Hypoxia-responsive micelles self-assembled from amphiphilic block copolymers for the controlled release of anticancer drugs

Hypoxia-Responsive Tetrameric Supramolecular Polypeptide Nanoprodrugs for Combination Therapy

Despite the intense progress of photodynamic and chemotherapy, however, they cannot prevent solid tumor invasion, metastasis, and relapse, along with inferior efficacy and severe side effects. The hypoxia-responsive nanoprodrugs integrating photodynamic functions are highly sought to address the above-mentioned problems and overcome the tumor hypoxia-reduced efficacy. Herein, a hypoxia-responsive tetrameric supramolecular polypeptide nanoprodrug (SPN-TAPP-PCB4) is constructed from the self-assembly of tetrameric porphyrin-central poly(l-lysine-azobenzene-chlorambucil) (TAPP-(PLL-Azo-CB)4) and an anionic water-soluble [2]biphenyl-extended-pillar[6]arene (AWBpP6) via the synergy of hydrophobic, π-π stacking, and host-guest interactions. Upon laser irradiation, the central TAPP can convert oxygen to generate single oxygen (1 O2 ) to kill tumor cells. Furthermore, under the acidic and PDT-aggravated hypoxia tumor cell microenvironment, SPN-TAPP-PCB4 is rapidly disassembled, and then efficiently releases activated CB through the hypoxic-responsive cleavage of azobenzene linkages. Both in vitro and in vivo biological studies showcase synergistic cancer-killing actions between photodynamic therapy (PDT) and chemotherapy (CT) with negligible toxicity. Consequently, this supramolecular polypeptide nanoprodrug offers an effective strategy to design a hypoxia-responsive nanoprodrug for a potential combo PDT-CT transition.

Tumor Microenvironment-Responsive Drug Delivery Based on Polymeric Micelles for Precision Cancer Therapy: Strategies and Prospects

In clinical practice, drug therapy for cancer is still limited by its inefficiency and high toxicity. For precision therapy, various drug delivery systems, including polymeric micelles self-assembled from amphiphilic polymeric materials, have been developed to achieve tumor-targeting drug delivery. Considering the characteristics of the pathophysiological environment at the drug target site, the design, synthesis, or modification of environmentally responsive polymeric materials has become a crucial strategy for drug-targeted delivery. In comparison to the normal physiological environment, tumors possess a unique microenvironment, characterized by a low pH, high reactive oxygen species concentration, hypoxia, and distinct enzyme systems, providing various stimuli for the environmentally responsive design of polymeric micelles. Polymeric micelles with tumor microenvironment (TME)-responsive characteristics have shown significant improvement in precision therapy for cancer treatment. This review mainly outlines the most promising strategies available for exploiting the tumor microenvironment to construct internal stimulus-responsive drug delivery micelles that target tumors and achieve enhanced antitumor efficacy. In addition, the prospects of TME-responsive polymeric micelles for gene therapy and immunotherapy, the most popular current cancer treatments, are also discussed. TME-responsive drug delivery via polymeric micelles will be an efficient and robust approach for developing clinical cancer therapies in the future.

Hypoxia-Responsive Polymeric Nanoprodrugs for Combo Photodynamic and Chemotherapy

Hypoxia in most solid tumors is a major challenge for photodynamic therapy (PDT), and the combination of hypoxia-activated chemotherapy and PDT is a promising approach for enhanced anticancer activity. Herein, we designed hypoxia-responsive polymeric nanoprodrug PNPs to co-deliver photosensitizer 5,10,5,20-tetrakis(4-aminophenyl)-porphine (TAPP) and chlorambucil (CB) to improve the overall therapeutic efficacy. Upon laser irradiation, the central TAPP converted oxygen to produce single oxygen (1O2) for PDT and induced PDT-reduced hypoxia environment, which accelerated the release of activated CB for synergetic cancer cell killing. Consequently, these hypoxia-responsive polymeric nanoprodrugs with a considerable drug-loading content and synergistic therapeutic effect of PDT-CT had great potential for tumor therapy.

