CML-164 Dihydroorotate Dehydrogenase Inhibition Reveals Metabolic Vulnerability in Chronic Myeloid Leukemia

Context: There are chronic myeloid leukemia (CML) patients who show resistance to TKI therapy and are prone to progress to more advanced phases of the disease, and new therapeutic approaches are needed. Our study shows that CML cells are vulnerable to dihydroorotate dehydrogenase (DHODH) inhibition mediated by Meds433, a potent DHODH inhibitor developed by our group. Objective: Pyrimidine supply in resting and differentiated cells primarily relies on the salvage pyrimidine pathway, which is energetically affordable. This level of nucleotide production for fast-proliferating leukemic cells is insufficient, and they have to fulfill their needs via the de novo pathway. In this study, we shed light on the role of DHODH inhibition in CML and how it can be a promising approach for targeting leukemic cells. Design: Sixty bone marrow samples and peripheral blood of newly diagnosed CML patients and 4 TKI-resistant patients were collected. In-vivo, in-vitro, and ex-vivo experiments were performed on primary CML CD34+ and various CML cell lines. Results: Our data showed that DHODH is highly active in CML stem/progenitor cells, which supports a high proliferation capacity. Meds433, by targeting DHODH enzyme activity, induced apoptosis, cell growth, and cell cycle arrest in leukemic cells. Meanwhile, the administration of Meds433 reduced tumor growth and tumor burden in treated mice. Interestingly, the addition of exogenous uridine rescued all of the biological effects caused by DHODH inhibition, demonstrating the selectivity of Meds433. Based on RNA-seq data, most upregulated gene sets were related to apoptosis and immune response and most downregulated gene sets were related to MYC targets and metabolism pathways, which was confirmed by metabolic profile analysis. Also, we found that glutamic pyruvic acid transaminase 1 (GPT1) is among the top downregulated genes after treating CML cells with Meds433, and overexpressing GPT1 in CML cells interfered with the effect of Meds433. These data show that GPT1 downregulation could be one of the possible mechanisms in which Meds433 acts in CML. Conclusions: Our study shows that DHODH inhibition is a promising approach for targeting CML stem/progenitor cells and may help more patients discontinue the therapy. This work was supported by Associazione Italiana per la Ricerca sul Cancro: IG-23344