The role of metabolic ecosystem in cancer progression — metabolic plasticity and mTOR hyperactivity in tumor tissues

Despite advancements in cancer management, tumor relapse and metastasis are associated with poor outcomes in many cancers. Over the past decade, oncogene-driven carcinogenesis, dysregulated cellular signaling networks, dynamic changes in the tissue microenvironment, epithelial-mesenchymal transitions, protein expression within regulatory pathways, and their part in tumor progression are described in several studies. However, the complexity of metabolic enzyme expression is considerably under evaluated. Alterations in cellular metabolism determine the individual phenotype and behavior of cells, which is a well-recognized hallmark of cancer progression, especially in the adaptation mechanisms underlying therapy resistance. In metabolic symbiosis, cells compete, communicate, and even feed each other, supervised by tumor cells. Metabolic reprogramming forms a unique fingerprint for each tumor tissue, depending on the cellular content and genetic, epigenetic, and microenvironmental alterations of the developing cancer. Based on its sensing and effector functions, the mechanistic target of rapamycin (mTOR) kinase is considered the master regulator of metabolic adaptation. Moreover, mTOR kinase hyperactivity is associated with poor prognosis in various tumor types. In situ metabolic phenotyping in recent studies highlights the importance of metabolic plasticity, mTOR hyperactivity, and their role in tumor progression. In this review, we update recent developments in metabolic phenotyping of the cancer ecosystem, metabolic symbiosis, and plasticity which could provide new research directions in tumor biology. In addition, we suggest pathomorphological and analytical studies relating to metabolic alterations, mTOR activity, and their associations which are necessary to improve understanding of tumor heterogeneity and expand the therapeutic management of cancer.

Postmortem Study of Organ-Specific Toxicity in Glioblastoma Patients Treated with a Combination of Temozolomide, Irinotecan and Bevacizumab

Purpose Systemic monotherapy with temozolomide (TMZ) or bevacizumab (BEV); two-drug combinations, such as Irinotecan (IRI) and BEV, TMZ and BEV and a three-drug combination with TMZ, IRI and BEV (TIB) have been used in treating patients with progressive high-grade gliomas including glioblastoma. Most patients tolerated these regimens well with well-established sides effects of hypertension, proteinuria, and reversible clinical myelosuppression (CM). However, organ-specific toxicities have never been examined by postmortem studies. Methods Postmortem tissues (from all major organs) were prospectively collected and examined by standard institution autopsy and brain cutting procedures from 76 decedents, including gliomas (N=68, 44/M, and 24/F) and brain metastases (N=8, 5/M, and 3/F) between 2009 and 2019. Standard hematoxylin and eosin (H&E) were performed on all major organs and brain samples harvested. Electronic microscopic (EM) study was carried on selected subjects kidney samples per standard EM protocol. Results Twenty-four glioma subjects were treated with TIB [median: 5.5 (range: 1-25) cycles] at glioma recurrence. Exposure to IRI significantly increased the frequency of CM (p=0.05). No unexpected adverse events were detected clinically or permenant end-organ damage by postmortem examination among subjects who received TIB compared to subjects who received standard of care (SOC) therapies. Among glioma decedents, the most common causes of death (COD) were tumor progression (63.2%, N=43), followed by aspiration pneumonia (48.5%, N=33). No COD was attributed to acute toxicity from TIB. The study also demonstrated that postmortem kidney specimen is unsuitable for studying renal ultrastructural pathological changes due to autolysis. Conclusion IRI, but not the extended use of TMZ, significantly increased CM in recurrent glioma patients. There is no permanent organ-specific toxicity among glioma decedents who received prolonged BEV, TMZ or TIB regimen based chemotherapies except expected occasional myelosuppresson. COD are most commonly resulted from glioma tumor progression and aspiration pneumonia.

The Epithelial–Mesenchymal Transition at the Crossroads between Metabolism and Tumor Progression

The transition between epithelial and mesenchymal phenotype is emerging as a key determinant of tumor cell invasion and metastasis. It is a plastic process in which epithelial cells first acquire the ability to invade the extracellular matrix and migrate into the bloodstream via transdifferentiation into mesenchymal cells, a phenomenon known as epithelial–mesenchymal transition (EMT), and then reacquire the epithelial phenotype, the reverse process called mesenchymal–epithelial transition (MET), to colonize a new organ. During all metastatic stages, metabolic changes, which give cancer cells the ability to adapt to increased energy demand and to withstand a hostile new environment, are also important determinants of successful cancer progression. In this review, we describe the complex interaction between EMT and metabolism during tumor progression. First, we outline the main connections between the two processes, with particular emphasis on the role of cancer stem cells and LncRNAs. Then, we focus on some specific cancers, such as breast, lung, and thyroid cancer.

Genetic Impairment of Succinate Metabolism Disrupts Bioenergetic Sensing in Adrenal Neuroendocrine Cancer

Metabolic dysfunction mutations can impair energy sensing and cause cancer. Loss of function of mitochondrial TCA cycle enzyme, succinate dehydrogenase B (SDHB) results in various forms of cancer typified by pheochromocytoma (PC). Here we delineate a signaling cascade where the loss of SDHB induces the Warburg effect in PC tumors, triggers dysregulation of Ca2+ homeostasis, and aberrantly activates calpain and the protein kinase Cdk5, through conversion of its cofactor from p35 to p25. Consequently, aberrant Cdk5 initiates a cascade of phospho-signaling where GSK3 inhibition inactivates energy-sensing by AMP-kinase through dephosphorylation of the AMP-kinase γ subunit, PRKAG2. Overexpression of p25-GFP in mouse adrenal chromaffin cells also elicits this phosphorylation signaling and causes PC tumor formation. A novel Cdk5 inhibitor, MRT3-007, reversed this phospho-cascade, invoking an anti-Warburg effect, cell cycle arrest, and senescence-like phenotype. This therapeutic approach halted tumor progression in vivo. Thus, we reveal an important novel mechanistic feature of metabolic sensing and demonstrate that its dysregulation underlies tumor progression in PC and likely other cancers.