Lactic acidosis in patients with cancer

CRNDE silencing promotes apoptosis and enhances cisplatin sensitivity of colorectal carcinoma cells by inhibiting the Akt/mTORC1-mediated Warburg effect

Colorectal cancer (CRC) is one of the most prevalent gastrointestinal tumors worldwide, with a high mortality rate. The lncRNA colorectal neoplasia differentially expressed (CRNDE) is upregulated in CRC and is involved in regulating the apoptosis, proliferation, and drug sensitivity of CRC cells. However, the specific underlying mechanisms remain to be elucidated. The aim of the present study was to investigate the effects of CRNDE on the Warburg effect in CRC cells, as well as the associated mechanisms. The expression of CRNDE in HCT-116 cells was overexpressed or silenced by transfection. Apoptosis, cisplatin sensitivity, the Warburg effect, and Akt/mTOR activation were evaluated. The results demonstrated that CRNDE inhibition decreased the proliferation and increased the apoptosis and cisplatin sensitivity of HCT-116 cells. In addition, CRNDE inhibition attenuated the Warburg effect in HCT-116 cells, as verified by a decrease in ATP production, lactic acid levels, glucose uptake, and the expression of Warburg effect-related enzymes (GLUT1, LDHA, HK2, and PKM2). CRNDE inhibition also suppressed the activity of the Akt/mTORC1 pathway, as demonstrated by the decreased phosphorylation of Akt, S6K, S6, and mTOR and the increased phosphorylation of 4EBP-1 and EIF-4E. The CRNDE overexpression-induced increase in ATP and lactic acid levels and glucose uptake in HCT-116 cells was reversed by Akt and mTOR inhibitors. These findings indicate that CRNDE silencing promotes apoptosis and enhances cisplatin sensitivity in colorectal carcinoma cells, which may be mediated by the regulation of the Warburg effect via the Akt/mTORC1 pathway. The present study thus provides a potential strategy for the treatment of CRC.

l-lactic acidosis confers insensitivity to PKC inhibitors by competing for uptake via monocarboxylate transporters

Targeting protein kinase C (PKC) family was found to repress the migration and resistance of non-small cell lung cancer cells to epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors (TKIs). However, none of the PKC inhibitors has been approved for anticancer therapy yet due to the limited efficacy in clinical trials, and the underlying mechanisms remain unclear. l-lactic acidosis, a common condition comprising high l-lactate concentration and acidic pH in the tumor microenvironment, has been known to induce tumor metastasis and drug resistance. In this study, l-lactic acid was found to reverse the inhibitory effects of pan-PKC inhibitors GO6983 on PKC activity, cell migration, and EGFR-TKI resistance, but these effects were not affected by the modulators of lactate receptor GPR81. Interestingly, blockade of lactate transporters, monocarboxylate transporter-1 and -4 (MCT1 and MCT4), attenuated the intracellular level of GO6983, and its inhibitory effect on PKC activity, suggesting that lactic acid promotes the resistance to PKC inhibitors by competing for the uptake through these transporters rather than by activating its receptor, GPR81. Our findings explain the underlying mechanisms of the limited response of PKC inhibitors in clinical trials.

Circular RNAs Regulate Glucose Metabolism in Cancer Cells

Circular RNAs (circRNAs) were originally thought to result from RNA splicing errors. However, it has been shown that circRNAs can regulate cancer onset and progression in various ways. They can regulate cancer cell proliferation, differentiation, invasion, and metastasis. Moreover, they modulate glucose metabolism in cancer cells through different mechanisms such as directly regulating glycolytic enzymes and glucose transporter (GLUT) or indirectly regulating signal transduction pathways. In this review, we elucidate on the role of circRNAs in regulating glucose metabolism in cancer cells, which partly explains the pathogenesis of malignant tumors, and provides new therapeutic targets or new diagnostic and prognostic markers for human cancers.

Exosomal Non-Coding RNAs: Regulatory and Therapeutic Target of Hepatocellular Carcinoma

Exosomes are small extracellular vesicles secreted by most somatic cells, which can carry a variety of biologically active substances to participate in intercellular communication and regulate the pathophysiological process of recipient cells. Recent studies have confirmed that non-coding RNAs (ncRNAs) carried by tumor cell/non-tumor cell-derived exosomes have the function of regulating the cancerous derivation of target cells and remodeling the tumor microenvironment (TME). In addition, due to the unique low immunogenicity and high stability, exosomes can be used as natural vehicles for the delivery of therapeutic ncRNAs in vivo. This article aims to review the potential regulatory mechanism and the therapeutic value of exosomal ncRNAs in hepatocellular carcinoma (HCC), in order to provide promising targets for early diagnosis and precise therapy of HCC.

