Photochemical internalization (PCI) of HER2-targeted toxins

► This is the first report on photochemical internalization (PCI) of a HER2-targeted immunotoxin. ► Synergistic cytotoxicity of PCI of trastuzumab-saporin in trastuzumab-resistant Zr-75-1 cells ► Photochemical effects on HER2-mediated endocytosis with impact on PCI on trastuzumab-saporin ► PCI effect only observed when the immunotoxin is administered prior to the photochemical treatment ► PCI of trastuzumab-saporin; a method to treat HER2 + and trastuzumab-resistant breast cancer