Stepwise-acid-active organic/inorganic hybrid drug delivery system for cancer therapy

Current status of controlled onco-therapies based on metal organic frameworks

Despite consecutive efforts devoted to the establishment of innovative therapeutics for cancer control, cancer remains as a primary global public health concern. Achieving controlled release of anti-cancer agents may add great value to the field of oncology that requires the involvement of nanotechnologies. Metal organic frameworks (MOFs) hold great promise in this regard owing to their unique structural properties. MOFs can act as superior candidates for drug delivery given their porous structure and large loading area, and can be prepared into anti-cancer therapeutics by incorporating stimuli-sensitive components into the ligands or nodes of the framework. By combing through chemical and physical features of MOFs favorable for onco-therapeutic applications and current cancer treatment portfolios taking advantages of these characteristics, this review classified MOFs feasible for establishing controlled anti-cancer modalities into 6 categories, outlined the corresponding strategies currently available for each type of MOF, and identified understudied areas and future opportunities towards innovative MOF design for improved or expanded clinical anti-cancer applications.

Metal-polyphenol nanodots loaded hollow MnO2 nanoparticles with a "dynamic protection" property for enhanced cancer chemodynamic therapy

Chemodynamic therapy (CDT) is a novel cancer therapeutic strategy. However, barriers such as high glutathione (GSH) concentration and low concentration of metal ions intracellular reduce its treatment effect. In this work, a nanosystem named GA-Fe@HMDN-PEI-PEG with a "dynamic protection" property was reported for enhanced cancer CDT. Mesoporous hollow manganese dioxide (MnO₂) nanoparticle (HMDN) was prepared to load gallic acid-ferrous (GA-Fe) nanodots fabricated from gallic acid (GA) and ferrous ion (Fe²⁺). Then the pores of HMDN were blocked by polyethyleneimine (PEI), which was then grafted with methoxy poly(ethylene glycol) (mPEG) through a pH-sensitive benzoic imine bond. mPEG could protect the nanoparticles (NPs) against the nonspecific uptake by normal cells and enhance their accumulation in the tumor. However, in the slightly acidic tumor microenvironment, hydrolysis of benzoic imine led to DePEGylation to reveal PEI for enhanced uptake by cancer cells. The reaction between HMDN and GSH could consume GSH and obtain manganese ion (Mn²⁺) for the Fenton-like reaction for CDT. GA-Fe nanodots could also offer Fe for the Fenton reaction, and reductive GA could reduce the high-valence ions to low-valence for reusing in Fenton and Fenton-like reactions. These properties allowed GA-Fe@HMDN-PEI-PEG for precise medicine with a high utilization rate and common side effects.

Drug Delivery Systems with a "Tumor-Triggered" Targeting or Intracellular Drug Release Property Based on DePEGylation

Coating nanosized anticancer drug delivery systems (DDSs) with poly(ethylene glycol) (PEG), the so-called PEGylation, has been proven an effective method to enhance hydrophilicity, aqueous dispersivity, and stability of DDSs. What is more, as PEG has the lowest level of protein absorption of any known polymer, PEGylation can reduce the clearance of DDSs by the mononuclear phagocyte system (MPS) and prolong their blood circulation time in vivo. However, the "stealthy" characteristic of PEG also diminishes the uptake of DDSs by cancer cells, which may reduce drug utilization. Therefore, dynamic protection strategies have been widely researched in the past years. Coating DDSs with PEG through dynamic covalent or noncovalent bonds that are stable in blood and normal tissues, but can be broken in the tumor microenvironment (TME), can achieve a DePEGylation-based "tumor-triggered" targeting or intracellular drug release, which can effectively improve the utilization of drugs and reduce their side effects. In this review, the stimuli and methods of "tumor-triggered" targeting or intracellular drug release, based on DePEGylation, are summarized. Additionally, the targeting and intracellular controlled release behaviors of the DDSs are briefly introduced.

