Mesoporous silica nanoparticle-based intelligent drug delivery system for bienzyme-responsive tumour targeting and controlled release

Identification of pancreatic cancer-specific protease substrates for protease-dependent targeted delivery

Pancreatic ductal adenocarcinoma (PDAC) presents significant challenges due to the inadequacy of existing chemotherapeutics, which often result in toxicity-dependent dose limitations and premature cessation of therapy. Targeted delivery of therapeutic molecules offers a promising solution. Given that PDAC is marked by a desmoplastic reaction with extensive aberrant protease activity, protease-dependent targeted delivery could minimize off-target toxicities and is of increasing interest. The efficacy of targeted delivery hinges on the specificity of the substrates used; insufficient specificity can lead to off-target effects, reducing the advantage over non-targeted methods. Here, we employ an unbiased library approach to screen over 7 million peptide substrates for proteolytic cleavage by PDAC cell lysates, identifying 37 substrates enriched by at least 500-fold after three rounds of selection. As systemically administered targeted delivery depends on the absence of substrate cleavage in circulation, the peptide library was also screened against whole blood lysates, and enriched substrates were removed from the PDAC-enriched dataset to obtain PDAC-specific substrates. In vitro validation using FRET-peptides showed that 13 of the selected 15 substrates are cleaved by a panel of PDAC cell line lysates. Moreover, evaluation against healthy murine organ and human blood lysates to assess off-target cleavage revealed that the identified substrates are indeed PDAC-specific and that several substrates may be superior with respect to PDAC specificity over the CAPN2-responsive substrate, which has recently shown preclinical potential in targeted therapy, but future animal models should address the potential superiority. Overall, we thus identified substrates with high selectivity and sensitivity for PDAC that could be employed in protease-dependent targeted therapies.

Biopolymer-based tumor microenvironment-responsive nanomedicine for targeted cancer therapy

Nanomedicine has opened up new avenues for cancer treatment by enhancing drug solubility, permeability and targeted delivery to cancer cells. Despite its numerous advantages over conventional therapies, nanomedicine may exhibit off-target drug distribution, harming nontarget regions. The increased permeation and retention effect of nanomedicine in tumor sites also has its limitations, as abnormal tumor vasculature, dense stroma structure and altered tumor microenvironment (TME) may result in limited intratumor distribution and therapeutic failure. However, TME-responsive nanomedicine has exhibited immense potential for efficient, safe and precise delivery of therapeutics utilizing stimuli specific to the TME. This review discusses the mechanistic aspects of various TME-responsive biopolymers and their application in developing various types of TME-responsive nanomedicine.

A review of matrix metalloproteinase-2-sensitive nanoparticles as a novel drug delivery for tumor therapy

Matrix metalloproteinase-2 (MMP-2)-responsive nanodrug vehicles have garnered significant attention as antitumor drug delivery systems due to the extensive research on matrix metalloproteinases (MMPs) within the tumor extracellular matrix (ECM). These nanodrug vehicles exhibit stable circulation in the bloodstream and accumulate specifically in tumors through various mechanisms. Upon reaching tumor tissues, their structures are degraded in response to MMP-2 within the ECM, resulting in drug release. This controlled drug release significantly increases drug concentration within tumors, thereby enhancing its antitumor efficacy while minimizing side effects on normal organs. This review provides an overview of MMP-2 characteristics, enzyme-sensitive materials, and current research progress regarding their application as MMP-2-responsive nanodrug delivery system for anti-tumor drugs, as well as considering their future research prospects. In conclusion, MMP-2-sensitive drug delivery carriers have a broad application in all kinds of nanodrug delivery systems and are expected to become one of the main means for the clinical development and application of nanodrug delivery systems in the future.

Environmental stimulus-responsive mesoporous silica nanoparticles as anticancer drug delivery platforms

Currently, cancer poses a significant health challenge in the medical community. Traditional chemotherapeutic agents are often accompanied by toxic side effects and limited therapeutic efficacy, restricting their application and advancement in cancer treatment. Therefore, there is an urgent need for developing intelligent drug release systems. Mesoporous silica nanoparticles (MSNs) have many advantages, such as a large specific surface area, substantial pore volume and size, adjustable mesoporous material pore size, excellent biocompatibility, and thermodynamic stability, making them ideal carriers for drug delivery and release. Additionally, they have been widely used to develop novel anticancer drug carriers. Recently, MSNs have been employed to design responsive systems that react to the tumor microenvironment and external stimuli for controlled release of anticancer drugs. This includes factors within the intratumor environment, such as pH, temperature, enzymes, and glutathione as well as external tumor stimuli, such as light, magnetic field, and ultrasound, among others. In this review, we discuss the research progress on environmental stimulus-responsive MSNs in anticancer drug delivery systems, including internal and external environment single stimulus-responsive release and combined stimulus-responsive release. We also summarize the current challenges associated with environmental stimulus-responsive MSNs and elucidate future directions, providing a reference for the functionalization modification and practical application of these MSNs.

