On the Role of Glycolysis in Early Tumorigenesis-Permissive and Executioner Effects

Genomic Deletion of PFKFB3 Decreases In Vivo Tumorigenesis

Rapidly proliferative processes in mammalian tissues including tumorigenesis and embryogenesis rely on the glycolytic pathway for energy and biosynthetic precursors. The enzyme 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase-3 (PFKFB3) plays an important regulatory role in glycolysis by activating the key rate-limiting glycolytic enzyme, 6-phosphofructo-1-kinase (PFK-1). We have previously determined that decreased PFKFB3 expression reduced glycolysis and growth in transformed cells in vitro and suppressed xenograft growth in vivo. In earlier studies, we created a constitutive knockout mouse to interrogate the function of PFKFB3 in vivo but failed to generate homozygous offspring due to the requirement for PFKFB3 for embryogenesis. We have now developed a novel transgenic mouse model that exhibits inducible homozygous pan-tissue Pfkfb3 gene deletion (Pfkfb3fl/fl). We have induced Pfkfb3 genomic deletion in these mice and found that it effectively decreased PFKFB3 expression and activity. To evaluate the functional consequences of Pfkfb3 deletion in vivo, we crossed Cre-bearing Pfkfb3fl/fl mice with oncogene-driven tumor models and found that Pfkfb3 deletion markedly decreased their glucose uptake and growth. In summary, our studies reveal a critical regulatory function for PFKFB3 in glycolysis and tumorigenesis in vivo and characterize an effective and powerful model for further investigation of its role in multiple biological processes.

Transcriptional regulation and post-translational modifications in the glycolytic pathway for targeted cancer therapy

Cancer cells largely rely on aerobic glycolysis or the Warburg effect to generate essential biomolecules and energy for their rapid growth. The key modulators in glycolysis including glucose transporters and enzymes, e.g. hexokinase 2, enolase 1, pyruvate kinase M2, lactate dehydrogenase A, play indispensable roles in glucose uptake, glucose consumption, ATP generation, lactate production, etc. Transcriptional regulation and post-translational modifications (PTMs) of these critical modulators are important for signal transduction and metabolic reprogramming in the glycolytic pathway, which can provide energy advantages to cancer cell growth. In this review we recapitulate the recent advances in research on glycolytic modulators of cancer cells and analyze the strategies targeting these vital modulators including small-molecule inhibitors and microRNAs (miRNAs) for targeted cancer therapy. We focus on the regulation of the glycolytic pathway at the transcription level (e.g., hypoxia-inducible factor 1, c-MYC, p53, sine oculis homeobox homolog 1, N6-methyladenosine modification) and PTMs (including phosphorylation, methylation, acetylation, ubiquitination, etc.) of the key regulators in these processes. This review will provide a comprehensive understanding of the regulation of the key modulators in the glycolytic pathway and might shed light on the targeted cancer therapy at different molecular levels.

Immune checkpoints between epithelial-mesenchymal transition and autophagy: A conflicting triangle

Inhibitory immune checkpoint (ICP) molecules are pivotal in inhibiting innate and acquired antitumor immune responses, a mechanism frequently exploited by cancer cells to evade host immunity. These evasion strategies contribute to the complexity of cancer progression and therapeutic resistance. For this reason, ICP molecules have become targets for antitumor drugs, particularly monoclonal antibodies, collectively referred to as immune checkpoint inhibitors (ICI), that counteract such cancer-associated immune suppression and restore antitumor immune responses. Over the last decade, however, it has become clear that tumor cell-associated ICPs can also induce tumor cell-intrinsic effects, in particular epithelial-mesenchymal transition (EMT) and macroautophagy (hereafter autophagy). Both of these processes have profound implications for cancer metastasis and drug responsiveness. This article reviews the positive or negative cross-talk that tumor cell-associated ICPs undergo with autophagy and EMT. We discuss that tumor cell-associated ICPs are upregulated in response to the same stimuli that induce EMT. Moreover, ICPs themselves, when overexpressed, become an EMT-inducing stimulus. As regards the cross-talk with autophagy, ICPs have been shown to either stimulate or inhibit autophagy, while autophagy itself can either up- or downregulate the expression of ICPs. This dynamic equilibrium also extends to the autophagy-apoptosis axis, further emphasizing the complexities of cellular responses. Eventually, we delve into the intricate balance between autophagy and apoptosis, elucidating its role in the broader interplay of cellular dynamics influenced by ICPs. In the final part of this article, we speculate about the driving forces underlying the contradictory outcomes of the reciprocal, inhibitory, or stimulatory effects between ICPs, EMT, and autophagy. A conclusive identification of these driving forces may allow to achieve improved antitumor effects when using combinations of ICIs and compounds acting on EMT and/or autophagy. Prospectively, this may translate into increased and/or broadened therapeutic efficacy compared to what is currently achieved with ICI-based clinical protocols.

mTORC2-AKT signaling to PFKFB2 activates glycolysis that enhances stemness and tumorigenicity of intestinal epithelial cells