Preparation and application of pH-responsive drug delivery systems

Microenvironment-responsive drug delivery systems (DDSs) can achieve targeted drug delivery, reduce drug side effects and improve drug efficacies. Among them, pH-responsive DDSs have gained popularity since the pH in the diseased tissues such as cancer, bacterial infection and inflammation differs from a physiological pH of 7.4 and this difference could be harnessed for DDSs to release encapsulated drugs specifically to these diseased tissues. A variety of synthetic approaches have been developed to prepare pH-sensitive DDSs, including introduction of a variety of pH-sensitive chemical bonds or protonated/deprotonated chemical groups. A myriad of nano DDSs have been explored to be pH-responsive, including liposomes, micelles, hydrogels, dendritic macromolecules and organic-inorganic hybrid nanoparticles, and micron level microspheres. The prodrugs from drug-loaded pH-sensitive nano DDSs have been applied in research on anticancer therapy and diagnosis of cancer, inflammation, antibacterial infection, and neurological diseases. We have systematically summarized synthesis strategies of pH-stimulating DDSs, illustrated commonly used and recently developed nanocarriers for these DDSs and covered their potential in different biomedical applications, which may spark new ideas for the development and application of pH-sensitive nano DDSs.

The combination of MnO2@Lipo-coated gefitinib and bevacizumab inhibits the development of non-small cell lung cancer

It can be found from a large number of cancer treatments that use of anti-cancer drugs alone often presents low efficacy and high side effects. This study aims to develop a new drug carrier with tumor-specific response, controlled release in vivo and high tumor-suppressive property. Inorganic nano-materials MnO₂ with pH and glutathione (GSH, abundant in cancer cells) responsiveness were used to construct sustained-release functional nano-liposome to be an excellent in vivo pH-sensitive drug delivery system. Some hydrophilic MnO₂, gefitinib (Geb), and bevacizumab (Beb) were encapsulated in the phospholipid vesicles (liposomes), so as to integrate several anti-tumor drugs (MnO₂-PDA@Lipo@Geb@Beb) to achieve effective treatment of non-small cell lung cancer (NSCLC). Part of the MnO₂ nanorods on the lipid shell had the properties of pH and GSH responsiveness, which could further enhance anti-cancer efficacy. Cell assay results showed that MnO₂-PDA@Lipo@Geb@Beb nano-drug had an effective inhibition on A549 cell progression and showed excellent biocompatibility. In vivo results further confirmed that MnO₂-PDA@Lipo@Geb@Beb nano-drug could effectively inhibit the growth of NSCLC cells. Overall, it can be inferred from the above experimental results that the nanocomposite drug is expected to be widely used in the clinical application of lung cancer.

A chitosan/mesoporous silica nanoparticle-based anticancer drug delivery system with a "tumor-triggered targeting" property

To enhance drug utilization and reduce their side effects, the strategy of "tumor-triggered targeting" was introduced to fabricate dual-pH-sensitive chitosan (CHI)/mesoporous silica nanoparticle (MSN)-based anticancer drug delivery system (DDS) in this work. Model drug doxorubicin hydrochloride (DOX) was loaded in MSN, which was modified with benzimidazole (Bz) group. Then chitosan-graft-β-cyclodextrin (CHI-g-CD) was applied as the "gatekeeper" to cover MSN through host-guest interaction between β-CD and Bz. After being coated with targeting peptide adamantane-glycine-arginine-glycine-aspartic acid-serine (Ad-GRGDS), methoxy poly(ethylene glycol) benzaldehyde (mPEG-CHO) was finally grafted on CHI through the pH-sensitive benzoic imine bond. Due to the dynamic protection of PEG, the obtained carriers were "stealthy" at pH 7.4, but could reveal the shielded targeting peptide and the positive charge of CHI in the weakly acidic environment achieved a "tumor-triggered targeting". Inside cancer cells, the interaction between β-CD and Bz group could be destroyed due to the lower pH, resulted in DOX release. Both in vitro and in vivo studies proved the DDS could targeting induce cancer cell apoptosis, inhibit tumor growth, and reduce the cytotoxicity of DOX against normal cells. It is expected that the system named DOX@MSN-CHI-RGD-PEG could be a potential choice for cancer therapy.

