Effects of selective lactate dehydrogenase A inhibitors and their mechanism in neoplastic and non-neoplastic cells

The Warburg effect is a widely known process in which cancer cells produce energy through anaerobic glycolysis, even in the presence of oxygen which correlates with cancer resistance, aggressiveness, and metastasis. The last reversible reaction of anaerobic glycolysis is the conversion of pyruvate to lactate catalyzed by lactate dehydrogenase A (LDH-A). A high LDH-A expression was shown to be prognostic in various cancers such as thoracic and pancreatic cancers and was associated with shorter patient survival. The main goal of this study was to investigate the effect of LDH-A inhibition in cancer and non-cancer cells and the mechanism of secondary effects. This thesis is structured into three sections, with Part I featuring a collection of reviews on Cancer Metabolism. Chapter2, describes the role of the pentose phosphate pathway(PPP) in cancer development and proposes potential anti-cancer treatments targeting PPP enzymes for which a high expression correlates with cancer resistance. Chapter3 presents the impact of mitochondrial energy production and 1-carbon(1C) metabolism on cancer resistance mechanisms. Additionally, it includes the summary of clinical studies on drugs targeting NAD+, oxidative phosphorylation(OXPHOS), and 1C metabolism and proposes their combination with other chemotherapeutic agents. Chapter4 focuses on the exosome-mediated cell-to-cell communication, the involvement in changes in cancer metabolism and therapeutic applications. PartII emphasizes the important contribution of lactate dehydrogenase on tumor metabolism and the effect of its inhibition. Chapter5 provides a comprehensive insight on the role of LDH in pancreatic and thoracic cancers as a biomarker, its impact on tumor aggressiveness and resistance, and treatment strategies focused on targeting LDH. Chapter6 describes the studies on a novel LDH-A inhibitor(NHI-Glc-2) linked to glucose to improve cellular uptake by the glucose transporter GLUT-1. NHI-Glc-2 inhibits the growth of pancreatic cancer cells(PANC-1) and disrupts spheroid integrity, with a more pronounced effect when combined with gemcitabine. Furthermore, Chapter7 shows the mechanism of LDH-A inhibition by NHI-Glc-2 in pancreatic cancer cells by reducing the nucleotide levels and mitochondrial respiration. In non-cancer cells (endothelial cells), inhibitors of LDH-A(NHI-2) and of glucose transporter type 1(GLUT-1; PGL) impair migration and the energy charge, as outlined in Chapter 8. The third part is dedicated to exploring therapeutic options for rare and aggressive cancers such as malignant mesothelioma(MM). Chapter9 reviews the primary targeted therapies for pleural MM with detailed descriptions and examination of potential reasons behind treatment failures. The role of microRNAs, spliceosome deregulation, and overexpression of Notch signaling in the development and resistance of pleural MM is emphasized in Chapter10. Chapter11 presents the effects of LDH-A and GLUT-1 inhibitors in MM cells focusing on nucleotide imbalance, reduction of ATP/ADP ratio (energy charge), and the increase of NADH/NAD+ (redox status). With the Seahorse analyzer it was demonstrated show that LDH-A inhibition leads to mitochondrial dysfunction as measured by oxygen consumption rate and glycolysis, especially in pleural MM. Chapter12 describes additional effects of LDH-A and GLUT-1 inhibition in pleural and peritoneal MM. The cells' ability to migrate decreased, along with the induction of apoptosis and the production of reactive oxygen species (ROS). In a 3-dimensional model of MM, LDH-A inhibition caused visible spheroids disintegration and cell number reduction. Additionally, following standard chemotherapy (platinum-based with pemetrexed), an increase in GLUT-1 expression was detected in pleural MM patients' tissues. Chapter13 describes that inhibition of LDH-A did not enhance the efficacy of gemcitabine and carboplatin in MM cells. The thesis pays special attention to cancer cell reprogramming. The efficacy of new LDH-A and GLUT-1 inhibitors, especially in pleural and peritoneal MM, reveals new promising possibilities for cancer treatment. Furthermore, the tracked metabolic cellular changes after treatment, provide valuable insights into understanding the unique tumors' character leading to their aggressiveness.