Enzyme responsive drug delivery systems in cancer treatment

Nanoplatform-based natural products co-delivery system to surmount cancer multidrug-resistant

The emergence of multidrug resistance (MDR) in malignant tumors is the primary reason for invalid chemotherapy. Antitumor drugs are often adversely affected by the MDR of tumor cells. Treatments using conventional drugs, which have specific drug targets, hardly regulate the complex signaling pathway of MDR cells because of the complex formation mechanism of MDR. However, natural products have positive advantages, such as high efficiency, low toxicity, and ability to target multiple mechanism pathways associated with MDR. Natural products, as MDR reversal agents, synergize with chemotherapeutics and enhance the sensitivity of tumor cells to chemotherapeutics, and the co-delivery of natural products and antitumor drugs with nanocarriers maximizes the synergistic effects against MDR in tumor cells. This review summarizes the molecular mechanisms of MDR, the advantages of natural products combined with chemotherapeutics in offsetting complicated MDR mechanisms, and the types and mechanisms of natural products that are potential MDR reversal modulators. Meanwhile, aiming at the low bioavailability of cocktail combined natural products and chemotherapeutic in vivo, the advantages of nanoplatform-based co-delivery system and recent research developments are illustrated on the basis of our previous research. Finally, prospective horizons are analyzed, which are expected to considerably improve the nano-co-delivery of natural products and chemotherapeutic systems for MDR reversal in cancer.

Protein nanogels with enhanced pH-responsive dynamics triggered by remote NIR for systemic protein delivery and programmable controlled release

Therapeutic proteins represent promising treatments in medical applications; however, direct administration of native proteins frequently suffers from in vivo enzymatic degradation or denaturation in hostile environments. Engineering proteins into biocompatible formulations can be used to solve these problems. Despite years of effort, efficient systemic delivery followed by successful release from the formulation remains a challenge. Herein, we describe a pH-responsive nanogel (PI825@PDC/protein NGs) formed by host-guest recognition of 6-arm PEGylated crystalline β-cyclodextrin (β-CD) and near-infrared IR825 dye, which affords highly efficient encapsulation of proteins during their self-assembly. PI825@PDC/protein NGs are robust enough to withstand hostile physiological conditions both in vitro and in vivo and could be slightly disassociated from protein release in acidic environments due to the anchored pH-responsive 2,3-dimethylmaleic anhydride (DMA) linker. Furthermore, the pH-responsive dynamics can be greatly enhanced by elevated temperature upon remote (Near-infrared spectroscopy) NIR irradiation of the IR825 within NGs, generating programmable release of loaded proteins for enhanced cancer treatment. This study describes a general method to load proteins with high efficiency for systemic delivery, followed by programmable protein release by remote NIR irradiation and offers new insights for protein engineering and potential medical applications.

Dual-Targeting and Stimuli-Triggered Liposomal Drug Delivery in Cancer Treatment

The delivery of chemotherapeutics to solid tumors using smart drug delivery systems (SDDSs) takes advantage of the unique physiology of tumors (i.e., disordered structure, leaky vasculature, abnormal extracellular matrix (ECM), and limited lymphatic drainage) to deliver anticancer drugs with reduced systemic side effects. Liposomes are the most promising of such SDDSs and have been well investigated for cancer therapy. To improve the specificity, bioavailability, and anticancer efficacy of liposomes at the diseased sites, other strategies such as targeting ligands and stimulus-sensitive liposomes have been developed. This review highlights relevant surface functionalization techniques and stimuli-mediated drug release for enhanced delivery of anticancer agents at tumor sites, with a special focus on dual functionalization and design of multistimuli responsive liposomes.

