Adaphostin-induced apoptosis in CLL B cells is associated with induction of oxidative stress and exhibits synergy with fludarabine.
B-cell chronic lymphocytic leukemia (CLL) is characterized by accumulation of clonal lymphocytes resistant to apoptosis. We evaluated the ability of the investigational antileukemic agent adaphostin to induce apoptosis in CLL B cells and synergize with fludarabine in vitro. Analysis by annexin V/propidium iodide (PI) staining revealed that the concentration of adaphostin required to induce 50% cell death (IC50) at 24 hours was 4.2 microM (range, 1.10-11.25 microM; median, 4.25 microM; n=29) for CLL isolates and more than 10 microM for B and T cells from healthy donors. Immunoblots demonstrated adaphostin induced poly(adenosine diphosphate-ribose) polymerase (PARP) cleavage and cleavage of caspase-3 substrates, suggesting that adaphostin induces apoptosis. Adaphostin increased the level of reactive oxygen species (ROS) within CLL B cells, and the antioxidant N-acetylcysteine blocked both adaphostin-induced ROS generation and apoptosis. Adaphostin also caused a decrease in the level of the antiapoptotic protein Bcl-2. When adaphostin was combined with fludarabine (F-ARA-AMP), a synergistic effect on cell death was observed in all 10 CLL samples. These findings not only indicate that adaphostin induces apoptosis selectively in CLL B cells through a mechanism that involves ROS generation but also demonstrate its ability to augment the effects of fludarabine. Further preclinical development of adaphostin as a novel agent for the treatment of CLL appears warranted.
Shanafelt
Tait D
TD
Department of Medicine, Division of Hematology, Mayo Clinic, 200 First St, SW, Rochester, MN 55905, USA. shanafelt.tait@mayo.edu
Lee
Yean K
YK
Bone
Nancy D
ND
Strege
Ann K
AK
Narayanan
Ven L
VL
Sausville
Edward A
EA
Geyer
Susan M
SM
Kaufmann
Scott H
SH
Kay
Neil E
NE
D000218:Adamantane / Q000031:analogs & derivatives* / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects*; D001402:B-Lymphocytes / Q000187:drug effects / Q000378:metabolism / Q000473:pathology; D002478:Cells, Cultured; D004357:Drug Synergism; D016044:Fusion Proteins, bcr-abl / Q000037:antagonists & inhibitors; D006801:Humans; D006873:Hydroquinones / Q000494:pharmacology*; D020128:Inhibitory Concentration 50; D015451:Leukemia, Lymphocytic, Chronic, B-Cell / Q000188:drug therapy / Q000473:pathology*; D018384:Oxidative Stress / Q000187:drug effects*; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000187:drug effects; D017382:Reactive Oxygen Species / Q000378:metabolism; D014740:Vidarabine / Q000031:analogs & derivatives* / Q000494:pharmacology*
D006873:Hydroquinones; C404397:NSC 680410; D019253:Proto-Oncogene Proteins c-bcl-2; D017382:Reactive Oxygen Species; D016044:Fusion Proteins, bcr-abl; D014740:Vidarabine; C024352:fludarabine; D000218:Adamantane