Mitochondrial glutamine metabolism regulates sensitivity of cancer cells after chemotherapy via amphiregulin

Targeting cellular adaptive responses to glutaminolysis perturbation for cancer therapy

Metabolic aberrations, notably deviations in glutamine metabolism, are crucial in the oncogenic process, offering vital resources for the unlimited proliferation and enhanced survival capabilities of cancer cells. The dependency of malignant cells on glutamine metabolism has led to the proposition of targeted therapeutic strategies. However, the capability of cancer cells to initiate adaptive responses undermines the efficacy of these therapeutic interventions. This review meticulously examines the multifaceted adaptive mechanisms that cancer cells deploy to sustain survival and growth following the disruption of glutamine metabolism. Emphasis is placed on the roles of transcription factors, alterations in metabolic pathways, the mechanistic target of rapamycin complex 1 signaling axis, autophagy, macropinocytosis, nucleotide biosynthesis, and the scavenging of ROS. Thus, the delineation and subsequent targeting of these adaptive responses in the context of therapies aimed at glutamine metabolism offer a promising avenue for circumventing drug resistance in cancer treatment.

Induction of Fatty Acid Oxidation Underlies DNA Damage-Induced Cell Death and Ameliorates Obesity-Driven Chemoresistance

The DNA damage response is essential for preserving genome integrity and eliminating damaged cells. Although cellular metabolism plays a central role in cell fate decision between proliferation, survival, or death, the metabolic response to DNA damage remains largely obscure. Here, this work shows that DNA damage induces fatty acid oxidation (FAO), which is required for DNA damage-induced cell death. Mechanistically, FAO induction increases cellular acetyl-CoA levels and promotes N-alpha-acetylation of caspase-2, leading to cell death. Whereas chemotherapy increases FAO related genes through peroxisome proliferator-activated receptor α (PPARα), accelerated hypoxia-inducible factor-1α stabilization by tumor cells in obese mice impedes the upregulation of FAO, which contributes to its chemoresistance. Finally, this work finds that improving FAO by PPARα activation ameliorates obesity-driven chemoresistance and enhances the outcomes of chemotherapy in obese mice. These findings reveal the shift toward FAO induction is an important metabolic response to DNA damage and may provide effective therapeutic strategies for cancer patients with obesity.

Real-Time Exposure to 3D-Printing Emissions Elicits Metabolic and Pro-Inflammatory Responses in Human Airway Epithelial Cells

Three-dimensional (3D) printer usage in household and school settings has raised health concerns regarding chemical and particle emission exposures during operation. Although the composition of 3D printer emissions varies depending on printer settings and materials, little is known about the impact that emissions from different filament types may have on respiratory health and underlying cellular mechanisms. In this study, we used an in vitro exposure chamber system to deliver emissions from two popular 3D-printing filament types, acrylonitrile butadiene styrene (ABS) and polylactic acid (PLA), directly to human small airway epithelial cells (SAEC) cultured in an air-liquid interface during 3D printer operation. Using a scanning mobility particle sizer (SMPS) and an optical particle sizer (OPS), we monitored 3D printer particulate matter (PM) emissions in terms of their particle size distribution, concentrations, and calculated deposited doses. Elemental composition of ABS and PLA emissions was assessed using scanning electron microscopy coupled with energy dispersive X-ray spectroscopy (SEM-EDX). Finally, we compared the effects of emission exposure on cell viability, inflammation, and metabolism in SAEC. Our results reveal that, although ABS filaments emitted a higher total concentration of particles and PLA filaments emitted a higher concentration of smaller particles, SAEC were exposed to similar deposited doses of particles for each filament type. Conversely, ABS and PLA emissions had distinct elemental compositions, which were likely responsible for differential effects on SAEC viability, oxidative stress, release of inflammatory mediators, and changes in cellular metabolism. Specifically, while ABS- and PLA-emitted particles both reduced cellular viability and total glutathione levels in SAEC, ABS emissions had a significantly greater effect on glutathione relative to PLA emissions. Additionally, pro-inflammatory cytokines including IL-1β, MMP-9, and RANTES were significantly increased due to ABS emissions exposure. While IL-6 and IL-8 were stimulated in both exposure scenarios, VEGF was exclusively increased due to PLA emissions exposures. Notably, ABS emissions induced metabolic perturbation on amino acids and energy metabolism, as well as redox-regulated pathways including arginine, methionine, cysteine, and vitamin B3 metabolism, whereas PLA emissions exposures caused fatty acid and carnitine dysregulation. Taken together, these results advance our mechanistic understanding of 3D-printer-emissions-induced respiratory toxicity and highlight the role that filament emission properties may play in mediating different respiratory outcomes.

Glutathione promotes the synergistic effects of venetoclax and azacytidine against myelodysplastic syndrome‑refractory anemia by regulating the cell cycle

