Targeting myddosome signaling in Waldenstrom's ^€ macroglobulinemia with the interleukin-1 receptor-associated kinase 1/4 inhibitor R191

Purpose: Waldenstrom's € macroglobulinemia is an incurable lymphoproliferative disorder driven by an L265P mutation in the myeloid differentiation primary response gene 88 (MYD88), which activates downstream NF-kB signaling through the Myddosome. As this pathway depends in part on activity of interleukin-1 receptor-associated kinases (IRAKs)-1 and -4, we sought to evaluate the potential of the IRAK1/4 inhibitor R191 in preclinical models. Experimental Design: Patient-derived cell lines and primary samples were used in both in vitro and in vivo experiments to model Waldenstrom's € macroglobulinemia and its response to IRAK1/4 inhibitors. Results: R191 induced a dose- and time-dependent reduction in viability of BCWM.1 and MWCL-1 Waldenstrom's € cell lines, and suppressed activation of IRAK1/4. This was associated with cell-cycle arrest at G ₀ –G ₁ , reduced levels of cyclin-dependent kinases 4 and 6, and induction of apoptosis in cell lines and primary patient samples. Further downstream, R191 exposure led to reduced activation of NF-kB, and of protein kinase B/Akt/mammalian target of rapamycin signaling, whereas expression of a constitutively active Akt mutant induced R191 resistance. Gene expression profiling and gene set enrichment analysis revealed a signature consistent with inhibition of c-Myc and activation of the endoplasmic reticulum stress response. In both subcutaneous and systemic murine models of Waldenstrom's, € R191 showed antitumor activity. Finally, the activity of R191 was enhanced when it was combined with novel chemotherapeutics such as bortezomib, afuresertib, and ibrutinib. Conclusions: Taken together, these data support the translation of R191 as an approach to target IRAK1/4 to the clinic for patients with Waldenstrom's € macroglobulinemia.