Abstract 5767: Vascular endothelial growth factor receptor 2 targeted photoimmunotherapy

Abstract

Abstract Background Photoimmunotherapy (PIT) is a new class of molecular targeted cancer theranostics, which employs monoclonal antibody (mAb) conjugated to a photosensitizer, IR700, that is activated by focal near-infrared (NIR) light irradiation leading to necrotic cell death by cell membrane rapture where mAb-IR700 conjugates binds to target membrane proteins specifically. We have previously demonstrated HER2-targeted PIT employing trastuzumab-IR700 conjugates for HER2 expressing cancers. However, some cancer cells were survived partly because of tumor heterogeneity and inhomogeneous micro-distribution of mAb-IR700 conjugates. In this study, we developed a new type of PIT agents targeting VEGFR-2 expressed on vascular endothelium in a tumor and evaluated the feasibility by comparing conventional PIT in vitro and in vivo. Methods HER2-positive human gastric cancer cells, NCI-N87, were used for the experiments. HER2-targeting trastuzumab and VEGFR-2-targeting ramucirumab were conjugated to IR700. Cells were treated with mAb-IR700 conjugates followed by NIR light irradiation after washing the cells. LIVE/DEAD assay was performed to assess short-term phototoxicity and trypan blue dye exclusion assay to assess long-term phototoxicity. Next, mouse tumor xenograft models were created for in vivo PIT. Tumor-bearing mice were randomized and treated with mAb-IR700 conjugates followed by NIR light irradiation under anesthesia. Antitumor effects were monitored by measuring tumor diameters with a caliper. Results PIT utilizing ramucirumab-IR700 conjugates did not induce phototoxic effect in vitro because of the absence of membranous expression of VEGFR-2 in NCI-N87 cells, while PIT utilizing trastuzumab-IR700 conjugates induced rapid phototoxic effect because of the strong membranous expression of HER2 in NCI-N87 cells. By contrast, antitumor effects were observed in NCI-N87 xenograft tumors in vivo utilizing both ramucirumab- and trastuzumab-IR700 conjugates followed by NIR light irradiation. Microscopic analysis of the harvested tumors showed decreasing tumor micro-vessel densities only when tumors were treated with PIT utilizing ramucirumab-IR700 conjugates but not trastuzumab-IR700, which represents a different mechanism than that of conventional PIT targeting antigens expressed on the tumor cell membrane. Conclusion We demonstrated a new mechanism of PIT utilizing ramucirumab-IR700 conjugates. As VEGFR-2 is upregulated in many types of solid cancers, this method may be considered as being applicable to various types of cancers in future clinical settings. Citation Format: Makoto Mitsunaga, Takashi Nishimura, Kimihiro Ito. Vascular endothelial growth factor receptor 2 targeted photoimmunotherapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 5767.