Smart metal organic frameworks: focus on cancer treatment

Metal–organic frameworks (MOFs), as a prominent category of hybrid porous materials, have been broadly employed as controlled systems of drug delivery due to their inherent interesting properties.

Clay nanoparticles as pharmaceutical carriers in drug delivery systems

INTRODUCTION

Clay minerals are a class of silicates with chemical inertness, colloid, and thixotropy, which have excellent physicochemical properties, good biocompatibility, low toxicity, and have high application potential in biomedical fields. These inorganic materials have been widely used in pharmaceutical excipients and active substances. In recent years, nanoclay mineral materials have been used as drug vehicles for the delivery of a variety of drugs based on their broad specific surface area, rich porosity, diverse morphology, good adsorption performance, and high ion exchange capacity.

AREAS COVERED

This review introduces the structures, properties, and applications of various common natural and synthetic nanoclay materials as drug carriers. Natural nanoclays have different morphologies including nanoplates, nanotubes, and nanofibers. Synthetic materials have controllable sizes and flexible structures, where mesoporous silica nanoparticles, laponite, and imogolite are typical ones. These inorganic nanoparticles are often linked to polymers to form multifunctional drug delivery systems for better pharmaceutical performance.

EXPERT OPINION

The clay nanomaterials have typical properties, including enhanced solubility of insoluble drugs, targeting therapeutic sites, controlled release, and stimulation of responsive drug delivery systems.

pH-Sensitive Biomaterials for Drug Delivery

The development of precise and personalized medicine requires novel formulation strategies to deliver the therapeutic payloads to the pathological tissues, producing enhanced therapeutic outcome and reduced side effects. As many diseased tissues are feathered with acidic characteristics microenvironment, pH-sensitive biomaterials for drug delivery present great promise for the purpose, which could protect the therapeutic payloads from metabolism and degradation during in vivo circulation and exhibit responsive release of the therapeutics triggered by the acidic pathological tissues, especially for cancer treatment. In the past decades, many methodologies, such as acidic cleavage linkage, have been applied for fabrication of pH-responsive materials for both in vitro and in vivo applications. In this review, we will summarize some pH-sensitive drug delivery system for medical application, mainly focusing on the pH-sensitive linkage bonds and pH-sensitive biomaterials.

pH/GSH-Dual-Sensitive Hollow Mesoporous Silica Nanoparticle-Based Drug Delivery System for Targeted Cancer Therapy

The purpose of developing novel anticancer drug delivery systems (DDSs) is to efficiently carry and release drugs into cancer cells and minimize side effects. In this work, based on hollow mesoporous silica nanoparticle (HMSN) and the charge-reversal property, a pH/GSH-dual-sensitive DDS named DOX@HMSN-SS-PLL(cit) was reported. HMSN encapsulated DOX with high efficacy and was then covered by the "gatekeeper" β-cyclodextrin (β-CD) through the glutathione (GSH)-sensitive disulfide bond. Thereafter, adamantine-blocked citraconic-anhydride-functionalized poly-l-lysine (PLL(cit)-Ad) was decorated on the surface of the particles via host-guest interaction. The negatively charged carriers were stable in the neutral environment in vivo and could be effectively transported to the tumor site. The surface charge of the nanoparticles could be reversed in the weakly acidic environment, which increased the cellular uptake ability of the carriers by the cancer cells. After cellular internalization, β-CD can be removed by breakage of the disulfide bond in the presence of a high concentration of GSH, leading to DOX release. The preparation process of the carriers was monitored. The charge-reversal capability and the controlled drug-release behavior of the carriers were also investigated. In vitro and in vivo experiments demonstrated the excellent cancer therapy effect with low side effects of the carriers. It is expected that dual-sensitive DOX@HMSN-SS-PLL(cit) could play an important role in cancer therapy.

