Development of selective HDAC6 inhibitors to improve cancer immunotherapy

Project Summary The median survival for metastatic melanoma is approximately 8–16 months, and few therapies offer a significant improvement in overall survival. However, immunotherapeutic strategies that abrogate immunologic checkpoints or improve immunosurveillance have shown promise, especially in melanoma.

We have found that both genetic abrogation and pharmacologic inhibition of HDAC6 leads to a decreased infiltration of pro-tumoral tumor-associated macrophages and downregulation of immunosuppressive mediators. These effects translated into a pronounced delay of in vivo melanoma tumor growth, which is, at least in part, dependent on intact immunity, as evidenced by the restoration of tumor

growth after CD4+ and CD8+ depletion. Our findings demonstrate a significant immunoregulatory role of HDAC6 in melanoma, providing a rationale for the use of selective HDAC6is to improve antitumor immunity. We are most interested in identifying HDAC6is that are best able to reduce the pro-tumoral phenotype of

tumor-associated macrophages and decrease the expression of immunosuppressive surface molecules such as PD-L1 and PD-L2 while showing little cytotoxicity on their own. Our goal is thus to design, synthesize, and test new HDAC6i both in vitro and in vivo for use in the treatment of melanoma and other malignancies. The aims to be accomplished under this grant are as follows:

1. Using molecular modeling, design, and synthesize ~50 new HDAC6is per year, for the first three years and test these for HDAC isozyme selectivity; the last two years of the grant will focus on compound scale-up, preclinical translational studies, and advanced ADMET testing. 2. Evaluate compounds that have IC50 values of