Research Status of Dendrimer Micelles in Tumor Therapy for Drug Delivery

Dendrimers are a family of polymers with highly branched structure, well-defined composition, and extensive functional groups, which have attracted great attention in biomedical applications. Micelles formed by dendrimers are ideal nanocarriers for delivering anticancer agents due to the explicit study of their characteristics of particle size, charge, and biological properties such as toxicity, blood circulation time, biodistribution, and cellular internalization. Here, the classification, preparation, and structure of dendrimer micelles are reviewed, and the specific functional groups modified on the surface of dendrimers for tumor active targeting, stimuli-responsive drug release, reduced toxicity, and prolonged blood circulation time are discussed. In addition, their applications are summarized as various platforms for biomedical applications related to cancer therapy including drug delivery, gene transfection, nano-contrast for imaging, and combined therapy. Other applications such as tissue engineering and biosensor are also involved. Finally, the possible challenges and perspectives of dendrimer micelles for their further applications are discussed.

Internal stimuli-responsive nanocarriers for controlled anti-cancer drug release: a review

Cancer disease is one of the most frequent life-threatening, with a high fatality rate worldwide. However, recent immunotherapy studies in various tumours have yielded unsatisfactory outcomes, with just a few individuals experiencing long-term responses. To overcome these issues, nowadays internal stimuli-responsive nanocarriers have been widely exploited to transport a wide range of active substances, including peptides, genes and medicines. These nanosystems could be chemically adjusted to produce target-based drug release at the target location, minimizing pathological and physiological difficulties while increasing therapeutic efficiency. This review highlights the various types of internal stimuli-responsive nanocarriers and applications in cancer diagnosis. This study can provide inspiration and impetus for exploiting more promising internal stimuli-responsive nanosystems for drug delivery.

Exploring the Application of Micellar Drug Delivery Systems in Cancer Nanomedicine

Various formulations of polymeric micelles, tiny spherical structures made of polymeric materials, are currently being investigated in preclinical and clinical settings for their potential as nanomedicines. They target specific tissues and prolong circulation in the body, making them promising cancer treatment options. This review focuses on the different types of polymeric materials available to synthesize micelles, as well as the different ways that micelles can be tailored to be responsive to different stimuli. The selection of stimuli-sensitive polymers used in micelle preparation is based on the specific conditions found in the tumor microenvironment. Additionally, clinical trends in using micelles to treat cancer are presented, including what happens to micelles after they are administered. Finally, various cancer drug delivery applications involving micelles are discussed along with their regulatory aspects and future outlooks. As part of this discussion, we will examine current research and development in this field. The challenges and barriers they may have to overcome before they can be widely adopted in clinics will also be discussed.

Self-Rectifiable and Hypoxia-Assisted Chemo-Photodynamic Nanoinhibitor for Synergistic Cancer Therapy

Photodynamic therapy (PDT) can eradicate cancer cells under light irradiation, mainly because of reactive singlet oxygen (¹O₂) being transformed from intratumoral oxygen. Nonetheless, the consumption of oxygen during PDT results in serious hypoxic conditions and an elevated hypoxia-inducing factor-1α (HIF-1α) level that hamper further photodynamic efficacy and induce tumor metastasis. To address this problem, we developed hypoxia-assisted NP-co-encapsulating Ce6 (photosensitizer) and YC-1 (HIF-1α inhibitor) as a self-rectifiable nanoinhibitor for synergistic antitumor treatment. PDT-aggravated intracellular hypoxic stress facilitated NP dissociation to release the drug (YC-1), which achieved tumor killing and HIF-1α inhibition to further enhance the therapeutic effect of PDT and prevent tumor metastasis. Besides, in vivo studies revealed that the HC/PI@YC-1 NPs afforded synergistic anticancer efficacy with minimal toxicity. Therefore, this study provides a prospective approach against PDT drawbacks and combination cancer therapy.

