Thioether-Based Polymeric Micelles with Fine-Tuned Oxidation Sensitivities for Chemotherapeutic Drug Delivery

Lipid Nanoparticle-Associated Inflammation is Triggered by Sensing of Endosomal Damage: Engineering Endosomal Escape Without Side Effects

Lipid nanoparticles (LNPs) have emerged as the dominant platform for RNA delivery, based on their success in the COVID-19 vaccines and late-stage clinical studies in other indications. However, we and others have shown that LNPs induce severe inflammation, and massively aggravate pre-existing inflammation. Here, using structure-function screening of lipids and analyses of signaling pathways, we elucidate the mechanisms of LNP-associated inflammation and demonstrate solutions. We show that LNPs' hallmark feature, endosomal escape, which is necessary for RNA expression, also directly triggers inflammation by causing endosomal membrane damage. Large, irreparable, endosomal holes are recognized by cytosolic proteins called galectins, which bind to sugars on the inner endosomal membrane and then regulate downstream inflammation. We find that inhibition of galectins abrogates LNP-associated inflammation, both in vitro and in vivo . We show that rapidly biodegradable ionizable lipids can preferentially create endosomal holes that are smaller in size and reparable by the endosomal sorting complex required for transport (ESCRT) pathway. Ionizable lipids producing such ESCRT-recruiting endosomal holes can produce high expression from cargo mRNA with minimal inflammation. Finally, we show that both routes to non-inflammatory LNPs, either galectin inhibition or ESCRT-recruiting ionizable lipids, are compatible with therapeutic mRNAs that ameliorate inflammation in disease models. LNPs without galectin inhibition or biodegradable ionizable lipids lead to severe exacerbation of inflammation in these models. In summary, endosomal escape induces endosomal membrane damage that can lead to inflammation. However, the inflammation can be controlled by inhibiting galectins (large hole detectors) or by using biodegradable lipids, which create smaller holes that are reparable by the ESCRT pathway. These strategies should lead to generally safer LNPs that can be used to treat inflammatory diseases.

Visualization and Quantification of Drug Release by GSH-Responsive Multimodal Integrated Micelles

Using molecular imaging techniques to monitor biomarkers and drug release profiles simultaneously is highly advantageous for cancer diagnosis and treatment. However, achieving the accurate quantification of both biomarkers and drug release with a single imaging modality is challenging. This study presents the development of a glutathione (GSH)-responsive polymer-based micelle, PEG-SS-FCy7/PEG-SS-GEM (PSFG), which can precisely localize the tumor using bimodal imaging and prevent drug leakage. These PSFG micelles exhibit a small particle size of 106.3 ± 12.7 nm with a uniform size distribution, and the drug loading efficiency can also be easily controlled by changing the PEG-SS-FCy7 (PSF) and PEG-SS-GEM (PSG) feeding ratio. The PSFG micelles display weak fluorescence emission and minimal drug release under physiological conditions but collapse in the presence of GSH to trigger near-infrared fluorescence and the 19F magnetic resonance imaging signal, allowing for real-time monitoring of intracellular GSH levels and drug release. GSH could synergistically promote the disassembly of the micellar structure, resulting in accelerated probe and drug release of up to about 93.1% after 24 h. These prodrug micelles exhibit high in vitro and in vivo antitumor abilities with minimal side effects. The GSH-responsive drug delivery system with dual-modal imaging capability provides a promising imaging-guided chemotherapeutic platform to probe the tumor microenvironment and quantify real-time drug release profiles with minimal side effects.

Controlled Dissociation of Polymeric Micelles in Response to Oxidative Stress

Nanoparticle-based drug carriers that can respond to oxidative stress in tumor tissue have attracted attention for site-specific drug release. Taking advantage of the characteristic microenvironment in tumors, one of the attractive directions in drug delivery research is to design drug carriers that release drugs upon oxidation. A strategy to incorporate oxidation-sensitive thioether motifs such as thiomorpholine acrylamide (TMAM) to drug carriers has been often used to achieve oxidation-induced dissociation, thereby targeted drug release. However, those delivery systems often suffer from a slow dissociation rate due to the intrinsic hydrophobicity of the thioether structures. In this study, we aimed to enhance the dissociation rate of TMAM-based micelles upon oxidation. The random copolymers of N-isopropylacrylamide and TMAM (P(NIPAM/TMAM)) were designed as an oxidation-sensitive segment that showed a fast response to oxidative stress. We first synthesized P(NIPAM/TMAM) copolymers with different NIPAM:TMAM molar ratios. Those copolymers exhibited low critical solution temperatures (LCSTs) below 32 °C, which shifted to higher temperatures after oxidation. The changes in LCSTs depend on the NIPAM:TMAM molar ratios. At the NIPAM:TMAM molar ratio of 82:18, the LCSTs before and after oxidation were 17 and 54 °C, respectively. We then prepared micelles from the diblock copolymers of poly(N-acryloyl morpholine) (PAM) and P(NIPAM/TMAM). The micelles showed an accelerated dissociation rate upon oxidation compared to the micelles without NIPAM units. Furthermore, the doxorubicin (Dox)-loaded micelles showed enhanced relative toxicity in human colorectal cancer (HT29) cells over human umbilical vein endothelial cells (HUVECs). Our novel strategy to design an oxidation-sensitive micellar core comprising a P(NIPAM/TMAM) segment can be used as a chemotherapeutic delivery system that responds to an oxidative tumor microenvironment in an appropriate time scale.

Manganese Porphyrin-Containing Polymeric Micelles: A Novel Approach for Intracellular Catalytic Formation of Per/Polysulfide Species from a Hydrogen Sulfide Donor

Per/polysulfide species that are generated from endogenously produced hydrogen sulfide have critical regulatory roles in a wide range of cellular processes. However, the lack of delivery systems that enable controlled and sustained release of these unstable species in biological systems hinders the advancement of sulfide biology research, as well as the translation of knowledge to therapeutic applications. Here, a novel approach is developed to generate per/polysulfide species in cells by combining an H2 S donor and manganese porphyrin-containing polymeric micelles (MnPMCs) that catalyze oxidization of H2 S to per/polysulfide species. MnPMCs serve as a catalyst for H2 S oxidation in aerobic phosphate buffer. HPLC-MS/MS analysis reveals that H2 S oxidation by MnPMCs in the presence of glutathione results in the formation of glutathione-SnH (n = 2 and 3). Furthermore, co-treatment of human umbilical vein endothelial cells with the H2 S donor anethole dithiolethione and MnPMCs increases intracellular per/polysulfide levels and induces a proangiogenic response. Co-delivery of MnPMCs and an H2 S donor is a promising approach for controlled delivery of polysulfides for therapeutic applications.

Recent Progress in Bio-Responsive Drug Delivery Systems for Tumor Therapy

Spatially- and/or temporally-controlled drug release has always been the pursuit of drug delivery systems (DDSs) to achieve the ideal therapeutic effect. The abnormal pathophysiological characteristics of the tumor microenvironment, including acidosis, overexpression of special enzymes, hypoxia, and high levels of ROS, GSH, and ATP, offer the possibility for the design of stimulus-responsive DDSs for controlled drug release to realize more efficient drug delivery and anti-tumor activity. With the help of these stimulus signals, responsive DDSs can realize controlled drug release more precisely within the local tumor site and decrease the injected dose and systemic toxicity. This review first describes the major pathophysiological characteristics of the tumor microenvironment, and highlights the recent cutting-edge advances in DDSs responding to the tumor pathophysiological environment for cancer therapy. Finally, the challenges and future directions of bio-responsive DDSs are discussed.