Enzyme responsive drug delivery system based on mesoporous silica nanoparticles for tumor therapy in vivo

An update review of smart nanotherapeutics and liver cancer: opportunities and challenges

Hepatocellular carcinoma (HCC) is the most common form of primary liver cancer, typically diagnosed in advanced stages. Chemotherapy is necessary for treating advanced liver cancer; however, several challenges affect its effectiveness. These challenges include low specificity, high dosage requirements, high systemic toxicity and severe side effects, which significantly limit the efficacy of chemotherapy. These limitations can hinder the treatment of HCC. This review focuses on the prevalence of HCC, different types of liver cancer and the staging of the disease, along with available treatment methods. Additionally, explores recent and relevant studies on smart drug- and gene-delivery systems specifically designed for HCC. These systems include targeted endogenous and exogenous stimuli-responsive platforms.

Inflammation-responsive drug delivery nanosystems for treatment of bacterial-induced sepsis

Sepsis, a complication of dysregulated host immune systemic response to an infection, is life threatening and causes multiple organ injuries. Sepsis is recognized by WHO as a big contributor to global morbidity and mortality. The heterogeneity in sepsis pathophysiology, antimicrobial resistance threat, the slowdown in the development of antimicrobials, and limitations of conventional dosage forms jeopardize the treatment of sepsis. Drug delivery nanosystems are promising tools to overcome some of these challenges. Among the drug delivery nanosystems, inflammation-responsive nanosystems have attracted considerable interest in sepsis treatment due to their ability to respond to specific stimuli in the sepsis microenvironment to release their payload in a precise, targeted, controlled, and rapid manner compared to non-responsive nanosystems. These nanosystems posit superior therapeutic potential to enhance sepsis treatment. This review critically evaluates the recent advances in the design of drug delivery nanosystems that are inflammation responsive and their potential in enhancing sepsis treatment. The sepsis microenvironment's unique features, such as acidic pH, upregulated receptors, overexpressed enzymes, and enhanced oxidative stress, that form the basis for their design have been adequately discussed. These inflammation-responsive nanosystems have been organized into five classes namely: Receptor-targeted nanosystems, pH-responsive nanosystems, redox-responsive nanosystems, enzyme-responsive nanosystems, and multi-responsive nanosystems. Studies under each class have been thematically grouped and discussed with an emphasis on the polymers used in their design, nanocarriers, key characterization, loaded actives, and key findings on drug release and therapeutic efficacy. Further, this information is concisely summarized into tables and supplemented by inserted figures. Additionally, this review adeptly points out the strengths and limitations of the studies and identifies research avenues that need to be explored. Finally, the challenges and future perspectives on these nanosystems have been thoughtfully highlighted.

Natural Biopolymers as Smart Coating Materials of Mesoporous Silica Nanoparticles for Drug Delivery

In recent years, the functionalization of mesoporous silica nanoparticles (MSNs) with different types of responsive pore gatekeepers have shown great potential for the formulation of drug delivery systems (DDS) with minimal premature leakage and site-specific controlled release. New nanotechnological approaches have been developed with the objective of utilizing natural biopolymers as smart materials in drug delivery applications. Natural biopolymers are sensitive to various physicochemical and biological stimuli and are endowed with intrinsic biodegradability, biocompatibility, and low immunogenicity. Their use as biocompatible smart coatings has extensively been investigated in the last few years. This review summarizes the MSNs coating procedures with natural polysaccharides and protein-based biopolymers, focusing on their application as responsive materials to endogenous stimuli. Biopolymer-coated MSNs, which conjugate the nanocarrier features of mesoporous silica with the biocompatibility and controlled delivery provided by natural coatings, have shown promising therapeutic outcomes and the potential to emerge as valuable candidates for the selective treatment of various diseases.

Role and Application of Biocatalysts in Cancer Drug Discovery

A biocatalyst is an enzyme that speeds up or slows down the rate at which a chemical reaction occurs and speeds up certain processes by 108 times. It is used as an anticancer agent because it targets drug activation inside the tumor microenvironment while limiting damage to healthy cells. Biocatalysts have been used for the synthesis of different heterocyclic compounds and is also used in the nano drug delivery systems. The use of nano-biocatalysts for tumor-targeted delivery not only aids in tumor invasion, angiogenesis, and mutagenesis, but also provides information on the expression and activity of many markers related to the microenvironment. Iosmapinol, moclobemide, cinepazide, lysine dioxygenase, epothilone, 1-homophenylalanine, and many more are only some of the anticancer medicines that have been synthesised using biocatalysts. In this review, we have highlighted the application of biocatalysts in cancer therapies as well as the use of biocatalysts in the synthesis of drugs and drug-delivery systems in the tumor microenvironment.

Tumor Microenvironment-Based Stimuli-Responsive Nanoparticles for Controlled Release of Drugs in Cancer Therapy

With the development of nanomedicine technology, stimuli-responsive nanocarriers play an increasingly important role in antitumor therapy. Compared with the normal physiological environment, the tumor microenvironment (TME) possesses several unique properties, including acidity, high glutathione (GSH) concentration, hypoxia, over-expressed enzymes and excessive reactive oxygen species (ROS), which are closely related to the occurrence and development of tumors. However, on the other hand, these properties could also be harnessed for smart drug delivery systems to release drugs specifically in tumor tissues. Stimuli-responsive nanoparticles (srNPs) can maintain stability at physiological conditions, while they could be triggered rapidly to release drugs by specific stimuli to prolong blood circulation and enhance cancer cellular uptake, thus achieving excellent therapeutic performance and improved biosafety. This review focuses on the design of srNPs based on several stimuli in the TME for the delivery of antitumor drugs. In addition, the challenges and prospects for the development of srNPs are discussed, which can possibly inspire researchers to develop srNPs for clinical applications in the future.

