Chain-shattering polymeric sulfur dioxide prodrug micelles for redox-triggered gas therapy of osteosarcoma

Biotinylated Theranostic Amphiphilic Polyurethane for Targeted Drug Delivery

In the area of drug delivery aided by stimuli-responsive polymers, the biodegradability of nanocarriers is one of the major challenges that needs to be addressed with the utmost sincerity. Herein, a hydrogen sulfide (H2S) responsive hydrophobic dansyl-based trigger molecule is custom designed and successfully incorporated into the water-soluble polyurethane backbone, which is made of esterase enzyme susceptible urethane bonds. The amphiphilic polyurethanes, PUx (x = 2 and 3) with a biotin chain end, formed self-assembled nanoaggregates. A hemolysis and cytotoxicity profile of doxorubicin (DOX)-loaded biotinylated PU3 nanocarriers revealed that it is nonhemolytic and has excellent selectivity toward HeLa cells (biotin receptor-positive cell lines) causing ∼60% cell death while maintaining almost 100% cell viability for HEK 293T cells (biotin receptor-negative cell lines). Furthermore, better cellular internalization of DOX-loaded fluorescent nanocarriers in HeLa cells than in HEK 293T cells confirmed receptor-mediated endocytosis. Thus, this work ensures that the synthesized polymers serve as biodegradable nanocarriers for anticancer therapeutics.

A Novel Polyamino Acid Sulfur Dioxide Prodrug Synergistically Elevates ROS with β-Lapachone in Cancer Treatment

Due to the distorted redox balance, cancer cells are considered more vulnerable to excessive reactive oxygen species (ROS). In a variety of oxidative stress-related therapies, gas therapy has emerged as a new therapeutic strategy owing to its efficacy and biosafety. Herein, a newly-discovered gasotransmitter sulfur dioxide (SO2) and a tumor specific ROS generation agent β-lapachone (Lapa) were firstly combined for anticancer therapy. Firstly, amphiphilic glutathione (GSH) responsive polypeptide SO2 prodrug PEG-b-poly(Lys-DNs) was synthesized by ring opening polymerization of SO2-containing N-carboxyanhydride. Then, Lapa was encapsulated into the polymeric micelles with loading content of 8.6 % and loading efficiency of 51.6 %. The obtained drug-loaded nanoparticles (NPs(Lapa)) exhibited a fast release of Lapa and SO2 in the stimuli of 10 mM GSH in PBS. Subsequently, in vitro experiment showed that NPs(Lapa) exhibited obvious cytotoxicity towards 4 T1 cancer cells at a concentration of 2.0 μg/mL, which may be attributed to the depletion of intracellular GSH and upregulation of ROS level both by SO2 release and by the ROS generation from lapachone transformation. In vivo fluorescence imaging showed that the NPs were gradually enriched in tumor tissues in 24 h, probably due to the enhanced permeability and retention effect of NPs. Finally, NPs(Lapa) showed the best anticancer effect in 4 T1 tumor bearing mice with a tumor inhibiting rate (IRT) of 61 %, whereas IRT for free Lapa group was only 23.6 %. This work may be a new attempt to combine SO2 gas therapy with ROS inducer for anticancer therapy through oxidative stress.

Glutathione-triggered release of SO2 gas to augment oxidative stress for enhanced chemodynamic and sonodynamic therapy

Recently, gas therapy has emerged as a promising alternative treatment for deep-seated tumors. However, some challenges regarding insufficient or uncontrolled gas generation as well as unclear therapeutic mechanisms restrict its further clinical application. Herein, a well-designed nanoreactor based on intracellular glutathione (GSH)-triggered generation of sulfur dioxide (SO2) gas to augment oxidative stress has been developed for synergistic chemodynamic therapy (CDT)/sonodynamic therapy (SDT)/SO2 gas therapy. The nanoreactor (designed as CCM@FH-DNs) is constructed by employing iron-doped hollow mesoporous silica nanoparticles as carriers, the surface of which was modified with the SO2 prodrug 2,4-dinitrobenzenesulfonyl (DNs) and further coated with cancer cell membranes for homologous targeting. The CCM@FH-DNs can not only serve as a Fenton-like agent for CDT, but also as a sonosensitizer for SDT. Importantly, CCM@FH-DNs can release SO2 for SO2-mediated gas therapy. Both in vitro and in vivo evaluations demonstrate that the CCM@FH-DNs nanoreactor performs well in augmenting oxidative stress for SO2 gas therapy-enhanced CDT/SDT via GSH depletion and glutathione peroxidase-4 enzyme deactivation as well as superoxide dismutase inhibition. Moreover, the doped iron ions ensure that the CCM@FH-DNs nanoreactors enable magnetic resonance imaging-guided therapy. Such a GSH-triggered SO2 gas therapy-enhanced CDT/SDT strategy provides an intelligent paradigm for developing efficient tumor microenvironment-responsive treatments.