Smart Nanoparticles for Chemo-Based Combinational Therapy

Cancer is a heterogeneous and complex disease. Traditional cancer therapy is associated with low therapeutic index, acquired resistance, and various adverse effects. With the increasing understanding of cancer biology and technology advancements, more strategies have been exploited to optimize the therapeutic outcomes. The rapid development and application of nanomedicine have motivated this progress. Combinational regimen, for instance, has become an indispensable approach for effective cancer treatment, including the combination of chemotherapeutic agents, chemo-energy, chemo-gene, chemo-small molecules, and chemo-immunology. Additionally, smart nanoplatforms that respond to external stimuli (such as light, temperature, ultrasound, and magnetic field), and/or to internal stimuli (such as changes in pH, enzymes, hypoxia, and redox) have been extensively investigated to improve precision therapy. Smart nanoplatforms for combinational therapy have demonstrated the potential to be the next generation cancer treatment regimen. This review aims to highlight the recent advances in smart combinational therapy.

A review of nanoparticle drug delivery systems responsive to endogenous breast cancer microenvironment

Breast cancer, as a malignant disease that seriously threatens women's health, urgently needs to be researched to develop effective and safe therapeutic drugs. Nanoparticle drug delivery systems (NDDS), provide a powerful means for drug targeting to the breast cancer, enhancing the bioavailability and reducing the adverse effects of anticancer drug. However, the breast cancer microenvironment together with heterogeneity of cancer, impedes the tumor targeting effect of NDDS. Breast cancer microenvironment, exerts endogenous stimuli, such as hypoxia, acidosis, and aberrant protease expression, shape a natural shelter for tumor growth, invasion and migration. On the basis of the ubiquitous of endogenous stimuli in the breast cancer microenvironment, researchers exploited them to design the stimuli-responsive NDDS, which response to endogenous stimulus, targeted release drug in breast cancer microenvironment. In this review, we highlighted the effect of the breast cancer microenvironment, summarized innovative NDDS responsive to the internal stimuli in the tumor microenvironment, including the material, the targeting groups, the loading drugs, targeting position and the function of stimuli-responsive nanoparticle drug delivery system. The limitations and potential applications of the stimuli-responsive nanoparticle drug delivery systems for breast cancer treatment were discussed to further the application.

Recent Progress in Stimuli-Responsive Intelligent Nano Scale Drug Delivery Systems: A Special Focus Towards pH-Sensitive Systems

Stimuli-responsive nanocarriers are gaining much attention due to their versatile multifunctional activities, including disease diagnosis and treatment. Recently, clinical applications of nano-drug delivery systems for cancer treatment pose a challenge due to their limited cellular uptake, low bioavailability, poor targetability, stability issues, and unfavourable pharmacokinetics. To overcome these issues, researchers are focussing on stimuli-responsive systems. Nanocarriers elicit their role through endogenous (pH, temperature, enzyme, and redox) or exogenous (temperature, light, magnetic field, ultrasound) stimulus. These systems were designed to overcome the shortcomings such as non-specificity and toxicity associated with the conventional drug delivery systems. The pH variation between healthy cells and tumor microenvironment creates a platform for the generation of pH-sensitive nano delivery systems. Herein, we propose to present an overview of various internal and external stimuli-responsive behavior-based drug delivery systems. Herein, the present review will focus specifically on the significance of various pH-responsive nanomaterials such as polymeric nanoparticles, nano micelles, inorganic-based pH-sensitive drug delivery carriers such as calcium phosphate nanoparticles, and carbon dots in cancer treatment. Moreover, this review elaborates the recent findings on pH-based stimuli-responsive drug delivery systems with special emphasis on our reported stimuli-responsive systems for cancer treatment.

Responsive optical probes for deep-tissue imaging: Photoacoustics and second near-infrared fluorescence

Optical imaging has played a vital role in development of biomedicine and image-guided theragnostic. Nevertheless, the clinical translation of optical molecular imaging for deep-tissue visualization is still limited by poor signal-to-background ratio and low penetration depth owing to light scattering and tissue autofluorescence. Hence, to facilitate precise diagnosis and accurate surgery excision in clinical practices, the responsive optical probes (ROPs) are broadly designed for specific reaction with biological analytes or disease biomarkers via chemical/physical interactions for photoacoustic and second near-infrared fluorescence (NIR-II, 900-1700 nm) fluorescence imaging. Herein, the recent advances in the development of ROPs including molecular design principles, activated mechanisms and treatment responses for photoacoustic and NIR-II fluorescence imaging are reviewed. Furthermore, the present challenges and future perspectives of ROPs for deep-tissue imaging are also discussed.