Stimuli-responsive image-guided nanocarriers as smart drug delivery platforms

INTRODUCTION

In recent years, to improve the precision of drug delivery and reduce toxicity associated from the uncontrolled drug release at off-target locations, extensive efforts have been paid to develop stimuli-responsive nanocarriers, which enable precise control over on-demand drug release due to internal stimuli like pH, redox, enzyme and external stimuli like light, magnetic field, and ultrasound. Moreover, some stimuli-responsive nanocarriers have been strategically incorporated with imaging probes for simultaneous monitoring of the drug delivery process and region of interest for treatment optimization.

AREAS COVERED

In this review, the state-of-art progress in developing stimuli-responsive image-guided nanocarriers are summarized, including their designed strategies, synergistic mechanism, and biomedical applications in cancer therapy, and the current challenges and new perspectives are discussed.

EXPERT OPINION

The stimuli-responsive nanocarriers provide assurance for precise release of drugs and imaging probes, and the molecular imaging techniques can monitor the pharmacokinetics, biodistribution and bioavailability of drugs in vivo, and feedback the drug delivery profile. Therefore, stimuli-responsive image-guided nanocarriers can integrate diagnosis and therapy in one nanoplatform and facilitate optimal therapeutic efficacy.

Enzyme-responsive strategy as a prospective cue to construct intelligent biomaterials for disease diagnosis and therapy

Stimuli-responsive materials have been widely studied and applied in biomedical field. Under the stimulation of enzymes, the enzyme-responsive materials (ERMs) can be triggered to change their structures, properties and functions....

Tumor-Microenvironment-Responsive Nanomedicine for Enhanced Cancer Immunotherapy

The past decades have witnessed great progress in cancer immunotherapy, which has profoundly revolutionized oncology, whereas low patient response rates and potential immune-related adverse events remain major clinical challenges. With the advantages of controlled delivery and modular flexibility, cancer nanomedicine has offered opportunities to strengthen antitumor immune responses and to sensitize tumor to immunotherapy. Furthermore, tumor-microenvironment (TME)-responsive nanomedicine has been demonstrated to achieve specific and localized amplification of the immune response in tumor tissue in a safe and effective manner, increasing patient response rates to immunotherapy and reducing the immune-related side effects simultaneously. Here, the recent progress of TME-responsive nanomedicine for cancer immunotherapy is summarized, which responds to the signals in the TME, such as weak acidity, reductive environment, high-level reactive oxygen species, hypoxia, overexpressed enzymes, and high-level adenosine triphosphate. Moreover, the potential to combine nanomedicine-based therapy and immunotherapeutic strategies to overcome each step of the cancer-immunity cycle and to enhance antitumor effects is discussed. Finally, existing challenges and further perspectives in this rising field with the hope for improved development of clinical applications are discussed.

Toward enzyme-responsive polymersome drug delivery

In drug delivery, enzyme-responsive drug carriers are becoming increasingly relevant because of the growing association of disease pathology with enzyme overexpression. Polymersomes are of interest to such applications because of their tunable properties. While polymersomes open up a wide range of chemical and physical properties to explore, they also present a challenge in developing generalized rules for the synthesis of novel systems. Motivated by this issue, in this perspective, we summarize the existing knowledge on enzyme-responsive polymersomes and outline the main design choices. Then, we propose heuristics to guide the design of novel systems. Finally, we discuss the potential of an integrated approach using computer simulations and experimental studies to streamline this design process and close the existing knowledge gaps.

Enzyme-polymeric/inorganic metal oxide/hybrid nanoparticle bio-conjugates in the development of therapeutic and biosensing platforms

Background

Because enzymes can control several metabolic pathways and regulate the production of free radicals, their simultaneous use with nanoplatforms showing protective and combinational properties is of great interest in the development of therapeutic nano-based platforms. However, enzyme immobilization on nanomaterials is not straightforward due to the toxic and unpredictable properties of nanoparticles in medical practice.

Aim of review

In fact, because of the ability to load enzymes on nano-based supports and increase their renewability, scientific groups have been tempted to create potential therapeutic enzymes in this field. Therefore, this study not only pays attention to the therapeutic and diagnostic applications of diseases by enzyme-nanoparticle (NP) bio-conjugate (abbreviated as: ENB), but also considers the importance of nanoplatforms used based on their toxicity, ease of application and lack of significant adverse effects on loaded enzymes. In the following, based on the published reports, we explained that the immobilization of enzymes on polymers, inorganic metal oxide and hybrid compounds provide hopes for potential use of ENBs in medical activities. Then, the use of ENBs in bioassay activities such as paper-based or wearing biosensors and lab-on-chip/microfluidic biosensors were evaluated. Finally, this review addresses the current challenges and future perspective of ENBs in biomedical applications.

Key scientific concepts of review

This literature may provide useful information regarding the application of ENBs in biosensing and therapeutic platforms.

