Hypoxia-Triggered Bioreduction of Poly(N-oxide)-Drug Conjugates Enhances Tumor Penetration and Antitumor Efficacy

Protein-polymer bioconjugation, immobilization, and encapsulation: a comparative review towards applicability, functionality, activity, and stability

Polymer-based biomaterials have received a lot of attention due to their biomedical, agricultural, and industrial potential. Soluble protein-polymer bioconjugates, immobilized proteins, and encapsulated proteins have been shown to tune enzymatic activity, improved pharmacokinetic ability, increased chemical and thermal stability, stimuli responsiveness, and introduced protein recovery. Controlled polymerization techniques, increased protein-polymer attachment techniques, improved polymer surface grafting techniques, controlled polymersome self-assembly, and sophisticated characterization methods have been utilized for the development of well-defined polymer-based biomaterials. In this review we aim to provide a brief account of the field, compare these methods for engineering biomaterials, provide future directions for the field, and highlight impacts of these forms of bioconjugation.

A convenient protonated strategy for constructing nanodrugs from hydrophobic drug-inhibitor conjugates to reverse tumor multidrug resistance

Combination therapy has proven effective in counteracting tumor multidrug resistance (MDR). However, the pharmacokinetic differences among various drugs and inherent water insolubility for most small molecule agents greatly hinder their synergistic effects, which makes the delivery of drugs for combination therapy in vivo a key problem. Herein, we propose a protonated strategy to transform a water-insoluble small molecule drug-inhibitor conjugate into an amphiphilic one, which then self-assembles into nanoparticles for co-delivery in vivo to overcome tumor MDR. Specifically, paclitaxel (PTX) is first coupled with a third-generation P-glycoprotein (P-gp) inhibitor zosuquidar (Zos) through a glutathione (GSH)-responsive disulfide bond to produce a hydrophobic drug-inhibitor conjugate (PTX-ss-Zos). Subsequently treated with hydrochloric acid ethanol solution (HCl/EtOH), PTX-ss-Zos is transformed into the amphiphilic protonated precursor and then forms nanoparticles (PTX-ss-Zos@HCl NPs) in water by molecular self-assembly. PTX-ss-Zos@HCl NPs can be administered intravenously and accumulated specifically at tumor sites. Once internalized by cancer cells, PTX-ss-Zos@HCl NPs can be degraded under the overexpressed GSH to release PTX and Zos simultaneously, which synergistically reverse tumor MDR and inhibit tumor growth. This offers a promising strategy to develop small molecule self-assembled nanoagents to reverse tumor MDR in combination therapy.

Hypoxia-Activated Theragnostic Prodrugs (HATPs): Current State and Future Perspectives

Hypoxia is a significant feature of solid tumors and frequently poses a challenge to the effectiveness of tumor-targeted chemotherapeutics, thereby limiting their anticancer activity. Hypoxia-activated prodrugs represent a class of bio-reductive agents that can be selectively activated in hypoxic compartments to unleash the toxic warhead and thus, eliminate malignant tumor cells. However, their applicability can be further elevated by installing fluorescent modalities to yield hypoxia-activated theragnostic prodrugs (HATPs), which can be utilized for the simultaneous visualization and treatment of hypoxic tumor cells. The scope of this review is to summarize noteworthy advances in recent HATPs, highlight the challenges and opportunities for their further development, and discuss their potency to serve as personalized medicines in the future.

Medicinal Chemistry of Drugs with N-Oxide Functionalities

Molecules with N-oxide functionalities are omnipresent in nature and play an important role in Medicinal Chemistry. They are synthetic or biosynthetic intermediates, prodrugs, drugs, or polymers for applications in drug development and surface engineering. Typically, the N-oxide group is critical for biomedical applications of these molecules. It may provide water solubility or decrease membrane permeability or immunogenicity. In other cases, the N-oxide has a special redox reactivity which is important for drug targeting and/or cytotoxicity. Many of the underlying mechanisms have only recently been discovered, and the number of applications of N-oxides in the healthcare field is rapidly growing. This Perspective article gives a short summary of the properties of N-oxides and their synthesis. It also provides a discussion of current applications of N-oxides in the biomedical field and explains the basic molecular mechanisms responsible for their biological activity.

