Current and Future Cancer Chemoprevention Strategies

Cancer is a leading cause of death worldwide, accounting for nearly 10 million deaths in 2020 and ranking as the second-leading cause of death in economically developed countries [...].

Hepatic glutamine synthetase controls N5-methylglutamine in homeostasis and cancer

Glutamine synthetase (GS) activity is conserved from prokaryotes to humans, where the ATP-dependent production of glutamine from glutamate and ammonia is essential for neurotransmission and ammonia detoxification. Here, we show that mammalian GS uses glutamate and methylamine to produce a methylated glutamine analog, N5-methylglutamine. Untargeted metabolomics revealed that liver-specific GS deletion and its pharmacological inhibition in mice suppress hepatic and circulating levels of N5-methylglutamine. This alternative activity of GS was confirmed in human recombinant enzyme and cells, where a pathogenic mutation in the active site (R324C) promoted the synthesis of N5-methylglutamine over glutamine. N5-methylglutamine is detected in the circulation, and its levels are sustained by the microbiome, as demonstrated by using germ-free mice. Finally, we show that urine levels of N5-methylglutamine correlate with tumor burden and GS expression in a β-catenin-driven model of liver cancer, highlighting the translational potential of this uncharacterized metabolite.

Mesenchymal stromal cells cultured in physiological conditions sustain citrate secretion with glutamate anaplerosis

Bone marrow mesenchymal stromal cells (MSCs) have immunomodulatory and regenerative potential. However, culture conditions govern their metabolic processes and therapeutic efficacy. Here we show that culturing donor-derived MSCs in Plasmax™, a physiological medium with the concentrations of nutrients found in human plasma, supports their proliferation and stemness, and prevents the nutritional stress induced by the conventional medium DMEM. The quantification of the exchange rates of metabolites between cells and medium, untargeted metabolomics, stable isotope tracing and transcriptomic analysis, performed at physiologically relevant oxygen concentrations (1%O₂), reveal that MSCs rely on high rate of glucose to lactate conversion, coupled with parallel anaplerotic fluxes from glutamine and glutamate to support citrate synthesis and secretion. These distinctive traits of MSCs shape the metabolic microenvironment of bone marrow niche and can influence nutrient cross-talks under physiological and pathological conditions.

Two parallel pathways connect glutamine metabolism and mTORC1 activity to regulate glutamoptosis

Glutamoptosis is the induction of apoptotic cell death as a consequence of the aberrant activation of glutaminolysis and mTORC1 signaling during nutritional imbalance in proliferating cells. The role of the bioenergetic sensor AMPK during glutamoptosis is not defined yet. Here, we show that AMPK reactivation blocks both the glutamine-dependent activation of mTORC1 and glutamoptosis in vitro and in vivo. We also show that glutamine is used for asparagine synthesis and the GABA shunt to produce ATP and to inhibit AMPK, independently of glutaminolysis. Overall, our results indicate that glutamine metabolism is connected with mTORC1 activation through two parallel pathways: an acute alpha-ketoglutarate-dependent pathway; and a secondary ATP/AMPK-dependent pathway. This dual metabolic connection between glutamine and mTORC1 must be considered for the future design of therapeutic strategies to prevent cell growth in diseases such as cancer.

Microbiome-derived carnitine mimics as previously unknown mediators of gut-brain axis communication

Alterations to the gut microbiome are associated with various neurological diseases, yet evidence of causality and identity of microbiome-derived compounds that mediate gut-brain axis interaction remain elusive. Here, we identify two previously unknown bacterial metabolites 3-methyl-4-(trimethylammonio)butanoate and 4-(trimethylammonio)pentanoate, structural analogs of carnitine that are present in both gut and brain of specific pathogen-free mice but absent in germ-free mice. We demonstrate that these compounds are produced by anaerobic commensal bacteria from the family Lachnospiraceae (Clostridiales) family, colocalize with carnitine in brain white matter, and inhibit carnitine-mediated fatty acid oxidation in a murine cell culture model of central nervous system white matter. This is the first description of direct molecular inter-kingdom exchange between gut prokaryotes and mammalian brain cells, leading to inhibition of brain cell function.