Host-guest fabrication of dual-responsive hyaluronic acid/mesoporous silica nanoparticle based drug delivery system for targeted cancer therapy

In this paper, a targeting hyaluronic acid (HA)/mesoporous silica nanoparticle (MSN) based drug delivery system (DDS) with dual-responsiveness was prepared for cancer therapy. To avoid the side reaction between the anti-cancer drug doxorubicin hydrochloride (DOX) and HA, host-guest interaction was applied to fabricate the DDS named DOX@MSN-SS-N=C-HA. The "nanocontainer" MSN was modified with benzene ring via both pH-sensitive benzoic imine bond and redox-sensitive disulfide linkage. When DOX was loaded in the pores of MSN, the channels were then capped by the "gatekeeper" β-CD grafted HA (HA-g-CD) through host-guest interaction between β-CD and benzene. HA endowed the drug carriers with the targeting capability in CD44 over-expressed cancer cells. After cellular uptake, the carriers could rapidly release DOX for cell apoptosis due to both the hydrolysis of benzoic imine bond at low pH and the cleavage of disulfide bond at a high concentration of glutathione (GSH) intracellular. In vitro drug release studies and in vitro cytotoxicity studies were taken to investigate the dual-responsiveness of the carriers. And the CD44-receptor mediated cancer cell targeting capability was investigated as well. In conclusion, the targeted dual-responsive complex DDS fabricated through host-guest interaction has promising potential in cancer therapy.

Macroporous bacterial cellulose grafted by oligopeptides induces biomimetic mineralization via interfacial wettability

Bacterial cellulose (BC) has a role in tissue repair and regenerative medicine, which has already attracted tremendous interest from researchers, especially those working in the field of hybrid materials. Herein, we designed BC-based macroporous functional materials by dialdehyde bacterial cellulose (DBC) cross-linking with oligopeptides under mild reactive conditions. The interfacial properties of the surface modified BC were examined by biomimetic mineralization. The results showed that a macroporous structure was achieved by using oligopeptides as chemical cross-linking agents with an interconnected macroporosity ranging from 20 μm to 80 μm. Their mechanical properties were barely altered compared to the pristine BC. Their enhanced surface charges stemmed from the carboxyl groups of the oligopeptides engaging in reactions with amine and aldehyde groups. The oligopeptides cross-linked DBC showed a faster initial induction towards minerals via interfacial wettability resulting in promotion of mineralization, the hybrid materials had excellent biocompatibility relative to the pristine BC. These findings are vital to the development of other biopolymers with essential macroporous structures as well as improved interfacial wettability, which enables their possible uses in tissue repair and regenerative medicine.

Poly(amino acid)/ZnO/mesoporous silica nanoparticle based complex drug delivery system with a charge-reversal property for cancer therapy

Negative-to-positive charge-reversal strategy employed in anti-cancer drug delivery systems (DDSs) can improve the utilization of the drugs as well as reduce their side effects efficiently. In this article, a complex DDS named DOX@MSN-ZnO-PLL-PLL(DMA) was prepared. Doxorubicin hydrochloride (DOX) was loaded in mesoporous silica nanoparticles (MSNs), which were then covered by ZnO in situ. Poly-_L-lysine (PLL) and 2,3-dimethylmaleic anhydride functionalized PLL (PLL(DMA)) were finally coated on the nanoparticles through a Layer-by-Layer (LbL) assembly process with PLL(DMA) outside to obtain the carriers. The negative charged PLL(DMA) avoided the unspecific uptake of the carriers by normal cells at pH 7.4. While the charge-reversal property could reverse the zeta-potential of the carriers to positive in weakly acidic tumor tissues at pH 6.5, which promoted the cytophagy of the carriers by cancer cells. ZnO which blocked the pores of MSNs could be dissolved intracellular due to the more acidic environment in endosome/lysosome, and resulting in drug release for cancer cell apoptosis. Zeta-potential measurements, the in vitro cellular uptake behaviors as well as cellular cytotoxicity of the carriers at different pH values were investigated to prove the charge-reversal property. The in vitro drug release studies and the cellular cytotoxicity studies were also investigated to prove the controlled DOX release behavior of the carriers. In summary, the complex DDS with charge-reversal property should be of consideration in cancer therapy.

Stepwise dual pH and redox-responsive cross-linked polypeptide nanoparticles for enhanced cellular uptake and effective cancer therapy

The systemic toxicity, reduced cellular internalization, and uncontrollable intracellular drug release of smart nanoparticles (NPs) still need to be overcome for effective cancer therapy.