Since inhibition of SIRT1 could down-regulate Hsp70/Hsp27 as well as P-gp in various human MDR cancer cells, combinatorial targeting of HSF1/Hsps and P-gp by combined treatment with Hsp90 inhibitor and SIRT1 inhibitor could be a more effective therapeutic approach for Hsp90 inhibitor-resistant MDR cells. This evidence concerns the gene PGP and cancer.