The interaction between taxoids and serine/threonine protein phosphatase activities during taxan-induced apoptosis of HL 60 leukemic cells.

Paclitaxel and docetaxel (taxoids) are chemotherapy agents whose mode of action is through an effect on cellular microtubules. Several studies have investigated their potential in the treatment of myeloid malignancies. The aim of our study was to investigate the potential role of the serine/threonine protein phosphatase system in docetaxel/paclitaxel induced cytotoxicity on HL 60 cells. The IC50 dose of paclitaxel and docetaxel were found as 20 and 5 nM respectively using trypan blue dye exclusion and XTT assays. Treating HL 60 cells with docetaxel and paclitaxel resulted in dose and time dependent cytotoxicity. Docetaxel induced the decrease in the activity of protein phosphatase 1 (PP1) and increase in the activity of PP2 subgroups, while paclitaxel induced the increase in the activity of PP1 and decrease in the activity of PP2 subgroups. Potential use of specific protein phosphatase inhibitors or activators in combination with taxoids will open new windows in the treatment of myeloid leukemias.