Synergic Thermo- and pH-Sensitive Hybrid Microgels Loaded with Fluorescent Dyes and Ultrasmall Gold Nanoparticles for Photoacoustic Imaging and Photothermal Therapy.

Smart microgels (µGels) made of polymeric particles doped with inorganic nanoparticles have emerged recently as promising multifunctional materials for nanomedicine applications. However, the synthesis of these hybrid materials is still a challenging task with the necessity to control several features, such as particle sizes and doping levels, in order to tailor their final properties in relation to the targeted application. We report herein an innovative modular strategy to achieve the rational design of well-defined and densely filled hybrid particles. It is based on the assembly of the different building blocks, i.e., µGels, dyes, and small gold nanoparticles (<4 nm), and the tuning of nanoparticle loading within the polymer matrix through successive incubation steps. The characterization of the final hybrid networks using UV-vis absorption, fluorescence, transmission electron microscopy, dynamic light scattering, and small-angle X-ray scattering revealed that they uniquely combine the properties of hydrogel particles, including high loading capacity and stimuli-responsive behavior, the photoluminescent properties of dyes (rhodamine 6G, methylene blue and cyanine 7.5), and the features of gold nanoparticle assembly. Interestingly, in response to pH and temperature stimuli, the smart hybrid µGels can shrink, leading to the aggregation of the gold nanoparticles trapped inside the polymer matrix. This stimuli-responsive behavior results in plasmon band broadening and red shift toward the near-infrared region (NIR), opening promising prospects in biomedical science. Particularly, the potential of these smart hybrid nanoplatforms for photoactivated hyperthermia, photoacoustic imaging, cellular internalization, intracellular imaging, and photothermal therapy was assessed, demonstrating well controlled multimodal opportunities for theranostics.

Two step promotion of a hot tumor immune environment by gold decorated iron oxide nanoflowers and light-triggered mild hyperthermia.

Nanoparticle-mediated photothermal therapy (PTT) is an emerging modality to treat tumors with both spatial and temporal control provided by light activation. Gold decorated iron oxide nanoflowers (GIONF) are good candidates for PTT due to their biocompatibility, biodegradability and light-to-heat conversion. Profound changes in the tumor immune environment might be early induced by the gold and iron oxide metallic agents in addition to the photothermal effects. This study aims to elucidate the outcome of GIONF on their own, and of GIONF-induced mild hyperthermia in the tumor immune infiltrate in a murine model of triple negative breast cancer. First we explored the effects of 24 h GIONF exposure on bone-marrow derived macrophages (BMDM), revealing significant effects on the BMDM phenotype and secretion, 6 days post-incubation, with important downregulation of several cytokines and MHCII expression, predominantly towards a pro-inflammatory response. Intratumoral administration of GIONF promoted an increase in monocyte recruitment at day 1 post-administration, shifting towards a pro-inflammatory anti-tumor microenvironment with lower Treg population and a 4 fold lower CD4/CD8 ratio compared to the control at day 12. On top of the GIONF effects, mild hyperthermia (43 °C for 15 min), although it does not induce significant changes in tumor growth, resulted in an additional increase of CD8+ T lymphocytes and pro-inflammatory cytokines. The combination of a timely controlled immune response to GIONF and to mild hyperthermia could be used as a remotely triggered adjuvant treatment to immunotherapy approaches at the best favorable time-window.

Tumor-Selective Immune-Active Mild Hyperthermia Associated with Chemotherapy in Colon Peritoneal Metastasis by Photoactivation of Fluorouracil-Gold Nanoparticle Complexes.

Peritoneal metastasis (PM) is considered as the terminal stage of metastatic colon cancer, with still poor median survival rate even with the best recent chemotherapy treatment. The current PM treatment combines cytoreductive surgery, which consists of resecting all macroscopic tumors, with hyperthermic intraperitoneal chemotherapy (HIPEC), which uses mild hyperthermia to boost the diffusion and cytotoxic effect of chemotherapeutic drugs. As HIPEC is performed via a closed circulation of a hot liquid containing chemotherapy, it induces uncontrolled heating and drug distribution in the whole peritoneal cavity with important off-site toxicity and a high level of morbidity. Here, we propose a safer precision strategy using near-infrared (NIR) photoactivated gold nanoparticles (AuNPs) coupled to the chemotherapeutic drug 5-fluorouracil (5-FU) to enable a spatial and temporal control of mild chemo-hyperthermia targeted to the tumor nodules within the peritoneal cavity. Both the 16 nm AuNPs and the corresponding complex with 5-FU (AuNP-5-FU) were shown as efficient NIR photothermal agents in the microenvironment of subcutaneous colon tumors as well as PM in syngeneic mice. Noteworthy, NIR photothermia provided additional antitumor effects to 5-FU treatment. A single intraperitoneal administration of AuNP-5-FU resulted in their preferential accumulation in tumor nodules and peritoneal macrophages, allowing light-induced selective hyperthermia, extended tumor necrosis, and activation of a pro-inflammatory immune response while leaving healthy tissues without any damage. From a translational standpoint, the combined and tumor-targeted photothermal and chemotherapy mediated by the AuNP-drug complex has the potential to overcome the current off-target toxicity of HIPEC in clinical practice.

Polyethyleneimine-assisted one-pot synthesis of quasi-fractal plasmonic gold nanocomposites as a photothermal theranostic agent.

Gold nanoparticles have been thoroughly used in designing thermal ablative therapies and in photoacoustic imaging in cancer treatment owing to their unique and tunable plasmonic properties. While the plasmonic properties highly depend on the size and structure, controllable aggregation of gold nanoparticles can trigger a plasmonic coupling of adjacent electronic clouds, henceforth leading to an increase of light absorption within the near-infrared (NIR) window. Polymer-engraftment of gold nanoparticles has been investigated to achieve the plasmonic coupling phenomenon, but complex chemical steps are often needed to accomplish a biomedically relevant product. An appealing and controllable manner of achieving polymer-based plasmon coupling is a template-assisted Au+3 reduction that ensures in situ gold reduction and coalescence. Among the polymers exploited as reducing agents are polyethyleneimines (PEI). In this study, we addressed the PEI-assisted synthesis of gold nanoparticles and their further aggregation to obtain fractal NIR-absorbent plasmonic nanoaggregates for photothermal therapy and photoacoustic imaging of colorectal cancer. PEI-assisted Au+3 reduction was followed up by UV-visible light absorption, small-angle X-ray scattering (SAXS), and photo-thermal conversion. The reaction kinetics, stability, and the photothermal plasmonic properties of the as-synthesized nanocomposites tightly depended on the PEI : Au ratio. We defined a PEI-Au ratio range (2.5-5) for the one-pot synthesis of gold nanoparticles that self-arrange into fractal nanoaggregates with demonstrated photo-thermal therapeutic and imaging efficiency both in vitro and in vivo in a colorectal carcinoma (CRC) animal model.