Azacitidine is a DNA methyltransferase inhibitor that has been used as a singular agent for the treatment of myelodysplastic syndrome-refractory anemia with excess blast-1 and -2 (MDS-RAEB I/II). However, recurrence and overall response rates following this treatment remain unsatisfactory. The combination of azacitidine and venetoclax has been used for the clinical treatment of a variety of hematological diseases due to the synergistic killing effect of the two drugs. Venetoclax is a BCL-2 inhibitor that can inhibit mitochondrial metabolism. In addition, azacitidine has been shown to reduce the levels of myeloid cell leukemia 1 (MCL-1) in acute myeloid leukemia cells. MCL-1 is an anti-apoptotic protein and a potential source of resistance to venetoclax. However, the mechanism underlying the effects of combined venetoclax and azacitidine treatment remains to be fully elucidated. In the present study, the molecular mechanism underlying the impact of venetoclax on the efficacy of azacitidine was investigated by examining its effects on cell cycle progression. SKM-1 cell lines were treated in vitro with 0-2 µM venetoclax and 0-4 µM azacytidine. After 24, 48 and 72 h of treatment, the impact of the drugs on the cell cycle was assessed by flow cytometry. Following drug treatment, changes in cellular glutamine metabolism pathways was analyzed using western blotting (ATF4, CHOP, ASCT2, IDH2 and RB), quantitative PCR (ASCT2 and IDH2), liquid chromatography-mass spectrometry (α-KG, succinate and glutathione) and ELISA (glutamine and glutaminase). Venetoclax was found to inhibit mitochondrial activity though the alanine-serine-cysteine transporter 2 (ASCT2) pathway, which decreased glutamine uptake. Furthermore, venetoclax partially antagonized the action of azacitidine through this ASCT2 pathway, which was reversed by glutathione (GSH) treatment. These results suggest that GSH treatment can potentiate the synergistic therapeutic effects of venetoclax and azacitidine combined treatment on a myelodysplastic syndrome-refractory anemia cell line at lower concentrations.

Fatty acid oxidation supports melanoma cell migration through autophagy regulation

Metastasis is one of the most malignant characteristics of cancer cells, in which metabolic reprogramming is crucial for promoting and sustaining multi-steps of metastasis, including invasion, migration and infiltration. Recently, it has been shown that melanoma cells undergo a metabolic switching toward the upregulation of fatty acid oxidation (FAO) during metastasis. However, the underlying mechanisms by which FAO contributes to metastasis of melanoma cells remain obscure. Here, we report that FAO contributes to melanoma cell migration and invasion by regulating the formation of autophagosomes. Pharmacological or genetic inhibition of FAO impairs migration of melanoma cells, which seems not to be linked to energy production or redox homeostasis. Importantly, we reveal that acetyl-CoA production by FAO contributes to melanoma cell migration through autophagy regulation. Mechanistically, FAO inhibition results in increased autophagosome formation, which suppresses migration and invasion properties of melanoma cells. Our results underscore the crucial role of FAO in melanoma cell migration and support the potential therapeutic relevance of modulating cellular acetyl-CoA levels to inhibit cancer metastasis.

Rewiring of mitochondrial metabolism in therapy-resistant cancers: permanent and plastic adaptations

Deregulation of tumor cell metabolism is widely recognized as a "hallmark of cancer." Many of the selective pressures encountered by tumor cells, such as exposure to anticancer therapies, navigation of the metastatic cascade, and communication with the tumor microenvironment, can elicit further rewiring of tumor cell metabolism. Furthermore, phenotypic plasticity has been recently appreciated as an emerging "hallmark of cancer." Mitochondria are dynamic organelles and central hubs of metabolism whose roles in cancers have been a major focus of numerous studies. Importantly, therapeutic approaches targeting mitochondria are being developed. Interestingly, both plastic (i.e., reversible) and permanent (i.e., stable) metabolic adaptations have been observed following exposure to anticancer therapeutics. Understanding the plastic or permanent nature of these mechanisms is of crucial importance for devising the initiation, duration, and sequential nature of metabolism-targeting therapies. In this review, we compare permanent and plastic mitochondrial mechanisms driving therapy resistance. We also discuss experimental models of therapy-induced metabolic adaptation, therapeutic implications for targeting permanent and plastic metabolic states, and clinical implications of metabolic adaptations. While the plasticity of metabolic adaptations can make effective therapeutic treatment challenging, understanding the mechanisms behind these plastic phenotypes may lead to promising clinical interventions that will ultimately lead to better overall care for cancer patients.

Fatty acid oxidation facilitates DNA double-strand break repair by promoting PARP1 acetylation

DNA repair is a tightly coordinated stress response to DNA damage, which is critical for preserving genome integrity. Accruing evidence suggests that metabolic pathways have been correlated with cellular response to DNA damage. Here, we show that fatty acid oxidation (FAO) is a crucial regulator of DNA double-strand break repair, particularly homologous recombination repair. Mechanistically, FAO contributes to DNA repair by activating poly(ADP-ribose) polymerase 1 (PARP1), an enzyme that detects DNA breaks and promotes DNA repair pathway. Upon DNA damage, FAO facilitates PARP1 acetylation by providing acetyl-CoA, which is required for proper PARP1 activity. Indeed, cells reconstituted with PARP1 acetylation mutants display impaired DNA repair and enhanced sensitivity to DNA damage. Consequently, FAO inhibition reduces PARP1 activity, leading to increased genomic instability and decreased cell viability upon DNA damage. Finally, our data indicate that FAO serves as an important participant of cellular response to DNA damage, supporting DNA repair and genome stability.

Suppression of fatty acid oxidation supports pancreatic cancer growth and survival under hypoxic conditions through autophagy induction

Hypoxia, one of the key features of solid tumors, induces autophagy, which acts as an important adaptive mechanism for tumor progression under hypoxic environment. Cellular metabolic reprogramming has been correlated with hypoxia, but the molecular connection to the induction of autophagy remains obscure. Here, we show that suppression of fatty acid oxidation (FAO) by hypoxia induces autophagy in human pancreatic ductal adenocarcinoma (PDAC) cells that is required for their growth and survival. Reduced cellular acetyl-CoA levels caused by FAO inhibition decreases LC3 acetylation, resulting in autophagosome formation. Importantly, PDAC cells are significantly dependent on this metabolic reprogramming, as improving FAO leads to a reduction in hypoxia-induced autophagy and an increase in cell death after chemotherapy. Thus, our study supports that suppression of FAO is an important metabolic response to hypoxia and indicates that targeting this pathway in PDAC may be an effective therapeutic approach.