6-Diazo-5-oxo-L-norleucine (DON) is a glutamine antagonist, which was isolated originally from Streptomyces bacteria found in Peruvian soil, and is one of a very few naturally occurring diazoketones. DON acts as an irreversible inhibitor of many glutamine utilizing enzymes critical for the synthesis of nucleic acids/ proteins and the generation of alpha-ketoglutarate for energy metabolism. The anticancer and autoimmune activities of DON has been shown repeatedly in both preclinical and clinical studies. Although promising, clinical studies with DON were halted due to its marked dose-limiting toxicities, which were mainly 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 cells and would permit significant dose reduction, greatly alleviating the GI adverse events. Our confidence in this approach was supported by the recent success of Gilead’s ell-targeted prodrug delivery of the antiviral agent tenofovir (tenfovir alafenamide) which was submitted for FDA approval in early 2015 and was shown to provide a 30-fold dose reduction versus the parent drug.
Herein we report the design, synthesis, and evaluation of several novel DON prodrugs targeted to Peripheral Blood Mononuclear Cells (PBMC’s). Using whole blood from mouse, pig, dog, monkey and human, we found that several of the new prodrugs selectively delivered DON into PBMC‘s versus plasma by >10-fold. These findings open an opportunity to develop therapeutics active at lower dose circumventing dose limiting toxicities.