Polyoxometalate-Polymer Composites for MR Imaging and Combined Photothermal-Chemotherapy

This work reports a nano-sized multicomponent composite of cationic poly(diallyldimethylammonium chloride) incorporating with ionic components of biocompatible block copolymer poly(poly(ethylene glycol) methyl ether methacrylate-b-methacrylic acid) (PPBM), gadolinium-coordinated polyoxometalate cluster K-7(Gd(H2O)(3)P2W17O61) and K-6(alpha-P2W18O62) at the reduction state, as a polymer-covered theranostic nanoplatform for MRI-guided chemo-photothermal combination tumor therapy. The as-prepared composites PDDA-PPBM-rPOMs with a hydrodynamic diameter of 67 nm show good structural stability and biocompatibility against HeLa cells. The internal electrostatic crosslinking structure and the surplus negative charges of the polymers/polyoxometalates composites facilitated the loading of antitumor drug doxorubicin (DOX). The PDDA-PPBM-rPOMs composites before and after drug loading both possess enhanced MRI efficacy as MRI contrast agents with high longitudinal relaxivities up to about 50 L.mmol(-1).s(-1) . With the aid of reduced K-6(alpha-P2W18O62) as photothermal therapy agent, the DOX loaded composites displayed unique photothermal conversion capacity. Meanwhile, the DOX loaded in the composite exhibited significant pH responsive drug release behavior. Cytotoxicity and flow cytometric apoptosis experiments showed that the drug-loaded composite can effectively inhibit tumor cell growth and achieve a photothermal-chemical synergistic therapeutic effect under laser irradiation, which provided a new strategy for the further development of polyoxometalate-based multifunctional composite for the integration of tumor diagnosis and treatment.