title: Targeting PKC-mediated signal transduction pathways using enzastaurin to promote apoptosis in acute myeloid leukemia-derived cell lines and blast cells.
abstract: Recent studies in acute myeloid leukemia (AML) suggest activation of pro-proliferative signaling cascades including those mediated by protein kinase C (PKC) represent a poor prognostic factor for patients. The classical PKC isoforms α and β generally support survival signaling and have emerged as important targets for anti-cancer therapy. Enzastaurin is a PKC β inhibitor and is in clinical trials for lymphomas, gliomas, and lung cancer. Presently, it is not known if enzastaurin could be effective against AML. In the current study, we found that high dose enzastaurin was found to promote apoptosis in the AML-derived cell lines and in blast cells from AML patients. The mechanism of cell death, however, likely does not involve PKC β as another PKC β inhibitor was not toxic to AML cell lines and did not promote enzastaurin-induced cell killing. While enzastaurin is fairly specific for PKC β, the agent can inhibit other PKC isoforms at higher concentrations. Enzastaurin was effective at inhibiting PKC α phosphorylation and membrane localization in the AML cell lines and suppressed phosphorylation of BCL2. Furthermore, enzastaurin suppressed activation of ERK (which can be activated by PKC α). Analysis of the serine/threonine phosphorylation profile in HL60 cells after enzastaurin treatment revealed that the drug inhibits the phosphorylation of a distinct set of proteins while promoting phosphorylation of another set of proteins. This suggests the drug may regulate multiple signaling pathways. Taken together, these findings suggest that enzastaurin could be effective in the therapy of AML.
authors.affiliation: Department of Leukemia, The University of Texas MD Anderson Cancer Center, Houston, Texas, USA.
authors.forename: Peter P
authors.initials: PP
authors.lastname: Ruvolo
authors.forename: Liran
authors.initials: L
authors.lastname: Zhou
authors.forename: Julie C
authors.initials: JC
authors.lastname: Watt
authors.forename: Vivian R
authors.initials: VR
authors.lastname: Ruvolo
authors.forename: Jared K
authors.initials: JK
authors.lastname: Burks
authors.forename: Tilahun
authors.initials: T
authors.lastname: Jiffar
authors.forename: Steven
authors.initials: S
authors.lastname: Kornblau
authors.forename: Marina
authors.initials: M
authors.lastname: Konopleva
authors.forename: Michael
authors.initials: M
authors.lastname: Andreeff
mesh_terms: D018952:Antigens, CD34 / Q000378:metabolism; D017209:Apoptosis / Q000187:drug effects*; D015153:Blotting, Western; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000187:drug effects; D015180:Electrophoresis, Gel, Two-Dimensional; D018922:HL-60 Cells; D006801:Humans; D007211:Indoles / Q000494:pharmacology*; D015470:Leukemia, Myeloid, Acute / Q000378:metabolism*; D008856:Microscopy, Fluorescence; D010766:Phosphorylation / Q000187:drug effects; D011493:Protein Kinase C / Q000378:metabolism*; D064546:Protein Kinase C beta; D015398:Signal Transduction / Q000187:drug effects / Q000235:genetics
chemical_list: D018952:Antigens, CD34; D007211:Indoles; D011493:Protein Kinase C; D064546:Protein Kinase C beta; C504878:enzastaurin