Abstract 1421: The HDAC6-specific inhibitor AVS100 (SS208) blocks M2 polarization of tumor associated macrophages and potentiates immunotherapy in preclinical tumor models

Abstract Inhibition of HDAC6 was associated with an increased proinflammatory tumor microenvironment and an antitumoral response. Here, we show that a highly specific HDAC6 inhibitor AVS100 (SS208), blocks M2 polarization in murine and human macrophages while partially affecting M1 polarization. AVS100 effects were observed as blocked upregulation of M2-related gene signature under M2 polarizing conditions and blocked generation of CD206+ and Arg1+ macrophages. Oral administration of AVS100 had an antitumoral effect in SM1 melanoma and CT26 colon cancer models and increased the efficacy of anti-PD1 treatment, leading to complete remission in melanoma and increased response in colon cancer. Flow cytometry and scRNAseq analysis of tumor-infiltrating immune cells revealed an increase of proinflammatory/anti-inflammatory ratio in tumor-associated macrophages as well as an increase of intratumoral CD8 effector T-cells after AVS100 treatment. Interestingly, cured mice didn’t relapse and became resistant to a subsequent tumor challenge, suggesting acquired antitumoral T-cell immunity. T-cell repertoire analysis of effector/memory T-cells in cured mice revealed a higher number of immunodominant T-cell clones after AVS100 treatment, indicating increased T-cell expansion. Finally, AVS100 has demonstrated no mutagenicity and a strong safety profile in rats and dogs, leading to its recent U. S. FDA clearance of an Investigational New Drug (IND) application and planned initiation of Phase Ia/b clinical trials targeting locally advanced or metastatic solid tumors in the first half of 2024. Altogether, we have performed the preclinical characterization of a novel small molecule inhibitor targeting HDAC6 for solid cancers. AVS100 had an antitumoral effect as single agent and improved the efficacy of immune checkpoint inhibition by blocking the immunoregulatory tumor microenvironment and increasing T-cell immunity. Citation Format: Damian Kovalovsky, Satish Noonepalle, Manasa Suresh, Dileep Kumar, Michael Berrigan, Anelia Horvath, Allen Kim, David Quiceno-Torres, Karthik Musunuri, Alejandro Villagra. The HDAC6-specific inhibitor AVS100 (SS208) blocks M2 polarization of tumor associated macrophages and potentiates immunotherapy in preclinical tumor models abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts) ; 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84 (6Suppl): Abstract nr 1421.