myeloid Differentiation Using Potent 2-Hydroxypyrazolo[1,5- a]pyridine Scaffold-Based Human Dihydroorotate Dehydrogenase Inhibitors. J. Med. Chem. 2018, 61, 6034-6055. 3. Sainas, S. et al. Targeting Acute Myelogenous Leukemia using potent human dihydroorotate dehydrogenase inhibitors based on the 2-hydroxypyrazolo[1,5- a]pyridine scaffold: SAR of the biphenyl moiety. J. Med. Chem. 2021, in press. 4. Testa, B. and Clement, B. Biotransformation Reactions and Their Enzymes. The Practice of Medicinal Chemistry: Fourth Edition. 2015, 561-584.