To investigate the toxicity profile and establish an optimal dosing schedule of zotiraciclib with temozolomide (TMZ) in patients with recurrent high-grade astrocytoma.Experimental Design: This two-stage phase 1 trial determined the maximum tolerated dose (MTD) of zotiraciclib combined with either dose-dense (Arm1) or metronomic (Arm2) TMZ using a Bayesian Optimal Interval design; then a randomized cohortexpansion compared the progression-free survival rate at 4 month (PFS4) of the two arms for an efficient determination of a TMZ schedule to combine with zotiraciclib at MTD. Pharmacokinetics (PK) and pharmacogenomic (PG) profiling were included. Patient-reported outcome was evaluated by longitudinal symptom burden.Results: Fifty-three patients were enrolled. Dose-limiting toxicities were neutropenia, diarrhea, elevated liver enzymes, and fatigue. MTD of zotiraciclib was 250mg in both arms and thus selected for the cohort expansion. Dose-dense TMZ plus zotiraciclib (PSF4 40%) compared favorably with metronomic TMZ (PFS4 25%). Symptom burden worsened at Cycle 2 but stabilized by Cycle 4 in both arms. A significant decrease in absolute neutrophil count and neutrophil reactive oxygen species production occurred 12-24 hours after an oral dose of zotiraciclib but both recovered by 72 hours. PK/PG analyses revealed that the CYP1A2_5347T>C (rs2470890) polymorphism was associated with higher AUC inf value.Conclusions: Zotiraciclib combined with TMZ is safe in patients with recurrent highgrade astrocytomas. Zotiraciclib-induced neutropenia can be profound but mostly transient, warranting close monitoring rather than treatment discontinuation. Once validated, polymorphisms predicting drug metabolism may allow personalized dosing of zotiraciclib.
Background Glioblastoma-associated macrophages and microglia (GAMs) are the predominant immune cells in the tumor microenvironment. Activation of MerTK, a receptor tyrosine kinase, polarizes GAMs to an immunosuppressive phenotype, promoting tumor growth. Here, the role of MerTK inhibition in the glioblastoma microenvironment is investigated in vitro and in vivo. Methods Effects of MRX-2843 in glioblastoma microenvironment regulation were determined in vitro by cell viability, cytokine array, in vitro tube formation, Western blotting, and wound healing assays. A syngeneic GL261 orthotopic glioblastoma mouse model was used to evaluate the survival benefit of MRX-2843 treatment. Multiplex fluorescent immunohistochemistry was used to evaluate the expression of CD206, an anti-inflammatory marker on GAMs, and angiogenesis in murine brain tumor tissues. Results MRX-2843 inhibited cell growth and induced apoptosis in human glioblastoma cells and decreased protein expression of phosphorylated MerTK, AKT, and ERK, which are essential for cell survival signaling. Interleukin-8 and C-C motif chemokine ligand 2, the pro-glioma and pro-angiogenic cytokines, were decreased by MRX-2843. Decreased vascular formation and numbers of immunosuppressive (CD206+) GAMs were observed following MRX-2843 treatment in vivo, suggesting that in addition to alleviating immunosuppression, MRX-2843 also inhibits neoangiogenesis in the glioma microenvironment. These results were supported by a prolonged survival in the syngeneic mouse orthotopic GL261 glioblastoma model following MRX-2843 treatment. Conclusion Our findings suggest that MRX-2843 has a therapeutic benefit via promoting GAM polarization away from immunosuppressive condition, inhibiting neoangiogenesis in the glioblastoma microenvironment and inducing tumor cell death.
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