Targeting glutamine metabolism via pharmacological inhibition of glutaminase has been translated into clinical trials as a novel cancer therapy, but available drugs lack optimal safety and efficacy. In this study, we used a proprietary emulsification process to encapsulate bis-2-(5-phenylacetamido-1,2,4-thiadiazol-2-yl)ethyl sulfide (BPTES), a selective but relatively insoluble glutaminase inhibitor, in nanoparticles. BPTES nanoparticles demonstrated improved pharmacokinetics and efficacy compared with unencapsulated BPTES. In addition, BPTES nanoparticles had no effect on the plasma levels of liver enzymes in contrast to CB-839, a glutaminase inhibitor that is currently in clinical trials. In a mouse model using orthotopic transplantation of patient-derived pancreatic tumor tissue, BPTES nanoparticle monotherapy led to modest antitumor effects. Using the HypoxCR reporter in vivo, we found that glutaminase inhibition reduced tumor growth by specifically targeting proliferating cancer cells but did not affect hypoxic, noncycling cells. Metabolomics analyses revealed that surviving tumor cells following glutaminase inhibition were reliant on glycolysis and glycogen synthesis. Based on these findings, metformin was selected for combination therapy with BPTES nanoparticles, which resulted in significantly greater pancreatic tumor reduction than either treatment alone. Thus, targeting of multiple metabolic pathways, including effective inhibition of glutaminase by nanoparticle drug delivery, holds promise as a novel therapy for pancreatic cancer.pancreatic ductal adenocarcinoma | glutaminolysis | glucose metabolism | KRAS mutation | intratumoral hypoxia P atients with pancreatic ductal adenocarcinoma (PDAC) have among the highest fatality rates of all cancers (1). Pancreatic cancer is predicted to become the second-leading cause of cancer death in the United States by the year 2030 (2). Over 90% of PDACs display mutations in oncogenic KRAS (Kirsten rat sarcoma viral oncogene homolog) (3, 4), a known regulator of glutamine metabolism that can render cancer cells dependent on glutamine for survival and proliferation (5, 6)-a state known as "glutamine addiction" (7, 8)-suggesting that dependency on glutamine could be exploited to develop new therapies for KRAS-mutated PDAC. The first step of glutamine metabolism is the conversion of glutamine to glutamate and ammonia, which is catalyzed by glutaminase (GLS). Bis-2-(5-phenylacetamido-1,2,4-thiadiazol-2-yl)ethyl sulfide (BPTES), which is an allosteric, time-dependent (9), and specific inhibitor of GLS1, exhibits unique binding at the oligomerization interface of the glutaminase tetramer (10, 11). Although BPTES is more selective than other prototype glutaminase inhibitors, such as 6-diazo-5-oxo-L-norleucine (12) or ebselen (9), and can effectively inhibit GLS1 (13) and tumor growth (13-15), poor solubility (0.144 μg/mL) (16) has limited its clinical development. Recently, CB-839 (17) was tested in a phase I clinical trial. Abnormal liver and kidney function tests, lymphop...

The glutamine antagonist 6-diazo-5-oxo-l-norleucine (DON, 1) has shown robust anticancer efficacy in preclinical and clinical studies, but its development was halted due to marked systemic toxicities. Herein we demonstrate that DON inhibits glutamine metabolism and provides antitumor efficacy in a murine model of glioblastoma, although toxicity was observed. To enhance DON's therapeutic index, we utilized a prodrug strategy to increase its brain delivery and limit systemic exposure. Unexpectedly, simple alkyl ester-based prodrugs were ineffective due to chemical instability cyclizing to form a unique diazo-imine. However, masking both DON's amine and carboxylate functionalities imparted sufficient chemical stability for biological testing. While these dual moiety prodrugs exhibited rapid metabolism in mouse plasma, several provided excellent stability in monkey and human plasma. The most stable compound (5c, methyl-POM-DON-isopropyl-ester) was evaluated in monkeys, where it achieved 10-fold enhanced cerebrospinal fluid to plasma ratio versus DON. This strategy may provide a path to DON utilization in glioblastoma multiforme patients.

SUMMARY N-acetyl-aspartyl-glutamate (NAAG) is a peptide-based neurotransmitter that has been extensively studied in many neurological diseases. In this study, we show a specific role of NAAG in cancer. We found that NAAG is more abundant in higher grade cancers and is a source of glutamate in cancers expressing glutamate carboxypeptidase II (GCPII), the enzyme that hydrolyzes NAAG to glutamate and N-acetyl-aspartate (NAA). Knocking down GCPII expression through genetic alteration or pharmacological inhibition of GCPII results in a reduction of both glutamate concentrations and cancer growth. Moreover, targeting GCPII in combination with glutaminase inhibition accentuates these effects. These findings suggest that NAAG serves as an important reservoir to provide glutamate to cancer cells through GCPII when glutamate production from other sources is limited. Thus, GCPII is a viable target for cancer therapy, either alone or in combination with glutaminase inhibition.

The targeting of glutamine metabolism specifically via pharmacological inhibition of glutaminase 1 (GLS1) has been translated into clinical trials as a novel therapy for several cancers. The results, though encouraging, show room for improvement in terms of tumor reduction. In this study, the glutaminase II pathway is found to be upregulated for glutamate production upon GLS1 inhibition in pancreatic tumors. Moreover, genetic suppression of glutamine transaminase K (GTK), a key enzyme of the glutaminase II pathway, leads to the complete inhibition of pancreatic tumorigenesis in vivo unveiling GTK as a new metabolic target for cancer therapy. These results suggest that current trials using GLS1 inhibition as a therapeutic approach targeting glutamine metabolism in cancer should take into account the upregulation of other metabolic pathways that can lead to glutamate production; one such pathway is the glutaminase II pathway via GTK.

No abstract

DOI: https://doi.org/10.1002/pmic.201800451 Much like the classic arcade game “Whack‐a‐Mole”, cancer cells are able to upregulate a different metabolic pathway when one pathway is inhibited. Specifically, using metabolomics technologies with isotopic labelling, Sunag Udupa et al. demonstrate in article number 1800451 the production of glutamate from glutamine via the glutaminase II pathway when the glutaminase 1 pathway is inhibited. This metabolic adaptability of tumors justifies the need for targeting multiple metabolic pathways, aiming at both main and adaptive metabolic networks.