Inhibition of the TPL2-MKK1/2-ERK1/2 pathway has cytostatic effect on B-Cell Lymphoma

1) Diffuse Large B-Cell Lymphoma (DLBCL) are the most common form of non-Hodgkin lymphoma. Their molecular origin is heterogeneous and therefore treatments aimed at DLBCL must be adapted in function of the underlying molecular mechanisms driving cellular transformation. Constitutive activation of the protein kinases ERK1/2 is a hallmark of many B-cell malignancies. ERK1/2 activation which can occur downstream of the classical MAPK cascade via RAF or, in response to TLR stimulation, via the Tumor Promoting Locus 2 (TPL2) protein kinase. This pathway also relays signals from the MYD88 oncogenic mutant L265P, frequently found in hematologic malignancies. We report here that TPL2 participate to ERK1/2 activation downstream of BCR in a DLBCL cell line (OCI-Ly2). Moreover, we showed that a ERK2[Y316F] mutant increased c-Myc -luciferase reporter expression. We then investigated the impact of ERK1/2 inhibition on the proliferation of OCI-Ly2 cells. We found that blocking ERK1/2 MAPK signaling cascade using either MKK1/2 inhibitors (PD184352 and MEK162) or TPL2 inhibitor (Compound 1) was mainly cytostatic. Finally, we showed that while TPL2-MKK1/2 inhibition leads to cytostatic effect, Compound 1 has cytocidal effect at high concentrations, that is mediated via additional targets. Taken together, this study demonstrates the involvement of TPL2 in oncogenic signaling of DLBCL and supports the idea that combination therapy targeting multiple molecular pathways linked to cellular transformation is a superior avenue for future therapies.