Mirabody–IR700: A novel EGFR-targeting platform for photoimmunotherapy

Near-infrared photoimmunotherapy (NIR-PIT) is a targeted cancer treatment based on antibody–IR700, a photoabsorber conjugate. NIR-PIT with IR700-conjugated anti-EGFR antibodies is currently used in clinical practice; however, the development of various drug types is essential to advance NIR-PIT. In this study, we evaluated mirabody, an engineered protein with a target-binding peptide, as a novel target platform for NIR-PIT. A cyclic peptide that binds human EGFR (A6–2f) was lasso-grafted onto the Fc region of IgG to generate eight types of mirabodies. Two of these, M3 and B1, were selected based on in vitro flow cytometry and cell-binding studies. Further, in vitro therapeutic studies were performed using the IR700-conjugated M3 and B1. M3– and B1–IR700 induced cell death in EGFR-positive cells upon NIR light exposure. Because the cell-killing activity of M3–IR700 was slightly better than that of B1–IR700, an in vivo therapeutic study was performed using M3–IR700. M3–IR700 accumulated in tumors and significantly suppressed tumor growth following tumor-directed light irradiation in a human EGFR-expressing xenograft model. These results demonstrate that M3–IR700 is a promising NIR-PIT agent, and that mirabody could serve as a potential platform for NIR-PIT agents.