Alone and together: current approaches to targeting glutaminase enzymes as part of anti-cancer therapies

Glutaminolysis inhibition boosts photodynamic therapy to eliminate cancer stem cells

High reactive oxygen species (ROS) levels provide a therapeutic opportunity to eradicate cancer stem cells (CSCs), a population of cells responsible for tumorigenesis, progression, metastasis, and recurrence. However, enhanced antioxidant systems in this population of cells attenuate ROS-inducing therapies. Here, we developed a nanoparticle-assisted combination therapy to eliminate CSCs by employing photodynamic therapy (PDT) to yield ROS while disrupting ROS defense with glutaminolysis inhibition. Specifically, we leveraged an oleic acid-hemicyanine conjugate (CyOA) as photosensitizer, a new entity molecule HYL001 as glutaminolysis inhibitor, and a biocompatible folic acid-hydroxyethyl starch conjugate (FA-HES) as amphiphilic surfactant to construct cellular and mitochondrial hierarchical targeting nanomedicine (COHF NPs). COHF NPs inhibited glutaminolysis to reduce intracellular ROS scavengers, including glutathione (GSH) and nicotinamide adenine dinucleotide phosphate (NADPH), and to blunt oxidative phosphorylation (OXPHOS) for oxygen-conserved PDT. Compared to COLF NPs without glutaminolysis inhibitor, COHF NPs exhibited higher phototoxicity to breast cancer stem cells (BCSCs) both in vitro and in vivo. More importantly, we corroborated that marketed glutaminolysis inhibitors, such as CB839 and V9302, augment the clinically used photosensitizer (Hiporfin) for BCSCs elimination. This study develops a potent CSCs targeting strategy by combining glutaminolysis inhibition with PDT and provides significant implications for cancer therapy.

Filament formation drives catalysis by glutaminase enzymes important in cancer progression

The glutaminase enzymes GAC and GLS2 catalyze the hydrolysis of glutamine to glutamate, satisfying the 'glutamine addiction' of cancer cells. They are the targets of anti-cancer drugs; however, their mechanisms of activation and catalytic activity have been unclear. Here we demonstrate that the ability of GAC and GLS2 to form filaments is directly coupled to their catalytic activity and present their cryo-EM structures which provide a view of the conformational states essential for catalysis. Filament formation guides an 'activation loop' to assume a specific conformation that works together with a 'lid' to close over the active site and position glutamine for nucleophilic attack by an essential serine. Our findings highlight how ankyrin repeats on GLS2 regulate enzymatic activity, while allosteric activators stabilize, and clinically relevant inhibitors block, filament formation that enables glutaminases to catalyze glutaminolysis and support cancer progression.

Insights on the Role of Polyphenols in Combating Cancer Drug Resistance

Chemotherapy resistance is still a serious problem in the treatment of most cancers. Many cellular and molecular mechanisms contribute to both inherent and acquired drug resistance. They include the use of unaffected growth-signaling pathways, changes in the tumor microenvironment, and the active transport of medicines out of the cell. The antioxidant capacity of polyphenols and their potential to inhibit the activation of procarcinogens, cancer cell proliferation, metastasis, and angiogenesis, as well as to promote the inhibition or downregulation of active drug efflux transporters, have been linked to a reduced risk of cancer in epidemiological studies. Polyphenols also have the ability to alter immunological responses and inflammatory cascades, as well as trigger apoptosis in cancer cells. The discovery of the relationship between abnormal growth signaling and metabolic dysfunction in cancer cells highlights the importance of further investigating the effects of dietary polyphenols, including their ability to boost the efficacy of chemotherapy and avoid multidrug resistance (MDR). Here, it is summarized what is known regarding the effectiveness of natural polyphenolic compounds in counteracting the resistance that might develop to cancer drugs as a result of a variety of different mechanisms.