Recent Advances in Gelatin-Based Nanomedicine for Targeted Delivery of Anti-Cancer Drugs

Nanoparticles based on natural polymers are utilized for the development of a wide range of drug delivery systems (DDS) in the current era. Gelatin-based nanoparticles, for example, are a remarkable cancer therapy with high efficacy and specificity. This paper reviews the recent advancements in gelatin-based nanomedicine for use in cancer therapeutics. Due to the characteristics features of gelatin, such as biocompatibility, biodegradability, stability, and good surface properties, these nanoparticles provide high therapeutic potency in cancer nanomedicine. The surface of gelatin can be modified in a number of ways using various ligands to explore the platform for the development of a more novel DDS. Various methods are available for the preparation of gelatin nanomedicine discussed in this review. In addition, various cross-linkers to stabilized nanocarriers and stimuli base gelatin nanoparticles are reviewed. Furthermore, recent advances and research in gelatin-based nanomedicine are discussed. Also, some drawbacks and challenges are evaluated. In general, this paper paves the pathway to identify the details about the gelatin-based DDS for cancer therapy.

Key Points in Remote-Controlled Drug Delivery: From the Carrier Design to Clinical Trials

The increased research activity aiming at improved delivery of pharmaceutical molecules indicates the expansion of the field. An efficient therapeutic delivery approach is based on the optimal choice of drug-carrying vehicle, successful targeting, and payload release enabling the site-specific accumulation of the therapeutic molecules. However, designing the formulation endowed with the targeting properties in vitro does not guarantee its selective delivery in vivo. The various biological barriers that the carrier encounters upon intravascular administration should be adequately addressed in its overall design to reduce the off-target effects and unwanted toxicity in vivo and thereby enhance the therapeutic efficacy of the payload. Here, we discuss the main parameters of remote-controlled drug delivery systems: (i) key principles of the carrier selection; (ii) the most significant physiological barriers and limitations associated with the drug delivery; (iii) major concepts for its targeting and cargo release stimulation by external stimuli in vivo. The clinical translation for drug delivery systems is also described along with the main challenges, key parameters, and examples of successfully translated drug delivery platforms. The essential steps on the way from drug delivery system design to clinical trials are summarized, arranged, and discussed.

Redox-responsive amphiphilic camptothecin prodrug nanoparticles for targeted liver tumor therapy

Tumor cell-targeting drug delivery systems are of great importance to anti-tumor therapy in clinics. Owing to the overexpression of the asialoglycoprotein receptor (ASGPR) on the membrane of hepatoma carcinoma cells, the conjugation of lactose on the surface of drug delivery systems has already shown significant advantages for targeting tumor cells. In this study, a disulfide bond-conjugated prodrug targeting delivery system consisting of camptothecin (CPT) and lactose (LA) was synthesized, which was denoted as CPT-S-S-LA. Camptothecin and lactose act as the chemotherapy drug and targeting ligand in the drug delivery system, respectively. Since CPT-S-S-LA is an amphiphilic compound, it can self-assemble into nanoparticles with a diameter of around 110 nm. The CPT-S-S-LA nanoparticles displayed controllable drug release behavior in the physiological environment. Unlike the free CPT, the CPT-S-S-LA nanoparticles firstly assembled at the tumor sites via the enhanced permeability and retention (EPR) effect, and then were phagocytized by the tumor cells with ASGP receptor-mediated endocytosis. Finally, the antitumor agent CPT was released for killing tumor cells, which have a high glutathione (GSH) concentration environment. The nanoparticles displayed favorable ability to target hepatoma carcinoma cells rather than the normal HUVEC cells in vitro. Both the in vitro and in vivo studies demonstrated that the CPT-S-S-LA nanoparticles display enhanced antitumor ability and reduced side effects. Thus, active targeting prodrug delivery systems should be a promising strategy for liver tumor therapy.

Thermo- and ROS-Responsive Self-Assembled Polymer Nanoparticle Tracers for 19F MRI Theranostics

Fluorine-19 magnetic resonance imaging (¹⁹F MRI) enables detailed in vivo tracking of fluorine-containing tracers and is therefore becoming a particularly useful tool in noninvasive medical imaging. In previous studies, we introduced biocompatible polymers based on the hydrophilic monomer N-(2-hydroxypropyl)methacrylamide (HPMA) and the thermoresponsive monomer N-(2,2-difluoroethyl)acrylamide (DFEA). These polymers have abundant magnetically equivalent fluorine atoms and advantageous properties as ¹⁹F MRI tracers. Furthermore, in this pilot study, we modified these polymers by introducing a redox-responsive monomer. As a result, our polymers changed their physicochemical properties once exposed to an oxidative environment. Reactive oxygen species (ROS)-responsive polymers were prepared by incorporating small amounts (0.9-4.5 mol %) of the N-[2-(ferrocenylcarboxamido)ethyl]acrylamide (FcCEA) monomer, which is hydrophobic and diamagnetic in the reduced electroneutral (Fe(II), ferrocene) state but hydrophilic and paramagnetic in the oxidized (Fe(III), ferrocenium cation) state. This property can be useful for theranostic purposes (therapy and diagnostic purposes), especially, in terms of ROS-responsive drug-delivery systems. In the reduced state, these nanoparticles remain self-assembled with the encapsulated drug but release the drug upon oxidation in ROS-rich tumors or inflamed tissues.

