Background: Near-infrared photoimmunotherapy (NIR-PIT) is a newly developed cancer therapy that employs a selective monoclonal antibody (mAb) conjugated to a photosensitizer phthalocyanine dye, IR700. The complex mAb-IR700 binds to the specific antigen on the cellular membrane, and then NIR light is delivered, leading to rapid and target-selective cell death. The type I trans-membrane protein, TROP2, is found to be expressed at high levels in many epithelial cancers, including pancreatic carcinoma. Further, TROP2 overexpression correlates with poor prognosis and tumor aggressiveness. In this study, we investigated the antitumor effect of TROP2-targeted PIT in an experimental human pancreatic cancer model using anti-TROP2 mAb-IR700 conjugate.

Methods: The experiments were performed on TROP2-overexpressing human pancreatic cancer cells (PK-59 and KP-3L) and 3T3/HER2 cells were used as the negative control. Anti-TROP2 antibody (Chiome Bioscience, Tokyo, Japan) was conjugated with IR700 and purified (TROP2-IR700). The expression and localization of TROP2 were determined by fluorescence microscopy and flow cytometry. LIVE/DEAD assay was performed to determine cytotoxicity exerted by NIR light irradiation in vitro. Subsequently, for in vivo studies, PIT was tested on a mouse tumor xenograft model (PK-59 cells). Specifically, tumor-bearing mice were intravenously injected with TROP2-IR700 and tumors were irradiated with NIR laser light, 1 day after the injection. Distribution of TROP2-IR700 was then monitored with small animal imaging system and the antitumor effects were determined by measuring the tumor diameter using a caliper. Additionally, the expression patterns of TROP2 and EGFR in human pancreatic cancer were analyzed by immunohistochemistry, using tissue microarray samples.

Results: We found that TROP2-IR700 specifically localized on the cellular membrane as well as on lysosomes, in TROP2-overexpressing PK-59 and KP-3L cells, whereas no specific signals were observed in TROP2-negative 3T3/HER2 cells. Moreover, TROP2-IR700-mediated PIT was able to induce a strong cytotoxic effect in PK-59 and KP-3L cells, which was NIR-light dose dependent. The localization of TROP2-selective IR700 fluorescence was observed in the mouse xenograft, 1 day after intravenous injection with TROP2-IR700, and the tumor growth was significantly inhibited by NIR light irradiation compared to the control groups. Moreover, pancreatic cancer tissue microarray analysis revealed that 80% of the tumors were positive for TROP2 and 50% were positive for EGFR and the expression patterns were independent from each other.

Conclusions: We demonstrated that TROP2-IR700-targeted PIT exerts an antitumor effect against TROP2 positive pancreatic cancer, both in vitro and in vivo, and could be a promising therapeutic option for human pancreatic cancer.

Citation Format: Takashi Nishimura, Makoto Mitsunaga. TROP2-targeted photoimmunotherapy in experimental human pancreatic cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2386.