Autocrine IL-6 Production Indicates the Level of Activated STAT3 and NF-Kb of Chronic Lymphocytic Leukemia Cells

Abstract 1784

Interleukin-6 (IL-6) is a multifunctional cytokine that plays an important role in survival, apoptosis and proliferation of cancer cells. Previous studies have shown that IL-6 levels are significantly elevated in most cancer cells, while elevated serum levels of IL-6 correlated with adverse prognostic features and shorter survival in patients with chronic lymphocytic leukemia (CLL). IL-6 production is controled by transcription factors NF-kB and STAT3, which are themselves controled by tyrosine kinase phosphorylation, such as that mediated by JAK2. This creates a positive feedback loop, as JAK2 can be stimulated by IL-6.

In this study we investigated the relationship between autocrine IL-6 production and activation of STAT3 and NF-kB in CLL patients. The levels of IL-6 production in cell culture medium were measured by ELISA and activation of STAT3 and NF-kB was indicated by the ratio of p-STAT3/STAT3 and p-NF-kB/NF-kB. Patients with high levels of p-STAT3/STAT3 and/or p-NF-kB/NF-kB had higher levels of IL-6 production. The level of IL-6 production significantly correlated with STAT3 activation (R=0.856, p < 0.001) and NF-kB activation (R=0.815, p < 0.001). Inhibition of constitutive STAT3 and NF-kB activation by the STAT3 phosphorylation inhibitor, DPP, and the NF-kB inhibitor, CAPE, blocked IL-6 production 40% in average (p = 0.004, p = 0.003). Analysing the level of autocrine IL-6 production and in vitro spontaneous apoptosis in CLL cells from 38 patients, we found that patients with higher levels of IL-6 production (more than median) had significantly less apoptosis compared with those below the median (23% vs. 42.2% in average, p <0.0001). In this cohort, 60% of CD38+ cases, 78% of 17p- cases and 67% of cases with a lymphocyte doubling time of less than12 months were in the high IL-6 producer group. High IL-6 production was also associated with a shorter average time to first treatment (0.5 vs. 3 years, p=0.0023).

This study demonstrates that autocrine IL6 production correlates with STAT3 and NF-kB activation and apoptosis resistance in CLL. Furthermore, higher IL-6 production is associated with biological markers of poor prognosis and earlier treatment. The IL6/JAK2/STAT3 signal pathway may offer new therapeutic targets for CLL.