Abstract 4999: Hyaluronan-rich ECM contributes to resistance to antibody-dependent cell-mediated cytotoxicity in solid tumors.

Accumulation of Hyaluronan (HA), an important glycosaminoglycan of the extracellular matrix (ECM), has been detected in about 25% of human tumors, and 56% of breast cancers 1-2 . HA is produced by malignant and stromal cells and acts to cross-link ECM proteins, contributing to the desmoplastic phenotype. Aberrant accumulation of HA in tumors has been associated with more aggressive malignancy 1-2 . We have observed that >50% of human epidermal growth factor receptor 2 (HER2) triple-positive breast tumors have a high accumulation of HA (HA 3+ ). Monoclonal antibodies (MAbs) have been developed successfully as part of the anticancer armamentarium. However, even in cases where the target of the antibody is stably and abundantly expressed, efficacy often falls below expectations. In this work, we present a novel HA-dependent ECM-mediated mechanism of resistance to antibody-dependent cell-mediated cytotoxicity (ADCC) and this resistance can be reduced by PEGPH20 (a pegylated human PH20) treatment. Human hyaluronan synthase 2 (HAS2)-overexpressing tumor cells formed an HA-rich pericellular matrix which can restrict human NK cells from accessing tumor cells. This HA-dependent ECM-mediated physical barrier in HAS2- overexpressing tumor cells contributed to resistance to trastuzumab/cetuximab-dependent ADCC. Removal of HA from ECM by PEGPH20 treatment sensitized HAS2-overexpressing tumor cells to trastuzumab/cetuximab-mediated ADCC in vitro. HAS2-overexpressing ovarian cancer cell SKOV3 showed more aggressive growth pattern (median survival on 42 days) compared to parental SKOV3 (median survival of 61 days) in an intra-peritoneal xenograft model. In the same model with HAS2-overexpressing SKOV3, PEGPH20 in combination with trastuzumab and NK cell treatment (to simulate ADCC in vivo) resulted in 70% tumor growth inhibition (TGI) in comparison to 40% TGI with trastuzumab and NK cell treatment, indicating that PEGPH20 enhanced in vivo ADCC by trastuzumab and NK cell. Our results demonstrated a mechanism of high HA-content pericellular matrix-mediated resistance to MAb-mediated ADCC. These results may help explain why tumors with high levels of HA (HA 3+ phenotype) are more aggressive, and suggest that removal of HA by PEGPH20 treatment may be an effective combinatorial therapy together with anti-cancer MAbs. 1. Kultti A, Li X, Jiang P, Thompson C.B., Frost G.I., Shepard H.M. 2012. Therapeutic targeting of Hyaluronan in the tumor stroma. Cancers, 4:873-903; doi:10.3390/cancers4030873. 2. Sironen, R.K., Tammi, M., Tammi, R., Auvinen, P.K., Anttila, M., and Kosma, V.M. 2011. Hyaluronan in human malignancies. Exp. Cell. Res. 317:383-391. doi: 10.1016/j.yexcr.2010.11.017 Citation Format: Netai C. Singha, Tara Nekoroski, Susan Zimmerman, Chunmei Zhao, Ping Jiang, Robert Connor, Gregory I. Frost, Zhondong Huang, Michael H. Shepard. Hyaluronan-rich ECM contributes to resistance to antibody-dependent cell-mediated cytotoxicity in solid tumors. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 4999. doi:10.1158/1538-7445.AM2013-4999