Effect of the protein kinase C inhibitor staurosporine on chemosensitivity
to daunorubicin of normal and leukemic fresh myeloid cells
J Laredo, A Huynh, C Muller, JP Jaffrezou, JD Bailly, G Cassar, G Laurent and C Demur
Laboratoire de Pharmacologie et de Toxicologie Fondamentales, CNRS,
Toulouse, France.
The effect of the protein kinase C (PKC) inhibitor staurosporine (ST) on
the chemosensitivity of normal (colony-forming unit granulocyte- macrophage
[CFU-GM]) and leukemic (acute myeloid leukemia-CFU [AML- CFU]) myeloid
progenitors to daunorubicin (DNR) was evaluated. Primary colony inhibition
assays allowed us to characterize two distinct groups of AML, a
DNR-resistant group (patients no. 1 through 6), which displayed
significantly lower DNR sensitivity than normal CFU-GM (D50 = 11.3 +/- 1.4
ng/mL v 1.8 +/- 0.5 ng/mL, after 7 days of exposure, respectively; P <
0.01) and a DNR-sensitive group (patients no. 7 through 12) with D50 = 2.7
+/- 0.4 ng/mL. This classification remained unaltered when assessed by
secondary colony inhibition assay (evaluating the self-renewal fraction of
AML-CFU) or by viability assay (evaluating the ultimately differentiated
blast cell population), suggesting that the DNR sensitivity profile in
maintained throughout AML-CFU differentiation. DNR resistance of the
differentiated blast cell population was not correlated with the level of
P-glycoprotein (P- gp) expression but rather with the ability to extrude
rhodamine 123 (Rh123). ST used at subtoxic concentrations induced a twofold
to threefold enhancement of DNR cytotoxicity, increased Rh123 accumulation,
and decreased Rh123 efflux kinetics in resistant AML cells. These effects
were observed for ST concentrations much lower than those required to
displace the P-gp-binding probe azidoprazosin, suggesting that ST might act
through its PKC inhibitory effect and not through P-gp binding. Finally,
this study provides evidence that DNR resistance in AML cells is, at least
in part, related to the multidrug- resistance (MDR) phenotype. Because P-gp
function can be downregulated by ST, it seems likely that the MDR
pheno-type can be functionally regulated by cellular signalization in AML
cells.
Volume 84,
Issue 1,
pp. 229-237,
07/01/1994
Copyright © 1994 by The American Society of Hematology