Hyaluronic Acid Derived Hypoxia-Sensitive Nanocarrier for Tumor Targeted Drug Delivery

Hyaluronic acid (HA) is conjugated with BHQ3 moiety with azo bonds to prepare hypoxia-responsive polymer conjugate. Because of the amphiphilic nature, the polymer conjugate self-assembles to HA-BHQ3 nanoparticles (NPs). The anticancer drug doxorubicin (DOX) is loaded into the NPs. In the physiological environment, DOX is released slowly. In contrast, under hypoxic conditions, the azo bond in BHQ3 is cleaved, thus significantly enhancing the DOX release rate. For instance, after 24 h, 25% of DOX is released under normal conditions, while 74% of DOX is released under hypoxic conditions. In vitro cytotoxicity demonstrates higher toxicity in the hypoxic conditions. DOX@HA-BHQ3 NPs exhibit greater toxicity levels against 4T1 cells in hypoxic conditions. The fluorescent microscope images confirm the oxygen-dependent intracellular DOX release from the NPs. The in vivo biodistribution results suggest the tumor targetability of HA-BHQ3 NPs in 4T1 tumor-bearing mice.

Hypoxia-responsive block copolymer polyprodrugs for complementary photodynamic-chemotherapy

The inherent hypoxic microenvironment of solid tumors has an important influence on tumor growth, distant metastasis, and invasiveness. The heterogeneous distribution of hypoxic regions inside tumors limits the therapeutic efficacy of O₂-assisted therapeutic strategy (e.g. photodynamic therapy (PDT)). On the other hand, the hypoxia-activable prodrugs cannot work effectively in the regions with enough O₂ concentration. To address the issues, we prepare a block copolymer polyprodrug consisting of polyethylene glycol (PEG) and copolymerized segments of nitroimidazole-linked camptothecin (CPT) methacrylate and 5,10,15,20-tetraphenylporphyrin (TPP)-containing methacrylate monomers for complementary photodynamic-chemotherapy. The polyprodrug can self-assemble into polymeric micelles in aqueous solution with suitable size and high stability. After intravenous injection, the polyprodrug micelles show tumor accumulation. Followed by light irradiation (650 nm) at tumor sites, TPP moieties induce singlet oxygen (¹O₂) production in the oxygen-rich area to exert PDT and cause transformation of the oxygen-rich areas into hypoxia. Simultaneously, in the hypoxic areas, the hypoxia-responsive polyprodrugs can be activated to release free CPT due to the cleavage of nitroimidazole linkages. The polyprodrug micelles with the segments for PDT and hypoxia-activable CPT efficiently suppress the growth of HeLa tumors. The well-defined polyprodrug amphiphiles offer an effective strategy to overcome the disadvantages of single treatment of PDT or hypoxia-responsive prodrugs for complementary photodynamic-chemotherapy of cancers.

Hypoxia-Responsive Polyprodrug Nanocarriers for Near-Infrared Light-Boosted Photodynamic Chemotherapy

The hypoxia environment inside tumors is tightly associated with tumor growth, metastasis, and drug resistance. However, the heterogonous distribution of hypoxic areas limits the efficacy of hypoxia-activatable drug delivery systems. Herein, we report the hypoxia-activable block copolymer polyprodrugs, which are composed of poly(ethylene glycol) (PEG) and copolymerized segments of ortho-nitrobenzyl-linked camptothecin (CPT) methacrylate and 2-(piperidin-1-yl)ethyl methacrylate (PEMA) monomers. After self-assembly in aqueous solution, indocyanine green (ICG) photosensitizers were encapsulated to formulate ICG-loaded micellar nanoparticles (ICG@CPTNB) for near-infrared (NIR) light-boosted photodynamic therapy (PDT), tumor hypoxia aggravation, and responsive drug activation. Through intravenous injection and prolonged blood circulation, the nanoparticles can accumulate into tumor efficiently. Tumor acidity-triggered charge transition of PEMA units remarkably promotes cellular internalization of the nanoparticles. Upon exposure to NIR laser irradiation, ICG inside the nanoparticles produced reactive oxygen species (ROS) along with local hypothermia. Simultaneously, the oxygen consumption during ROS production aggravated the intratumoral hypoxia, which amplified hypoxia-responsive self-immolative CPT release from the nanoparticles. The combined photodynamic chemotherapy using hypoxia-responsive polyprodrug nanoparticles, ICG@CPTNB, overcomes the limitations of single therapy of hypoxia-activable prodrugs or PDT, which remarkably improves the efficiency of tumor growth suppression.

