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.