Engineered mesoporous silica nanoparticles, new insight nanoplatforms into effective cancer gene therapy

The use of nucleic acid to control the expression of genes relevant to tumor progression is a key therapeutic approach in cancer research. Therapeutics based on nucleic acid provide novel concepts for untreatable targets. Nucleic acids as molecular medications must enter the target cell to be effective and obstacles in the systemic delivery of DNA or RNA limit their use in a clinical setting. The creation of nucleic acid delivery systems based on nanoparticles in order to circumvent biological constraints is advancing quickly. The ease of synthesis and surface modification, biocompatibility, biodegradability, cost-effectiveness and high loading capability of nucleic acids have prompted the use of mesoporous silica nanoparticles (MSNs) in gene therapy. The unique surface features of MSNs facilitate their design and decoration for high loading of nucleic acids, immune system evasion, cancer cell targeting, controlled cargo release, and endosomal escape. Reports have demonstrated successful therapeutic outcomes with the administration of a variety of engineered MSNs capable of delivering genes to tumor sites in laboratory animals. This comprehensive review of studies about siRNA, miRNA, shRNA, lncRNA and CRISPR/Cas9 delivery by MSNs reveals engineered MSNs as a safe and efficient system for gene transfer to cancer cells and cancer mouse models.

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.

Recent Advances in Nanomaterials of Group XIV Elements of Periodic Table in Breast Cancer Treatment

Breast cancer is one of the most common malignancies and a leading cause of cancer-related mortality among women worldwide. The elements of group XIV in the periodic table exhibit a wide range of chemical manners. Recently, there have been remarkable developments in the field of nanobiomedical research, especially in the application of engineered nanomaterials in biomedical applications. In this review, we concentrate on the recent investigations on the antiproliferative effects of nanomaterials of the elements of group XIV in the periodic table on breast cancer cells. In this review, the data available on nanomaterials of group XIV for breast cancer treatment has been documented, providing a useful insight into tumor biology and nano-bio interactions to develop more effective nanotherapeutics for cancer patients.

Application of Mesoporous Silica Nanoparticle-Chitosan-Loaded BMP-2 in the Repair of Bone Defect in Chronic Osteomyelitis

In order to test the effectiveness of nanoparticle- (NP-) loaded bone morphogenetic protein 2 (BMP-2) in chronic osteomyelitis (CO) complicated with bone defect, a new nanodrug delivery system composed of mesoporous silica NP (MSN) and chitosan were used to load BMP-2 and transfer it to the target region. Bone marrow mesenchymal stem cells (BMSCs) were purchased and cultivated to detect the osteogenesis of chitosan-MSN (Chi-MSN) and polylactic acid glycolic acid (PLGA) delivery system. In addition, the osteogenesis of Chi-MSN was further determined by constructing a bone defect mouse model. In physicochemical property test, we found Chi-MSN NPs could effectively maintain stability in vivo and had pH response characteristics. As a result, the release efficiency of dexamethasone (Dex) and BMP-2 in the environment with pH 7.4 was less, while it increased significantly in pH 6, so as to reduce the BMP-2 and Dex loss during transportation in vivo. Otherwise, we found that the permeation efficiency of Chi-MSN was significantly higher than that of PLGA delivery system, so as to effectively transport BMP-2 and Dex to action target. In the BMSC test, we found that Chi-MSN could better promote their activity and osteogenesis, and the expression of osteogenesis-related genes (runt-related transcription factor 2 (RUNX-2), osteopontine (OPN), alkaline phosphatase (ALP), and osteopontine (OCN)) in the Chi-MSN group was higher. In the bone defect mouse model test, we also found obviously increased bone trabecula number and thickness by Chi-MSN, contributing to better repair of bone defects. Therefore, BMP-2@Chi-MSN may be a better choice for the therapy of CO complicated with bone defect in the future.

