Abstract 679: Selective targeting of immunosuppressive tumor macrophage from systemic administration

Macrophage in tumors in the M2 immunosuppressive state have been shown to play a role in reducing the effectiveness of immunotherapy and facilitating metastases formation. Many current approaches to targeting macrophage are not selective to the tumor microenvironment potentially resulting in systemic proinflammatory responses. Hydroxyl dendrimers without targeting moieties have been shown to be selectively endocytosed by reactive macrophages in solid tumors but not by normal quiescent macrophages. To evaluate the effect of hydroxyl dendrimer size and circulation time on targeting M2 tumor associated macrophages (TAMs), we generated fluorescently tagged hydroxyl dendrimers of two types, Generation 4 dendrimer (~14,000 Da, 4 nm) conjugated with Cy5 (D4-Cy5) and Generation 6 dendrimer (~58,000 Da, 7 nm) conjugated with VivoTag 680 (D6-V). A novel CSF1R tyrosine kinase inhibitor was also conjugated to the G6 hydroxyl dendrimer along with VivoTag 680 (C-D6-V). The syngeneic murine colon cancer line, MC38, was subcutaneously injected in C57BL/6 mice (n=10/group) and tumors were allowed to grow to a minimum average size of 80-120 mm3. After tumor establishment, either D4-Cy5, D6-V, or C-D6-V was injected IV (55 mg/kg, 10 mL/kg) and mice were sacrificed 48 hrs post-dose (D4 and D6 are systemically cleared within 48 hr). Tumors were analyzed for total radiant fluorescence, FACS analysis for immune cell subpopulations, and immunohistochemistry. Analysis of total fluorescence indicated a greater tumor uptake of D6-V compared to D4-Cy5 consistent with previous studies. Selective uptake and retention was observed in M2 macrophage, M1 macrophage, and mMDSCs. Tumors consisted of ~56% CD45+ cells of which ~20-25% were M2 macrophage, ~13% were M1 macrophage, and ~8% were mMDSCs. 34 ± 4 % of all M2 macrophage, 6.5% ± 1.7% of all M1 macrophage, and 8.1 ± 1.6% of all mMDSCs contained D4-Cy5 after the single IV dose. The fraction of dendrimer in other immune cell populations was less than 5%. The C-D6-V had greater tumor uptake than D6-V suggesting that CSF1R binding may further enhance tumor targeting as well as potentially impact M2 TAMs. These results indicate the potential to selectively target M2 TAMs and other tumor resident immune cells after systemic administration. Hydroxyl dendrimers may provide a novel carrier for delivery of immune modulators to tumors while minimizing their systemic toxicity. Efficacy studies are ongoing to evaluate CSF1R inhibitors and other therapeutics conjugated to the hydroxyl dendrimers. Citation Format: Jeffrey L. Cleland, Rishi Sharma, Santiago Appiani, Emily O9Koren, Lindsay Usher, Kannan Rangaramanujam. Selective targeting of immunosuppressive tumor macrophage from systemic administration [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 679.