The importance of thiol-mediated detoxification of anticancer drugs that produce toxic electrophiles has been of considerable interest to many investigators. Glutathione and glutathione S-transferases (GST) are the focus of much attention in characterizing drug resistant cells. However, ambiguous and sometimes conflicting data have complicated the field.
This article attempts to clarify some of the confusion. The following observations are well established: (a) tumors express high levels of GST, especially GST psi, although the isozyme components vary quite markedly between tissues and the isozymes are inducible; (b) nitrogen mustards are good substrates for the GST alpha family of isozymes which are frequently overexpressed in cells with acquired resistance to these drugs; (c) most drugs of the multidrug-resistant phenotype have not been shown to be GST substrates and although GST psi is frequently overexpressed in multidrug-resistant cells, most indications are that this is an accompaniment to, rather than a cause of, the resistant phenotype; (d) transfection of GST complementary DNAs has produced some lines with increased resistance to alkylating agents.
Most studies of the relationships between GST and resistance have overlooked the potential importance of other enzymes involved in the maintenance of cellular glutathione homeostasis, and this has complicated data interpretation.
Translational research aimed at applying our knowledge of glutathione pathways has produced preclinical and clinical testing of some glutathione and GST inhibitors, with some encouraging preliminary results. In brief, GSTs are important determinants of drug response for some, not all, anticancer drugs. Caution should be encouraged in assessing cause/effect relationships between GST overexpression and resistance mechanisms.
The right ventricle under pressure: cellular and molecular mechanisms of right-heart failure in pulmonary hypertension.
Pulmonary arterial hypertension (PAH) is a deadly disease in which vasoconstriction and vascular remodeling both lead to a progressive increase in pulmonary vascular resistance. The response of the right ventricle (RV) to the increased afterload is an important determinant of patient outcome. Little is known about the cellular and molecular mechanisms that underlie the transition from compensated hypertrophy to dilatation and failure that occurs during the course of the disease.
Moreover, little is known about the direct effects of current PAH treatments on the heart. Although the increase in afterload is the first trigger for RV adaptation in PAH, neurohormonal signaling, oxidative stress, inflammation, ischemia, and cell death may contribute to the development of RV dilatation and failure. Here we review cellular signaling cascades and gene expression patterns in the heart that follow pressure overload.
Most data are derived from research on the left ventricle, but where possible specific information on the RV response to pressure overload is provided. This overview identifies the gaps in our understanding of RV failure and attempts to fill them, when possible. Together with the online supplement, it provides a starting point for new research and aims to encourage the pulmonary hypertension research community to direct some of their attention to the RV, in parallel to their focus on the pulmonary vasculature.
Global analyses of cellular lipidomes directly from crude extracts of biological samples by ESI mass spectrometry: a bridge to lipidomics.
Lipidomics is a rapidly expanding research field in which multiple techniques are utilized to quantitate the hundreds of chemically distinct lipids in cells and determine the molecular mechanisms through which they facilitate cellular function.
Recent developments in electrospray ionization mass spectrometry (ESI/MS) have made possible, for the first time, the precise identification and quantification of alterations in a cell’s lipidome after cellular perturbations. This review provides an overview of the essential role of ESI/MS in lipidomics, presents a broad strategy applicable for the generation of lipidomes directly from cellular extracts of biological samples by ESI/MS, and summarizes salient examples of strategies utilized to conquer the lipidome in physiologic signaling as well as pathophysiologically relevant disease states.
Because of its unparalleled sensitivity, specificity, and efficiency, ESI/MS has provided a critical bridge to generate highly accurate data that fingerprint cellular lipidomes to facilitate insight into the functional role of subcellular membrane compartments and microdomains in mammalian cells. We believe that ESI/MS-facilitated lipidomics has now opened a critical door that will greatly increase our understanding of human disease.
A genome-wide RNAi screen for modifiers of the circadian clock in human cells.
Two decades of research identified more than a dozen clock genes and defined a biochemical feedback mechanism of circadian oscillator function. To identify additional clock genes and modifiers, we conducted a genome-wide small interfering RNA screen in a human cellular clock model. Knockdown of nearly 1000 genes reduced rhythm amplitude. Potent effects on period length or increased amplitude were less frequent; we found hundreds of these and confirmed them in secondary screens.
Characterization of a subset of these genes demonstrated a dosage-dependent effect on oscillator function. Protein interaction network analysis showed that dozens of gene products directly or indirectly associate with known clock components. Pathway analysis revealed these genes are overrepresented for components of insulin and hedgehog signaling, the cell cycle, and the folate metabolism. Coupled with data showing many of these pathways are clock regulated, we conclude the clock is interconnected with many aspects of cellular function.
Tumor glycolysis as a target for cancer therapy: progress and prospects
Altered energy metabolism is a biochemical fingerprint of cancer cells that represents one of the “hallmarks of cancer”. This metabolic phenotype is characterized by preferential dependence on glycolysis (the process of conversion of glucose into pyruvate followed by lactate production) for energy production in an oxygen-independent manner.
Although glycolysis is less efficient than oxidative phosphorylation in the net yield of adenosine triphosphate (ATP), cancer cells adapt to this mathematical disadvantage by increased glucose up-take, which in turn facilitates a higher rate of glycolysis.
Apart from providing cellular energy, the metabolic intermediates of glycolysis also play a pivotal role in macromolecular biosynthesis, thus conferring selective advantage to cancer cells under diminished nutrient supply.
lating data also indicate that intracellular ATP is a critical determinant of chemoresistance. Under hypoxic conditions where glycolysis remains the predominant energy producing pathway sensitizing cancer cells would require intracellular depletion of ATP by inhibition of glycolysis.
Together, the oncogenic regulation of glycolysis and multifaceted roles of glycolytic components underscore the biological significance of tumor glycolysis. Thus targeting glycolysis remains attractive for therapeutic intervention. Several preclinical investigations have indeed demonstrated the effectiveness of this therapeutic approach thereby supporting its scientific rationale.
Recent reviews have provided a wealth of information on the biochemical targets of glycolysis and their inhibitors. The objective of this review is to present the most recent research on the cancer-specific role of glycolytic enzymes including their non-glycolytic functions in order to explore the potential for therapeutic opportunities. Further, we discuss the translational potential of emerging drug candidates in light of technical advances in treatment modalities such as image-guided targeted delivery of cancer therapeutics.