Metabolic Codependencies in the Tumor Microenvironment

Abstract

Metabolic reprogramming enables cancer cell growth, proliferation, and survival. This reprogramming is driven by the combined actions of oncogenic alterations in cancer cells and host cell factors acting on cancer cells in the tumor microenvironment. Cancer cell-intrinsic mechanisms activate signal transduction components that either directly enhance metabolic enzyme activity or upregulate transcription factors that in turn increase expression of metabolic regulators. Extrinsic signaling mechanisms involve host-derived factors that further promote and amplify metabolic reprogramming in cancer cells. This review describes intrinsic and extrinsic mechanisms driving cancer metabolism in the tumor microenvironment and how such mechanisms may be targeted therapeutically. SIGNIFICANCE: Cancer cell metabolic reprogramming is a consequence of the converging signals originating from both intrinsic and extrinsic factors. Intrinsic signaling maintains the baseline metabolic state, whereas extrinsic signals fine-tune the metabolic processes based on the availability of metabolites and the requirements of the cells. Therefore, successful targeting of metabolic pathways will require a nuanced approach based on the cancer's genotype, tumor microenvironment composition, and tissue location.

Figure 1.. Intrinsic drivers of metabolic pathways.

This schematic summarizes specific oncogenes and tumor suppressor genes that modulate metabolic pathways for tumor progression. PI3K-AKT, mTOR and cMyc pathway are integral to the maintenance of core metabolic functions in normal and cancer cells, while aberrant activation is central to tumor progression and maintenance. GLUT, Glucose transporter; HK1/2, Hexokinase 1/2; PFKM1, phosphofructokinase-M 1; ENO1, Enolase 1; MCT1, Monocarboxylate transporter 1; ACC1, Acetyl-CoA carboxylase; ACLY, ATP Citrate Lyase; HMGCR, HMG-CoA reductase.

Figure 2.. Extrinsic drivers of metabolic pathways.

This schematic summarizes the factors derived from the microenvironment that dictate the metabolic profile of the tumor. Extrinsic factors such as cytokines, hormones and metabolites regulate cellular metabolism in discrete ways driven by the availability of these factors in anatomically distinct sites and by differences in the composition of resident immune, endothelial, and fibroblast cells. MPC, Mitochondrial Pyruvate; SREBP, Sterol regulatory element-binding protein.