pH, Lactate, and Hypoxia: Reciprocity in Regulating High-Affinity Monocarboxylate Transporter Expression in Glioblastoma.

Highly malignant brain tumors harbor the aberrant propensity for aerobic glycolysis, the excessive conversion of glucose to lactic acid even in the presence of ample tissue oxygen. Lactic acid is rapidly effluxed to the tumor microenvironment via a group of plasma-membrane transporters denoted monocarboxylate transporters (MCTs) to prevent "self-poisoning." One isoform, MCT2, has the highest affinity for lactate and thus should have the ability to respond to microenvironment conditions such as hypoxia, lactate, and pH to help maintain high glycolytic flux in the tumor.

A Lab Assembled Microcontroller-Based Sensor Module for Continuous Oxygen Measurement in Portable Hypoxia Chambers.

Background: Hypoxia-based cell culture experiments are routine and essential components of in vitro cancer research. Most laboratories use low-cost portable modular chambers to achieve hypoxic conditions for cell cultures, where the sealed chambers are purged with a gas mixture of preset O2 concentration. Studies are conducted under the assumption that hypoxia remains unaltered throughout the 48 to 72 hour duration of such experiments.

Low-cost media formulation for culture of brain tumor spheroids (neurospheres).

Recent studies have found that the biological features of primary tumors are faithfully recapitulated when a patient's tumor is processed and then maintained as a 3-D spheroid in specialized cell culture media. However, a major drawback for maintenance and routine passage of primary tumors as spheroids has been the high cost of custom-formulated media compared to regular serum-supplemented media. Here we report the formulation of a cost-effective, serum-free medium in which high-grade primary brain tumor (glioblastoma) explants can be established and maintained as spheroids.

Metabolic targeting of lactate efflux by malignant glioma inhibits invasiveness and induces necrosis: an in vivo study.

Glioblastoma multiforme (GBM) are the most malignant among brain tumors. They are frequently refractory to chemotherapy and radiotherapy with mean patient survival of approximately 6 months, despite surgical intervention. The highly glycolytic nature of glioblastomas describes their propensity to metabolize glucose to lactic acid at an elevated rate.

Metabolic targeting of malignant tumors: small-molecule inhibitors of bioenergetic flux.

Metabolism in tumors deviates significantly from that of normal tissues. Increasingly, the underlying aberrant metabolic pathways are being considered as novel targets for cancer therapy. Denoted "metabolic targeting", small molecule drugs are under investigation for focused inhibition of key metabolic steps that are utilized by tumors, since such inhibitors should harbor minimal toxicity towards surrounding normal tissues.

The pivotal roles of mitochondria in cancer: Warburg and beyond and encouraging prospects for effective therapies.

Tumors usurp established metabolic steps used by normal tissues for glucose utilization and ATP production that rely heavily on mitochondria and employ a route that, although involving mitochondria, includes a much greater dependency on glycolysis. First described by Otto Warburg almost nine decades ago [1], this aberrant phenotype becomes more pronounced with increased tumor malignancy [2]. Thus, while maintaining their capacity for respiration, tumors "turn more parasitic" by enhancing their ability to scavenge glucose from their surroundings.

Delivery of small-interfering RNA (siRNA) to the brain.

Background: Two fundamental difficulties in the delivery of drugs to treat central nervous system (CNS) diseases are the systemic delivery of therapeutics across the bloodbrain-barrier (BBB), and the targeting of drugs to specific tissues or cells within the brain. With the advent and promise of RNA-based therapeutics that utilize RNA interference (RNAi) to trigger specific silencing of genes within diseased tissues, the necessity to surmount such obstacles has become even more urgent.

Objective: Most pre-clinical and clinical studies on delivery of RNAi to the CNS have utilized invasive, intra-cerebral delivery of RNA to the targeted tissue.

Hexokinase-2 bound to mitochondria: cancer's stygian link to the "Warburg Effect" and a pivotal target for effective therapy.