The Opportunities and Challenges of Silica Nanomaterial for Atherosclerosis

Atherosclerosis (AS) as the leading cause of cardiovascular and cerebrovascular events has been paid much attention all the time. With the continuous development of modern medical drug treatment, surgical treatment, interventional treatment and other methods, the mortality rate of AS has shown a downward trend, while the morbidity rate is still increasing. Oral lipid-lowering or anti-inflammatory drugs are generally used for early AS, but the relatively low accumulation efficiency in lesions and the unavoidable side effects required researchers to develop more effective drug delivery approaches for the therapy of AS. Mesoporous silica nanoparticles as nanocarrier for drug delivery have received extensive attentions due to their flexible size, high specific surface area, controlled pore volume, high drug loading capacity and excellent biocompatibility. Series of good reviews about the mesoporous silica nanoparticles loaded drugs for cancer therapy have been well documented. However, their roles as nanocarrier for drug delivery to treat AS have few reports. In this review, the applications and challenges of mesoporous silica nanomaterials in the field of the diagnosis and therapy of AS have been summarized. The classification, synthesis, formation mechanism, surface modification and functionalization of mesoporous silica nanomaterials which were closely related to the theranostic effect of AS have also been included. Last but not the least, the future prospects’ suggestions of mesoporous silica nanomaterial-based drug delivery system for AS are also provided.

Stimuli-Responsive Biomaterials for Vaccines and Immunotherapeutic Applications

The immune system is the key target for vaccines and immunotherapeutic approaches aimed at blunting infectious diseases, cancer, autoimmunity, and implant rejection. However, systemwide immunomodulation is undesirable due to the severe side effects that typically accompany such strategies. In order to circumvent these undesired, harmful effects, scientists have turned to tailorable biomaterials that can achieve localized, potent release of immune-modulating agents. Specifically, "stimuli-responsive" biomaterials hold a strong promise for delivery of immunotherapeutic agents to the disease site or disease-relevant tissues with high spatial and temporal accuracy. This review provides an overview of stimuli-responsive biomaterials used for targeted immunomodulation. Stimuli-responsive or "environmentally responsive" materials are customized to specifically react to changes in pH, temperature, enzymes, redox environment, photo-stimulation, molecule-binding, magnetic fields, ultrasound-stimulation, and electric fields. Moreover, the latest generation of this class of materials incorporates elements that allow for response to multiple stimuli. These developments, and other stimuli-responsive materials that are on the horizon, are discussed in the context of controlling immune responses.

Influence of the Surface Functionalization on the Fate and Performance of Mesoporous Silica Nanoparticles

Mesoporous silica nanoparticles have been broadly applied as drug delivery systems owing to their exquisite features, such as excellent textural properties or biocompatibility. However, there are various biological barriers that prevent their proper translation into the clinic, including: (1) lack of selectivity toward tumor tissues, (2) lack of selectivity for tumoral cells and (3) endosomal sequestration of the particles upon internalization. In addition, their open porous structure may lead to premature drug release, consequently affecting healthy tissues and decreasing the efficacy of the treatment. First, this review will provide a comprehensive and systematic overview of the different approximations that have been implemented into mesoporous silica nanoparticles to overcome each of such biological barriers. Afterward, the potential premature and non-specific drug release from these mesoporous nanocarriers will be addressed by introducing the concept of stimuli-responsive gatekeepers, which endow the particles with on-demand and localized drug delivery.

Therapeutic Nanoparticles and Their Targeted Delivery Applications

Nanotechnology offers many advantages in various fields of science. In this regard, nanoparticles are the essential building blocks of nanotechnology. Recent advances in nanotechnology have proven that nanoparticles acquire a great potential in medical applications. Formation of stable interactions with ligands, variability in size and shape, high carrier capacity, and convenience of binding of both hydrophilic and hydrophobic substances make nanoparticles favorable platforms for the target-specific and controlled delivery of micro- and macromolecules in disease therapy. Nanoparticles combined with the therapeutic agents overcome problems associated with conventional therapy; however, some issues like side effects and toxicity are still debated and should be well concerned before their utilization in biological systems. It is therefore important to understand the specific properties of therapeutic nanoparticles and their delivery strategies. Here, we provide an overview on the unique features of nanoparticles in the biological systems. We emphasize on the type of clinically used nanoparticles and their specificity for therapeutic applications, as well as on their current delivery strategies for specific diseases such as cancer, infectious, autoimmune, cardiovascular, neurodegenerative, ocular, and pulmonary diseases. Understanding of the characteristics of nanoparticles and their interactions with the biological environment will enable us to establish novel strategies for the treatment, prevention, and diagnosis in many diseases, particularly untreatable ones.

Stimuli-responsive nanocarriers for drug delivery, tumor imaging, therapy and theranostics

In recent years, much progress has been motivated in stimuli-responsive nanocarriers, which could response to the intrinsic physicochemical and pathological factors in diseased regions to increase the specificity of drug delivery. Currently, numerous nanocarriers have been engineered with physicochemical changes in responding to external stimuli, such as ultrasound, thermal, light and magnetic field, as well as internal stimuli, including pH, redox potential, hypoxia and enzyme, etc. Nanocarriers could respond to stimuli in tumor microenvironments or inside cancer cells for on-demanded drug delivery and accumulation, controlled drug release, activation of bioactive compounds, probes and targeting ligands, as well as size, charge and conformation conversion, etc., leading to sensing and signaling, overcoming multidrug resistance, accurate diagnosis and precision therapy. This review has summarized the general strategies of developing stimuli-responsive nanocarriers and recent advances, presented their applications in drug delivery, tumor imaging, therapy and theranostics, illustrated the progress of clinical translation and made prospects.

