Abstract 3298: Neotargeting HER2 negative cancer cells with Trastuzumab-based photoimmunotherapy by viral transduction of HER2-extracellular domain

The prognosis of HER2 positive breast cancer has been improved by Trastuzumab which features high specificity and limited side effects. Numerous randomized trials have confirmed the efficacy and safety of Trastuzumab in HER2-overexpressing cancers. However, many patients who initially respond to Trastuzumab ultimately develop disease progression. Strategies to overcome Trastuzumab-refractory cancer are sought, and drug-conjugation is one of candidates. Trastuzumab-IR700 which is Trastuzumab conjugated with a near-infrared (NIR) photosensitizer, phthalocyanine dye, IR700, has recently been developed as a new type of molecular-target photoimmunotherapy(PIT). This PIT can induce target-selective necrotic cell death only at the place which have Trastuzumab's target part and where exposure of NIR light. Disappointingly, HER2-targeting therapy is applicable to only Her2-expressig tumors which consist of approximately 20-25% of primary breast cancers. In previous study, we developed the adenoviral vector to express HER2-extracellular domain (HER2-ECD), Ad/HER-ECD, and confirmed that it efficiently induced HER2 expression for HER2 negative and HER2-downregulated human cancer cells. So, we hypothesized that Ad/HER-ECD expand the range of tumor entities suitable for Trastuzumab-based PIT. By using Ad/HER-ECD and Trastuzumab-IR700 with PIT we revealed that the direct cell membrane destruction are induced at HER2 negative cancer cells, similarly at HER2 positive cancer cells, in vitro. These results suggest that combination of virally-transduction of target antigen and an antibody-based PIT would expand and potentiate target therapy even for target-negative or attenuated cancer cells. Citation Format: Michihiro Ishida, Shunsuke Kagawa, Kyoko Shimoyama, Shinichiro Watamabe, Kazuhiro Noma, Hiroshi Tazawa, Yuuri Hashimoto, Junji Matsuoka, Hisataka Kobayashi, Toshiyoshi Fujiwara. Neotargeting HER2 negative cancer cells with Trastuzumab-based photoimmunotherapy by viral transduction of HER2-extracellular domain. [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 3298. doi:10.1158/1538-7445.AM2013-3298