The most common metabolic hallmark of malignant tumors, i.e., the "Warburg effect" is their propensity to metabolize glucose to lactic acid at a high rate even in the presence of oxygen.

MicroRNA and brain tumors: a cause and a cure?

Malignant brain tumors, including high-grade gliomas, are among the most lethal of all cancers. Despite considerable advances, including multi-modal treatments with surgery, radiotherapy, and chemotherapy, the overall prognosis remains dismal for patients diagnosed with these tumors. With the discovery of RNA interference (RNAi) for target-specific gene silencing via small interfering RNA (siRNA), a novel method to target malignant gliomas has been exposed, an endeavor that is aggressively being carried out in numerous laboratories.

Lactate and malignant tumors: a therapeutic target at the end stage of glycolysis.

Metabolic aberrations in the form of altered flux through key metabolic pathways are primary hallmarks of many malignant tumors. Primarily the result of altered isozyme expression, these adaptations enhance the survival and proliferation of the tumor at the expense of surrounding normal tissue. Consequently, they also expose a unique set of targets for tumor destruction while sparing healthy tissues.

Metabolic remodeling of malignant gliomas for enhanced sensitization during radiotherapy: an in vitro study.

Objective: To investigate a novel method to enhance radiosensitivity of gliomas via modification of metabolite flux immediately before radiotherapy. Malignant gliomas are highly glycolytic and produce copious amounts of lactic acid, which is effluxed to the tumor microenvironment via lactate transporters. We hypothesized that inhibition of lactic acid efflux would alter glioma metabolite profiles, including those that are radioprotective.

RNAi based approaches to the treatment of malignant glioma.

RNA interference (RNAi) is a recently discovered, powerful molecular mechanism that can be harnessed to engineer gene-specific silencing in mammalian tissues. A mechanism, where short double-stranded RNA (dsRNA) molecules, when introduced into cells elicit specific "knock-down" of gene expression via degradation of targeted messenger RNA, has lately become the technique of choice for analysis of gene function in oncology research. Thus, RNAi is currently being extensively evaluated as a potential therapeutic strategy against malignant gliomas, since surgical, radiological, and chemotherapeutic interventions during the past few decades have done little to improve the poor prognosis rate for patients with these dreaded tumors.

Silencing of monocarboxylate transporters via small interfering ribonucleic acid inhibits glycolysis and induces cell death in malignant glioma: an in vitro study.

Objective: Dependence on glycolysis is a hallmark of malignant tumors. As a consequence, these tumors generate more lactate, which is effluxed from cells by monocarboxylate transporters (MCTs). We hypothesized that 1) MCT expression in malignant tumors may differ from normal tissue in quantity, isoform, or both; and 2) silencing MCT expression would induce intracellular acidification, resulting in decreased proliferation and/or increased cell death.

Glucose metabolism in cancer. Evidence that demethylation events play a role in activating type II hexokinase gene expression.

One of the "signature" phenotypes of highly malignant, poorly differentiated tumors, including hepatomas, is their remarkable propensity to utilize glucose at a much higher rate than normal cells, a property frequently dependent on the marked overexpression of type II hexokinase (HKII). As the expression of the gene for this enzyme is nearly silent in liver tissue, we tested the possibility that DNA methylation/demethylation events may be involved in its regulation. Initial studies employing methylation restriction endonuclease analysis provided evidence for differential methylation patterns for the HKII gene in normal hepatocytes and hepatoma cells, the latter represented by a highly glycolytic model cell line (AS-30D).

"In-gel" purified ditags direct synthesis of highly efficient SAGE Libraries.

Background: SAGE (serial analysis of gene expression) is a recently developed technique for systematic analysis of eukaryotic transcriptomes. The most critical step in the SAGE method is large scale amplification of ditags which are then are concatemerized for the construction of representative SAGE libraries. Here, we report a protocol for purifying these ditags via an 'in situ' PAGE purification method.