A Novel Cu(II) Loaded Polypeptide SO2 Prodrug Nanoformulation Combining Chemodynamic and Gas Anticancer Therapies

Sulfur dioxide (SO2)-based gas therapy and chemodynamic therapyare both reactive oxygen species (ROS)-mediated anticancer strategies, but there are few reports of their combined application. To this end, a novel graft-type copolymeric SO2 prodrug, PLG-g-mPEG-DNs, is designed and synthesized in this work. The amphiphilic polypeptides can self-assemble into nanoparticles (NPs) and encapsulated Cu(II) ions by metal-carboxyl coordination. In vitro release results showed that the obtained NPs-Cu can respond to the acidic pH and high glutathione levels typical of a tumor microenvironment to release Cu(II) and SO2 simultaneously. Both a Cu(II)-triggered Fenton-like reaction and the SO2 gas would promote ROS production and upregulate the oxidative stress in tumor cells, leading to an enhanced killing effect towards 4T1 cancer cells compared to either Cu(II) or the NPs alone. Furthermore, the in vitro hemolysis of NPs-Cu is less than 1.0% at a high concentration of 8 mg/mL, indicating good blood compatibility and the potential for in vivo tumor inhibition application.

Recent advances in sulfur dioxide releasing nanoplatforms for cancer therapy

Sulfur dioxide (SO2), long considered to be a harmful atmospheric pollutant, has recently been posited as the fourth gasotransmitter, as it is produced endogenously in mammals and has important pathophysiological effects. The field of tumor therapy has witnessed a paradigm shift with the emergence of SO2-based gas therapy. This has been possible because SO2 is a potent glutathione consumer that can promote the production of reactive oxygen species, eventually leading to oxidative-stress-induced cancer cell death. Nevertheless, this therapeutic gas cannot be directly administrated in gaseous form. Thus, various nano formulations incorporating SO2 donors or prodrugs capable of storing and releasing SO2 have been developed in an attempt to achieve active/passive intratumoral accumulation and SO2 release in the tumor microenvironment. In this review article, the advances over the past decade in nanoplatforms incorporating sulfur SO2 prodrugs to provide controlled release of SO2 for cancer therapy are summarized. We first describe the synthesis of polypeptide SO2 prodrugs to overcome multiple drug resistance that was pioneered by our group, followed by other macromolecular SO2 prodrug structures that self-assemble into nanoparticles for tumor therapy. Second, we describe nanoplatforms composed of various small-molecule SO2 donors with endogenous or exogenous stimuli responsiveness, including thiol activated, acid-sensitive, and ultraviolet or near-infrared light-responsive SO2 donors, which have been used for tumor inhibition. Combinations of SO2 gas therapy with photodynamic therapy, chemotherapy, photothermal therapy, sonodynamic therapy, and nanocatalytic tumor therapy are also presented. Finally, we discuss the current limitations and challenges and the future outlook for SO2-based gas therapy. STATEMENT OF SIGNIFICANCE: Gas therapy is attracting increasing attention in the scientific community because it is a highly promising strategy against cancer owing to its inherent biosafety and avoidance of drug resistance. Sulfur dioxide (SO2) is recently found to be produced endogenously in mammals with important pathophysiological effects. This review summarizes recent advances in SO2 releasing nanosystems for cancer therapy, including polymeric prodrugs, endogenous or exogenous stimulus-activated SO2 donors delivered by nanoplatform and combination therapy strategies.

Structural Determinants of Stimuli-Responsiveness in Amphiphilic Macromolecular Nano-assemblies

Stimuli-responsive nano-assemblies from amphiphilic macromolecules could undergo controlled structural transformations and generate diverse macroscopic phenomenon under stimuli. Due to the controllable responsiveness, they have been applied for broad material and biomedical applications, such as biologics delivery, sensing, imaging, and catalysis. Understanding the mechanisms of the assembly-disassembly processes and structural determinants behind the responsive properties is fundamentally important for designing the next generation of nano-assemblies with programmable responsiveness. In this review, we focus on structural determinants of assemblies from amphiphilic macromolecules and their macromolecular level alterations under stimuli, such as the disruption of hydrophilic-lipophilic balance (HLB), depolymerization, decrosslinking, and changes of molecular packing in assemblies, which eventually lead to a series of macroscopic phenomenon for practical purposes. Applications of stimuli-responsive nano-assemblies in delivery, sensing and imaging were also summarized based on their structural features. We expect this review could provide readers an overview of the structural considerations in the design and applications of nanoassemblies and incentivize more explorations in stimuli-responsive soft matters.