Nanotechnology-Based Drug Delivery to Improve the Therapeutic Benefits of NRF2 Modulators in Cancer Therapy

The disadvantages of conventional anticancer drugs, such as their low bioavailability, poor targeting efficacy, and serious side effects, have led to the discovery of new therapeutic agents and potential drug delivery systems. In particular, the introduction of nano-sized drug delivery systems (NDDSs) has opened new horizons for effective cancer treatment. These are considered potential systems that provide deep tissue penetration and specific drug targeting. On the other hand, nuclear factor erythroid 2-related factor 2 (NRF2)-based anticancer treatment approaches have attracted tremendous attention and produced encouraging results. However, the lack of effective formulation strategies is one of the factors that hinder the clinical application of NRF2 modulators. In this review, we initially focus on the critical role of NRF2 in cancer cells and NRF2-based anticancer treatment. Subsequently, we review the preparation and characterization of NDDSs encapsulating NRF2 modulators and discuss their potential for cancer therapy.

Azo-inserted responsive hybrid liposomes for hypoxia-specific drug delivery

Stimuli-responsive drug delivery systems using endogenous stimuli from tumor microenvironments such as acidic pH, over-expressed enzyme, and high redox potential as triggers have shown tremendous promise in cancer therapy. However, their clinical application is severely limited because of tumor heterogeneity. Hypoxia, a physiological feature observed in almost all solid tumors and even in nodules with very small size, has currently emerged as a more general but efficient stimulus to trigger release. Herein, we developed hypoxia-responsive hybrid liposomes (HR-HLPs), composed of azo-inserted organokoxysilane-based lipid analogue as a responsive component and commercial phospholipid for reducing the rigidity of liposomal membrane caused by azo, for drug delivery targeting tumor hypoxia. HR-HLPs had the advantages of high structural stability to avoid premature drug leakage when circulating in the blood and high sensitivity in responding to hypoxia once reaching tumor sites. HR-HLPs exhibit deep tumor penetration capability, enabling effective delivery to hypoxic regions distant from tumor vessels. Moreover, HR-HLPs could selectively release their payload, co-localizing with over-expressed hypoxia inducible factor 1α (HIF-1α) in vitro and in vivo. As a result, HR-HLPs showed improved therapeutic outcome accompanied by reduced adverse effects. The results highlighted the potential application of azo-inserted responsive hybrid liposomes for hypoxia-targeted drug delivery. STATEMENT OF SIGNIFICANCE.

Light-enhanced hypoxia-responsive and azobenzene cleavage-triggered size-shrinkable micelles for synergistic photodynamic therapy and chemotherapy

The micelles self-assembled from POEGMA-b-PCL-Azo-PCL-b-POEGMA present light-enhanced hypoxia-responsive and azobenzene cleavage-triggered size-shrinkable properties for synergistic photodynamic therapy and chemotherapy.

Hypoxia and temperature dual-stimuli-responsive random copolymers: facile synthesis, self-assembly and controlled release of drug

The micelles self-assembled from P(NIPAM-co-AA-co-NIA) copolymers presented hypoxia and temperature dual-stimuli-responsive properties and a controlled release of drug was achieved using them.