Enzyme-Responsive Nanoparticles and Coatings Made from Alginate/Peptide Ciprofloxacin Conjugates as Drug Release System

Infection-controlled release of antibacterial agents is of great importance, particularly for the control of peri-implant infections in the postoperative phase. Polymers containing antibiotics bound via enzymatically cleavable linkers could provide access to drug release systems that could accomplish this. Dispersions of nanogels were prepared by ionotropic gelation of alginate with poly-l-lysine, which was conjugated with ciprofloxacin as model drug via a copper-free 1,3-dipolar cycloaddition (click reaction). The nanogels are stable in dispersion and form films which are stable in aqueous environments. However, both the nanogels and the layers are degraded in the presence of an enzyme and the ciprofloxacin is released. The efficacy of the released drug against Staphylococcus aureus is negatively affected by the residues of the linker. Both the acyl modification of the amine nitrogen in ciprofloxacin and the sterically very demanding linker group with three annellated rings could be responsible for this. However the basic feasibility of the principle for enzyme-triggered release of drugs was successfully demonstrated.

Application of Nano-Drug Delivery System Based on Cascade Technology in Cancer Treatment

In the current cancer treatment, various combination therapies have been widely used, such as photodynamic therapy (PDT) combined with chemokinetic therapy (CDT). However, due to the complexity of the tumor microenvironment (TME) and the limitations of treatment, the efficacy of current treatment options for some cancers is unsatisfactory. Nowadays, cascade technology has been used in cancer treatment and achieved good therapeutic effect. Cascade technology based on nanotechnology can trigger cascade reactions under specific tumor conditions to achieve precise positioning and controlled release, or amplify the efficacy of each drug to improve anticancer efficacy and reduce side effects. Compared with the traditional treatment, the application of cascade technology has achieved the controllability, specificity, and effectiveness of cancer treatment. This paper reviews the application of cascade technology in drug delivery, targeting, and release via nano-drug delivery systems in recent years, and introduces their application in reactive oxygen species (ROS)-induced cancer treatment. Finally, we briefly describe the current challenges and prospects of cascade technology in cancer treatment in the future.

Recent progress on charge-reversal polymeric nanocarriers for cancer treatments

Nanocarriers (NCs) for delivery anticancer therapeutics have been under development for decades. Although great progress has been achieved, the clinic translation is still in the infancy. The key challenge lies in the biological barriers which lie between the NCs and the target spots, including blood circulation, tumor penetration, cellular uptake, endo-/lysosomal escape, intracellular therapeutics release and organelle targeting. Each barrier has its own distinctive microenvironment and requires different surface charge. To address this challenge, charge-reversal polymeric NCs have been a hot topic, which are capable of overcoming each delivery barrier, by reversing their charges in response to certain biological stimuli in the tumor microenvironment. In this review, the triggering mechanisms of charge reversal, including pH, enzyme and redox approaches are summarized. Then the corresponding design principles of charge-reversal NCs for each delivery barrier are discussed. More importantly, the limitations and future prospects of charge-reversal NCs in clinical applications are proposed.