Functionalization of Nanoparticulate Drug Delivery Systems and Its Influence in Cancer Therapy

Research into the application of nanocarriers in the delivery of cancer-fighting drugs has been a promising research area for decades. On the other hand, their cytotoxic effects on cells, low uptake efficiency, and therapeutic resistance have limited their therapeutic use. However, the urgency of pressing healthcare needs has resulted in the functionalization of nanoparticles' (NPs) physicochemical properties to improve clinical outcomes of new, old, and repurposed drugs. This article reviews recent research on methods for targeting functionalized nanoparticles to the tumor microenvironment (TME). Additionally, the use of relevant engineering techniques for surface functionalization of nanocarriers (liposomes, dendrimers, and mesoporous silica) and their critical roles in overcoming the current limitations in cancer therapy-targeting ligands used for targeted delivery, stimuli strategies, and multifunctional nanoparticles-were all reviewed. The limitations and future perspectives of functionalized nanoparticles were also finally discussed. Using relevant keywords, published scientific literature from all credible sources was retrieved. A quick search of the literature yielded almost 400 publications. The subject matter of this review was addressed adequately using an inclusion/exclusion criterion. The content of this review provides a reasonable basis for further studies to fully exploit the potential of these nanoparticles in cancer therapy.

Protease-triggered bioresponsive drug delivery for the targeted theranostics of malignancy

Proteases have a fundamental role in maintaining physiological homeostasis, but their dysregulation results in severe activity imbalance and pathological conditions, including cancer onset, progression, invasion, and metastasis. This striking importance plus superior biological recognition and catalytic performance of proteases, combining with the excellent physicochemical characteristics of nanomaterials, results in enzyme-activated nano-drug delivery systems (nanoDDS) that perform theranostic functions in highly specific response to the tumor phenotype stimulus. In the tutorial review, the key advances of protease-responsive nanoDDS in the specific diagnosis and targeted treatment for malignancies are emphatically classified according to the effector biomolecule types, on the premise of summarizing the structure and function of each protease. Subsequently, the incomplete matching and recognition between enzyme and substrate, structural design complexity, volume production, and toxicological issues related to the nanocomposites are highlighted to clarify the direction of efforts in nanotheranostics. This will facilitate the promotion of nanotechnology in the management of malignant tumors.

Mesoporous Silica Nanoparticles: Properties and Strategies for Enhancing Clinical Effect

Due to the theragnostic potential of mesoporous silica nanoparticles (MSNs), these were extensively investigated as a novel approach to improve clinical outcomes. Boasting an impressive array of formulations and modifications, MSNs demonstrate significant in vivo efficacy when used to identify or treat myriad malignant diseases in preclinical models. As MSNs continue transitioning into clinical trials, a thorough understanding of the characteristics of effective MSNs is necessary. This review highlights recent discoveries and advances in MSN understanding and technology. Specific focus is given to cancer theragnostic approaches using MSNs. Characteristics of MSNs such as size, shape, and surface properties are discussed in relation to effective nanomedicine practice and projected clinical efficacy. Additionally, tumor-targeting options used with MSNs are presented with extensive discussion on active-targeting molecules. Methods for decreasing MSN toxicity, improving site-specific delivery, and controlling release of loaded molecules are further explained. Challenges facing the field and translation to clinical environments are presented alongside potential avenues for continuing investigations.

Folic acid-hydrophilic polymer coated mesoporous silica nanoparticles target doxorubicin delivery

Mesoporous silica nanoparticles (MSNs) gained significant attention, particularly in the pharmaceutical field. Folic acid (FA) shows marked promise as a targeting agent for its specific interaction with the folate receptor. This receptor is over-expressed on the cell surface of several cancerous cells like breast cancer. Polyethylene glycol (PE), as well as polypropylene glycol (PEG), is used to decorate nanoparticles to improve their biodistribution. Moreover, carboxymethyl beta-cyclodextrin (CM-β-CD), is used as a complexation molecule. In this study, we described the chemical synthesis, in vitro drug release and antiproliferative activity of doxorubicin-loaded/decorated MSNs further coupled with FA in two conditions: chemically bound or as a complex with CM-β-CD. Fourier Transform Infrared Spectroscopy with Transmission Electron Microscopy confirmed the successful surface change. Dynamic Light Scattering confirmed the change in surface characters like zeta potential, polydispersity index (PI), and size. PI improved from 0.58 to 0.23 while the size enlarged from 200 to 348 and 532 nm. Functionalized nanoparticles demonstrated more significant drug entrapment with (97%) while undecorated MSNs only showed (63%). Accordingly, we effectively synthesized FA-PEG2000-MSNs with IC₅₀: 0.015 mg/mL targeting HeLa cells. This approach may allow potential applications as a drug delivery system in cancer chemotherapy.HighlightsMesoporous silica nanoparticles (MSNs) with a carboxylic acid or amine surface group can be successfully decorated with long-chain hydrophilic polymer via an amide bond.Carboxymethyl-β-cyclodextrin coupled with long-chain polymer as host to form a complex with targeting molecule folic acid.Folic acid can be anchored directly to a polymer coat.TEM; DLS and FTIR confirmed the surface modification.The drug encapsulation efficiency; cytotoxicity and selectivity of functionalized nanoparticles with PEG and conjugated with FA were the best.Chemical modification has improved cytotoxicity of doxorubicin and selectivity against Hela cells.