Nilotinib as Coadjuvant Treatment with Doxorubicin in Patients with Sarcomas: A Phase I Trial of the Spanish Group for Research on Sarcoma

Purpose: Nilotinib plus doxorubicin showed to be synergistic regarding apoptosis in several sarcoma cell lines. A phase I/II trial was thus designed to explore the feasibility of nilotinib as coadjuvant of doxorubicin by inhibiting MRP-1/P-gp efflux activity. The phase I part of the study is presented here.Patients and Methods: Nilotinib 400 mg/12 hours was administered in fixed dose from day 1 to 6, and doxorubicin on day 5 of each cycle. Three dose escalation levels for doxorubicin at 60, 65, and 75 mg/m² were planned. Cycles were repeated every 3 weeks for a total of 4 cycles. Eligible subtypes were retroperitoneal liposarcoma, leiomyosarcoma, and unresectable/metastatic high-grade chondrosarcoma.Results: Thirteen patients were enrolled: 7 chondrosarcoma, 4 liposarcoma, and 2 leiomyosarcoma. In 46 cycles administered, the most relevant grade 3/4 adverse effects per patient were neutropenia 54%, febrile neutropenia 15%, and asthenia 8%. No cardiac toxicity was observed. Only one dose-limiting toxicity (febrile neutropenia) was reported in the third dose level. With regard to efficacy, 1 partial response (1 liposarcoma), 9 stable diseases (5 chondrosarcoma, 2 liposarcoma, 1 leiomyosarcoma), and 3 progressive diseases (2 chondrosarcoma and 1 leiomyosarcoma) were present. ABCB1 and ABCC1 RNA expression levels decreased by 58.47-fold and 1.47-fold, respectively, on day 5 of the cycle.Conclusions: Combination of MRP-1/P-gp inhibitor, nilotinib, as coadjuvant with doxorubicin is feasible; it appears not to add substantial toxicity compared with doxorubicin alone. Pharmacodynamic study supports this concept. The recommended dose for the phase II part for doxorubicin was 75 mg/m² Clin Cancer Res; 24(21); 5239-49. ©2018 AACR.

Glutamoptosis: A new cell death mechanism inhibited by autophagy during nutritional imbalance

Glutaminolysis plays a critical role in nutrient sufficiency and cell signaling activation in mammalian cells. Unexpectedly, our recent investigations revealed that the unbalanced activation of glutaminolysis during nutritional restriction causes a particular form of apoptotic cell death, that we termed “glutamoptosis.“ We found that the inhibition of autophagy is a key step to allow glutamoptosis-mediated cell death. Thus, autophagy controls glutamoptosis during nutritional imbalance.

Escaping mTOR inhibition for cancer therapy: Tumor suppressor functions of mTOR

A master promoter of cell growth, mammalian target of rapamycin (mTOR) is upregulated in a large percentage of cancer cells. Still, targeting mTOR using rapamycin has a limited outcome in patients. Our recent results highlight the additional role of mTOR as a tumor suppressor, explaining these modest results in the clinic.

mTORC1 inhibition in cancer cells protects from glutaminolysis-mediated apoptosis during nutrient limitation

A master coordinator of cell growth, mTORC1 is activated by different metabolic inputs, particularly the metabolism of glutamine (glutaminolysis), to control a vast range of cellular processes, including autophagy. As a well-recognized tumour promoter, inhibitors of mTORC1 such as rapamycin have been approved as anti-cancer agents, but their overall outcome in patients is rather poor. Here we show that mTORC1 also presents tumour suppressor features in conditions of nutrient restrictions. Thus, the activation of mTORC1 by glutaminolysis during nutritional imbalance inhibits autophagy and induces apoptosis in cancer cells. Importantly, rapamycin treatment reactivates autophagy and prevents the mTORC1-mediated apoptosis. We also observe that the ability of mTORC1 to activate apoptosis is mediated by the adaptor protein p62. Thus, the mTORC1-mediated upregulation of p62 during nutrient imbalance induces the binding of p62 to caspase 8 and the subsequent activation of the caspase pathway. Our data highlight the role of autophagy as a survival mechanism upon rapamycin treatment.

Glutaminolysis and autophagy in cancer

The remarkable metabolic differences between cancer cells and normal cells result in the potential for targeted cancer therapy. The upregulation of glutaminolysis provides energetic advantages to cancer cells. The recently described link between glutaminolysis and autophagy, mediated by MTORC1, may constitute an attractive target for therapeutic strategies. A combination of therapies targeting simultane-ously cell signaling, cancer metabolism, and autophagy can solve therapy resistance and tumor relapse problems, commonly observed in patients treated with most of the current targeted therapies. In this review we summarize the mechanistic link between glutaminolysis and autophagy, and discuss the impacts of these processes on cancer progression and the potential for therapeutic intervention.