Polymeric nanocarriers as stimuli-responsive systems for targeted tumor (cancer) therapy: Recent advances in drug delivery

In the last decade, considerable attention has been devoted to the use of biodegradable polymeric materials as potential drug delivery carriers. However, bioavailability and drug release at the disease site remain uncontrollable even with the use of polymeric nanocarriers. To address this issue, successful methodologies have been developed to synthesize polymeric nanocarriers incorporated with regions exhibiting a response to stimuli such as redox potential, temperature, pH, and light. The resultant stimuli-responsive polymeric nanocarriers have shown tremendous promise in drug delivery applications, owing to their ability to enhance the bioavailability of drugs at the disease site. In such systems, drug release is controlled in response to specific stimuli, either exogenous or endogenous. This review reports recent advances in the design of stimuli-responsive nanocarriers for drug delivery in cancer therapy. In particular, the synthetic methodologies investigated to date to introduce different types of stimuli-responsive elements within the biomaterials are described. The sufficient understanding of these stimuli-responsive nanocarriers will allow the development of a better drug delivery system that will allow us to solve the challenges encountered in targeted cancer therapy.

Size-adaptable and ligand (biotin)-sheddable nanocarriers equipped with avidin scavenging technology for deep tumor penetration and reduced toxicity

The conventional active-targeting nano-chemotherapy suffers from poor tumor tissue penetration and non-negligible toxicity due to the size/ligand dilemmas and insufficient target selectivity. In this report, a stimuli-responsive size-adaptable and ligand (biotin)-sheddable drug delivery system (DDS) combined with two-step strategy of biotin-avidin system was designed to seek a balance between tumor targeting and penetration as well as to self-scavenge the nonresponsive nanocarriers in normal tissues. This DDS was composed of 'multi-seed' polymeric liposomes (ASL-BIO-MPL) with asulacrine-loaded micelles as seeds in their aqueous cavities. The shell of such liposomes was modified with MMP-9 cleavable polymer-polypeptide functionalized with the tumor targeting ligand biotin. ASL-BIO-MPL could disintegrate into mixture of irregularly-shaped liposomes (~200 nm) and scattered tiny micelles (~40 nm) after incubation with MMP-9. The fluorescence-labeled BIO-MPL could travel to the center of the 4T1 breast tumor spheroids under the action of MMP-9, possibly benefited from the relay of released tiny micelles. Conversely, neither the biotin-modified micelles nor non-MMP-9-responsive multi-seed liposomes could penetrate into the spheroids possibly due to the potent binding-site barrier of biotin and large size, respectively. In tumor-bearing mice, ASL-BIO-MPL exhibited the strongest drug penetrability and thus the optimal inhibition of tumor growth compared to other formulations. Following administration of avidin with a rational dosage regimen, the number of apoptotic cells in normal tissues induced by ASL-BIO-MPL reduced without affecting their targeting effect, suggesting the followed administration of adivin could scavenge the DDS in non-target site. Overall, the size/ligand adapting MPL system combined with two-step strategy of biotin-avidin may provide potential avenues for nanocarriers to enhance deep tumor tissue targeting and protect normal tissues.

Mesoporous Silica Nanoparticles for the Treatment of Complex Bone Diseases: Bone Cancer, Bone Infection and Osteoporosis

Bone diseases, such as bone cancer, bone infection and osteoporosis, constitute a major issue for modern societies as a consequence of their progressive ageing. Even though these pathologies can be currently treated in the clinic, some of those treatments present drawbacks that may lead to severe complications. For instance, chemotherapy lacks great tumor tissue selectivity, affecting healthy and diseased tissues. In addition, the inappropriate use of antimicrobials is leading to the appearance of drug-resistant bacteria and persistent biofilms, rendering current antibiotics useless. Furthermore, current antiosteoporotic treatments present many side effects as a consequence of their poor bioavailability and the need to use higher doses. In view of the existing evidence, the encapsulation and selective delivery to the diseased tissues of the different therapeutic compounds seem highly convenient. In this sense, silica-based mesoporous nanoparticles offer great loading capacity within their pores, the possibility of modifying the surface to target the particles to the malignant areas and great biocompatibility. This manuscript is intended to be a comprehensive review of the available literature on complex bone diseases treated with silica-based mesoporous nanoparticles-the further development of which and eventual translation into the clinic could bring significant benefits for our future society.

Intracellular Restructured Reduced Glutathione-Responsive Peptide Nanofibers for Synergetic Tumor Chemotherapy

Self-assembled peptide nanofibers have been widely studied in cancer nanotherapeutics with their excellent biocompatibility and low toxicity of degradation products, showing the significant potential in inhibiting tumor progression. However, poor solubility prevents direct intravenous administration of nanofibers. Although water-soluble peptide precursors have been formed via the method of phosphorylation for intravenous administration, their opportunities for broad in vivo application are limited by the weak capacity of encapsulating drugs. Herein, we designed a novel restructured reduced glutathione (GSH)-responsive drug delivery system encapsulating doxorubicin for systemic administration, which achieved the intracellular restructuration from three-dimensional micelles into one-dimensional nanofibers. After a long blood circulation, micelles endocytosed by tumor cells could degrade in response to high GSH levels, achieving more release and accumulation of doxorubicin at desired sites. Further, the synergistic chemotherapy effects of self-assembled nanofibers were confirmed in both in vitro and in vivo experiments.

A magnetic nanoparticle functionalized reduced graphene oxide-based drug carrier system for a chemo-photodynamic cancer therapy

The proposed work shows the dual therapeutic impact of an external stimulus responsive CPT loaded MrGO-AA-g-4-HC carrier system for cancer treatments.

