Dasatinib Induces Apoptosis in Chronic Lymphocytic Leukemia and Enhances the Activity of Rituximab and Fludarabine

[Guest guest]

Blood (ASH Annual Meeting Abstracts) 2007 110: Abstract 1116

Dasatinib Induces Apoptosis in Chronic Lymphocytic Leukemia and Enhances the

Activity of Rituximab and Fludarabine.

Robier A. Aguillon, M.D1,2,*, Cesar A. Llanos, M.D, M.Sc1,2,*, J. Suarez,

M.D1,2,*, Olivier J. Loria, B.S1,2,*, J. Kipps, M.D, Ph.D1,2 and Januario

E. Castro, MD1,2

1 s Cancer Center, University of California San Diego, La Jolla, CA, USA

and 2 Chronic Lymphocytic Leukemia Research Consortium (CRC), University of

California San Diego, La Jolla, CA, USA.

Abstract

Chronic lymphocytic leukemia (CLL) is a disease characterized by the monoclonal

accumulation of well-differentiated CD5 B cells. Previously, we reported that

CLL cells that use unmutated immunoglobulin VH (IgVH) genes and/or express

ZAP-70 are more responsive to signaling induced by ligation of surface IgM

compared to cells that use mutated IgVH and lack expression of ZAP-70 (Chen et

al. Blood 2005) Because signaling through the Ig receptor appears to play a role

in the pathogenesis or progression of CLL, targeting the Ig signal transduction

pathway in CLL might have therapeutic utility, particularly for those patients

with high-risk disease. Dasatinib (Sprycel) is a tyrosine kinase inhibitor (TKI)

with antiproliferative activity against hematological and solid tumor cell lines

and it is FDA approved for the treatment of patients with CML and Ph+ ALL.

Contrary to Imatinib (Gleevec), Dasatinib is a potent TKI not only of the Abl

family of kinases but also of Src kinases, which regulate Ig-receptor signal

transduction and govern the early events following Ig receptor ligation. Because

Dasatinib TKI profile and its potential role inhibiting BCR signaling we studied

its in vitro activity in CLL. Primary leukemia cells from 40 different CLL

patients were evaluated. We found that Dasatinib, but not Imatinib, induced

apoptosis in CLL cells at doses that were pharmacologically achievable. The IC50

for Dasatinib was in the 30-100 nM range. Interestingly, the pro-apoptotic

activity of Dasatinib in CLL cells was not observed in normal B, T cells or

blood mononuclear cells of healthy donors, suggesting that Dasatinib has a

specific effect on CLL cells. Dasatinib induced apoptosis in CLL cells in a time

and concentration dependent manner. Peak apoptosis occurred after 2 hours of in

vitro exposure. Leukemia cells that expressed ZAP-70 were significantly more

sensitive to Dasatinib-induced apoptosis than CLL cells lacking expression of

ZAP-70. In addition, Dasatinib enhanced in vitro the pro-apoptotic activity of

Rituximab and Fludarabine in CLL cells. Dasatinib treatment of CLL cells induced

changes in the expression profile of apoptosis related genes as well as changes

in apoptosis related proteins such as cleavage of PARP-1 and Caspases. Moreover,

CLL cells treated in vitro with Dasatinib showed reduced tyrosine kinase

activity measured by ELISA and also by immunoblots of CLL-cell lysates using

specific phospho-TK antibodies. In addition, Ig receptor signaling following

surface IgM ligation was decreased in CLL cells that were pre-treated with

Dasatinib relative to that of untreated CLL cells. In conclusion, Dasatinib

induces apoptosis of CLL cells at low nanomolar concentrations that do not

appear to affect the viability of B cells, T cells, or blood mononuclear cells

of healthy adults. CLL cells that expressed ZAP-70 were significantly more

sensitive to Dasatinib than CLL cells that lacked expression of ZAP-70. This

process was associated with impairment of BCR signaling, decrease TK activity

and regulation of genes and proteins related to apoptosis. In addition,

treatment of CLL cells with Dasatinib enhanced the in vitro activity of

Rituximab and Fludarabine. These results reveal that Dasatinib is potentially

active in CLL, providing a rationale for clinical trials evaluating its clinical

activity in the treatment of patients with this disease.

Footnotes

Disclosure: No relevant conflicts of interest to declare