Effect of bovine serum albumin (BSA) variants on the photophysical and biological properties of a NIR-responsive BSA–indocyanine green complex†

Abstract

In this study, we have investigated the effect of variants of BSA on the NIR-induced phototherapeutic performance of the BSA–ICG complex to identify the best BSA variant for complexing with ICG. Three variants of BSA, namely BSA-A7030 (protease, fatty acid, and globulin free), BSA-A3059 (protease & globulin free), and BSA-A3294 (only protease free), were chosen. UV-vis-NIR absorption, fluorescence, and CD spectroscopy studies showed no significant difference in the spectra of all the BSAs, but in the presence of Cu²⁺, a differential reactivity of the three BSA variants was noticed. The biophysical study of the BSA–ICG complexes (1 : 1 molar ratio) showed that post-binding, there was a significant red shift of the ICG peak (both absorption and fluorescence) for BSA-A7030 with a widening of the excitation–emission hotspot. The photothermal properties of the BSA–ICG complexes under NIR (808 nm) exposure were similar to those of free ICG, whereas the photodynamic property increases for BSA-A3059. All the BSA–ICG complexes were found to be cytocompatible when tested with the NIH 3T3 cell line in vitro. The effect of the BSA type on the 808 nm NIR-mediated phototherapeutic properties of the BSA–ICG complex was tested in vitro on lung cancer cell line A549 (2D model) and a 3D osteosarcoma spheroid model. The study showed a NIR-induced cytoskeletal disruption of A549 cells with maximum damage caused by the BSA-A7030–ICG complex. The same complex was found to show the highest phototherapeutic effect on the 3D spheroid model. This study implied that an appropriate BSA variant is crucial for BSA–ICG complex-mediated NIR phototherapy.