Magnetically Stimulated Drug Release Using Nanoparticles Capped by Self-Assembling Peptides

A novel self-assembling peptide-functionalized core-shell mesoporous silica nanoparticle was developed as a drug carrier. Superparamagnetic manganese- and cobalt-doped iron oxide nanoparticles formed the core for the mesoporous silica shell coating. On the silica outer shell, the peptide Boc-Phe-Phe-Gly-Gly-COOH was covalently conjugated by 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride and N-hydroxysulfosuccinimide sodium salt coupling. The self-assembling property of the peptide at physiological temperature was utilized to block the pore openings, while the disassembly at elevated local particle temperature released cargo molecules without bulk heating that would cause cell damage. Both conventional heating and heating in an alternating magnetic field were tested for the release of fluorescein and daunorubicin. In vitro experiments showed high cytotoxicity on pancreatic carcinoma cells (PANC-1) when this delivery system was activated by an alternating magnetic field, while control particles without drugs showed no obvious cytotoxicity.

Therapeutic impacts of enzyme-responsive smart nanobiosystems

An important arena of the sophisticated nanosystems (NSs) is the combination of the responsive features of NSs with the biocatalytic properties of enzymes. The development of such smart drug delivery systems (DDSs) has seminal effectiveness in targeting, imaging, and monitoring of cancer. These NSs can exhibit site-specific delivery of the toxic cargo in response to the endogenous/exogenous stimuli. Enzyme responsive/targeted DDSs display enhanced accumulation of cargo molecules in the tumor microenvironment (TME) with a spatiotemporal controlled-release behavior. Based on the unique features of enzyme responsive/targeted DDSs, they offer incredible promise in overcoming some limitations of the currently used conventional DDSs. Taken all, targeting TME with the enzyme-responsive targeted DDSs may lead to versatile clinical outcomes in various malignancies.

Targeted and stimuli-responsive mesoporous silica nanoparticles for drug delivery and theranostic use

For cancer therapy, the usefulness of mesoporous silica nanoparticles (MPSNPs) has been widely discussed, likely due to its inorganic nature and excellent structural features. The MPSNPs-based chemotherapeutics have been promisingly delivered to their target sites that help to minimize side effects and improve therapeutic effectiveness. A wide array of studies have been conducted to functionalize drug-loaded MPSNPs using targeting ligands and stimuli-sensitive substances. In addition, anticancer drugs have been precisely delivered to their target sites using MPSNPs, which respond to multi-stimuli. Furthermore, MPSNPs have been extensively tested for their safety and compatibility. The toxicity level of MPSNPs is substantially lower as compared to that of colloidal silica; however, in oxidative stress, they exhibit cytotoxic features. The biocompatibility of MPSNPs can be improved by modifying their surfaces. This article describes the production procedures, functionalization, and applications of biocompatible MPSNPs in drug delivery.

Enzyme responsive drug delivery systems in cancer treatment

Recent technological approaches in drug delivery have attracted scientist interest for improving therapeutic index of medicines and drug compliance. One of the powerful strategies to control the transportation of drugs is implementation of intelligent stimuli-responsive drug delivery system (DDS). In this regard, tumor tissues with unique characteristics including leaky vasculature and diverse enzyme expression profiles facilitate the development of efficient enzyme-responsive nanoscale delivery systems. Based on the stimuli nature (physical, chemical and biological), these systems can be categorized into three groups according to the nature of trigger initiating the drug release. Enzymes are substantial constituents of the biotechnology toolbox offering promising capabilities and ideal characteristics to accelerate chemical reactions. Nanoparticles which have the ability to trigger their cargo release in the presence of specific enzymes are fabricated implementing fascinating physico-chemical properties of different materials in a nanoscale dimension. In order to reduce the adverse effects of the therapeutic agents, nanocarriers can be utilized and modified with enzyme-labile linkages to provide on-demand enzyme-responsive drug release. In the current review, we give an overview of drug delivery systems which can deliver drugs to the tumor microenvironment and initiate the drug release in response to specific enzymes highly expressed in particular tumor tissues. This strategy offers a versatile platform for intelligent drug release at the site of action.

Controlled drug delivery systems for cancer based on mesoporous silica nanoparticles

The implementation of nanotechnology in medicine has opened new research horizons particularly in the field of therapeutic delivery. Mesoporous silica particles have emerged as biocompatible drug delivery systems with an enormous potential in the treatment of cancer among many other pathologies. In this review, we focus on the unique properties of these particles as chemotherapy delivery carriers. Here, we summarize the general characteristics of these nanomaterials - including their physicochemical properties and customizable surfaces - different stimuli that can be used to trigger targeted drug release, biocompatibility and finally, the drawbacks of these types of nanomaterials, highlighting some of the most important features of mesoporous silica nanoparticles in drug delivery.

Advances in mesoporous silica nanoparticles for targeted stimuli-responsive drug delivery: an update

INTRODUCTION

Mesoporous silica nanoparticles (MSNs) are outstanding nanoplatforms for drug delivery. Herein, the most recent advances to turn MSN-based carriers into minimal side effect drug delivery agents are covered.

AREAS COVERED

This review summarizes the scientific advances dealing with MSNs for targeted and stimuli-responsive drug delivery since 2015. Delivery aspects to diseased tissues together with approaches to obtain smart MSNs able to respond to internal or external stimuli and their applications are here described. Special emphasis is done on the combination of two or more stimuli on the same nanoplatform and on combined drug therapy.

