Natural abundance isotope ratios to differentiate sources of carbon used during tumor growth in vivo

BackgroundRadioactive or stable isotopic labeling of metabolites is a strategy that is routinely used to map the cellular fate of a selected labeled metabolite after it is added to cell culture or to the circulation of an animal. However, a labeled metabolite can be enzymatically changed in cellular metabolism, complicating the use of this experimental strategy to understand how a labeled metabolite moves between organs. These methods are also technically demanding, expensive and potentially toxic. To allow quantification of the bulk movement of metabolites between organs, we have developed a novel application of stable isotope ratio mass spectrometry (IRMS).ResultsWe exploit natural differences in C-13/C-12 ratios of plant nutrients for a low-cost and non-toxic carbon labeling, allowing a measurement of bulk carbon transfer between organs in vivo. IRMS measurements were found to be sufficiently sensitive to measure organs from individual Drosophila melanogaster larvae, giving robust measurements down to 2.5 mu g per sample. We apply the method to determine if carbon incorporated into a growing solid tumor is ultimately derived from food or host tissues.ConclusionMeasuring tumor growth in a D. melanogaster larvae tumor model reveals that these tumors derive a majority of carbon from host sources. We believe the low cost and non-toxic nature of this methodology gives it broad applicability to study carbon flows between organs also in other animals and for a range of other biological questions.

Automated summary

A novel application of stable isotope ratio mass spectrometry (IRMS) utilizing natural differences in C-13/C-12 ratios of plant nutrients allows for low-cost and non-toxic carbon labeling, enabling the measurement of bulk carbon transfer between organs in vivo. The method is sensitive enough to measure carbon content in individual organs of Drosophila melanogaster larvae, providing robust measurements down to 2.5 μg per sample. This methodology, with its low cost and non-toxic nature, has broad applicability for studying carbon flows between organs in various animals and for addressing a range of biological questions.