PGP and cancer: Besides the classical apoptotic pathway, Sal has been demonstrated to activate a unique apoptotic pathway that is not accompanied by cell cycle arrest and is independent of tumor suppressor protein p53, caspase activation, the CD95/CD95L system and the proteasome, which has been thought to overcome the high resistance to other anti-cancer drugs of cancer cells by increasing the expression of the Bcl-2 protein, P-gp as well as the 26S proteasome [16].