EXPERT OPINION

The use of MSNs in nanomedicine is a promising research field because they are outstanding platforms for treating different pathologies. This is possible thanks to their structural, chemical, physical and biological properties. However, there are certain issues that should be overcome to improve the suitability of MSNs for clinical applications. All materials must be properly characterized prior to their in vivo evaluation; furthermore, preclinical in vivo studies need to be standardized to demonstrate the MSNs clinical translation potential.

Stimulus-responsive nanoscale delivery systems triggered by the enzymes in the tumor microenvironment

The tumor microenvironment is the cellular environment that is also described as the "soil" for supporting tumor growth, proliferation, invasion and metastasis, as well as protecting tumor cells from immunological recognition. Notably, tumor cells can grow much faster than other normal organs and invade surrounding tissues more easily, which results in abnormal expression of enzymes in the tumor microenvironment, including matrix metalloproteinases, cathepsins, phospholipases, oxidoreductases, etc. In opposite, due to the high selectivity and catalytic activity, these enzymes can promote nanoparticles to recognize tumor tissues more accurately, and the more accumulation of drugs at primal tumor sites will enhance therapeutic efficacy with lower systemic toxicity. Therefore, one promising antitumor strategy is to design stimulus-responsive nanoscale delivery systems triggered by the enzymes with the support of various nanocarriers, such as liposomes, micelles and inorganic nanoparticles, etc. In this review, numerous facts were cited to summarize and discuss the typical types of enzyme-stimulus responsive nanoscale delivery systems. More importantly, we also focused on their recent advancements in antitumor therapy, and offered the direction for further studies.

Exogenous/Endogenous-Triggered Mesoporous Silica Cancer Nanomedicine

Recent advances in nanomedicine-based theranostic platforms have catalyzed the generation of new theranostic modalities for pathological abnormalities, such as cancer. Mesoporous silica-based nanomedicines, which feature unique physicochemical properties and specific applicability, are extensively explored for numerous oncological applications. Due to the well-defined morphology, specific surface area, and pore volume, mesoporous silica nanoparticle (MSN)-based theranostic platforms have provided unprecedented opportunities for the development of next-generation cancer nanomedicine. However, current understanding on the underlying mechanisms of how these feasible theranostic platforms interact with exogenous/endogenous triggers and how this unique responsiveness for optimized cancer therapy can be taken advantage of is still preliminary. In this progress report, efforts are made to give a comprehensive overview of the development of MSN-based "smart" theranostic platforms, from exogenous physical irradiation-triggered platforms for localized therapy to endogenous biological stimulus-triggered platforms for tumor microenvironment responsiveness. It is highly expected that these elaborately fabricated MSN-based nanoformulations will play an indispensable role in the efficient cancer therapy based on their high therapeutic outcome and reduced side effects.

Stimuli-Responsive Polypeptides for Biomedical Applications

Stimuli-responsive polypeptides have gained attention because desirable bioactive properties can be easily imparted to them while keeping their biocompatibility and biodegradability intact. In this review, we summarize the most recent advances in various stimuli-responsive polypeptides (pH, reduction, oxidation, glucose, adenosine triphosphate (ATP), and enzyme) over the past five years. Various synthetic strategies exploited for advanced polypeptide-based materials are introduced, and their applicability in biomedical fields is discussed. The recent polypeptides imparted with new stimuli-responsiveness and their novel chemical and physical properties are explained in this review.

Approaches to improve the biocompatibility and systemic circulation of inorganic porous nanoparticles

The exploitation of various inorganic nanoparticles as drug carriers and therapeutics is becoming increasingly common. The first issue to be considered with regard to the nanomaterials being utilized in medicine centers on their safety. The functionality of nanocarriers in real-life environments explains the enthusiasm for their use. Several functionalities are typically added onto nanocarriers but the most crucial feature of those carriers intended to be administered intravenously is that they should possess a long residence time in blood circulation. The present review focusses on the mesoporous nanoparticles due to their great promise in nanomedicine and concentrates on their coatings because it is the outmost layer which dictates their first interactions with the surroundings and often determines their biofate.

Beyond Traditional Hyperthermia: In Vivo Cancer Treatment with Magnetic-Responsive Mesoporous Silica Nanocarriers

In this study, we present an innovation in the tumor treatment in vivo mediated by magnetic mesoporous silica nanoparticles. This device was built with iron oxide magnetic nanoparticles embedded in a mesoporous silica matrix and coated with an engineered thermoresponsive polymer. The magnetic nanoparticles act as internal heating sources under an alternating magnetic field (AMF) that increase the temperature of the surroundings, provoking the polymer transition and consequently the release of a drug trapped inside the silica pores. By a synergic effect between the intracellular hyperthermia and chemotherapy triggered by AMF application, significant tumor growth inhibition was achieved in 48 h after treatment. Furthermore, the small magnetic loading used in the experiments indicates that the treatment is carried out without a global temperature rise of the tissue, which avoids the problem of the necessity to employ large amounts of magnetic cores, as is common in current magnetic hyperthermia.

