Pharmacological activation of WASp potentiates macrophage phagocytosis and enhances ibrutinib efficacy against mouse models of brain tumors

Both primary and metastatic brain malignancies are fatal and highly infiltrated with tumor-associated macrophages (TAMs). Enhancing the phagocytosis of neoplastic cells by TAMs is pivotal for slowing tumor growth. Great endeavors have been made to develop tyrosine kinase inhibitors (TKIs) for brain malignancies, yet whether tumor-targeting TKIs affect the phagocytic capacity of TAMs remains largely unknown. In this preclinical study, we report that repurposing ibrutinib, a blood-brain barrier-penetrable TKI, effectively suppresses the growth of several primary and metastatic brain tumors highly expressing Bruton's tyrosine kinase (BTK) or bone marrow X-linked nonreceptor tyrosine kinase (BMX) but concurrently dampens the TAM phagocytic function. Mechanistically, BTK, which is activated in TAMs, interacts with and phosphorylates Wiskott-Aldrich syndrome protein (WASp) to organize the actin cytoskeleton, which is imperative for phagocytosis. Ibrutinib treatment disrupts BTK-mediated WASp activation, thereby compromising TAM phagocytic efficacy. Pharmacological activation of WASp by its selective small-molecular activator EG-011 restores the ibrutinib-impaired TAM engulfment of tumor cells and effectively improves ibrutinib efficacy in mice bearing glioblastomas, primary central nervous system lymphomas, and lung carcinoma brain metastases. Furthermore, elevated expression of phosphorylated BTK or phosphorylated WASp in TAMs correlates with an increased phagocytic TAM subset identified by single-cell RNA sequencing and correlates with prolonged patient survival in a cohort with glioblastoma. Our preclinical study highlights the necessity of evaluating the on-target, off-tumor attack of TAMs during TKI administration and provides a proof of concept for reinvigorating the TAM phagocytic function to achieve additional clinical benefit.