Photothermal/matrix metalloproteinase-2 dual-responsive gelatin nanoparticles for breast cancer treatment

The chemotherapy combined with photothermal therapy has been a favorable approach for the treatment of breast cancer. In present study, nanoparticles with the characteristics of photothermal/matrix metalloproteinase-2 (MMP-2) dual-responsive, tumor targeting, and size-variability were designed for enhancing the antitumor efficacy and achieving "on-demand" drug release markedly. Based on the thermal sensitivity of gelatin, we designed a size-variable gelatin nanoparticle (GNP) to encapsulate indocyanine green (ICG) and doxorubicin (DOX). Under an 808 nm laser irradiation, GNP-DOX/ICG responded photothermally and swelled in size from 71.58 ± 4.28 to 160.80 ± 9.51 nm, which was beneficial for particle retention in the tumor sites and release of the loaded therapeutics. Additionally, GNP-DOX/ICG showed a size reduction of the particles to 33.24 ± 4.11 nm and further improved drug release with the degradation of overexpressed MMP-2 in tumor. In the subsequently performed in vitro experiments, it was confirmed that GNP-DOX/ICG could provide a therapeutic effect that was enhanced and synergistic. Consequently, GNP-DOX/ICG could efficiently suppress the growth of 4T1 tumor in vivo. In conclusion, this study may provide a promising strategy in the rational design of drug delivery nanosystems based on gelatin for chemo-photothermal therapy to achieve synergistically enhanced therapeutic efficacy against breast cancer.

Stimulus-Responsive Sequential Release Systems for Drug and Gene Delivery

In recent years, a range of studies have been conducted with the aim to design and characterize delivery systems that are able to release multiple therapeutic agents in controlled and programmed temporal sequences, or with spatial resolution inside the body. This sequential release occurs in response to different stimuli, including changes in pH, redox potential, enzyme activity, temperature gradients, light irradiation, and by applying external magnetic and electrical fields. Sequential release (SR)-based delivery systems, are often based on a range of different micro- or nanocarriers and may offer a silver bullet in the battle against various diseases, such as cancer. Their distinctive characteristic is the ability to release one or more drugs (or release drugs along with genes) in a controlled sequence at different times or at different sites. This approach can lengthen gene expression periods, reduce the side effects of drugs, enhance the efficacy of drugs, and induce an anti-proliferative effect on cancer cells due to the synergistic effects of genes and drugs. The key objective of this review is to summarize recent progress in SR-based drug/gene delivery systems for cancer and other diseases.

Multimodal Decorations of Mesoporous Silica Nanoparticles for Improved Cancer Therapy

The presence of leaky vasculature and the lack of lymphatic drainage of small structures by the solid tumors formulate nanoparticles as promising delivery vehicles in cancer therapy. In particular, among various nanoparticles, the mesoporous silica nanoparticles (MSN) exhibit numerous outstanding features, including mechanical thermal and chemical stability, huge surface area and ordered porous interior to store different anti-cancer therapeutics with high loading capacity and tunable release mechanisms. Furthermore, one can easily decorate the surface of MSN by attaching ligands for active targeting specifically to the cancer region exploiting overexpressed receptors. The controlled release of drugs to the disease site without any leakage to healthy tissues can be achieved by employing environment responsive gatekeepers for the end-capping of MSN. To achieve precise cancer chemotherapy, the most desired delivery system should possess high loading efficiency, site-specificity and capacity of controlled release. In this review we will focus on multimodal decorations of MSN, which is the most demanding ongoing approach related to MSN application in cancer therapy. Herein, we will report about the recently tried efforts for multimodal modifications of MSN, exploiting both the active targeting and stimuli responsive behavior simultaneously, along with individual targeted delivery and stimuli responsive cancer therapy using MSN.

