Phospho-SFKs (Y416) As a Potential Predictive Marker for Dasatinib Therapy in B-Cell Non-Hodgkin Lymphoma and Chronic Lymphocytic Leukemia,

Abstract 3727

The Src family of protein tyrosine kinases (SFKs) plays an important role in regulating multiple signaling networks including B-cell receptors (BCR) mediated pathways and abnormal SFK kinase activation promotes B lymphoma cell survival. Dasatinib is an oral BCR/ABL1 and SKF inhibitor useful in the treatment of imatinib-resistant CML and Ph+ALL. Given its broad inhibitory activity, dasatinib may be useful in the treatment of other hematologic malignancies and having a biologic predictor of response would be helpful in rational selection of this targeted therapeutic. We hypothesized this agent could have therapeutic potential against lymphoma patients with p-SFK (Y416) expression.

Constitutive p-SFK (Y416) expression (indicating active SFK signaling) was detected in both B-lymphoma cell lines and a subset of primary lymphoma tissues including diffuse large B-cell lymphoma (DLBCL), follicular lymphoma (FL), mantle cell lymphoma (MCL), Burkitt lymphoma and small lymphocytic leukemia (SLL). Dasatinib induced apoptosis of B-lymphoma Raji cells correlated with high level expression of constitutive p-SFK (Y416) and dasatinib rapidly reduced the global level of tyrosine phosphorylations including p-SFK (Y416) in Raji cells. 19 of 28 lymphoma cases (67.9%) were positive for p-SFK (Y416) by Western blot analysis. Dasatinib displayed in vitro dose-dependent (10–200 nM) killing activity against 17 of those 19 p-SFK (Y416) cases (89.5%). In contrast, only 2 of 9 p-SFK (Y416) negative cases (22.2%) had response to dasatinib exposure. Thus presence of p-SFK (Y416) was associated with in vitro response to dasatinib (p <0.0001). Similar to tested Raji cells, dasatinib induced apoptosis of primary B-cell lymphoma cells was accompanied with de-phosphorylation of p-SFK (Y416) and cleavage of caspase-3. 6 of 9 tested CLL cases were p-SFK (Y416) positive. Dasatinib displayed in vitro killing activities against 5 of 6 positive cases with a range of killing from 12% to 53% (mean 26.5%) of malignant B-cells. Meanwhile, one of three negative cases showed response to dasatinib (17% killing).

We conclude that p-SFK (Y416) may be a useful predictive marker of response to dasatinib. Potential uses include pharmacodynamic monitoring or integral biomarker for selecting appropriate patients with B-cell malignancies for clinical trials.