Abstract CT094: Targeting CSF1R with BLZ945 results in effective peripheral and tumor immune microenvironment modulation in advanced solid tumors and may be associated with limited efficacy in recurrent non-mesenchymal glioblastoma

Abstract Colony-stimulating factor 1 receptor (CSF-1R) signaling is involved in regulating monocyte differentiation, and the recruitment and survival of tumor-associated macrophages (TAMs). BLZ945 is a small molecule, highly selective, orally bioavailable, potent kinase inhibitor of CSF-1R that has shown the ability to reduce the recruitment of TAMs in animal models and promote infiltration of effector T cells into the tumor in preclinical models. Given the potential effects of BLZ945 on effector T-cell activity, a combination of BLZ945 with the programmed death 1 (PD-1) inhibitor spartalizumab was investigated in 1) a dose escalation phase I clinical trial with advanced solid tumor patients; and 2) an expansion phase II clinical trial in adult patients with relapsed/refractory glioblastoma (GBM) after standard of care and other lines of therapy (NCT02829723). The percentages of non-classical and intermediate monocytes in the PBMC fraction were decreased after treatment at multiple doses and schedules of treatment tested in the escalation phase. Screening and on-treatment paired tumor biopsy samples from the escalation phase were analyzed by RNA sequencing. Downregulated genes have been noted as macrophage-specific genes, suggesting that treatment with BLZ945 is downregulating macrophages in the tumor microenvironment. There appeared to be a trend for a reduction in TAM gene signatures and increase in T-cell inflammation signatures upon treatment with single-agent BLZ945 or BLZ945 + spartalizumab. RNA-sequencing analysis from archival surgical resection GBM samples from the expansion phase, revealed a potential correlation between PDGFRA gene expression and best percent change in tumor size. This suggests that non-mesenchymal GBM, for which PDGFRA is part of the defining signature, are more sensitive to the treatment. DNA-sequencing of these archival samples also revealed mutations in p53 in the tumors with partial responses but no mutations in EGFR or TERT. Citation Format: Carlos Rodrigo Gil Del Alcazar, Virginia Xu, Chia-chi Lin, Marta Gil-Martin, Aung Naing, Liqiong Fan, Fang Yang, David Quinn, Jincheng Wu, Cornelia Quadt, Jennifer Mataraza. Targeting CSF1R with BLZ945 results in effective peripheral and tumor immune microenvironment modulation in advanced solid tumors and may be associated with limited efficacy in recurrent non-mesenchymal glioblastoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(7_Suppl):Abstract nr CT094.