Selective inhibitors epigenetically modify and eradicate tumor‐initiating stem‐like cells through downregulating microRNA 22‐mediated TET induction and apoptosis

A critical barrier to improved cancer therapy is the recurrence of drug‐resistant tumors expanded from tumor‐initiating stem‐like cells (TICs). Discovery of a drug that specifically targets the TIC population is critical for effective treatment. We first performed drug screening on TICs for the identification of cell‐type specific drugs and found that all‐trans retinoic acid (ATRA) specifically inhibited cell viability. Additionally, transduction of human TICs with a lentivirus Nanog‐GFP reporter was used to perform high‐throughput screening for Nanog‐inhibitory drugs. HDAC inhibitor (SAHA), among several candidates, suppressed Nanog expression. Three high‐throughput screenings identified the best combination of repurposed FDA‐approved drugs (ATRA and SAHA). Moreover, combination of RA with SAHA synergistically reduced Nanog expression and inhibited the self‐renewal abilities of TICs resulting in apoptosis in vitro and in vivo. Genome‐wide transcriptome analysis by using of RNA‐seq showed that combined treatment reduced microRNA‐22, which induced phosphatase and tensin homolog (PTEN) and ten‐eleven translocation (TET). PTEN‐mediated FOXO activation promotes BIM‐mediated apoptosis. TET induction demethylates p53‐binding sites within the Nanog promoter proximal region. The drug combination epigenetically altered DNA methylation of Nanog promoter leading to inactivation of Nanog in TICs. Taken together, ATRA and SAHA may serve as a novel strategy for HCC treatment. Support or Funding Information This project was supported by NIH research grants R01AA018857, P50AA011999 (Southern California Research Center for ALPD and Cirrhosis, pilot project, program, animal core, morphology core), Lee‐Summer‐Project funding, P30DK048522 (USC Research Center for Liver Diseases, pilot project program), Non‐Parenchymal Liver Cell Core (R24AA012885) and UO‐021898. This research was also supported by a Research Scholar Grant (RSG‐12‐177‐01‐MPC); pilot funding from American Cancer Society (IRG‐58‐007‐48); The Cell and Tissue Imaging Core ‐ USC Research Center for Liver Diseases (P30 DK048522).