A new pro-apoptotic therapy for Acute Myeloid Leukaemia using MEDS433, a potent human Dihydroorotate Dehydrogenase inhibitor

In acute myeloid leukaemia (AML), blasts lose their ability to differentiate into mature cells and undergo apoptosis. Accordingly, a proapoptotic and differentiating therapy (arsenic and all trans retinoic acid, ATRA) has dramatically improved survival in acute promyelocytic leukaemia; however, such combination therapy is not available for other AML subtypes. While, in 2016, inhibition of dihydroorotate dehydrogenase (DHODH), a key enzyme of the pyrimidine biosynthesis, was found to induce differentiation in several AML models. In fact, brequinar (BRQ) was utilized in vivo studies.1We are optimising hDHODH inhibitors to improve potency and drug-like proprieties. Moreover, we would like to evaluate how different parameters such as, pKa, LogD7.4 of different carboxylic acid bioisosteres can influence in vitro and in vivo studies. The main objective is to identify the best inhibitor suitable for use in in vivo studies on AML animal model. In this work we will present a new generation of hDHODH inhibitors able to reach the enzymatic BRQ inhibition potency levels. Our data showed that MEDS433, the best of two series, induced apoptosis in multiple AML cell lines, not only because of differentiation, but also directly. Its combination with antileukemic agents further increased the apoptotic rate, but when experiments were performed in the presence of physiological uridine concentrations, results were less impressive. Conversely, the combination of MEDS433 with dipyridamole induced metabolic lethality and differentiation in all AML cell lines; this extraordinary synergism was confirmed on AML primary cells with different genetic backgrounds and was unaffected by physiological uridine concentrations, predicting in human activity. 3 Finally, our preliminary results from in vivo experiments showed that i) MEDS433 wasn’t toxic on Balb/c mice after 5 weeks of intraperitoneal administration at two different doses 10 and 25 mg/Kg and during acute toxicity experiment was not toxic ad dose of 1 g/Kg; ii) the half-life was limited to 3-4 hours and iii) MEDS433 had a good antileukemic activity (approximately 50% reduction of the tumour volume compared with control, after 18 days of treatment in THP1-xenograft models obtained from NSG mice). Theoretical design, modeling, synthesis, SAR, X-ray crystallographic data, biological assays, Drug-Like proprieties, pharmacokinetic studies, and in vivo evaluations on AML models will be here presented and discussed.