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.

Recent advantage of hyaluronic acid for anti-cancer application: a review of "3S" transition approach

In recent years, nano drug delivery system has been widely concerned because of its good therapeutic effect. However, the process from blood circulation to cancer cell release of nanodrugs will be eliminated by the human body's own defense trap, thus reducing the therapeutic effect. In recent years, a "3S" transition concept, including stability transition, surface transition and size transition, was proposed to overcome the barriers in delivery process. Hyaluronic (HA) acid has been widely used in delivery of anticancer drugs due to its excellent biocompatibility, biodegradability and specific targeting to cancer cells. In this paper, the strategies and methods of HA-based nanomaterials using "3S" theory are reviewed. The applications and effects of "3S" modified nanomaterials in various fields are also introduced.

Fabrication of Carboxylmethyl Chitosan Nanocarrier via Self-Assembly for Efficient Delivery of Phenylethyl Resorcinol in B16 Cells

Micro-molecular drugs have special advantages to cope with challenging diseases, however their structure, physical and chemical properties, stability, and pharmacodynamics have more requirements for the way they are delivered into the body. Carrier-based drug delivery systems can circumvent many limited factors of drug delivery and increase their bioavailability. In this context, stable drug nanocarriers of alkaline amino acids (arginine, Arg) modified conjugated linoleic acid-carboxymethyl chitosan (CLA-CMCS) conjugate were developed, which could generate supramolecular micelles to effectively encapsulate the tyrosinase inhibitor phenylethyl resorcinol (PR). The resulting CCA-NPs were spherical nanoparticles with a mean size around 175 nm. The 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2-H-tetrazolium bromide (MTT) assay and cellular uptake investigation demonstrated that the CCA-NPs were non-cytotoxic and had excellent cell transport ability. In addition, these CCA-NPs were able to effectively deliver PR and inhibited melanin formation to reduce pigmentation by enhancing cellular uptake. In conclusion, our research indicated that nanocarriers based on self-assembly amphiphilic polymers constituted a promising and effective drug delivery system in hyperpigmentation targeting.

Chemistry Routes for Copolymer Synthesis Containing PEG for Targeting, Imaging, and Drug Delivery Purposes

Polyethylene glycol (PEG) is one of the most frequently used polymers for coating nanocarriers to enhance their biocompatibility, hydrophilicity, stability, and biodegradability. PEG is now considered to be among the best biocompatible polymers. It offers sterical hindrance against other nanoparticles and blood components such as opsonin, preventing their macrophage phagocytosis and resulting in a prolonged circulation time in blood stream, consequently a ‘stealth character’ in vivo. Therefore, PEG has a very promising future for the development of current therapeutics and biomedical applications. Moreover, the vast number of molecules that PEG can conjugate with might enhance its ability to have an optimistic perspective for the future. This review will present an update on the chemistry used in the modern conjugation methods for a variety of PEG conjugates, such methods include, but are not limited to, the synthesis of targeting PEG conjugates (i.e., Peptides, Folate, Biotin, Mannose etc.), imaging PEG conjugates (i.e., Coumarin, Near Infrared dyes etc.) and delivery PEG conjugates (i.e., doxorubicin, paclitaxel, and other hydrophobic low molecular weight drugs). Furthermore, the type of nanoparticles carrying those conjugates, along with their biomedical uses, will be briefly discussed.

Hyaluronidase-Responsive Mesoporous Silica Nanoparticles with Dual-Imaging and Dual-Target Function

