Synergistic antileukemic interactions between 17-AAG and UCN-01 involve interruption of RAF/MEK- and AKT-related pathways.
Interactions between the protein kinase C (PKC) and Chk1 inhibitor UCN-01 and the heat shock protein 90 (Hsp90) antagonist 17-AAG have been examined in human leukemia cells in relation to effects on signal transduction pathways and apoptosis. Simultaneous exposure (30 hours) of U937 monocytic leukemia cells to minimally toxic concentrations of 17-AAG (eg, 400 nM) and UCN-01 (eg, 75 nM) triggered a pronounced increase in mitochondrial injury (ie, loss of mitochondrial membrane potential [Deltapsim]; cytosolic release of cytochrome c), caspase activation, and apoptosis. Synergistic induction of apoptosis was also observed in other human leukemia cell types (eg, Jurkat, NB4). Coexposure of human leukemia cells to 17-AAG and the PKC inhibitor bisindolylmaleimide (GFX) did not result in enhanced lethality, arguing against the possibility that the PKC inhibitory actions of UCN-01 are responsible for synergistic interactions. The enhanced cytotoxicity of this combination was associated with diminished Akt activation and marked down-regulation of Raf-1, MEK1/2, and mitogen-activated protein kinase (MAPK). Coadministration of 17-AAG and UCN-01 did not modify expression of Hsp90, Hsp27, phospho-JNK, or phospho-p38 MAPK, but was associated with further p34cdc2 dephosphorylation and diminished expression of Bcl-2, Mcl-1, and XIAP. In addition, inducible expression of both a constitutively active MEK1/2 or myristolated Akt construct, which overcame inhibition of ERK and Akt activation, respectively, significantly attenuated 17-AAG/UCN-01-mediated lethality. Together, these findings indicate that the Hsp90 antagonist 17-AAG potentiates UCN-01 cytotoxicity in a variety of human leukemia cell types and suggest that interference with both the Akt and Raf-1/MEK/MAP kinase cytoprotective signaling pathways contribute to this phenomenon.
Division of Hematology/Oncology, MCV Station Box 230, Virginia Commonwealth University/Medical College of Virginia, Richmond, VA 23298, USA.
Wentao
W
Jia
Chunrong
C
Yu
Mohamed
M
Rahmani
Geoffrey
G
Krystal
Edward A
EA
Sausville
Paul
P
Dent
Steven
S
Grant
D000470:Alkaloids / Q000494:pharmacology*; D000970:Antineoplastic Agents / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects; D016227:Benzoquinones; D020169:Caspases / Q000378:metabolism; D004357:Drug Synergism; D018922:HL-60 Cells; D006801:Humans; D019169:Jurkat Cells; D047029:Lactams, Macrocyclic; D007938:Leukemia; D048728:MAP Kinase Kinase Kinase 1; D020935:MAP Kinase Signaling System / Q000187:drug effects*; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt; D019908:Proto-Oncogene Proteins c-raf / Q000378:metabolism; D017828:Rifabutin / Q000031:analogs & derivatives* / Q000494:pharmacology*; D019311:Staurosporine / Q000031:analogs & derivatives; D020298:U937 Cells
D000470:Alkaloids; D000970:Antineoplastic Agents; D016227:Benzoquinones; D047029:Lactams, Macrocyclic; D011518:Proto-Oncogene Proteins; D017828:Rifabutin; C112765:tanespimycin; C054852:7-hydroxystaurosporine; C494918:AKT1 protein, human; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt; D019908:Proto-Oncogene Proteins c-raf; D020928:Mitogen-Activated Protein Kinases; D048728:MAP Kinase Kinase Kinase 1; C482576:MAP3K1 protein, human; D020169:Caspases; D019311:Staurosporine