Abstract A09: Photoimmunotherapy (PIT) for treatment of bladder cancer

Abstract

Abstract Introduction: The use of light as a means of therapy for bladder cancer (BC) has a long history but has been hampered by a lack of tumor specificity and therefore, damage to the normal bladder mucosa. Here, we describe a targeted form of phototherapy called photoimmunotherapy (PIT). To begin with, anti-EGFR antibody panitumumab (pan) was labeled with the photo-absorber (PA), IRDye 700Dx (IR700), to create pan IR700, an antibody-PA conjugate that is activated by near-infrared radiation (NIR). However, PIT may be less effective when a tumor lacks “overwhelming” expression of a single target such as EGFR. Hence, a combinatorial PIT approach for targeting BC expressing EGFR and HER2, using PA-labeled pan and trastuzumab (tra), respectively. Methods: Human BC tissue microarray (TMAs) and BC cell lines were analyzed for expression of EGFR and HER2. Mechanism of PIT-induced cell death was studied using proliferation assays, transmission electron microscopy (TEM), and production of reactive and singlet oxygen species (ROS/SOS). Finally, efficacy of PA-labeled antibodies singly and in combination was analyzed in vitro and in vivo. Results: Most BC tissues have some expression of EGFR, but squamous cell carcinoma (SCC) of bladder has maximum EGFR expression. About 45% of BC tissues stain for both EGFR and HER2. Pan IR700 activated by NIR light rapidly killed UMUC-5 cells, a bladder SCC line. Pan alone, pan IR700 without NIR, or NIR alone had no effect on cells. TEM demonstrated that cell death is due to necrosis. Singlet oxygen species (SOS) had a substantially larger contribution towards cell death than reactive oxygen species (ROS). NIR-PIT with pan IR700 demonstrated reduced growth compared to only pan IR700-treated UMUC-5 xenograft tumors. In non-SCC BCs we used a combinatorial PIT approach using pan IR700 and tra IR700 to target EGFR and HER2, respectively. In vitro, PIT in the presence of combination pan IR700 and tra IR700 was more efficacious than either agent alone with lethal dose 50 (LD50) of 28.66 J/cm2 for combination PIT compared to 71.55 J/cm2 for the PanIR700 alone. In vivo, tumor xenografts treated with combination PIT showed significant tumor growth retardation compared to single-agent therapy. Conclusion: PIT is a new targeted treatment for BC. Our data demonstrate that pan IR700-induced PIT selectively kills EGFR-expressing bladder cancer. Combination PIT is a promising approach for treating BC by selectively inducing death in BC cells with low/moderate expression of surface receptors. Citation Format: Reema Railkar, Mohammad Rashid Siddiqui, Thomas Sanford, Hisataka Kobayashi, Peter L. Choyke, Piyush K. Agarwal. Photoimmunotherapy (PIT) for treatment of bladder cancer [abstract]. In: Proceedings of the AACR Special Conference on Bladder Cancer: Transforming the Field; 2019 May 18-21; Denver, CO. Philadelphia (PA): AACR; Clin Cancer Res 2020;26(15_Suppl):Abstract nr A09.