Abstract
In cancer cells, aerobic glycolysis rather than oxidative phosphorylation (OxPhos) is generally preferred for the production of ATP. In many cancers, highly expressed pyruvate dehydrogenase kinase 1 (PDK1) reduces the activity of pyruvate dehydrogenase (PDH) by inducing the phosphorylation of its E1α subunit (PDHA1) and subsequently, shifts the energy metabolism from OxPhos to aerobic glycolysis. Thus, PDK1 has been regarded as a target for anticancer treatment. Here, we report that ilimaquinone (IQ), a sesquiterpene quinone isolated from the marine sponge Smenospongia cerebriformis, might be a novel PDK1 inhibitor. IQ decreased the cell viability of human and murine cancer cells, such as A549, DLD-1, RKO, and LLC cells. The phosphorylation of PDHA1, the substrate of PDK1, was reduced by IQ in the A549 cells. IQ decreased the levels of secretory lactate and increased oxygen consumption. The anticancer effect of IQ was markedly reduced in PDHA1-knockout cells. Computational simulation and biochemical assay revealed that IQ interfered with the ATP binding pocket of PDK1 without affecting the interaction of PDK1 and the E2 subunit of the PDH complex. In addition, similar to other pyruvate dehydrogenase kinase inhibitors, IQ induced the generation of mitochondrial reactive oxygen species (ROS) and depolarized the mitochondrial membrane potential in the A549 cells. The apoptotic cell death induced by IQ treatment was rescued in the presence of MitoTEMPO, a mitochondrial ROS inhibitor. In conclusion, we suggest that IQ might be a novel candidate for anticancer therapeutics that act via the inhibition of PDK1 activity.
Highlights
It is known that, under oxygen-abundant conditions, glycolysis rather than oxidative phosphorylation (OxPhos) is normally preferred as the energy source in cancer cells; this phenomenon is termed the Warburg effect [1]
Four different isoforms of Pyruvate dehydrogenase kinases (PDKs) have been found in mammals, and these enzymes regulate the activity of the pyruvate dehydrogenase complex (PDC) by phosphorylating its E1 alpha subunit (PDHA1) [2]
We revealed that IQ isolated from S. cerebriformis induced the apoptosis of lung cancer cells by inhibiting the activity of pyruvate dehydrogenase kinase 1 (PDK1)
Summary
Under oxygen-abundant conditions, glycolysis rather than oxidative phosphorylation (OxPhos) is normally preferred as the energy source in cancer cells; this phenomenon is termed the Warburg effect [1]. Pyruvate dehydrogenase kinases (PDKs) are the primary metabolic enzymes involved in the Warburg effect. Four different isoforms of PDK have been found in mammals, and these enzymes regulate the activity of the pyruvate dehydrogenase complex (PDC) by phosphorylating its E1 alpha subunit (PDHA1) [2]. The PDC is divided into mainly three parts: pyruvate dehydrogenase E1 subunit, dihydrolipoamide acetyltransferase (the E2 subunit), and lipoamide dehydrogenase (the E3 subunit); PDKs bind to the E2 subunit and phosphorylate PDHA1 [3]. The reprogramming of cancer metabolism through the enhancement of PDC activity via the inhibition of PDK1 increases the anticancer effects on several cancer cell lines, including NSCLC [10,11]. Our group has continued the efforts to discover novel PDK1 inhibitors from natural compounds as candidates for anticancer drugs [2,12,13]
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