Mechanisms of Pathogenic Metabolic Manipulation
Both cancerous cells and viruses depend on the metabolic resources provided by the host to supply the energy and biochemical building blocks necessary for their replication. Many anti-viral and anti-cancer compounds, such as nucleotide analogs, target these parasites' utilization of cellular metabolic resources and have proven to be clinically successful. Despite these successes, very little is known about the mechanisms governing the pathogenic manipulation of the small molecule metabolic network. Our laboratory's goal is to elucidate these mechanisms and thereby identify potential therapeutic targets to block cancer- and virally-associated disease.
A major focus of our laboratory is on human cytomegalovirus (HCMV), a herpes virus, which is the leading cause of congenital viral infection, occurring in approximately %1 of all live births. Congenital HCMV infection results in central nervous system damage in the majority of symptomatic newborns. HCMV infection also poses a serious health risk to immunosuppressed individuals, such as the elderly, and patients receiving immunosuppressive chemotherapy, including cancer patients, transplant recipients, and AIDS patients.
Another major focus in my laboratory is to elucidate novel metabolic activities induced by the transformation of cells from normal to cancerous. It has been known for decades that this cancerous transformation induces gross metabolic changes. However, many questions remain about the specific activities induced and the upstream mechanisms that are responsible. More recently, several reports indicate the importance of these metabolic changes for tumorigenesis highlighting the likelihood that inhibition of these activities could prevent cancer associated disease.
Global Measurement of Metabolic Activity: Liquid Chromatography-Mass Spectrometry
In order to elucidate pathogenic manipulation of the metabolic network (either viral or cancer-associated), we utilize liquid chromatography/ tandem mass spectrometry (LC-MS/MS) to measure the concentrations of specific metabolite pools. Utilizing this technology, we can measure the concentrations of a wide variety of metabolites, covering a large proportion of metabolic chemical diversity.
In addition to measuring metabolite concentrations, we also measure the rate of molecular conversion from one metabolite to another, i.e. metabolic flux. The speed of metabolic flux is crucial to understanding metabolic network behavior and how it is affected by a cellular perturbation, e.g. viral infection or oncogenic transformation. We measure metabolic flux by feeding cells with stable-isotope-labeled nutrient, e.g. 13C-glucose, which because of its heavier composition (as compared to 12C) produces a unique mass signature. As 13C incorporates into the metabolic network it can be distinguished from 12C-metabolites by mass spectrometry. By measuring the speed of 13C incorporation into various metabolite pools we can estimate metabolic flux values and how they are affected by various perturbations.
With respect to our HCMV project, we have found that HCMV infection activates several metabolic pathways including various aspects of central carbon metabolism and nucleotide biosynthesis. We find that inhibition of certain virally-up-regulated pathways blocks normal viral replication. In our cancer project, we have begun to identify activities specifically induced by oncogenesis that appear to be important for cancer-cell replication. Utilizing molecular genetic techniques, we are now beginning to dissect the mechanisms responsible for viral and cancer-induced metabolic changes. Increased understanding of these mechanisms and the roles they play during viral infection and cancer-cell transformation will continue to illuminate potential therapeutic avenues.