Abstract 3134: Preclinical anti-glioblastoma pharmacology of HX301, a novel CSF-1R inhibitor

Abstract Background. GBM is the most malignant and frequently occurring glioma (>60% of all brain tumors in adults) with poor prognosis (12-18 months survival time after diagnosis and 5-year survival of ∼5%) and an unmet medical need. Glioma-associated macrophages/microglia (GAMs) are the prominent and suppressive immune cells in the tumor microenvironment (TME), promoting the growth, migration, invasion and stemness of tumor cell . GAMs also secret VEGF to promote angiogenesis and TGF-β to suppress immunity. Notably, the numbers of surrounding GAM inversely correlate with the prognosis. CSF1R, together with its two ligands, CSF1 (M-CSF) and IL-34, governs the proliferation, polarization, differentiation and functions of the myeloid lineage cells, including macrophage/microglia in GBM. Blocking CSF1/CSF1R signaling inhibits microglia/macrophage proliferation and delayed tumor growth by depleting GAMs and diminishing their tumor-promoting activities. HX301 (Narazaciclib or ON123300) is a clinical-stage tyrosine kinase inhibitor (TKI, NCT#05731934) with great potency against CSF1R (IC50 0.285nM) and has demonstrated significant inhibition on macrophage proliferation in vitro/in vivo as well as capability of penetrating brain-blood-barrier (BBB). We hypothesized it has anti-GBM activity. Methods. A single dose of HX301 (30 mg/kg) was orally administrated in NOD/Scid mice, followed by plasma and brain tissues collection at designated timepoints and the drug concentration determination by LC-MS. Anti-GBM pharmacology of the drug was assessed in the following preclinical models: 1) subcutaneous U87-MG xenograft; 2) orthotopic GL261-Red-Fluc syngeneic mouse GBM model; and 3) orthotopic BN2289-Luc PDX model, respectively. HX301, Temozolomide (TMZ), or their combination were oral-administrated daily. tumor-focused-irradiation was also performed using a X-RAD320 (Precision X-Ray, 15-Gy two days after randomization). Results. The mouse PK study showed that HX301 efficiently penetrate BBB resulting in adequate exposure in brain for activity. In the three GBM pharmacology modeling, HX301 alone significantly inhibited the tumor growth, of which the anti-tumor activity seen in the orthotopic GL261-Red-Fluc and BN2289-Luc models also confirmed HX301 penetration BBB to exert its anti-tumor effects, possibly acting on the macrophages or microglia in the TME. Moreover, although HX301 and radiation combo failed to show any synergistic effects in orthotopic GL261-Red-Fluc model, HX301 in combination with TMZ exhibited significantly stronger anti-tumor activities over either HX301 alone or TMZ alone in the subcutaneous U87-MG model, suggesting a synergistic effect between the two. Conclusions. HX301 demonstrated great ability to penetrate BBB and robust anti-tumor efficacy, as well as enhanced activity when combined with TMZ, in GBM models, which warrants a further clinical investigation. Citation Format: Tao Yang, Hang Ke, Jessie Wang, Steven Xiong, Lei Zhang, Faming Zhang, Henry Qixiang Li. Preclinical anti-glioblastoma pharmacology of HX301, a novel CSF-1R inhibitor [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 3134.