Cell-targeted glutamine antagonists as a novel therapy for lymphoma

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Every 3 minutes approximately one person in the United States is diagnosed with a blood cell cancer with an estimated 171,550 new cases in 2016. A projected 1,237,824 people are either living with the disease, or are in remission. In spite of the fact there are a number of approved therapies, the American Cancer Society estimates there will be almost 58,000 deaths this year alone. While a number of hematologic malignancies are cured using cytotoxic chemotherapy in younger patients (e.g. Hodgkins Disease, Acute Lymphocytic Leukemia, Diffuse Large Cell Lymphoma, Burkitt's lymphoma), the more intense side effects in older patients results in less sanguine outcomes. Thus an alternative approach is not only needed in general, but particularly desirable in older patients. We and others have shown that the transcription factor proto-oncogene c-Myc drives certain cancers to change their energy metabolic requirements, and become “glutamine addicted” for their growth and survival. Lymphoma is a clear example of such a cancer. The glutamine antagonist 6-diazo-5-oxo-L-norleucine (DON) broadly blocks glutamine utilizing reactions critical for the synthesis of nucleic acids, proteins and the generation of alpha-ketoglutarate for energy metabolism. DON has shown robust efficacy in both lymphoma animal models and exploratory clinical studies, but its development was halted due to marked dose-limiting toxicities, many of which were gastrointestinal (GI)- related, as the GI system is highly dependent on glutamine utilization. We hypothesized that a novel cell- directed prodrug of DON which could deliver the drug selectively to the lymphoid cells would permit significant dose reduction, greatly alleviating the adverse events. The feasibility of this approach is supported by the recent success of Gilead's lymphoid cell-targeted prodrug of the antiviral agent tenofovir, called tenofovir alafenamide (TAF), which in Ph 3 clinical trials provided similar efficacy with a 30-fold dose reduction and less toxicity. By exploiting a similar concept yet taking a unique molecular design strategy, we have identified an initial lead DON prodrug, JHU-083, which preferentially delivers 30-fold more DON to peripheral blood mononuclear cells (PBMCs) versus human plasma, and exhibits similar efficacy to DON with substantially reduced toxicity in murine lymphoma models. Findings from a tissue distribution/tolerability study in swine confirms the PBMC targeting of the prodrug. In head-to-head comparison versus equimolar DON, the DON prodrug showed enhanced DON delivery to PBMCs and reduced delivery to GI tissues resulting in less GI pathology and fewer clinical symptoms. Although promising, JHU-083 is not ideal for translation as it exhibits high clearance. Thus, our main drug discovery focus will be to create novel DON prodrugs which remain intact in plasma and microsomes, such that their lymphocyte delivery of DON can be sustained. In this grant, two PIs with complimentary expertise will design novel DON prodrugs with optimized pharmacokinetic parameters and characterize their efficacy/ toxicity profiles in lymphoma mouse models. At the completion of these studies we will have developed a novel, robust and safe inhibitor of glutamine metabolism. Our studies will lay the ground work for the rapid introduction of such compounds into clinical trials.