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Metabolic flux analysis of cultured human breast cancer cells - by Adam Meadows

Medical science has yet to develop highly effective drug treatments for the class of cellular growth regulation diseases known as cancer.  One reason for this is the absence of an efficient drug development strategy, particularly with regard to drug target identification.  We hypothesize that cancer cells exhibit a characteristic metabolic flux profile and that the crucial enzymes responsible for this altered metabolism will provide novel targets for future anticancer drugs. 

Our research employs metabolic flux analysis to accurately quantify the flux profile of cultured human breast cancer cells in order to discover potential enzymatic targets.  Metabolic profiling of MCF7 breast cancer cells will be accomplished under conditions closely mimicking those found in tumors.  These cells will be grown on 13C glucose and glutamine and the distribution of 13C will be measured by 13C NMR and GC-MS analysis.  This data, along with extracellular flux measurements, will be used as input for a computer program that numerically solves a system of isotopomer mass balances for the intracellular fluxes of interest. 

Thus far, we have compiled data on the extracellular flux and growth response of breast cancer cells to the female hormone estrogen, the anti-breast cancer drug tamoxifen, and lowered oxygen availability. 

These preliminary results indicate the following:

  • Metabolic flare (a sharp increase in aerobic glycolysis) is evident with the addition of tamoxifen only in the presence of estrogen under adequate oxygenation.

  • Low oxygen conditions increase the yield of lactate from glucose.

  • High lactate yields correlate with, and may be partially responsible for, increased growth rates.

These observations suggest several environmental conditions worthy of a more complete metabolic analysis.  We plan to explore breast cancer’s internal metabolic response to variations in oxygen availability, in order to identify pathways that are responsible for increased growth rate under reduced oxygen conditions.  These flux profiles will be compared to the profiles of cells that are unable to produce lactate via the specific chemical inhibition of lactate dehydrogenase.  This will reveal the importance of a large lactate yield, under both high and low oxygen availability, in cancer cell proliferation.  We will also explore whether or not metabolic flare is limited to the aerobic glycolytic pathway.  These results will elucidate which fluxes correlate with a high growth rate phenotype and provide insight into why cancer cells almost ubiquitously undergo high rates of aerobic glycolysis despite its energetic inefficiency relative to respiration.  Furthermore, these data – when compared to flux results obtained from analogous experiments conducted on a noncancerous cell line – will aid in the development of a rational strategy of metabolic drug targeting through the identification of flux characteristics unique to the cancerous phenotype

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