Effects of the proteasome inhibitor, bortezomib, on apoptosis in isolated lymphocytes obtained from patients with chronic lymphocytic leukemia

Clin Cancer Res. 2003 Oct 1;9(12):4570-7.

Abstract

Purpose: Bortezomib is a peptide boronic acid inhibitor of the proteasome developed for cancer therapy. The compound is being evaluated currently in Phase II and III clinical trials. Here we characterized the effects and mechanisms of action of bortezomib in cells obtained from patients with chronic lymphocytic leukemia (CLL).

Experimental design: We exposed isolated CLL lymphocytes from >100 patients to various concentrations of bortezomib or other proapoptotic stimuli, and measured DNA fragmentation by propidium iodide staining and flow cytometry. We characterized the effects of bortezomib on release of apoptosis-associated mitochondrial factors and measured downstream effects on caspase activation using a fluorogenic substrate cleavage assay. We assessed potential effects of the drug on inhibitor of apoptosis protein family apoptosis inhibitors by immunoblotting. Finally, we quantified the effects of bortezomib on apoptosis in 5 patients on a Phase II clinical trial.

Results: Bortezomib stimulated apoptosis more rapidly than positive controls (glucocorticoid and fludarabine), although substantial heterogeneity was noted with respect to the concentration of drug required to induce cell death. Bortezomib-induced apoptosis was associated with release of SMAC, apoptosis-inducing factor, and cytochrome c from mitochondria, but the drug did not affect levels of inhibitor of apoptosis protein family cell death inhibitors. Levels of apoptosis were marginally elevated in CLL cells obtained from 2 of 5 fludarabine-refractory patients treated with bortezomib in vivo.

Conclusion: Our data confirm that bortezomib, like other proteasome inhibitors, has proapoptotic activity in CLL cells.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Antineoplastic Agents / pharmacology
  • Apoptosis / drug effects*
  • Boronic Acids / pharmacology*
  • Bortezomib
  • Caspases / metabolism
  • Complement Membrane Attack Complex
  • Complement System Proteins
  • Cysteine Endopeptidases / drug effects
  • Cytochromes c / metabolism
  • DNA (Cytosine-5-)-Methyltransferases / antagonists & inhibitors
  • Drug Resistance, Neoplasm
  • Enzyme Activation
  • Glucocorticoids / pharmacology
  • Glycoproteins / metabolism
  • Humans
  • Inhibitor of Apoptosis Proteins
  • Leukemia, Lymphocytic, Chronic, B-Cell / drug therapy*
  • Leukemia, Lymphocytic, Chronic, B-Cell / metabolism
  • Leukemia, Lymphocytic, Chronic, B-Cell / pathology
  • Lymphocytes / drug effects*
  • Mitochondria / drug effects
  • Multienzyme Complexes / drug effects
  • Neoplasm Recurrence, Local / drug therapy
  • Neoplasm Recurrence, Local / metabolism
  • Neoplasm Recurrence, Local / pathology
  • Protease Inhibitors / pharmacology*
  • Proteasome Endopeptidase Complex
  • Proteins / metabolism
  • Pyrazines / pharmacology*
  • Tumor Cells, Cultured
  • Vidarabine / analogs & derivatives*
  • Vidarabine / pharmacology
  • X-Linked Inhibitor of Apoptosis Protein

Substances

  • Antineoplastic Agents
  • Boronic Acids
  • Complement Membrane Attack Complex
  • Glucocorticoids
  • Glycoproteins
  • Inhibitor of Apoptosis Proteins
  • Multienzyme Complexes
  • Protease Inhibitors
  • Proteins
  • Pyrazines
  • SC5b-9 protein complex
  • X-Linked Inhibitor of Apoptosis Protein
  • XIAP protein, human
  • Bortezomib
  • Complement System Proteins
  • Cytochromes c
  • DNA (Cytosine-5-)-Methyltransferases
  • Caspases
  • Cysteine Endopeptidases
  • Proteasome Endopeptidase Complex
  • Vidarabine
  • fludarabine