Matrix Metalloproteinase-9-Responsive Nanogels for Proximal Surface Conversion and Activated Cellular Uptake

Here, we have exploited the heightened extracellular concentration of matrix metalloproteinase-9 (MMP-9) to induce surface-conversional properties of nanogels with the aim of tumor-specific enhanced cellular uptake. A modular polymeric nanogel platform was designed and synthesized for facile formulation and validation of MMP-9-mediated dePEGylation and generation of polyamine-type surface characteristics through peptide N-termini. Nanogels containing MMP-9-cleavable motifs and different poly(ethylene glycol) corona lengths (350 and 750 g/mol) were prepared, and enzymatic surface conversional properties were validated by MALDI characterization of cleaved byproducts, fluorescamine assay amine quantification, and zeta potential. The nanogel with a shorter PEG length, mPEG350-NG, exhibited superior surface conversion in response to extracellular concentrations of MMP-9 compared to that of the longer PEG length, mPEG750-NG. Confocal microscopy images of HeLa cells incubated with both fluorescein-labeled nanogels and DiI-encapsulated nanogels demonstrated greater uptake following MMP-9 "activation" for mPEG350-NG compared to its nontreated "passive" mPEG350-NG parent, demonstrating the versatility of such systems to achieve stimuli-responsive uptake in response to cancer-relevant proteases.

Mesoporous silica nanoparticles for drug and gene delivery

Mesoporous silica nanoparticles (MSNs) are attracting increasing interest for potential biomedical applications. With tailored mesoporous structure, huge surface area and pore volume, selective surface functionality, as well as morphology control, MSNs exhibit high loading capacity for therapeutic agents and controlled release properties if modified with stimuli-responsive groups, polymers or proteins. In this review article, the applications of MSNs in pharmaceutics to improve drug bioavailability, reduce drug toxicity, and deliver with cellular targetability are summarized. Particularly, the exciting progress in the development of MSNs-based effective delivery systems for poorly soluble drugs, anticancer agents, and therapeutic genes are highlighted.

Mesoporous Silica and Organosilica Nanoparticles: Physical Chemistry, Biosafety, Delivery Strategies, and Biomedical Applications

Predetermining the physico-chemical properties, biosafety, and stimuli-responsiveness of nanomaterials in biological environments is essential for safe and effective biomedical applications. At the forefront of biomedical research, mesoporous silica nanoparticles and mesoporous organosilica nanoparticles are increasingly investigated to predict their biological outcome by materials design. In this review, it is first chronicled that how the nanomaterial design of pure silica, partially hybridized organosilica, and fully hybridized organosilica (periodic mesoporous organosilicas) governs not only the physico-chemical properties but also the biosafety of the nanoparticles. The impact of the hybridization on the biocompatibility, protein corona, biodistribution, biodegradability, and clearance of the silica-based particles is described. Then, the influence of the surface engineering, the framework hybridization, as well as the morphology of the particles, on the ability to load and controllably deliver drugs under internal biological stimuli (e.g., pH, redox, enzymes) and external noninvasive stimuli (e.g., light, magnetic, ultrasound) are presented. To conclude, trends in the biomedical applications of silica and organosilica nanovectors are delineated, such as unconventional bioimaging techniques, large cargo delivery, combination therapy, gaseous molecule delivery, antimicrobial protection, and Alzheimer's disease therapy.

Superparamagnetic iron oxide nanocargoes for combined cancer thermotherapy and MRI applications

Nanoparticle-based cancer diagnosis-therapy integrative systems (cancer theranostics) represent an emerging approach in oncology. To address this issue in the present work iron oxide (γ-Fe2O3-maghemite) nanoparticles (IONPs) were encapsulated within the matrix of (bis(p-sulfonatophenyl)phenylphosphine)-methoxypolyethylene glycol-thiol (mPEG) polymer vesicles using a two-step process for active chemotherapeutic cargo loading in cancer theranostics. This formation method gives simple access to highly reactive surface groups present on IONPs together with good control over the vesicle size (50-100 nm). The simultaneous loading of a chemotherapeutic drug cargo (doxorubicin) and its in vitro release in cancer cells was achieved. The feasibility of controlled drug release under different pH conditions was demonstrated in the case of encapsulated doxorubicin molecules, showing the viability of the concept of stimulated drug delivery for magneto-chemotherapy. These polymer-magnetic nanocargoes (PMNCs) exhibit enhanced contrast properties that open potential applications for magnetic resonance imaging. These self-assembled magnetic polymersomes can be used as efficient multifunctional nanocarriers for combined therapy and imaging.

One-pot synthesis of biodegradable polydopamine-doped mesoporous silica nanocomposites (PMSNs) as pH-sensitive targeting drug nanocarriers for synergistic chemo-photothermal therapy

Polydopamine-doped mesoporous silica nanocomposites (PMSNs) were controllably synthesized by a one-pot approach. They were demonstrated to be good biodegradability, pH-responsive drug release and targeting synergistic chemo-photothermal therapy.

Mesoporous Silica Nanoparticles

Integration of nanotechnology and biomedicine has offered great opportunities for the development of nanoscaled therapeutic platforms. Amongst various nanocarriers, mesoporous silica nanoparticles (MSNs) is one of the most developed and promising inorganic materials-based drug delivery system for clinical translations due to their simple composition and nanoporous structure. MSNs possess unique structural features, for example, well-defined morphology, large surface areas, uniform size, controllable structure, flexible pore volume, tunable pore sizes, extraordinarily high loading efficiency, and excellent biocompatibility. Progress in structure control and functionalization may endow MSNs with functionalities that enable medical applications of these integrated nanoparticles such as molecularly targeted drug delivery, multicomponent synergistic therapy, in vivo imaging and therapeutic capability, on-demand/stimuli-responsive drug release, etc. In this chapter, the authors overview MSNs' characteristics and the scientific efforts developed till date involving drug delivery and biomedical applications.