AACR 2017 | Poster 2686/15 – Dual inhibition of BCR and TLR signaling has therapeutic potential in Chronic Lymphocytic Leukemia

On Monday 3^rd April during this year’s American Association for Cancer Research (AACR) annual meeting, a poster (2686 / 15) by Eman L. Dadashian, from NIH/NHLBI, Bethesda, MD, et al. titled “Dual inhibition of BCR and TLR signaling has therapeutic potential in Chronic Lymphocytic Leukemia” was presented.

The group treated CLL PMBCs with ibrutinib and/or calbiochem (an IRAK1/4 inhibitor) for 1h and then stimulated with soluble αIgM, CpG, or both. They measured changes in phosphorylation of BTK, PLCγ2, and ERK (BCR pathway), as well as STAT3, STAT1, and total IRAK1 (TLR pathway).

Key Highlights:

• Ibrutinib decreased phosphorylation of BTK, PLCγ2, and ERK (P < 0.05) and reduced the survival of CLL cells stimulated with αIgM (P = 0.001)
• CpG stimulated TLR signaling degraded IRAK1 and stimulated cytokine secretion that activates STAT phosphorylation
• Calbiochem effectively inhibited TLR signaling resulting in stabilization of IRAK1 (P = 0.002), reduced phosphorylation of STAT1/3 (P = 0.04), and decreased viability compared to CpG stimulated, but not IRAK inhibitor treated, cells
• Ibrutinib did not affect CpG-induced IRAK1 degradation, but was comparable to IRAK1/4 inhibition in decreasing phosphorylation of STAT
  • Indicates BTK inhibition antagonizes downstream effects of TLR activation but not upstream IRAK dependent steps
• IRAK1/4 inhibition did not affect αIgM-induced BCR activation
• In vitro, when ibrutinib and calbiochem were administered in combination, activation of both BCR and TLR signaling was blocked causing a significant decrease in CLL cell viability (P = 0.01) compared to co-activation of both pathways

The poster concluded by stating that when TLR9 signaling is activated, IRAK1 is phosphorylated by IRAK4 signaling for it to be degraded, resulting in activation of NF-kB, STAT1/3 phosphorylation, and increasing cell survival. The combination of BTK and IRAK1/4 inhibition “prevents propagation of TLR9 signaling downstream of NF-kB” and therefore reduces cell survival.