Photothermal-Triggered Sulfur Oxide Gas Therapy Augments Type I Photodynamic Therapy for Potentiating Cancer Stem Cell Ablation and Inhibiting Radioresistant Tumor Recurrence

Despite advances in cancer therapy, the existence of self-renewing cancer stem cells (CSC) can lead to tumor recurrence and radiation resistance, resulting in treatment failure and high mortality in patients. To address this issue, a near-infrared (NIR) laser-induced synergistic therapeutic platform has been developed by incorporating aggregation-induced emission (AIE)-active phototheranostic agents and sulfur dioxide (SO2 ) prodrug into a biocompatible hydrogel, namely TBH, to suppress malignant CSC growth. Outstanding hydroxyl radical (·OH) generation and photothermal effect of the AIE phototheranostic agent actualizes Type I photodynamic therapy (PDT) and photothermal therapy through 660 nm NIR laser irradiation. Meanwhile, a large amount of SO2 is released from the SO2 prodrug in thermo-sensitive TBH gel, which depletes upregulated glutathione in CSC and consequentially promotes ·OH generation for PDT enhancement. Thus, the resulting TBH hydrogel can diminish CSC under 660 nm laser irradiation and finally restrain tumor recurrence after radiotherapy (RT). In comparison, the tumor in the mice that were only treated with RT relapsed rapidly. These findings reveal a double-boosting ·OH generation protocol, and the synergistic combination of AIE-mediated PDT and gas therapy provides a novel strategy for inhibiting CSC growth and cancer recurrence after RT, which presents great potential for clinical treatment.

Thiol-Responsive Polypeptide Sulfur Dioxide Prodrug Nanoparticles for Effective Tumor Inhibition

Sulfur dioxide (SO2) based gas therapy has emerged as a novel anticancer therapeutic strategy because of its high therapeutic efficacy and biosafety. To precisely adjust the SO2 content and control gas release, herein, a thiol-responsive polypeptide SO2 prodrug mPEG-block-poly(2-amino-6-(2,4-dinitrophenylsulfonamido)hexanoic acid) (PEG-b-PLys-DNs) was designed and facilely synthesized by polymerization of a novel N-carboxyanhydride SO2-NCA. The anticancer potential of the self-assembled nanoparticles (SO2-NPs) was investigated in detail. First, PEG-b-PLys-DNs were synthesized by ring-opening polymerization of SO2-NCA, which self-assembled into NPs sized 88.4 nm in aqueous. Subsequently, SO2-NPs were endocytosed into 4T1 cells and quickly released SO2 under a high concentration of glutathione in tumor cells. This process depleted cellular glutathione, generated reactive oxygen species, and dramatically increased oxidative stress, which led to cancer cell apoptosis. Finally, the in vivo anticancer efficacy of SO2-NPs was verified in 4T1-tumor-bearing mice. Our results indicated that this novel SO2 polymeric prodrug has great potential in eradicating tumors.

Nanobiotechnological approaches in osteosarcoma therapy: Versatile (nano)platforms for theranostic applications

Constructive achievements in the field of nanobiotechnology and their translation into clinical course have led to increasing attention towards evaluation of their use for treatment of diseases, especially cancer. Osteosarcoma (OS) is one of the primary bone malignancies that affects both males and females in childhood and adolescence. Like other types of cancers, genetic and epigenetic mutations account for OS progression and several conventional therapies including chemotherapy and surgery are employed. However, survival rate of OS patients remains low and new therapies in this field are limited. The purpose of the current review is to provide a summary of nanostructures used in OS treatment. Drug and gene delivery by nanoplatforms have resulted in an accumulation of therapeutic agents for tumor cell suppression. Furthermore, co-delivery of genes and drugs by nanostructures are utilized in OS suppression to boost immunotherapy. Since tumor cells have distinct features such as acidic pH, stimuli-responsive nanoparticles have been developed to appropriately target OS. Besides, nanoplatforms can be used for biosensing and providing phototherapy to suppress OS. Furthermore, surface modification of nanoparticles with ligands can increase their specificity and selectivity towards OS cells. Clinical translation of current findings suggests that nanoplatforms have been effective in retarding tumor growth and improving survival of OS patients.