Abstract 5696: Genetic reprogramming of TAMs by engineered exosomes results in potent single agent anti-tumor activity
Authors: Kamerkar Sushrut , Burzyn Dalia , Burenkova Olga , Leng Charan , Yang Raymond , Kirwin Katherin , Zi Tong , Jang Su Chul , Dahlberg William , Zhang Eric , Estes Scott , Maubant Sylvie , Duchamp Olivier , Economides Kyriakos , Soos Timothy , Sathyanarayanan Sriram 
Published: September 2020

Abstract
Background: Tumor-associated macrophages (TAMs) are potent drivers of an immunosuppressive tumor microenvironment by reducing T cell recruitment and activation, promoting resistance to immune checkpoint inhibition. Experimental therapies blocking monocyte differentiation or eliminating TAMs show minimal anti-tumor activity. STAT6 and C/EBPβ have key roles in regulating the immunosuppressive state of TAMs however previous attempts to selectively target these transcription factors were unsuccessful. We have developed proprietary engineered exosome therapeutic candidates loaded with antisense oligos (ASOs) targeting STAT6 and C/EBPβ (exoASO). exoASO is designed to selectively deliver ASOs to TAMs and decrease STAT6 and C/EBPβ expression, leading to reprogramming of M2-like TAMs to a M1-like immune stimulatory phenotype.
Results: exoASO-STAT6 and exoASO-C/EBPβ induced dose-dependent knockdown (KD) of target genes in primary human M2 macrophages with greater potency (IC50) than free ASO. Gene expression analysis and cytokine assays showed that exoASO-mediated KD resulted in a marked reprogramming to a proinflammatory (M1) phenotype. IV administration of exoASO in a TAM-rich model (CT-26) demonstrates selective uptake by myeloid derived suppressor cells and macrophages. We evaluated efficacy of exoASO-STAT6 or exoASO-C/EBPβ alone or in combination with anti-PD1 therapy. Both exoASO-STAT6 and exoASO-C/EBPβ were efficacious as monotherapies (50% and 60% complete responses (CR) respectively), whereas anti-PD1 or anti-CSFR1 mAb were not effective (0% CR). exoASO-C/EBPβ in combination with anti-PD1 mAb resulted in greater efficacy (80% CR), and enhanced survival (70% at day 55) compared to exoASO-C/EBPβ monotherapy (50% survival at day 55). In contrast, combination of anti-PD1 with exoASO-STAT6 did not show improved efficacy as compared to monotherapy. Durable anti-tumor responses were observed with both exoASO therapies as mice achieving CR against the primary tumor had no tumor growth upon re-challenge. We evaluated anti-tumor efficacy using an orthotopic hepatocellular carcinoma (HCC) model. Mice were dosed IV using: exoASO-C/EBPβ; free C/EBPβ ASO; anti-PD1 or; anti-CSF1R mAbs. exoASO-C/EBPβ treatment attenuated HCC-mediated increase in liver to body weight ratios (≤ 10%) and showed little to no observable tumor lesions in 50% of treated mice. In contrast, increased liver to body weight ratios (≥ 10%) and observable tumor lesions occurred in all mice (100%) treated with either free C/EBPβ ASO or anti-CSF1R mAb.
Conclusion: exoASO-STAT6 and exoASO-C/EBPβ are efficacious as monotherapies in TAM-rich tumors when administered locally or systemically. exoASO-C/EBPβ has increased potency when administered in combination with checkpoint antibodies. Collectively, exoASOs against STAT6 and C/EBPβ are a first-in-class strategy to target TAMs in a highly selective manner.
Citation Format: Sushrut Kamerkar, Dalia Burzyn, Olga Burenkova, Charan Leng, Raymond Yang, Katherin Kirwin, Tong Zi, Su Chul Jang, William Dahlberg, Eric Zhang, Scott Estes, Sylvie Maubant, Olivier Duchamp, Kyriakos Economides, Timothy Soos, Sriram Sathyanarayanan. Genetic reprogramming of TAMs by engineered exosomes results in potent single agent anti-tumor activity [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 5696.