RESUMEN
Pyruvate dehydrogenase kinase 4 (PDK4) is an important regulator of energy metabolism. Previously, knockdown of PDK4 by specific small interfering RNAs (siRNAs) have been shown to suppress the expression of Κirsten rat sarcoma viral oncogene homolog (KRAS) and the growth of lung and colorectal cancer cells, indicating that PDK4 is an attractive target of cancer therapy by altering energy metabolism. The authors previously reported that a novel small molecule, cryptotanshinone (CPT), which inhibits PDK4 activity, suppresses the in vitro threedimensional (3D)spheroid formation and in vivo tumorigenesis of KRASactivated human pancreatic and colorectal cancer cells. The present study investigated the molecular mechanism of CPTinduced tumor suppression via alteration of glutamine and lipid metabolism in human pancreatic and colon cancer cell lines with mutant and wildtype KRAS. The antitumor effect of CPT was more pronounced in the cancer cells containing mutant KRAS compared with those containing wildtype KRAS. CPT treatment decreased glutamine and lipid metabolism, affected redox regulation and increased reactive oxygen species (ROS) production in the pancreatic cancer cell line MIAPaCa2 containing mutant KRAS. Suppression of activated KRAS by specific siRNAs decreased 3Dspheroid formation, the expression of acetylCoA carboxylase 1 and fatty acid synthase (FASN) and lipid synthesis. The suppression also reduced glutathioneSH/glutathione disulfide and increased the production of ROS. Knockdown of FASN suppressed lipid synthesis in MIAPaCa2 cells, partially promoted ROS production and mildly suppressed 3Dspheroid formation. These results indicated that CPT reduced tumorigenesis by inhibiting lipid metabolism and promoting ROS production in a mutant KRASdependent manner. This PDK4 inhibitor could serve as a novel therapeutic drug for KRASdriven intractable cancers via alteration of cell metabolism.