Cancer Immunotherapy Targeting Tn Antigen

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Abstract Cancer immunotherapeutic bi-specific proteins and engineered Chimeric Antigen Receptor T cells (CAR T) have shown remarkable clinical activity, with complete response rates as high as ~90% for B cell malignancies. However, applying these two therapeutic approaches to the vast majority of cancer types is restricted by multiple factors. First, there are only a small number of known cell-surface proteins that are sufficiently specific to cancer to safely allow targeting by antibodies. This is particularly true for solid cancers, where unlike hematopoietic malignancies; loss of healthy cells cannot be readily replenished by stem cell progenitors. Second, as each individual bi-specific protein and/or CAR T cell only target a single cancer type, different bi-specific and/or CAR T cells will need to be developed for each cancer type. This greatly increases development time and costs. Third, neither therapy is able to effectively target the most abundant and widely expressed cell surface cancer antigens known, namely Tumor associated carbohydrate antigens (TACA’s). Many cancer specific antigens are not proteins, but rather complex carbohydrates that have limited or no expression in normal tissues. Indeed, altered glycosylation is a near universal feature of cancer. While TACA’s have been known for decades, generation of effective monoclonal antibodies specific to complex carbohydrates has proven to be very challenging, greatly limiting their usefulness as targets for cancer immunotherapy. Here we propose to address these issues and develop a novel class of immunotherapeutics that target the Tn antigen, an abnormal O-linked carbohydrate common on many solid and hematopoietic cancers but not present on normal tissue. We have termed this technology as Glycan-dependent T cell Recruiter (GlyTR, pronounced ‘glitter’). We have generated and optimized a GlyTR bi-specific protein that 1) specifically binds to both Tn antigen and CD3, 2) activated T cells in the presence but not absence of Tn+ cancer cells and 3) induced T cell dependent killing of diverse solid and liquid cancer cells in vitro and in vivo. However, serum half-life was ~2 hrs, which is similar to the FDA approved bi-specific protein Blincyto that requires continuous intravenous infusion (via a pump) over 28-days (first 9 days in hospital). To avoid this cumbersome treatment regimen for GlyTR, here we propose to extend the half-life by adding a human-serum albumin (HSA) domain. The half-life of HSA is ~3 weeks and has been successfully fused to therapeutic proteins to markedly increase half-life, including two FDA approved therapeutics. Here we propose to genetically fuse HSA to GlyTR (HSA-GlyTR) and confirm binding to Tn antigen, cancer-killing activity and improved half-life. Specifically, we propose the following two Aims. Aim 1 optimizes the HSA-GlyTR bi-specific protein for activity and drug development. Aim 2 explores the efficacy and safety of the optimized HSA-GlyTR bi-specific protein. If successful, these experiments will allow subsequent IND enabling studies to develop an entire new class of cancer killing immunotherapeutic’s uniquely capable of targeting multiple solid and hematopoietic cancers with a single therapeutic.