Hypoxia Reversion by Low-Immunogenic Ultra-Acid-Sensitive Comicelles of Protein-Polymer Conjugates Sensitizes Tumors to Photodynamic Therapy

Hypoxia is characteristic of the tumor microenvironment, which is correlated with resistance to photodynamic therapy (PDT), radiotherapy, chemotherapy, and immunotherapy. Catalase is potentially useful to catalyze the conversion of endogenous H2O2 to O2 for hypoxia reversion. However, the efficient delivery of catalase into the hypoxia regions of tumors is a huge challenge. Here, we report the self-assembly of ultra-acid-sensitive polymer conjugates of catalase and albumin into nanomicelles that are responsive to the acidic tumor microenvironment. The immunogenicity of catalase is mitigated by the presence of albumin, which reduces the cross-linking of catalase with B cell receptors, resulting in improved pharmacokinetics. The ultra acid sensitivity of the nanomicelles makes it possible to efficiently escape the lysosomal degradation after endocytosis and permeate into the interior of tumors to reverse hypoxia in vitro and in vivo. In mice bearing triple-negative breast cancer, the nanomicelles loaded with a photosensitizer effectively accumulate and penetrate into the whole tumors to generate a sufficient amount of O2 to reverse hypoxia, leading to enhanced efficacy of PDT without detectable side effects. These findings provide a general strategy of self-assembly to design low-immunogenic ultra-acid-sensitive comicelles of protein-polymer conjugates to reverse tumor hypoxia, which sensitizes tumors to PDT.

Ribonuclease A-polymer conjugates via in situ growth for cancer treatment

Efficient delivery of therapeutic proteins is a critical aspect for protein-based cancer treatment. Herein, an in situ growth approach was employed to prepare ribonuclease A (RNase A)-polymer conjugates by incorporating a cationic polymer, poly(N,N'-dimethylamino-2-ethyl methacrylate) (P(DMAEMA)), and a hydrophobic polymer, poly(N-isopropylacrylamide) (P(NIPAM)), through atom transfer radical polymerization (ATRP). The synthesized RNase A-polymer conjugates (namely R-P(D-b-N)) could preserve the integrity of RNase A and exhibit a unique combination of cationic and hydrophobic properties, leading to enhanced intracellular delivery efficiency. The successful delivery of RNase A by R-P(D-b-N) conjugates effectively triggered the cell apoptosis through the mitochondria-dependent signaling pathway to achieve the anti-proliferative response. Additionally, the conjugates could inhibit cell migration and thus possess the potential for the suppression of tumor metastasis. Overall, our findings highlight that the introduction of cationic and hydrophobic moieties via ATRP provides a versatile platform for the intracellular delivery of therapeutic proteins, offering a new avenue for treating diverse diseases.

Lonidamine liposomes to enhance photodynamic and photothermal therapy of hepatocellular carcinoma by inhibiting glycolysis

Phototherapy, including photodynamic therapy (PDT) and photothermal therapy (PTT), has great promise in the treatment of cancer. However, there are many obstacles that can restrict the therapeutic efficacy of phototherapy. The hypoxic tumor microenvironment can restrict the production of reactive oxygen species (ROS) in PDT. As for PTT, the thermotolerance of cancer cells may lead to ineffective PTT. In this study, IR780 and glycolysis inhibitor lonidamine (LND)-encapsulated liposomes are prepared for photodynamic and photothermal therapy of hepatocellular carcinoma. IR780 can be used as a photosensitizer and photothermal agent for simultaneous PDT and PTT after being irradiated with 808 nm laser. LND can reduce the oxygen consumption of cancer cells by inhibiting glycolysis, which will relieve tumor hypoxia and produce more ROS for PDT. On the other hand, energy supply can be blocked by LND-induced glycolysis inhibition, which will inhibit the production of heat shock proteins (HSPs), reduce the thermotolerance of tumor cells, and finally enhance the therapeutic efficacy of PTT. The enhanced PTT is studied by measuring intracellular HSPs, ATP level, and mitochondrial membrane potential. The antitumor effect of IR780 and LND co-loaded liposomes is extensively investigated by in vitro and in vivo experiments. This research provides an innovative strategy to simultaneously enhance the therapeutic efficacy of PDT and PTT by inhibiting glycolysis, which is promising for future creative approaches to cancer phototherapy.

Multistage Self-Assembled Nanomaterials for Cancer Immunotherapy

Advances in nanotechnology have brought innovations to cancer therapy. Nanoparticle-based anticancer drugs have achieved great success from bench to bedside. However, insufficient therapy efficacy due to various physiological barriers in the body remains a key challenge. To overcome these biological barriers and improve the therapeutic efficacy of cancers, multistage self-assembled nanomaterials with advantages of stimuli-responsiveness, programmable delivery, and immune modulations provide great opportunities. In this review, we describe the typical biological barriers for nanomedicines, discuss the recent achievements of multistage self-assembled nanomaterials for stimuli-responsive drug delivery, highlighting the programmable delivery nanomaterials, in situ transformable self-assembled nanomaterials, and immune-reprogramming nanomaterials. Ultimately, we perspective the future opportunities and challenges of multistage self-assembled nanomaterials for cancer immunotherapy.

