Elevated Serum IL-10 Levels in Patients with Diffuse Large B Cell Lymphoma: A Mechanism of Aberrant JAK2 Kinase Activation

Abstract 960

Diffuse large B cell lymphoma (DLBCL) is an aggressive lymphoma whose survival depends on various signaling pathways one of which is Signal transducer and activator of transcription 3 (STAT3)/Janus kinase 2 (JAK2). We have demonstrated that JAK2 is constitutively activated at the auto-phosphorylation site in many cases of DLBCL. The most common mechanism causing abnormal JAK2 activation is through dysregulated cytokine signaling. Cytokines are deregulated in several hematological malignancies and may play a role in tumor cell growth through receptor-mediated and ligand dependent activation of the JAK2 kinase. In this study we investigated the role of cytokine signaling in JAK2 activation in DLBCL and use of a novel JAK2 inhibitor (JAK2i) to inhibit IL-10 induced JAK/STAT signaling.

We studied serum cytokines from 70 patients with new untreated DLBCL who participated in a clinical trial in the North Central Cancer Treatment Group (Micallef, IN et al Blood 2011). Compared to control sera, patients with DLBCL had higher levels of several JAK2 kinase related cytokines (IL-2, IL-6, IL-10, and EGF). IL-10 and IL-6 were significantly higher in DLBCL patients vs controls with p values >0.03 and >0.001, respectively. We next examined whether DLBCL cell lines produced IL-10. The phospho-JAK2 (pJAK2) positive DLBCL cell lines Ly10, DHL2 and HBL1 produced more IL-10 (40–80 pg/ml) than the pJAK2 negative cell lines Ly1, Ly19 and DHL6 (0–5 pg/ml). Analysis of the surface expression of IL-10 receptors (IL-10R) determined that most p-JAK2 positive DLBCL cells express either IL-10Ra or IL-10Rb or both. IL-10 had no effect on DLBCL cell survival in vitro; however, it did promote their proliferation. Only IL-10 (but not the other elevated cytokines) was specifically able to activate JAK2 and STAT3 phosphorylation in a subgroup of DLBCL cell lines. IL-10 was not able to activate JAK1, STAT1 and STAT5, which suggests a specific role of IL-10 in the JAK2 pathway. Moreover, neutralizing antibody to IL-10 inhibited IL-10-induced JAK2 and STAT3 tyrosine phosphorylation. We studied the effect of SAR302503 (SAR503, Sanofi, Cambridge, MA), a selective JAK2i currently in clinical trial for myelofibrosis on constitutive JAK2 signaling in DLBCL cells. SAR503 was able to inhibit JAK2 and STAT3 phosphorylation in a dose and time dependent manner in a variety of DLBCL cell lines and patient samples. JAK2 inhibition with SAR2503 caused a dose-dependent inhibitory effect on survival of pJAK2 positive DLBCL cells not observed in pJAK2 negative cells. Activation of STAT3 signaling up-regulates the expression of various genes involved in cell survival and proliferation such as bcl-xl, bcl-2, mcl-1 and c-myc. We observed a dose-dependent decrease in c-myc protein and mRNA levels in Ly3 and DHL2 cells with SAR503 treatment; however, SAR503 did not effect expression of bcl2, mcl-1 and bcl-xl proteins in DLBCL cells. Interestingly, JAK2 inhibition with SAR503 inhibited the autocrine secretion of IL-10 in a dose-dependent manner. Next, we determined if higher pre-treatment serum IL-10 correlates with the overall survival of 81 DLBCL patients. IL-10 by ELISA demonstrated that IL-10 levels were high in 51% (41/81) of patients (median, 57.7pg/ml; range, 26.1–503.7), and low in 49% (40/81) (median, 15.9 pg/ml; range, 0–25.9). Using a cut-off value of 26.1pg/ml, patients with a high serum IL-10 level had a significantly worse event-free survival (p=0.01). Clinical correlation of serum IL-10 with disease parameters showed that the IL-10 level was correlated with elevated serum LDH (p= 0.0085) and IPI score (p=0.01); there was no correlation with the number of extranodal sites, age, or B symptoms. DLBCL tumors from 40 patients were classified into germinal center B-cell type (GCB) and non-GCB type using the Hans algorithm. There was a clear trend towards a higher serum IL-10 in non-GCB DLBCL patients (p <0.06).

In summary, our data identifies mechanisms of JAK2 kinase activation in DLBCL and supports the hypothesis that the IL-10-JAK2-cmyc pathway is activated in patients with DLBCL. Finally our data provide a mechanistic basis of selecting and targeting DLBCL tumor cells with high IL-10 levels and/or constitutive JAK2 activity with potent and novel JAK2 inhibitors such as SAR503.