LDH5 overexpression is associated with poor survival in patients with solid tumors: a meta-analysis

Peptide-based LDH5 inhibitors enter cancer cells and impair proliferation

Lactate dehydrogenase 5 (LDH5) is overexpressed in many cancers and is a potential target for anticancer therapy due to its role in aerobic glycolysis. Small-molecule drugs have been developed as competitive inhibitors to bind substrate/cofactor sites of LDH5, but none reached the clinic to date. Recently, we designed the first LDH5 non-competitive inhibitor, cGmC9, a peptide that inhibits protein-protein interactions required for LDH5 enzymatic activity. Peptides are gaining a large interest as anticancer agents to modulate intracellular protein-protein interactions not targetable by small molecules; however, delivery of these peptides to the cytosol, where LDH5 and other anticancer targets are located, remains a challenge for this class of therapeutics. In this study, we focused on the cellular internalisation of cGmC9 to achieve LDH5 inhibition in the cytosol. We designed cGmC9 analogues and compared them for LDH5 inhibition, cellular uptake, toxicity, and antiproliferation against a panel of cancer cell lines. The lead analogue, [R/r]cGmC9, specifically impairs proliferation of cancer cell lines with high glycolytic profiles. Proteomics analysis showed expected metabolic changes in response to decreased glycolysis. This is the first report of a peptide-based LDH5 inhibitor able to modulate cancer metabolism and kill cancer cells that are glycolytic. The current study demonstrates the potential of using peptides as inhibitors of intracellular protein-protein interactions relevant for cancer pathways and shows that active peptides can be rationally designed to improve their cell permeation.

Designed β-Hairpins Inhibit LDH5 Oligomerization and Enzymatic Activity

Lactate dehydrogenase 5 (LDH5) is overexpressed in metastatic tumors and is an attractive target for anticancer therapy. Small-molecule drugs have been developed to target the substrate/cofactor sites of LDH5, but none has reached the clinic to date, and alternative strategies remain almost unexplored. Combining rational and computer-based approaches, we identified peptidic sequences with high affinity toward a β-sheet region that is involved in protein-protein interactions (PPIs) required for the activity of LDH5. To improve stability and potency, these sequences were grafted into a cyclic cell-penetrating β-hairpin peptide scaffold. The lead grafted peptide, cGmC9, inhibited LDH5 activity in vitro in low micromolar range and more efficiently than the small-molecule inhibitor GNE-140. cGmC9 inhibits LDH5 by targeting an interface unlikely to be inhibited by small-molecule drugs. This lead will guide the development of new LDH5 inhibitors and challenges the landscape of drug discovery programs exclusively dedicated to small molecules.

Lactate and cancer: a "lactatic" perspective on spinal tumor metabolism (part 1)

Spine tumors are among the most difficult tumors to treat given their proximity to the spinal cord. Despite advances in adjuvant therapies, surgery remains a critical component of treatment, both in primary tumors and metastatic disease. Given the significant morbidity of these surgeries and with other current adjuvant therapies (e.g., radiation, chemotherapy), interest has grown in other methods of targeting tumors of the spine. Recent efforts have highlighted the tumor microenvironment, and specifically lactate, as central to tumorigenesis. Once erroneously considered a waste product that indicated hypoxia/hypoperfusion, lactate is now known to be at the center of whole-body metabolism, shuttling between tissues and being used as a fuel. Diffusion-driven transporters and the near-equilibrium enzyme lactate dehydrogenase (LDH) allow rapid mobilization of large stores of muscle glycogen in the form of lactate. In times of stress, catecholamines can bind muscle cell receptors and trigger the breakdown of glycogen to lactate, which can then diffuse out into circulation and be used as a fuel where needed. Hypoxia, in contrast, is rarely the reason for an elevated arterial [lactate]. Tumors were originally described in the 1920's as being "glucose-avid" and "lactate-producing" even in normoxia (the "Warburg effect"). We now know that a broad range of metabolic behaviors likely exist, including cancer cells that consume lactate as a fuel, others that may produce it, and still others that may change their behavior based on the local microenvironment. In this review we will examine the relationship between lactate and tumor metabolism with a brief look at spine-specific tumors. Lactate is a valuable fuel and potent signaling molecule that has now been implicated in multiple steps in tumorigenesis [e.g., driving vascular endothelial growth factor (VEGF) expression in normoxia]. Future work should utilize translational animal models to target tumors by altering the local tumor microenvironment, of which lactate is a critical part.

Prognostic value of preoperative serum lactate dehydrogenase in thymic carcinoma

BACKGROUND

The prognostic value of serum lactate dehydrogenase (LDH) has been demonstrated in various solid tumors. We attempted to determine whether serum LDH was predictive of survival in thymic carcinoma after surgical resection.

METHODS

Ninety-five patients with thymic carcinoma treated in our hospital between January 2005 and December 2015 were retrospectively enrolled. Serum LDH was measured before surgery and categorized as low or high relative to the upper limit of normal (ULN) (225 U/L). The relationships of serum LDH level and other clinical variables with survival were estimated by Cox regression and Kaplan-Meier survival analysis.

