Enhanced CML stem cell elimination in vitro by bryostatin priming with imatinib mesylate.
OBJECTIVE
In chronic myeloid leukemia (CML), imatinib mesylate (IM; Gleevec, Glivec) induces a G0/G1 cell-cycle block in total CD34(+) cells without causing significant apoptosis. Bryostatin-1 (bryo), a protein kinase C (PKC) modulator, was investigated for its ability to increase IM-mediated apoptosis either through induction of cycling of G0/G1 Ph(+) cells or antagonism of the IM-induced cell-cycle block.


METHODS
The Ph(+) K562 cell line and primary CD34(+) CML cells were studied for cell-cycle progression (PI staining), proliferation ((3)H thymidine uptake), and survival (dye exclusion).


RESULTS
Following 48 hours exposure to IM, on average more than 80% of surviving K562 cells were in G0/G1 as compared to approximately 50% for untreated control cultures (p < 0.001). After accounting for IM-induced cell kill, the absolute number of viable G0/G1 cells was significantly increased, confirming its anti-proliferative effect. However, pretreatment for 24 hours with bryo both increased K562 total cell kill and normalized the percentage of cells recovered in G0/G1, thus reducing their absolute number. For primary CML CD34(+) cells, pretreatment with bryo prior to IM significantly enhanced cell death of both total and, critically, G0/G1 populations.


CONCLUSIONS
These results suggest that carefully scheduled drug combinations that include an agent to antagonize the anti-proliferative effect of IM may prove more efficacious within the Ph(+) stem cell compartment than IM monotherapy.
Jørgensen
Heather G
HG
Section of Experimental Haematology, University of Glasgow, Scotland, UK. hgj1b@clinmed.gla.ac.uk
Allan
Elaine K
EK
Mountford
Joanne C
JC
Richmond
Linda
L
Harrison
Simon
S
Elliott
Moira A
MA
Holyoake
Tessa L
TL
D018952:Antigens, CD34 / Q000378:metabolism; D000970:Antineoplastic Agents / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects*; D001549:Benzamides; D054713:Bryostatins; D004336:Drug Antagonism; D016193:G1 Phase / Q000187:drug effects; D006412:Hematopoietic Stem Cells / Q000378:metabolism* / Q000473:pathology; D006801:Humans; D000068877:Imatinib Mesylate; D020014:K562 Cells; D015464:Leukemia, Myelogenous, Chronic, BCR-ABL Positive / Q000188:drug therapy / Q000378:metabolism* / Q000473:pathology; D018942:Macrolides / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D010879:Piperazines / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000378:metabolism; D011743:Pyrimidines / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D016192:Resting Phase, Cell Cycle / Q000187:drug effects
D018952:Antigens, CD34; D000970:Antineoplastic Agents; D001549:Benzamides; D054713:Bryostatins; D018942:Macrolides; D010879:Piperazines; D011743:Pyrimidines; C046785:bryostatin 1; D000068877:Imatinib Mesylate; D011493:Protein Kinase C