Light excitation of gold Nanorod-Based hybrid nanoplatforms for simultaneous bimodal phototherapy

Abstract

In this work, we developed a hybrid nanosystem able to simultaneously combine its potential as a photodynamic (PDT) and plasmonic photothermal (PPTT) therapeutic agent to kill malignant cells. To do that, AuNRs were functionalized by means of the layer-by-layer (LbL) assembly technique using alternating layers of anionic poly(styrene sulfonate) (PSS) and cationic poly-L-lysine (PLL) as polyelectrolytes (PEs), and an outer final layer of hyaluronic acid (HA) to provide the hybrid particles with both sufficient colloidal stability and targeting ability to tumoral cells overexpressing CD44 receptors. To provide the nanoplatform with PDT capabilities, the near-infrared (NIR) sensitive photosensitizer (PS) indocyanine green (ICG) was previously grafted to the PLL PE and assembled on the particle surface coating; in this manner, PSS/PLL-ICG/HA-coated AuNRs hybrid particles were obtained. Then, the conditions for optimized reactive oxygen species (ROS) production under NIR light excitation were elucidated, reaching ca. 80% after 5 min irradiation at 2.0 W/cm2 compared to positive control (H2O2). Since ICG can also absorb near infrared (NIR) light and transforms it by internal conversion into heat under suitable irradiation conditions, which adds to the photothermal plasmonic effect provided by the metallic NP, the heating profiles provided by the present hybrid nanoparticles (NPs) were measured, being observed temperature increments ranging from 9 to 22 °C. The potential contribution of its different components to both PDT and PPTT were deeply analyzed in vitro for intended cancer therapeutics at several power intensities but also at different temperatures with the aim of elucidating the role played by both phototherapies on cell cytotoxicity, the optimal illumination conditions for effective bimodal phototherapy as well as the elucidation of the main cell death mechanism involved. Under optimized conditions and after the administration of 2.5 ·1010 NPs/mL, cell cytotoxicites of up to ca. 70% were determined by combination of PDT + PPTT therapeutic effect.