RRx-001 is a phase III aerospace-derived small molecule that immunonormalizes the tumor microenvironment.

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156 Background: Tumor associated macrophages (TAMs) with M2-like phenotypes produce angiogenic factors and cytokines which lead to vascular immaturity. M2 cytokines also impair immune cell activity. CD47 and SIRP⍺ are innate immune checkpoints which inhibit macrophage phagocytosis and enhance M2 polarization. Disruption of the CD47/SIRP⍺ axis polarize TAMs away from an M2-like phenotype to normalize tumor vessels and stimulate antitumor immunity. Normalized vessels facilitate delivery of drugs and immune cells and also sensitizes tumors to therapy and promotes M1-like TAM phenotype. RRx-001 modulates TAM infiltration and phenotype via CD47/SIRP⍺ downregulation, which normalizes both the tumor vasculature, and the immune cell milieu. Methods: The effect of RRx-001 on intratumoral blood flow was evaluated both preclinically and clinically with dynamic contrast MRI. An in vitro phagocytotic assay was used to determine whether RRx-001 promoted engulfment of A549 tumor cells by macrophages. Transcriptional mRNA profiling in murine tumor associated macrophages (TAMs) was performed to analyze the cytokine profile of TAMs in the presence or absence of RRx-001. Athymic mice with intracranial GBM43 were administered RRx-001 (10 mg/kg) followed 4 hours later by 0.4 mg of irinotecan by tail vein on days 12, 18, 24 and 30 after implantation of tumor cells. Mice were euthanized 24 hours after last irinotecan administration, with brains immediately resected and tumor tissue dissected prior to snap-freezing by immersion in liquid nitrogen. Results: RRx-001 was shown to induce: vascular normalization with increased intratumoral perfusion, dual downregulation of CD47 and SIRP⍺, increased phagocytosis, improved delivery of chemotherapy and increased T cell infiltration. Conclusions: RRx-001 leads to vascular normalization and enhanced delivery of chemotherapy and immune cell infiltration. The increase in tumor perfusion diminishes hypoxia and also serves to polarize TAMs away from an M2-like state. These results also suggest and are borne out by clinical biopsies that the effect of RRx-001 depends on the number of TAMs present in the tumor microenvironment with higher numbers leading to better activity.