Linda Pestano

Abstract 762: ONT-10, a liposomal vaccine targeting hypoglycosylated MUC1, induces a potent cellular and humoral response and suppresses the growth of MUC1 expressing tumors

MUC1 is highly expressed in multiple tumor histologies and is hypoglycosylated relative to normal tissue, with prematurely terminated carbohydrate modifications including αN-acetylgalactosamine (Tn). The aberrant glycosylation state of MUC1 makes this antigen immunologically distinct in tumor relative to normal tissues and an attractive vaccine target. ONT-10 is a liposomal formulated vaccine that incorporates a synthetic glycopeptide antigen that includes two complete 20 amino acid tandem repeats from human MUC1, including six glycosylated sites modified by Ser- or Thr-O- Tn, and is incorporated into the liposomal drug product via two C-terminal lipid serines. The ONT-10 drug product is formulated with the novel, fully synthetic lipid A adjuvant, penta erythritol lipid A (PET Lipid A). PET Lipid A displays a similar spatial distribution of lipid chains as natural Lipid A, but is composed of pure 6-acyl moieties, resulting in enhanced potency as an activator of Toll-like Receptor 2 and 4 (TLR2, TLR4). In preclinical studies, immunization of mice with ONT-10 induces a prominent T cell and antibody response to MUC1 and results in a substantial growth inhibition of MUC1 expressing tumors. T cell recall assays show a Th1 cytokine pattern with strong IFNγ production in spleen derived CD4 and CD8 cells in response to Tn-MUC1. At doses as low as 5μg/mouse ONT-10 results in a high titer anti-MUC1 antibody response composed principally of IgG2b and IgG3 that show preferential binding to Tn-MUC1 and selectively target tumor cells that express human MUC1. In a preventative B16-MUC1 tumor model, vaccination with 5μg ONT-10 potently suppresses tumor growth, resulting in 99% mean tumor growth inhibition relative to controls with 9/12 animals tumor free four weeks after tumor cell implantation. Similarly, in a MC38-MUC1 tumor model 5μg ONT-10 results in an 90% reduction in tumor growth relative to controls. Based on these preclinical data, we propose that the combination of the glycopeptide antigen structure and improved Lipid A adjuvant in ONT-10 offer advantages relative to previous MUC1 targeted vaccines by potently activating both humoral and cellular immunity against hypoglycosylated MUC1 and that these features may provide additional therapeutic benefit to patients with MUC1 expressing cancers. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 762. doi:10.1158/1538-7445.AM2011-762