Inhibition of Lactate Dehydrogenase A (LDH-A) by Diclofenac Sodium Induces Apoptosis in HeLa Cells by Activation of AMPK

Cancer cells exhibit a unique metabolic preference for choosing the glycolytic pathway over oxidative phosphorylation for maintaining the tumor microenvironment. Lactate dehydrogenase-A (LDH-A) is a key enzyme that facilitates glycolysis by converting pyruvate to lactate and has been shown to be upregulated in multiple cancers due to the hypoxic tumor microenvironment. Diclofenac (DCF), a non-steroidal anti-inflammatory drug, has been shown to exhibit anti-cancer effects by interfering with the glucose metabolism pathway. However, the specific targets remain unknown. Using in-silico, biochemical, and biophysical studies, we show that DCF binds to LDH-A adjacent to the substrate binding site and dose-dependently inhibits its activity in an allosteric manner in HeLa cells. Thus, DCF inhibits the hypoxic microenvironment and induces apoptosis-mediated cell death. DCF fails to induce cytotoxicity in LDH-A knocked-down HeLa cells, confirming that DCF renders its anti-mitotic effects via LDH-A inhibition. DCF-induced LDH-A inhibition alters pyruvate, lactate, NAD+, and ATP production in cells, and this could be a possible mechanism by which DCF inhibits glucose uptake in cancer cells. DCF-induced ATP deprivation leads to mitochondria-mediated oxidative stress, which results in DNA damage, lipid peroxidation, and apoptosis-mediated cell death. Reduction in intracellular ATP levels additionally activates AMPK, a sensor kinase, which further downregulates p-S6K, leading to apoptosis-mediated cell death. We find that in LDH-A knocked-down cells, intracellular ATP levels were depleted, resulting in the inhibition of p-S6K, implying the involvement of DCF-induced LDH-A inhibition in the activation of the AMPK/S6K signaling pathway.