Tocilizumab Overcomes Chemo-Resistance Of CLL Cells

IL-6 in the cancer microenvironment plays a crucial role in the constitutive activation of STAT3, which contributes to cancer cell progression. IL-6 binds to a heterodimer of membrane-bound receptors, IL-6R (CD126) and gp130, that triggers phosphorylation of JAK2 and downstream STAT3. The phosphorylated STAT3 acts as a transcription factor, binding target DNA and promoting tumorigenesis, cell proliferation and survival. IL-6 signaling pathways have been extensively studied as therapeutic targets in both cancer and autoimmune conditions. The anti-IL6R antibody Tocilizumab is a humanized anti CD126 antibody, approved by the FDA (Food and Drug Administration) for treatment of rheumatoid arthritis, that can block IL-6 classic and trans-signalling pathways. We investigated IL-6R expression in CLL cells and analysed the correlation of IL-6R expression with chemo-sensitization and the potential of targeting IL-6R to overcome drug resistance in vitro.

41 CLL patients were studied. Membrane-bound and soluble IL-6 receptors, CD126 and gp130, were measured by flow cytometry or ELISA. Constitutive activation of STAT3 and the expression of Bcl-2 family proteins were detected by western blotting. Cell cycle distribution was assessed with Ki67 and cell viability indicated by propidium iodide (PI) negative staining.

CLL cells were found to express variable levels of membrane-bound receptors of IL-6, CD126 (average 22%, range 3-60%) and gp130 (average 12%, range 3-25%), which was significantly higher than normal B-cells (CD126 average 1.7%, range 0-6.3%; gp130 average 1.3%, rage 0-7.9%). Although in vitro Chlorambucil-induced cell death was variable among the cases, there was a strong correlation with CD126 expression (Figure 1): higher CD126 expression was associated with increased resistance to Chlorambucil.

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Treatment of CLL cells with Tocilizumab led to inhibition of constitutive STAT3 activation decreased Mcl-1, Bcl-xl expression and cells exited from G0 phase of the cell cycle. Tocilizumab did not induce cell death in CLL cells. Combined treatment with both Chlorambucil and Tocilizumab significantly increased cell death (p < 0.01). Interestingly, higher CD126 expression was highly significantly correlated with the increased cell death seen with combined Chlorambucil and Tocilizumab (p < 0.0001, Figure 2)

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These results suggest that inhibiting IL6 signal pathways via IL-6R blockade with Tocilizumab is a new approach in CLL, leading to increased chemo-sensitisation to standard chemotherapeutic agents. Although CLL cells with higher CD126 expression exhibited more drug resistance in vitro, they also showed better response to Tocilizumab. Targeting the combination of Tocilizumab with anti-cancer therapy to CLL patients with high IL-6R expression might achieve clinical therapeutic efficacy.