Reprogramming of tumor-associated M2 macrophages with antisense oligonucleotide-loaded exosomes results in potent single-agent antitumor activity.

Tumor-associated macrophages (TAMs) are potent drivers of an immunosuppressive tumor microenvironment and may be an attractive therapeutic target. Experimental therapies tested thus far block myeloid cell differentiation, leading to ineffective antigen presentation and minimal antitumor activity. Exosomes serve as an efficient, natural, intercellular communication system that can deliver nucleic acids and other macromolecules. We have developed novel, engineered exosome therapeutic candidates that selectively deliver antisense oligos (ASOs) to TAMs, targeting key transcription factors that control the immunosuppressive program, such as STAT6 and C/EBPβ. These transcription factors, which are otherwise “undruggable” with current therapeutic strategies, are activated through various signaling molecules such as IL-4 and IL-10, which results in a protumorigenic macrophage phenotype (M2). Exosomes loaded with STAT6 or C/EBPβ ASOs (exoASO) induced dose-dependent knockdown (KD) of target genes in primary human M2 macrophages with greater potency than the free ASO. Gene expression analysis and cytokine assays showed that exoASO-mediated KD resulted in a marked reprogramming to a proinflammatory (M1) phenotype, as measured by a significant decrease in CD163 and TGF-β1 expression, and a concomitant induction of TNFα and IL-12p40 production. Intratumorally dosed exoASO preferentially associated with tumor myeloid cells, resulting in a 50% KD of STAT6 and C/EBPβ mRNA transcripts in tumor-associated CD11b+ cells, compared to a 20% KD with an equivalent dose of free ASO. Modulation of mRNAs for CD206, Csf1r, and iNos was also observed, and is consistent with M2 to M1 conversion. ExoASO-STAT6 treatment of mice with CT26 tumors showed significant antitumor activity as a monotherapy (80% tumor growth inhibition, 30% complete responses). Similar monotherapy activity was also observed in vivo with exoASO C/EBPβ therapy. In contrast, equivalent doses of free ASO or anti-CSF1R monotherapy did not have any significant effects on tumor growth. Thus, exoASO therapeutics can specifically target and effectively reduce the expression of transcription factors in TAMs, inducing effective reprogramming and resulting in potent antitumor activity. Collectively, exoASOs against STAT6 and C/EBPβ represent a first-in-class strategy to target tumor-associated myeloid cells in a highly selective manner. Citation Format: Suhrut Kamerkar, Dalia Burzyn, Charan Leng, Olga Burenkova, Su Chul Jang, Raymond Yang, Adam Boutin, Katherine Kirwin, Tong Zi, William Dahlberg, Eric Zhang, Kelvin Zhang, Scott Estes, Kyriakos Economides, Timothy Soos, Sriram Sathyanarayanan. Reprogramming of tumor-associated M2 macrophages with antisense oligonucleotide-loaded exosomes results in potent single-agent antitumor activity [abstract]. In: Proceedings of the AACR Special Conference on Tumor Immunology and Immunotherapy; 2019 Nov 17-20; Boston, MA. Philadelphia (PA): AACR; Cancer Immunol Res 2020;8(3 Suppl):Abstract nr A50.