Glutamine or glucose starvation in hybridoma cultures induces death receptor and mitochondrial apoptotic pathways

Single cell dielectrophoresis study of apoptosis progression induced by controlled starvation

Nutrient depletion in fed-batch cultures and at the end of batch cultures is among the main causes of stress on cells and a trigger of apoptosis. In this study, we investigated changes in the cytoplasm conductivity of Chinese hamster ovary (CHO) cells under controlled starvation. Employing a single-cell dielectrophoresis (DEP) cytometer, we measured the DEP response of CHO cells incubated in a medium without glucose and glutamine over a 48-h period. Using the measured data in conjunction with numerical simulations, we determined the cytoplasm conductivity of viable and apoptotic cell subpopulations. The results show that a small subpopulation of apoptotic cells emerges after 24 to 36 h of starvation and increases rapidly over a short period of time, <12 h. The apoptotic cells have a dramatically lower cytoplasm conductivity, ∼0.05 S/m, than viable cells, ∼0.45 S/m. Viability of starvation cultures was measured by fluorescent cytometry, DEP cytometry, and trypan blue exclusion assays. DEP, Annexin V, caspase-8, and 7-AAD assays show a similar decline in viability after 36 h of starvation and indicate a very low viability after 48 h. Trypan blue exclusion assay fails to detect early-stage viability decline and estimates a much higher viability after 48 h.

A Simple Method to Reduce both Lactic Acid and Ammonium Production in Industrial Animal Cell Culture

Fed-batch animal cell culture is the most common method for commercial production of recombinant proteins. However, higher cell densities in these platforms are still limited due to factors such as excessive ammonium production, lactic acid production, nutrient limitation, and/or hyperosmotic stress related to nutrient feeds and base additions to control pH. To partly overcome these factors, we investigated a simple method to reduce both ammonium and lactic acid production—termed Lactate Supplementation and Adaptation (LSA) technology—through the use of CHO cells adapted to a lactate-supplemented medium. Using this simple method, we achieved a reduction of nearly 100% in lactic acid production with a simultaneous 50% reduction in ammonium production in batch shaker flasks cultures. In subsequent fed-batch bioreactor cultures, lactic acid production and base addition were both reduced eight-fold. Viable cell densities of 35 million cells per mL and integral viable cell days of 273 million cell-days per mL were achieved, both among the highest currently reported for a fed-batch animal cell culture. Investigating the benefits of LSA technology in animal cell culture is worthy of further consideration and may lead to process conditions more favorable for advanced industrial applications.

Reviving Lonidamine and 6-Diazo-5-oxo-L-norleucine to Be Used in Combination for Metabolic Cancer Therapy

Abnormal metabolism is another cancer hallmark. The two most characterized altered metabolic pathways are high rates of glycolysis and glutaminolysis, which are natural targets for cancer therapy. Currently, a number of newer compounds to block glycolysis and glutaminolysis are being developed; nevertheless, lonidamine and 6-diazo-5-oxo-L-norleucine (DON) are two old drugs well characterized as inhibitors of glycolysis and glutaminolysis, respectively, whose clinical development was abandoned years ago when the importance of cancer metabolism was not fully appreciated and clinical trial methodology was less developed. In this review, a PubMed search using the words lonidamine and 6-diazo-5-oxo-L-norleucine (DON) was undertaken to analyse existing information on the preclinical and clinical studies of these drugs for cancer treatment. Data show that they exhibit antitumor effects; besides there is also the suggestion that they are synergistic. We conclude that lonidamine and DON are safe and potentially effective drugs that need to be reevaluated in combination as metabolic therapy of cancer.

GAMT, a p53-inducible modulator of apoptosis, is critical for the adaptive response to nutrient stress

The p53 tumor suppressor protein has a well-established role in cell-fate decision-making processes. However, recent discoveries indicate that p53 has a non-tumor-suppressive role. Here we identify guanidinoacetate methyltransferase (GAMT), an enzyme involved in creatine synthesis, as a p53 target gene and a key downstream effector of adaptive response to nutrient stress. We show that GAMT is not only involved in p53-dependent apoptosis in response to genotoxic stress but is important for apoptosis induced by glucose deprivation. Additionally, p53-->GAMT upregulates fatty acid oxidation (FAO) induced by glucose starvation, utilizing this pathway as an alternate ATP-generating energy source. These results highlight that p53-dependent regulation of GAMT allows cells to maintain energy levels sufficient to undergo apoptosis or survival under conditions of nutrient stress. The p53-->GAMT pathway represents a new link between cellular stress responses and processes of creatine synthesis and FAO, demonstrating a further role of p53 in cellular metabolism.

Q's next: the diverse functions of glutamine in metabolism, cell biology and cancer

Several decades of research have sought to characterize tumor cell metabolism in the hope that tumor-specific activities can be exploited to treat cancer. Having originated from Warburg's seminal observation of aerobic glycolysis in tumor cells, most of this attention has focused on glucose metabolism. However, since the 1950s cancer biologists have also recognized the importance of glutamine (Q) as a tumor nutrient. Glutamine contributes to essentially every core metabolic task of proliferating tumor cells: it participates in bioenergetics, supports cell defenses against oxidative stress and complements glucose metabolism in the production of macromolecules. The interest in glutamine metabolism has been heightened further by the recent findings that c-myc controls glutamine uptake and degradation, and that glutamine itself exerts influence over a number of signaling pathways that contribute to tumor growth. These observations are stimulating a renewed effort to understand the regulation of glutamine metabolism in tumors and to develop strategies to target glutamine metabolism in cancer. In this study we review the protean roles of glutamine in cancer, both in the direct support of tumor growth and in mediating some of the complex effects on whole-body metabolism that are characteristic of tumor progression.

Control of mammalian gene expression by amino acids, especially glutamine

Molecular data rapidly accumulating on the regulation of gene expression by amino acids in mammalian cells highlight the large variety of mechanisms that are involved. Transcription factors, such as the basic-leucine zipper factors, activating transcription factors and CCAAT/enhancer-binding protein, as well as specific regulatory sequences, such as amino acid response element and nutrient-sensing response element, have been shown to mediate the inhibitory effect of some amino acids. Moreover, amino acids exert a wide range of effects via the activation of different signalling pathways and various transcription factors, and a number of cis elements distinct from amino acid response element/nutrient-sensing response element sequences were shown to respond to changes in amino acid concentration. Particular attention has been paid to the effects of glutamine, the most abundant amino acid, which at appropriate concentrations enhances a great number of cell functions via the activation of various transcription factors. The glutamine-responsive genes and the transcription factors involved correspond tightly to the specific effects of the amino acid in the inflammatory response, cell proliferation, differentiation and survival, and metabolic functions. Indeed, in addition to the major role played by nuclear factor-kappaB in the anti-inflammatory action of glutamine, the stimulatory role of activating protein-1 and the inhibitory role of C/EBP homology binding protein in growth-promotion, and the role of c-myc in cell survival, many other transcription factors are also involved in the action of glutamine to regulate apoptosis and intermediary metabolism in different cell types and tissues. The signalling pathways leading to the activation of transcription factors suggest that several kinases are involved, particularly mitogen-activated protein kinases. In most cases, however, the precise pathways from the entrance of the amino acid into the cell to the activation of gene transcription remain elusive.