Chloroquine sensitises hypoxic colorectal cancer cells to ROS-mediated cell death via structural disruption of pyruvate dehydrogenase kinase 1 (PDK1)

Chloroquine (CQ) an autophagy antagonist has been recently explored as a repurposable medicine for cancer; however the underlying mechanisms are still unclear. Here in this study we investigated the effect of CQ on colorectal cancer cells with an aim to elucidate the molecular mechanism involved. We report for the first time that CQ suppresses hypoxia-induced cell growth and survival of HCT-116 cells due to the reduction in glycolytic capacity and NAD+ production subsequent to the inhibition of PDK1 by CQ. Furthermore, in silico and in vitro studies show that CQ induces structural alteration in the PDK1 protein, leading to its destabilisation, thus favouring its enhanced protease mediated degradation which is inhibited by MG-132 protease inhibitor. In addition to this, suppression of PDK1 by CQ results in mitochondrial damage through excessive production of ROS as reflected by the reduction in MMP, with subsequent induction of apoptosis by promoting PARP cleavage and caspase activation. These findings advocate CQ as a potent repurposable chemotherapeutic medication against colorectal cancer and as a novel inhibitor of PDK1.