Antifouling Properties of Amine-Oxide-Containing Zwitterionic Polymers

Biofouling due to nonspecific proteins or cells on the material surfaces is a major challenge in a range of applications such as biosensors, medical devices, and implants. Even though poly(ethylene glycol) (PEG) has become the most widely used stealth material in medical and pharmaceutical products, the number of reported cases of PEG-triggered rare allergic responses continues to increase in the past decades. Herein, a new type of antifouling material poly(amine oxide) (PAO) has been evaluated as an alternative to overcome nonspecific foulant adsorption and impart comparable biocompatibility. Alkyl-substituted PAO containing diethyl, dibutyl, and dihexyl substituents are prepared, and their solution properties are studied. Photoreactive copolymers containing benzophenone as the photo-cross-linker are prepared by reversible addition-fragmentation chain-transfer polymerization and fully characterized by gel permeation chromatography and dynamic light scattering. Then, these water-soluble polymers are anchored onto a silicon wafer with the aid of UV irradiation. By evaluating the fouling resistance properties of these modified surfaces against various types of foulants, protein adsorption and bacterial attachment assays show that the cross-linked PAO-modified surface can efficiently inhibit biofouling. Furthermore, human blood cell adhesion experiments demonstrate that our PAO polymer could be used as a novel surface modifier for biomedical devices.

Zwitterionic Polymer: A New Paradigm for Protein Conjugation beyond PEG

To render protein drugs more suitable for clinical treatment, PEGylation has been widely used to ameliorate their inherent deficiencies, such as poor stability, rapid elimination in the bloodstream, and high immunogenicity. While increasingly PEGylated protein drugs have been approved by the FDA, the non-degradability of PEG and the emergence of anti-PEG antibodies after injection raise concerns about their cumulative chronic toxicity and long-term therapeutic efficacy. Zwitterionic polymer, with a unique structure containing equal amounts of positively charged and negatively charged groups, shows a different hydration behavior to PEG, which may be a superior PEG alternative for protein conjugation. In this concept review, a series of features beyond that of PEGylated protein exhibited by protein-zwitterionic polymer conjugate are discussed and some suggestions are presented for their future direction.

Dual Stimuli-Responsive Micelles for Imaging-Guided Mitochondrion-Targeted Photothermal/Photodynamic/Chemo Combination Therapy-Induced Immunogenic Cell Death

Introduction

As the special modality of cell death, immunogenic cell death (ICD) could activate immune response. Phototherapy in combination with chemotherapy (CT) is a particularly efficient tumor ICD inducing method that could overcome the defects of monotherapies.

Methods

In this study, new dual stimuli-responsive micelles were designed and prepared for imaging-guided mitochondrion-targeted photothermal/photodynamic/CT combination therapy through inducing ICD. A dual-sensitive methoxy-polyethylene glycol-SS-poly(L-γ-glutamylglutamine)-SS-IR780 (mPEG-SS-PGG-SS-IR780) polymer was synthesized by grafting IR780 with biodegradable di-carboxyl PGG as the backbone, and mPEG-SS-PGG-SS-IR780/paclitaxel micelles (mPEG-SS-PGG-SS-IR780/PTXL MCs) were synthesized by encapsulating PTXL in the hydrophobic core.

Results

In-vivo and -vitro results demonstrated that the three-mode combination micelles inhibited tumor growth and enhanced the therapeutic efficacy of immunotherapy. The dual stimuli-responsive mPEG-SS-PGG-SS-IR780/PTXL MCs were able to facilitate tumor cell endocytosis of nanoparticles. They were also capable of promoting micelles disintegration and accelerating PTXL release. The mPEG-SS-PGG-SS-IR780/PTXL MCs induced mitochondrial dysfunction by directly targeting the mitochondria, considering the thermo- and reactive oxygen species (ROS) sensitivity of the mitochondria. Furthermore, the mPEG-SS-PGG-SS-IR780/PTXL MCs could play the diagnostic and therapeutic roles via imaging capabilities.

Conclusion

In summary, this study formulated a high-efficiency nanoscale platform with great potential in combined therapy for tumors through ICD.

Engineered Living Materials for Advanced Diseases Therapy

Natural living materials serving as biotherapeutics exhibit great potential for treating various diseases owing to their immunoactivity, tissue targeting, and other biological activities. In this review, the recent developments in engineered living materials, including mammalian cells, bacteria, viruses, fungi, microalgae, plants, and their active derivatives that are used for treating various diseases are summarized. Further, the future perspectives and challenges of such engineered living material-based biotherapeutics are discussed to provide considerations for future advances in biomedical applications.