Anomalous constitutive Src kinase activity promotes B lymphoma survival and growth

Abstract

BackgroundPreviously we have shown that B cell receptor (BCR) expression and B cell receptor signaling pathways are important for the basal growth of B lymphoma cells. In particular we have shown that the activation of Syk, a non-src family protein tyrosine kinase and the mitogen activated protein kinases (MAPK), ERK and JNK that mediate BCR signals are required for the constitutive growth of B lymphoma cells. Since src family protein tyrosine kinases (SFKs) like Lyn are known to be needed for the phosphorylation of BCR co-receptors, Ig-α and Ig-β, we hypothesized that one or more SFKs will be constitutively activated in B lymphoma cells and may be necessary for B lymphoma growth.ResultsSrc kinase activity was found to be constitutively high in many murine and human B lymphoma cell lines and primary lymphoma samples. The specific pharmacological inhibitors of SFKs, PP1 and PP2 inhibited the proliferation of a number of both murine and human B lymphomas in a dose-dependent manner. Importantly, dasatinib (BMS-354825), an oral dual BCR-ABL and SFK specific inhibitor inhibited the growth of B lymphomas in the nanomolar range in vitro and strongly inhibited a mouse lymphoma growth in vivo. Among the SFKs, Lyn is predominantly phosphorylated and Lyn-specific small interfering RNA inhibited the growth of B lymphomas, supporting an important role for Lyn in B lymphoma growth. Suppression of SFK activity blocks BCR mediated signaling pathways. PMA or CpG can partially reverse the growth inhibition induced by SFK inhibition. Although blocking SFK activity inhibited the growth of a number of B lymphomas, some lymphomas such as SudHL-4, SudHL-6, OCI-Ly3 and OCI-Ly10 are more resistant due to an increased expression of the anti-apoptotic proteins Bcl-2 and Bcl-xL.ConclusionsThese studies further support our concept that BCR signaling pathways are important for the continued growth of established B lymphoma cells. Some of the intermediates in this BCR pathway are potential immunotherapeutic targets. In particular, inhibition of SFK activity alone or in synergy with inhibition of the prosurvival Bcl-2 proteins holds promise in developing more effective treatments for B lymphoma patients.

Anti-cancer activity of withaferin A in B-cell lymphoma

“…[47][48][49] These results are novel findings as we are the first to show that WA inhibits key survival kinases that are required for B cell growth. 2,8 In conclusion, we have proposed a mechanism of action by WA that encompasses the broad range of effects shown in DLBCL. It is clear that WA has anti-cancer activities not only in hematological malignancies but also in many solid tumor models previously described.…”

“…8 Therefore, we investigated the effect of WA treatment on the protein activity and expression of Lyn, a known SFK needed for the phosphorylation of the BCR co-receptors. 27 As shown in Figure 5B, there is a dramatic loss of expression of pSrc at late time point treatments with WA.…”

“…8,9,50 Luciferase and YFP expressing A20 B lymphoma cells were obtained from Dr. Scott Bryson with permission from Dr. Negrin. 51 Cell survival and proliferation was determined by the 3-(4,5-dimethylthiazole-2-yl)-2,5-biphenyl tetrazolium bromide (MTT) assay.…”

“…6,7 We and others have shown that similar to normal B cell survival, B cell lymphomas require B cell receptor (BCR) signaling for growth and survival. 2,8,9 The increased expression and activity of these kinases and NF-kB are known to promote B cell lymphoma survival and are significant targets in cancer therapies. 10 Current therapies for DLBCL involve a range of chemotherapeutics and immunotherapies (R-CHOP) with potential beneficial outcomes, yet result in many adverse side effects, warranting the need for novel therapies for the treatment of this disease.…”

Antitumor activity of new pyrazolo[3,4-d]pyrimidine SRC kinase inhibitors in Burkitt lymphoma cell lines and its enhancement by WEE1 inhibition

“…8 It has been recently shown that SRC family kinases are hyperactivated in many B lymphoma cell lines and primary lymphoma samples but not in normal B cells. [9][10][11] Moreover, SRC inhibition, mediated by the multitargeted tyrosine kinase inhibitor dasatinib and the SRC inhibitors PP1 (4-amino-5-(4-chlorophenyl)-7-(t-butyl)pyrazolo [3,4-d]pyrimidine) and PP2, induced an antiproliferative effect on diffuse large B-cell lymphoma cell lines. [9][10][11] Although these studies are mostly focused on a different lymphoma type, one includes the BL cell line, BJAB and shows that both PP1 and PP2 have antiproliferative effects on this cell line.…”