Flavopiridol and histone deacetylase inhibitors promote mitochondrial injury and cell death in human leukemia cells that overexpress Bcl-2.

Abstract

Interactions between the cyclin-dependent kinase (CDK) inhibitor flavopiridol and histone deacetylase (HDAC) inhibitors (suberoylanilide hydroxamide and sodium butyrate) were examined in human leukemia cells (U937 and HL-60) ectopically expressing Bcl-2/Bcl-x(L) and in primary AML cells. Coadministration of flavopiridol with HDAC inhibitors synergistically potentiated mitochondrial damage (cytochrome c, second mitochondria-derived activator of caspases/direct IAP binding protein with low pI, and apoptosis-inducing factor release), caspase activation, poly(ADP-ribose) polymerase degradation, and cell death in both wild type and Bcl-2- or Bcl-x(L)-overexpressing cells and induced a pronounced loss of clonogenicity. In contrast, Bcl-2 and Bcl-x(L) largely blocked these events in cells exposed to the cytotoxic agent 1-beta-d-arabinofuranosylcytosine (ara-C). Enforced expression of dominant-negative Fas-associated death domain failed to protect cells from the flavopiridol/histone deacetylase inhibitor (HDACI) regimen, arguing against the involvement of the receptor pathway in lethality. Ectopic expression of a phosphorylation loop-deleted Bcl-2 or Bcl-2 lacking the serine(70) phosphorylation site, which dramatically protected cells from ara-C lethality, delayed but did not prevent flavopiridol/HDAC inhibitor-induced mitochondrial injury, cell death, or loss of clonogenicity. Ectopic expression of Bcl-2 or Bcl-x(L) was also unable to prevent the flavopiridol/HDACI regimen from inducing a conformational change in and mitochondrial translocation of Bax, and it did not attenuate Bax dimerization. As a whole, these findings indicate that in contrast to certain conventional cytotoxic agents such as ara-C, overexpression of Bcl-2 or Bcl-x(L) are largely ineffective in preventing perturbations in Bax, mitochondrial injury, and cell death in human leukemia cells subjected to simultaneous CDK and HDAC inhibition. They also raise the possibility that a strategy combining CDK and HDAC inhibitors may be effective against drug-resistant leukemia cells overexpressing Bcl-2 or Bcl-x(L).

• Authors: Girija Dasmahapatra, Jorge A Almenara, Steven Grant
• Journal: Molecular pharmacology (Mol Pharmacol) Vol. 69 Issue 1 Pg. 288-98 (Jan 2006) ISSN: 0026-895X [Print] United States
• PMID: 16219908 (Publication Type: Journal Article, Research Support, N.I.H., Extramural, Research Support, Non-U.S. Gov't, Research Support, U.S. Gov't, Non-P.H.S., Retracted Publication)

Chemical References

• Enzyme Inhibitors
• Flavonoids
• Histone Deacetylase Inhibitors
• Piperidines
• Proto-Oncogene Proteins c-bcl-2
• alvocidib

Topics

• Blotting, Western
• Cell Death (drug effects)
• Enzyme Inhibitors (pharmacology)
• Flavonoids (pharmacology)
• Histone Deacetylase Inhibitors
• Humans
• Leukemia (metabolism, pathology)
• Mitochondria (drug effects)
• Piperidines (pharmacology)
• Proto-Oncogene Proteins c-bcl-2 (metabolism)
• U937 Cells