Targeting IL-6 receptor reduces IgM levels and tumor growth in Waldenström macroglobulinemia

Abstract

The tumor microenvironment (TME) plays an important role in cancer cell biology and is implicated in resistance to therapy. In Waldenström macroglobulinemia (WM), a subtype of Non-Hodgkin lymphoma, the TME modulates WM biology by secreting cytokines that promote the malignant phenotype. In previous work, we have shown that TME-IL-6 promotes WM cell growth and IgM secretion in WM. Tocilizumab/Actemra is an anti-IL-6R antibody, which can competitively block IL-6 binding to the IL-6R. We investigated the efficacy of Tocilizumab in a preclinical mouse model of WM that considers the role of the TME in disease biology. Hairless SCID mice were subcutaneously implanted with BCWM.1 or RPCI-WM1 and bone marrow stromal cells. Groups of mice were treated with Tocilizumab or control antibody three times/week for 5 weeks and the effect on tumor burden and disease biology were evaluated. Although Tocilizumab had no effect on mice survival, there was a significant reduction in tumor growth rate in mice injected with RPCI-WM1 cells treated with Tocilizumab. In mice injected with BCWM.1 cells, there was a significant reduction in human IgM secretion in mice sera with Tocilizumab treatment. There was no significant change in mice weight suggesting Tocilizumab induced no toxicities to the mice. Taken together, our data found that administration of Tocilizumab to tumor bearing mice, results in a significant reduction in tumor volume and IgM secretion. Therefore, the evaluation of the role of Tocilizumab in WM patients may provide therapeutic efficacy by reducing IgM production and slowing the rate of tumor growth.

Keywords: IL-6; Tocilizumab; Waldenström macroglobulinemia; tumor microenvironment.

Figure 1. Tocilizumab therapy does not affect overall survival.

(A) Hairless SCID mice (n = 10 mice/group) were subcutaneously injected with 10 × 10⁶ BCWM.1 or RPCI-WM1 cells + HS-5 stromal cells (5:1 ratio). Upon tumor appearance (day 7), groups of mice were treated with either Tocilizumab or Control antibody (IgG) at 100 μg/mouse i.p every other day for a total of 5 weeks. (B) Mice were monitored and survival was reported.

Figure 2. Targeting the TME with Tocilizumab reduces tumor growth.

(A) Relative tumor growth rate in BCWM.1 (left; n = 10/group) and RPCI-WM1 (p = 0.0394)(right; n = 10/group) (both with stromal cells) xenografted mice treated with either Tocilizumab or IgG control. The Y-axis indicates tumor volume relative to first recorded tumor size. (B) Tumor volume (left; p = 0.057) and relative tumor growth (right, p = 0.0306) on day 14 in mice xenografted with BCWM.1 cells and stromal cells. (C) Actual tumor volume (left, p = 0.057) and tumor growth rate (right, p = 0.0306) on day 14 in mice injected with BCWM.1 and stromal cells.

Figure 3. Tocilizumab reduces human IgM secretion in mice xenografted with BCWM.1 cells and stromal cells.

Serum was harvested from mice xenografted with BCWM.1 (left; p = 0.0029) and RPCI-WM1 (right) cells upon euthanasia and used to quantify human IgM levels in mice sera. IgM levels were determined using a human IgM ELISA.

Figure 4. Tocilizumb is not toxic to mice.

(A) Mice weights were monitored 3x/week and recoded to determine potential treatment toxicity for BCWM.1 (p = 0.005) and RPCI-WM1 xenografted mice. (B) Individual mice weights on day 9 (first recorded weight) and day 42 (experiment end point) for mice xenografted with BCWM.1 cells and stromal cells.

Figure 5. Histology of tumors post euthanasia.

H & E staining for tumors harvested from mice treated with Tocilizumab and control (BCWM.1 left, RPCI-WM1 right). Tumor samples were harvested and immediately fixed in 4% formaldehyde. Five μm sections were then stained with H & E as described in the methods.