title: Increased intracellular cAMP renders HL-60 cells resistant to cytotoxicity of taxol.
abstract: The treatment of advanced cancers with paclitaxel (taxol) is hindered by the development of drug resistance. Resistance to taxol is known to be associated with multidrug resistance (MDR) and a mutation affecting either the alpha- or beta-subunit of tubulin. In this study, we demonstrated that an intracellular cAMP level may also play an important role in resistance to taxol in HL-60, acute promyelocytic leukemia cells. Exposure of HL-60 cells to various doses of taxol for 18 hr resulted in cell death. However, pretreatment of the cells with cAMP analogs such as N6:O2-dibutyl cAMP (Db-cAMP), 8-(4-chlorophenylthio) cAMP (CPT-cAMP) and 8-bromo-cAMP (8-Br-cAMP) or an intracellular cAMP elevating agent such as forskolin apparently rendered HL-60 cells more resistant to taxol, but not with dimethyl sulfoxide (DMSO) or retinoic acid (RA), well known differentiating agents. To investigate whether protein kinase A (PKA) activated by an increase in intracellular cAMP level could be involved in increased taxol resistance of the cells, we examined the effects of PKA inhibitors, including H-89 and KT5720, on taxol resistance induced by Db-cAMP. The PKA inhibitors significantly abolished Db-cAMP-induced taxol resistance. These results suggest that cAMP analogs may render tumor cells more resistant to taxol via PKA activation.
mesh_terms: D000972:Antineoplastic Agents, Phytogenic / Q000494:pharmacology*; D003994:Bucladesine / Q000494:pharmacology; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000502:physiology*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000502:physiology; D004121:Dimethyl Sulfoxide / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D019008:Drug Resistance, Neoplasm; D018922:HL-60 Cells; D006801:Humans; D017239:Paclitaxel / Q000494:pharmacology*; D014212:Tretinoin / Q000494:pharmacology; D020298:U937 Cells