Triple Hit with Drug Carriers: pH- and Temperature-Responsive Theranostics for Multimodal Chemo- and Photothermal Therapy and Diagnostic Applications

Currently there is a strong need for new drug delivery systems, which enable targeted and controlled function in delivering drugs while satisfying highly sensitive imaging modality for early detection of the disease symptoms and damaged sites. To meet these criteria we develop a system that integrates therapeutic and diagnostic capabilities (theranostics). Importantly, therapeutic efficacy of the system is enhanced by exploiting synergies between nanoparticles, drug, and hyperthermia. At the core of our innovation is near-infrared (NIR) responsive gold nanorods (Au) coated with drug reservoirs--mesoporous silica shell (mSi)--that is capped with thermoresponsive polymer. Such design of theranostics allows the detection of the system using computed tomography (CT), while finely controlled release of the drug is achieved by external trigger, NIR light irradiation--ON/OFF switch. Doxorubicin (DOX) was loaded into mSi formed on the gold core (Au@mSi-DOX). Pores were then capped with the temperature-sensitive poly(N-isopropylacrylamide)-based N-butyl imidazolium copolymer (poly(NIPAAm-co-BVIm)) resulting in a hybrid system-Au@mSi-DOX@P. A 5 min exposure to NIR induces polymer transition, which triggers the drug release (pores opening), increases local temperature above 43 °C (hyperthermia), and upregulates particle uptake (polymer becomes hydrophilic). The DOX release is also triggered by drop in pH enabling localized drug release when particles are taken up by cancer cells. Importantly, the synergies between chemo- and photothermal therapy for DOX-loaded theranostics were confirmed. Furthermore, higher X-ray attenuation value of the theranostics was confirmed via X-ray CT test indicating that the nanoparticles act as contrast agent and can be detected by CT.