Although elevated glycolysis has been widely recognized as a hallmark for highly proliferating cells like stem cells and cancer, its regulatory mechanisms are still being updated. Here, we found a previously unappreciated mechanism of mammalian target of rapamycin complex 2 (mTORC2) in regulating glycolysis in intestinal stem cell maintenance and cancer progression. mTORC2 key subunits expression levels and its kinase activity were specifically upregulated in intestinal stem cells, mouse intestinal tumors, and human colorectal cancer (CRC) tissues. Genetic ablation of its key scaffolding protein Rictor in both mouse models and cell lines revealed that mTORC2 played an important role in promoting intestinal stem cell proliferation and self-renewal. Moreover, utilizing mouse models and organoid culture, mTORC2 loss of function was shown to impair growth of gut adenoma and tumor organoids. Based on these findings, we performed RNA-seq and noticed significant metabolic reprogramming in Rictor conditional knockout mice. Among all the pathways, carbohydrate metabolism was most profoundly altered, and further studies demonstrated that mTORC2 promoted glycolysis in intestinal epithelial cells. Most importantly, we showed that a rate-limiting enzyme in regulating glycolysis, 6-phosphofructo-2-kinase (PFKFB2), was a direct target for the mTORC2-AKT signaling. PFKFB2 was phosphorylated upon mTORC2 activation, but not mTORC1, and this process was AKT-dependent. Together, this study has identified a novel mechanism underlying mTORC2 activated glycolysis, offering potential therapeutic targets for treating CRC.

A comprehensive pan-cancer analysis identifies a novel glycolysis score and its hub genes as prognostic and immunological biomarkers

Background

Glycolysis plays significant roles in tumor progression and immune response. However, the exact role of glycolysis in prognosis and immune regulation has not been explored in all cancer types. This study first calculated a novel glycolysis score and screened out 12 glycolytic hub genes, and comprehensively analyzed molecular expression, clinical implications, and immune features of glycolysis among pan-cancer.

Methods

The glycolysis score was derived by the single sample gene set enrichment analysis (ssGSEA) algorithm. The correlations of glycolysis with clinical parameters were analyzed using "limma" package. Downstream pathways of glycolysis were identified by Gene Set Enrichment Analysis (GSEA). The immune cell infiltration was explored and validated by three databases. The association between glycolysis and some immunotherapy biomarkers was explored by Pearson correlation analysis. Single-nucleotide variation (SNV), copy number variation (CNV), DNA methylation, and drug sensitivity analyses of 12 glycolytic hub genes were investigated. IMvigor210 and GSE91061 immunotherapeutic cohorts were retrieved to assess the ability of glycolysis score to predict immunotherapy efficacy. The expression of glycolysis key genes was detected in normal and endometrial cancer cell lines.

Results

We found that glycolysis score was generally higher in tumor tissues compared to normal tissues and a high glycolysis score predominated as a risk prognostic factor. A high glycolysis score was associated with decreased immunostimulatory natural killer (NK) cells and CD8+ T cells infiltration, well increased immunosuppressive M2-tumor-associated macrophages (M2-TAM) cells infiltration. Tumor mutational burden (TMB), microsatellite instability (MSI), and immune checkpoints (ICPs) all closely interacted with glycolysis score and the frequency of gene mutation was confirmed to be higher in colon adenocarcinoma (COAD) patients with higher glycolysis score. The SNV, CNV, and DNA methylation of 12 glycolysis key genes occurred at different frequencies and showed different impacts on survival outcomes. The predictive and prognostic value of glycolysis score for immunotherapy outcomes was validated in two immunotherapy cohorts. The expression levels of key genes differ in normal endometrial and three endometrial cancer cell lines.

Conclusions

This work indicated that glycolysis score and 12 glycolytic hub genes were correlated with an immunosuppressive microenvironment. They could be served as promising biomarkers aiding diagnosis, predicting prognosis and immunotherapy response for some tumor patients.

Different hydration protocols for the quantification of healthy tissue uptake of half-dose 18F-FDG total-body positron emission tomography-computed tomography: a prospective study

Background

This study aimed to investigate the effects of the volume and time of hydration on the quantification of healthy tissue uptake for 2-deoxy-2-[18F]-fluoro-D-glucose (18F-FDG) total-body positron emission tomography (PET)-computed tomography (CT) with half-dose activity.

Methods

This study prospectively enrolled 180 patients who underwent a total-body PET-CT scan 10 min after injection of a half-dose (1.85 MBq/kg) of 18F-FDG. These patients were placed in hydration groups (30 patients in each group) according to different hydration volumes and times: oral hydration with 500 mL of water 20 min before (G1), 5 min after (G2), and 30 min after (G3) the 18F-FDG injection; and oral hydration with 200 mL of water 20 min before (G4), 5 min after (G5), and 30 min after (G6) the 18F-FDG injection. Another 30 patients underwent dynamic imaging without hydration and were used a nonhydration group. The analysis of quantification of healthy tissue uptake included the maximum standardized uptake value (SUVmax) and the mean SUV (SUVmean) of the blood pool and muscle, as well as the SUVmax, SUVmean, and signal-to-noise ratio (SNR) of the liver.

Results

The SUVmax of the blood pool (2.33±0.36), liver (3.03±0.42), and muscle (0.81±0.15) was significantly higher in the nonhydration group than in any of the 6 hydrated groups (P<0.05 for all hydration groups vs. nonhydration group). Muscle SUVmax and SUVmean were significantly (P<0.05) lower in G1 and G2 than in G3 and were lower in G4 and G5 than in G6. The SUVmax and SUVmean of the blood pool were significantly (P<0.05) lower in G1 than in G3 and G4 and lower in G3 than in G6.

Conclusions

When total-body PET-CT with a half dose of 18F-FDG activity is performed, hydration can significantly affect the quantification of healthy tissue uptake. Oral administration of 500 mL of water 20 min before injection could reduce background radioactivity.