Regulation of Glycolysis by Non-coding RNAs in Cancer: Switching on the Warburg Effect

The “Warburg effect” describes the reprogramming of glucose metabolism away from oxidative phosphorylation toward aerobic glycolysis, and it is one of the hallmarks of cancer cells. Several factors can be involved in this process, but in this review, the roles of non-coding RNAs (ncRNAs) are highlighted in several types of human cancer. ncRNAs, including microRNAs, long non-coding RNAs, and circular RNAs, can all affect metabolic enzymes and transcription factors to promote glycolysis and modulate glucose metabolism to enhance the progression of tumors. In particular, the 5′-AMP-activated protein kinase (AMPK) and the phosphatidylinositol 3-kinase (PI3K)/AKT/mammalian target of rapamycin (mTOR) pathways are associated with alterations in ncRNAs. A better understanding of the roles of ncRNAs in the Warburg effect could ultimately lead to new therapeutic approaches for suppressing cancer.

Prognostic effects of glycometabolism changes in lung adenocarcinoma: a prospective observational study

Background

Changes in glycometabolism of cancer cells provides cancer cells with growth advantages, which are also of great value in the prognosis prediction of the patients with lung adenocarcinoma. However, currently available studies are controversial.

Methods

We successively collected 100 paired surgical specimens from patients with lung adenocarcinoma. The content of glycometabolic intermediates in tissues was tested by liquid chromatography-mass spectrometry. Follow-up was conducted every 6 months for patients enrolled in this study.

Results

There were significant differences in the contents of six intermediates, including glucose (P<0.0001), pyruvate (P=0.0009), lactate (P<0.0001), citrate (P=0.0001), α-ketoglutarate (P=0.0002), and fumarate (P=0.0096). For different TNM stages, the pyruvate content (P<0.001) and lactate content (P<0.001) in the II/III/IV stage cancer tissues were significantly higher than those in the stage I cancer tissues. The overall survival (OS) of patients with high levels of glucose (P=0.0034), pyruvate (P<0.0001), lactate (P=0.049), and citrate (P=0.024) in cancer tissues was significantly worse than that of patients with low levels. N stage (P<0.001) and the contents of pyruvate (P=0.033) were independent prognostic factors for the OS.

Conclusions

The contents of glucose, pyruvate, lactate, and citrate in cancer tissues are higher than that in para-carcinoma tissues, and the long-term survival decrease in patients with higher glucose, pyruvate, lactate, and citrate.

Unappreciated Role of LDHA and LDHB to Control Apoptosis and Autophagy in Tumor Cells

Tumor cells possess a high metabolic plasticity, which drives them to switch on the anaerobic glycolysis and lactate production when challenged by hypoxia. Among the enzymes mediating this plasticity through bidirectional conversion of pyruvate and lactate, the lactate dehydrogenase A (LDHA) and lactate dehydrogenase B (LDHB), are indicated. LDHA has a higher affinity for pyruvate, preferentially converting pyruvate to lactate, and NADH to NAD⁺ in anaerobic conditions, whereas LDHB possess a higher affinity for lactate, preferentially converting lactate to pyruvate, and NAD⁺ to NADH, when oxygen is abundant. Apart from the undisputed role of LDHA and LDHB in tumor cell metabolism and adaptation to unfavorable environmental or cellular conditions, these enzymes participate in the regulation of cell death. This review presents the latest progress made in this area on the roles of LDHA and LDHB in apoptosis and autophagy of tumor cells. Several examples of how LDHA and LDHB impact on these processes, as well as possible molecular mechanisms, will be discussed in this article. The information included in this review points to the legitimacy of modulating LDHA and/or LDHB to target tumor cells in the context of human and veterinary medicine.

Role of multifaceted regulators in cancer glucose metabolism and their clinical significance

Aberrant glucose metabolism, "aerobic glycolysis" or "Warburg effect", is a hallmark of human cancers. There is a cluster of "multifaceted regulators", which plays a pivotal role in the regulation of glucose metabolism. They can not only modulate the activities of specific enzymes, but also act as transcriptional activators to regulate the expression of metabolism related genes. Additionally, they can crosstalk with other key factors involved in glucose metabolism and work together to initiate multiple oncogenic processes. These "multifaceted regulators", especially p53, HIF-1, TIGAR and microRNA, will be focused in this review. And we will comprehensively illustrate their regulatory effects on cancer glucose metabolism, and further elaborate on their clinical significance. In-depth elucidation the role of "multifaceted regulators" in cancer glucose metabolism will provide us novel insights in cancer research field and offer promising therapeutic targets for anti-cancer therapies.

Role of long non-coding RNAs in glucose metabolism in cancer

Long-noncoding RNAs (lncRNAs) are a group of transcripts that are longer than 200 nucleotides and do not code for proteins. However, this class of RNAs plays pivotal regulatory roles. The mechanism of their action is highly complex. Mounting evidence shows that lncRNAs can regulate cancer onset and progression in a variety of ways. They can not only regulate cancer cell proliferation, differentiation, invasion and metastasis, but can also regulate glucose metabolism in cancer cells through different ways, such as by directly regulating the glycolytic enzymes and glucose transporters (GLUTs), or indirectly modulating the signaling pathways. In this review, we summarized the role of lncRNAs in regulating glucose metabolism in cancer, which will help understand better the pathogenesis of malignant tumors. The understanding of the role of lncRNAs in glucose metabolism may help provide new therapeutic targets and novel diagnostic and prognosis markers for human cancer.