PTPA and cancer: These mechanisms have been confirmed in a variety of tumor cell lines such as leukemia K562 and HL-60 [18, 55], hepatoma HepG2, SMMC-7721 and BEL-7402 [56–58], colorectal cancer CT26 and HCT-15 cells [59, 60], etc. It is generally believed that serine/threonine protein phosphatases, such as protein phosphatase type 1 (PP1), protein phosphatase-2A (PP2A) and protein phosphatase-2B (PP2B), play important roles in intracellular signal transduction, whose inhibition is an excellent target for the development of novel anti-cancer agents [5, 61, 62].