Increased antileukemic effects in human acute myeloid leukemia by combining HSP70 and HSP90 inhibitors.

Background: Heat shock proteins (HSPs) are molecular chaperones that assist proteins in their folding to native structures. HSP90, and more recently HSP70, have emerged as possible therapeutic targets in human malignancies, including acute myeloid leukemia (AML).

Design And Methods: The authors investigated the effects of the HSP70 inhibitor VER-155008 tested alone or in combination with the HSP90 inhibitor 17-dimethylaminoethylamino-17-demethoxygeldanamycin (17-DMAG) on proliferation, viability, constitutive cytokine release and intracellular HSP levels of primary human AML cells.

Results: VER-155008 caused a dose-dependent inhibition of cytokine-dependent AML cell proliferation both in suspension cultures and in a colony formation assay, and the drug also had a proapoptotic effect. HSP70 and HSP90 inhibition had additive antiproliferative and proapoptotic effects. VER-155008 caused a strong inhibition of the constitutive AML cell release of several growth factors/regulators of hematopoiesis (i.e., TNF-α, VEGF, IL-3, IL-1β, IL-1 receptor antagonist), but had relatively weak effects on the constitutive chemokine release. HSP70 inhibition did not induce any compensatory increase of other HSPs.

Conclusion: HSP70 inhibition has antileukemic effects when tested alone, and the combination of HSP70 and HSP90 inhibition seems to have additive antileukemic effects for primary human AML cells in vitro.