Nanoparticle-based drug delivery systems are among the most popular research topics in recent years. Compared with traditional drug carriers, mesoporous silica nanoparticles (MSN) offer modifiable surfaces, adjustable pore sizes and good biocompatibility. Nanoparticle-based drug delivery systems have become a research direction for many scientists. With the active target factionalized, scientists could deliver drug carriers into cancer cells successfully. However, drugs in cancer cells could elicit drug resistance and induce cell exocytosis. Thus, the drug cannot be delivered to its pharmacological location, such as the nucleus. Therefore, binding the cell membrane and the nuclear target on the nanomaterial so that the anticancer drug can be delivered to its pharmacological action site is our goal. In this study, MSN-EuGd was synthesized by doping Eu3+ and Gd3+ during the synthesis of MSN. The surface of the material was then connected to the TAT peptide as the nucleus target for targeting the cancer nucleus and then loaded with the anticancer drug camptothecin (CPT). Then, the surface of MSN-EuGd was bonded to the hyaluronic acid as an active target and gatekeeper. With this system, it is possible and desirable to achieve dual imaging and dual targeting, as well as to deliver drugs to the cell nucleus under a hyaluronidase-controlled release. The experimental approach is divided into three parts. First, we conferred the material with fluorescent and magnetic dual-imaging property by doping Eu3+ and Gd3+ into the MSN. Second, modification of the cell membrane target molecule and the nucleus target molecule occurred on the surface of the nanoparticle, making the nanoparticle a target drug carrier. Third, the loading of drug molecules into the carrier gave the entire carrier a specific target profile and enabled the ability to treat cancer. In this study, we investigated the basic properties of the drug carrier, including physical properties, chemical properties, and in vitro tests. The result showed that we have successfully designed a drug delivery system that recognizes normal cells and cancer cells and has good anticancer effects.

Rational Design of Cancer Nanomedicine for Simultaneous Stealth Surface and Enhanced Cellular Uptake

Owing to the complex and still not fully understood physiological environment, the development of traditional nanosized drug delivery systems is very challenging for precision cancer therapy. It is very difficult to control the in vivo distribution of nanoparticles after intravenous injection. The ideal drug nanocarriers should not only have stealth surface for prolonged circulation time but also possess enhanced cellular internalization in tumor sites. Unfortunately, the stealth surface and enhanced cellular uptake seem contradictory to each other. How to integrate the two opposite aspects into one system is a very herculean but meaningful task. As an alternative drug delivery strategy, chameleon-like drug delivery systems were developed to achieve long circulation time while maintaining enhanced cancer cell uptake. Such drug nanocarriers can "turn off" their internalization ability during circulation. However, the enhanced cellular uptake can be readily activated upon arriving at tumor tissues. In this way, stealth surface and enhanced uptake are of dialectical unity in drug delivery. In this review, we focus on the surface engineering of drug nanocarriers to obtain simultaneous stealth surfaces in circulation and enhanced uptake in tumors. The current strategies and ongoing developments, including programmed tumor-targeting strategies and some specific zwitterionic surfaces, will be discussed in detail.

Functionalized mesoporous silica nanoparticles and biomedical applications

Since the first report in early 1990s, mesoporous silica nanoparticles (MSNs) have progressively attracted the attention of scientists due to their potential applications in physic, energy storage, imaging, and especially in biomedical engineering. Owning the unique physiochemical properties, such as highly porosity, large surface area and pore volume, functionalizable, tunable pore and particle sizes and biocompatibility, and high loading cavity, MSNs offer efficient encapsulation and then controlled release, and in some cases, intracellular delivery of bioactive molecules for biomedical applications. During the last decade, functionalized MSNs that show respond upon the surrounding stimulus changes, such as temperature, pH, redox, light, ultrasound, magnetic or electric fields, enzyme, redox, ROS, glucose, and ATP, or their combinations, have continuously revolutionized their potential applications in biomedical engineering. Therefore, this review focuses on discussion the recent fabrication of functionalized MSNs and their potential applications in drug delivery, therapeutic treatments, diagnostic imaging, and biocatalyst. In addition, some potential clinical applications and challenges will also be discussed.

Tumor Microenvironment Targeted Nanotherapy

Recent developments in nanotechnology have brought new approaches to cancer diagnosis and therapy. While enhanced permeability and retention effect promotes nano-chemotherapeutics extravasation, the abnormal tumor vasculature, high interstitial pressure and dense stroma structure limit homogeneous intratumoral distribution of nano-chemotherapeutics and compromise their imaging and therapeutic effect. Moreover, heterogeneous distribution of nano-chemotherapeutics in non-tumor-stroma cells damages the non-tumor cells, and interferes with tumor-stroma crosstalk. This can lead not only to inhibition of tumor progression, but can also paradoxically induce acquired resistance and facilitate tumor cell proliferation and metastasis. Overall, the tumor microenvironment plays a vital role in regulating nano-chemotherapeutics distribution and their biological effects. In this review, the barriers in tumor microenvironment, its consequential effects on nano-chemotherapeutics, considerations to improve nano-chemotherapeutics delivery and combinatory strategies to overcome acquired resistance induced by tumor microenvironment have been summarized. The various strategies viz., nanotechnology based approach as well as ligand-mediated, redox-responsive, and enzyme-mediated based combinatorial nanoapproaches have been discussed in this review.