DNMT1 and lung cancer: To determine whether P16 methylation directly increases the sensitivity of cancer cells to palbociclib, we stably transfected three P16-U cell lines (including two lung cancer cell lines, H661 and HCC827, and one gastric cancer cell line, BGC823) with the P16-Dnmt vector and induced P16-Dnmt expression in these cells by doxycycline treatment for 2 weeks.