Physiological impact of in vivo stable isotope tracing on cancer metabolism

Abstract

Background There is growing interest in the analysis of tumor metabolism to identify cancer-specific metabolic vulnerabilities and therapeutic targets. Finding of such candidate metabolic pathways mainly relies on the highly sensitive identification and quantitation of numerous metabolites and metabolic fluxes using metabolomics and isotope tracing analyses. However, nutritional requirements and metabolic routes used by cancer cells cultivated in vitro do not always reflect the metabolic demands of malignant cells within the tumor milieu. Therefore, to understand how the metabolism of tumor cells in its physiological environment differs from that of normal cells, these analyses must be performed in vivo . Scope of Review This review covers the physiological impact of the exogenous administration of a stable isotope tracer into cancer animal models. We discuss specific aspects of in vivo isotope tracing protocols based on discrete bolus injections of a labeled metabolite: the tracer administration per se and the fasting period prior to it. In addition, we illustrate the complex physiological scenarios that arise when studying tumor metabolism – by isotopic labeling in animal models fed with a specific amino acid restricted diet. Finally, we provide strategies to minimize these limitations. Major Conclusions There is growing evidence that metabolic dependencies in cancers are influenced by tissue environment, cancer lineage, and genetic events. An increasing number of studies describe discrepancies in tumor metabolic dependencies when studied in in vitro settings or in vivo models, including cancer patients. Therefore, in-depth in vivo profiling of tumor metabolic routes within the appropriate pathophysiological environment will be key to identify relevant alterations that contribute to cancer onset and progression.

Pancreatic tumors exhibit myeloid-driven amino acid stress and upregulate arginine biosynthesis

“…After glutamine injection, healthy pancreas, tumor tissue, and plasma samples were collected, and 15 N enrichment in arginine and arginine biosynthetic precursors was measured by LC–MS ( Figure 2—source data 2 ). Glutamine in plasma is also quickly metabolized by multiple organs, which can then release labeled arginine and other metabolites into the circulation, which contribute to arginine labeling in other organs and the tumor ( Grima-Reyes et al, 2021 ). One of the main examples of these interorgan exchange fluxes is the intestinal–renal axis, where glutamine metabolized by the small intestine is released as citrulline, which is then used by the kidneys to produce arginine for other tissues ( Boelens et al, 2005 ; Grima-Reyes et al, 2021 ).…”

Pancreatic tumors activate arginine biosynthesis to adapt to myeloid-driven amino acid stress

“…Glutamine in plasma is also quickly metabolized by multiple organs and reintroduced into the circulation as intermediate substrates that can contribute to intraorgan and intratumoral labelling (Grima-Reyes et al, 2021). One of the main examples of these interorgan exchange fluxes is the intestinal-renal axis, where glutamine metabolized by the small intestine is released as citrulline and uptaken by the kidneys and further released as arginine for uptake by different tissues (Boelens et al, 2005; Grima-Reyes et al, 2021). Consistent with this, we observed an enrichment of ∼14% 15 N 1 -arginine and ∼7% 15 N 2 -arginine in the circulation of healthy and tumor bearing mice (Fig.…”

Untargeted stable isotope-resolved metabolomics to assess the effect of PI3Kβ inhibition on metabolic pathway activities in a PTEN null breast cancer cell line

“…Notably, a recent comparison of metabolic flux analysis demonstrated that glucose metabolism in 3D spheroids differs significantly from 2D cultures (Tidwell et al, 2022), hence emphasizing the need to make use of 3D models for investigating cancer metabolism and drug response in cell culture. In this regard, in vivo profiling of tumor metabolic routes within the appropriate tissue environment will be key for interrogating drug action in human cancers (Lane et al, 2016) and to identify relevant alterations that contribute to cancer onset and progression (Grima-Reyes et al, 2021). While the adaption Frontiers in Molecular Biosciences frontiersin.org capability to different biological systems is one aspect of our workflow, usage of different tracers can also be readily implemented to gain complementary information (e.g.…”