In vitro and in vivo photothermal and photoacoustic activities of polymeric nanoparticles loaded with Nickel, Palladium and Platinum-bis(dithiolene) complexes.

The development of nanosystems with enhanced photothermal and photoacoustic properties is crucial for advancing theranostic applications in cancer therapy. This study explores polymeric nanoparticles constituted by a biocompatible poly(ethylene glycol)-block-poly(benzyl malate) copolymer and loaded with metal-bis(dithiolene) complexes (M = Ni, Pd, Pt). These nanoparticles, prepared via a robust nanoprecipitation method, demonstrate uniform morphology, efficient encapsulation (~70%), and tailored near-infrared (NIR) optical absorption properties. Photothermal and photoacoustic evaluations revealed superior performance of Palladium-loaded nanoparticles, offering high contrast for imaging and significant temperature increases under NIR laser irradiation. Cytotoxicity assays confirmed their non-toxicity without laser exposure, while effective cancer cell eradication was achieved upon irradiation at power densities ≥2 W/cm2. In vivo experiments on zebrafish embryos bearing human cancer xenografts showed significant tumor size reduction (20%) post-treatment with Palladium-loaded nanoparticles under 880 nm laser irradiation. These findings underscore that metal-bis(dithiolene)-loaded nanoparticles can be versatile agents for combined diagnostics and photothermal therapy, paving the way for further optimization and clinical translation.