Urinary IR700 Ligand as an Early Biomarker of Therapeutic Efficacy of Near-Infrared Photoimmunotherapy

Near-infrared photoimmunotherapy (NIR-PIT) is a cell-selective cancer therapy employing monoclonal antibody-photoabsorber conjugates (APCs) and near-infrared (NIR) light. When exposed to NIR light, the photoabsorber, IR700, releases an axial ligand, resulting in a transition of the remaining molecule from water-soluble to hydrophobic. This results in the death of APC-bound cells by physical damage to the cell membrane. The amount of released IR700 ligand reflects the completeness of the photochemical reaction and, therefore, can be a biomarker for treatment efficacy. In this study, we developed and validated a quantitative analytic method for detecting excreted IR700 ligands in urine using a liquid chromatograph-triple quadrupole mass spectrometer (LC-MS/MS). In A431 tumor-bearing mice treated with NIR-PIT, the urinary ligand increased with increasing the light dose, which was positively correlated with the loss of fluorescence and therapeutic effects. This study suggests that quantitative analysis of urinary ligands using LC-MS/MS can be a rapid biomarker of NIR-PIT efficacy.