RESULTS

Serum LDH levels were found to be significantly associated with overall survival (OS) and progression-free survival (PFS) of these patients. The 1-, 3-, and 5-year PFS were 76%, 51%, and 38%, and the 1-, 3- and 5-year OS were 97%, 75%, and 46%, respectively. Univariate analysis found that high serum LDH (>225 U/L) was associated with both lower OS [hazard ratio (HR) =2.710; 95% confidence interval (CI): 1.363-1.5.391; P=0.004] and PFS (HR =3.365; 95% CI: 1.776-6.374; P<0.001). Multivariate analysis found that high serum LDH was associated with lower PFS (HR =2.122; 95% CI: 1.056-4.267; P=0.035). Moreover, high LDH was significantly associated with advanced Masaoka stage (P=0.001).

CONCLUSIONS

High serum LDH (>225 U/L) was an independent predictor of decreased PFS in thymic carcinoma patients. It was also significantly associated with reduced OS, but was not an independent predictor of death in those patients.

Current relevance of hypoxia in head and neck cancer

Head and Neck cancer (HNC) is a complex mix of cancers and one of the more common cancers with a relatively poor prognosis. One of the factors that may assist us in predicting survival and allow us to adjust our treatment strategies is the presence of tumor hypoxia. In this overview we aim to evaluate the current evidence and potential clinical relevance of tumor hypoxia in head and neck cancer according to an extensive search of current literature.An abundance of evidence and often contradictory evidence is found in the literature. Even the contradictory evidence and comparisons are difficult to judge as criteria and methodologies differ greatly, furthermore few prospective observational studies exist for verification of the pre-clinical studies. Despite these discrepancies there is clear evidence of associations between prognosis and poor tumor oxygenation biomarkers such as HIF-1α, GLUT-1 and lactate, though these associations are not exclusive. The use of genetic markers is expanding and will probably lead to significantly more and complex evidence. The lack of oxygenation in head and neck tumors is of paramount importance for the prediction of treatment outcomes and prognosis. Despite the wide array of conflicting evidence, the drive towards non-invasive prediction of tumor hypoxia should continue.

Metabolic reprogramming in cancer cells: glycolysis, glutaminolysis, and Bcl-2 proteins as novel therapeutic targets for cancer

Nearly a century ago, Otto Warburg made the ground-breaking observation that cancer cells, unlike normal cells, prefer a seemingly inefficient mechanism of glucose metabolism: aerobic glycolysis, a phenomenon now referred to as the Warburg effect. The finding that rapidly proliferating cancer cells favors incomplete metabolism of glucose, producing large amounts of lactate as opposed to synthesizing ATP to sustain cell growth, has confounded scientists for years. Further investigation into the metabolic phenotype of cancer has expanded our understanding of this puzzling conundrum, and has opened new avenues for the development of anti-cancer therapies. Enhanced glycolytic flux is now known to allow for increased synthesis of intermediates for sustaining anabolic pathways critical for cancer cell growth. Alongside the increase in glycolysis, cancer cells transform their mitochondria into synthesis machines supported by augmented glutaminolysis, supplying lipid production, amino acid synthesis, and the pentose phosphate pathways. Inhibition of several of the key enzymes involved in these pathways has been demonstrated to effectively obstruct cancer cell growth and multiplication, sensitizing them to apoptosis. The modulation of various regulatory proteins involved in metabolic processes is central to cancerous reprogramming of metabolism. The finding that members of one of the major protein families involved in cell death regulation also aberrantly regulated in cancers, the Bcl-2 family of proteins, are also critical mediators of metabolic pathways, provides strong evidence for the importance of the metabolic shift to cancer cell survival. Targeting the anti-apoptotic members of the Bcl-2 family of proteins is proving to be a successful way to selectively target cancer cells and induce apoptosis. Further understanding of how cancer cells modify metabolic regulation to increase channeling of substrates into biosynthesis will allow for the discovery of novel drug targets to treat cancer. In the present review, we focused on the recent developments in therapeutic targeting of different steps in glycolysis, glutaminolysis and on the metabolic regulatory role of Bcl-2 family proteins.

Isoform switch of pyruvate kinase M1 indeed occurs but not to pyruvate kinase M2 in human tumorigenesis

Muscle type of pyruvate kinase (PKM) is one of the key mediators of the Warburg effect and tumor metabolism. Due to alternative splicing, there are at least 12 known isoforms of the PKM gene, of which PKM1 and PKM2 are two major isoforms with only a 23 amino acid sequenced difference but quite different characteristics and functions. It was previously thought the isoform switch from PKM1 to PKM2 resulted in high PKM2 expression in tumors, providing a great advantage to tumor cells. However, this traditional view was challenged by two recent studies; one study claimed that this isoform switch does not occur during the Warburg effect; the other study asserted that the isoform switch is tissue-specific. Here, we re-analyzed the RNA sequencing data of 25 types of human tumors from The Cancer Genome Atlas Data Portal, and confirmed that PKM2 was the major isoform in the tumors and was highly elevated in addition to the entire PKM gene. We further demonstrated that the expression level of PKM1 significantly declined even though there was substantially increased expression of the entire PKM gene. The proportion of PKM1 in total transcript variants also significantly declined in tumors but the proportion of PKM2 did not change accordingly. Therefore, we conclude that the isoform switch of PKM1 does indeed occur, but it switches to other isoforms rather than PKM2. Considering the change in the expression levels of PKM1, PKM2 and the entire PKM gene, we propose that the upregulation of PKM2 is primarily due to elevated transcriptional levels of the entire PKM gene, instead of the isoform switch.