LW1497, an Inhibitor of Malate Dehydrogenase, Suppresses TGF-β1-Induced Epithelial-Mesenchymal Transition in Lung Cancer Cells by Downregulating Slug

Malate dehydrogenase (MDH) in cancer: a promiscuous enzyme, a redox regulator, and a metabolic co-conspirator

Malate dehydrogenase (MDH) is an essential enzyme in the tricarboxylic acid cycle that functions in cellular respiration and redox homeostasis. Recent studies indicate that MDH facilitates metabolic plasticity in tumor cells, catalyzing the formation of an oncometabolite, contributing to altered epigenetics, and maintaining redox capacity to support the rewired energy metabolism and biosynthesis that enables cancer progression. This minireview summarizes current findings on the unique supporting roles played by MDH in human cancers and provides an update on targeting MDH in cancer chemotherapy.

Insights into the regulation of malate dehydrogenase: inhibitors, activators, and allosteric modulation by small molecules

Cellular metabolism comprises a complex network of biochemical anabolic and catabolic processes that fuel the growth and survival of living organisms. The enzyme malate dehydrogenase (MDH) is most known for its role in oxidizing malate to oxaloacetate (OAA) in the last step of the tricarboxylic acid (TCA) cycle, but it also participates in the malate-aspartate shuttle in the mitochondria as well as the glyoxylate cycle in plants. These pathways and the specific reactions within them are dynamic and must be carefully calibrated to ensure a balance between nutrient/energy supply and demand. MDH structural and functional complexity requires a variety of regulatory mechanisms, including allosteric regulation, feedback, and competitive inhibition, which are often dependent on whether the enzyme is catalyzing its forward or reverse reaction. Given the role of MDH in central metabolism and its potential as a target for therapeutics in both cancer and infectious diseases, there is a need to better understand its regulation. The involvement of MDH in multiple pathways makes it challenging to identify which effectors are critical to its activity. Many of the in vitro experiments examining MDH regulation were done decades ago, and though allosteric sites have been proposed, none to date have been specifically mapped. This review aims to provide an overview of the current knowledge surrounding MDH regulation by its substrate, products, and other intermediates of the TCA cycle while highlighting all the gaps in our understanding of its regulatory mechanisms.

Design, Synthesis and Biological Evaluation of Novel MDH Inhibitors Targeting Tumor Microenvironment

MDH1 and MDH2 enzymes play an important role in the survival of lung cancer. In this study, a novel series of dual MDH1/2 inhibitors for lung cancer was rationally designed and synthesized, and their SAR was carefully investigated. Among the tested compounds, compound 50 containing a piperidine ring displayed an improved growth inhibition of A549 and H460 lung cancer cell lines compared with LW1497. Compound 50 reduced the total ATP content in A549 cells in a dose-dependent manner; it also significantly suppressed the accumulation of hypoxia-inducible factor 1-alpha (HIF-1α) and the expression of HIF-1α target genes such as GLUT1 and pyruvate dehydrogenase kinase 1 (PDK1) in a dose-dependent manner. Furthermore, compound 50 inhibited HIF-1α-regulated CD73 expression under hypoxia in A549 lung cancer cells. Collectively, these results indicate that compound 50 may pave the way for the development of next-generation dual MDH1/2 inhibitors to target lung cancer.

Loss of EMP2 Inhibits Melanogenesis of MNT1 Melanoma Cells via Regulation of TRP-2

Melanogenesis is the production of melanin from tyrosine by a series of enzyme-catalyzed reactions, in which tyrosinase and DOPA oxidase play key roles. The melanin content in the skin determines skin pigmentation. Abnormalities in skin pigmentation lead to various skin pigmentation disorders. Recent research has shown that the expression of EMP2 is much lower in melanoma than in normal melanocytes, but its role in melanogenesis has not yet been elucidated. Therefore, we investigated the role of EMP2 in the melanogenesis of MNT1 human melanoma cells. We examined TRP-1, TRP-2, and TYR expression levels during melanogenesis in MNT1 melanoma cells by gene silencing of EMP2. Western blot and RT-PCR results confirmed that the expression levels of TYR and TRP-2 were decreased when EMP2 expression was knocked down by EMP2 siRNA in MNT1 cells, and these changes were reversed when EMP2 was overexpressed. We verified the EMP2 gene was knocked out of the cell line (EMP2 CRISPR/Cas9) by using a CRISPR/Cas9 system and found that the expression levels of TRP-2 and TYR were significantly lower in the EMP2 CRISPR/Cas9 cell lines. Loss of EMP2 also reduced migration and invasion of MNT1 melanoma cells. In addition, the melanosome transfer from the melanocytes to keratinocytes in the EMP2 KO cells cocultured with keratinocytes was reduced compared to the cells in the control coculture group. In conclusion, these results suggest that EMP2 is involved in melanogenesis via the regulation of TRP-2 expression.