The reversal of chemotherapy-induced multidrug resistance by nanomedicine for cancer therapy

Multidrug resistance (MDR) of cancer is a persistent problem in chemotherapy. Scientists have considered the overexpressed efflux transporters responsible for MDR and chemotherapy failure. MDR extremely limits the therapeutic effect of chemotherapy in cancer treatment. Many strategies have been applied to solve this problem. Multifunctional nanoparticles may be one of the most promising approaches to reverse MDR of tumor. These nanoparticles can keep stability in the blood circulation and selectively accumulated in the tumor microenvironment (TME) either by passive or active targeting. The stimuli-sensitive or organelle-targeting nanoparticles can release the drug at the targeted-site without exposure to normal tissues. In order to better understand reversal of MDR, three main strategies are concluded in this review. First strategy is the synergistic effect of chemotherapeutic drugs and ABC transporter inhibitors. Through directly inhibiting overexpressed ABC transporters, chemotherapeutic drugs can enter into resistant cells without being efflux. Second strategy is based on nanoparticles circumventing over-expressed efflux transporters and directly targeting resistance-related organelles. Third approach is the combination of multiple therapy modes overcoming cancer resistance. At last, numerous researches demonstrated cancer stem-like cells (CSCs) had a deep relation with drug resistance. Here, we discuss two different drug delivery approaches of nanomedicine based on CSC therapy.

Robotics for enzyme technology: innovations and technological perspectives

The use of robotics in the life science sector has created a considerable and significant impact on a wide range of research areas, including enzyme technology due to their immense applications in enzyme and microbial engineering as an indispensable tool in high-throughput screening applications. Scientists are experiencing the advanced applications of various biological robots (nanobots), fabricated based on bottom-up or top-down approaches for making nanotechnology scaffolds. Nanobots and enzyme-powered nanomotors are particularly attractive because they are self-propelled vehicles, which consume biocompatible fuels. These smart nanostructures are widely used as drug delivery systems for the efficient treatment of various diseases. This review gives insights into the escalating necessity of robotics and nanobots and their ever-widening applications in enzyme technology, including biofuel production and biomedical applications. It also offers brief insights into high-throughput robotic platforms that are currently being used in enzyme screening applications for monitoring and control of microbial growth conditions. KEY POINTS: • Robotics and their applications in biotechnology are highlighted. • Robotics for high-throughput enzyme screening and microbial engineering are described. • Nanobots and enzyme-powered nanomotors as controllable drug delivery systems are reviewed.

Recent advances in the design of inorganic and nano-clay particles for the treatment of brain disorders

Inorganic materials, in particular nanoclays and silica nanoparticles, have attracted enormous attention due to their versatile and tuneable properties, making them ideal candidates for a wide range of biomedical applications, such as drug delivery. This review aims at overviewing recent developments of inorganic nanoparticles (like porous or mesoporous silica particles) and different nano-clay materials (like montmorillonite, laponites or halloysite nanotubes) employed for overcoming the blood brain barrier (BBB) in the treatment and therapy of major brain diseases such as Alzheimer's, Parkinson's, glioma or amyotrophic lateral sclerosis. Recent strategies of crossing the BBB through invasive and not invasive administration routes by using different types of nanoparticles compared to nano-clays and inorganic particles are overviewed.

Polymer particles for the intra-articular delivery of drugs to treat osteoarthritis

Osteoarthritis (OA) is a leading cause of chronic disability. It is a progressive disease, involving pathological changes to the entire joint, resulting in joint pain, stiffness, swelling, and loss of mobility. There is currently no disease-modifying pharmaceutical treatment for OA, and the treatments that do exist suffer from significant side effects. An increasing understanding of the molecular pathways involved in OA is leading to many potential drug targets. However, both current and new therapies can benefit from a targeted approach that delivers drugs selectively to joints at therapeutic concentrations, while limiting systemic exposure to the drugs. Delivery systems including hydrogels, liposomes, and various types of particles have been explored for intra-articular drug delivery. This review will describe progress over the past several years in the development of polymer-based particles for OA treatment, as well as their in vitro, in vivo, and clinical evaluation. Systems based on biopolymers such as polysaccharides and polypeptides, as well as synthetic polyesters, poly(ester amide)s, thermoresponsive polymers, poly(vinyl alcohol), amphiphilic polymers, and dendrimers will be described. We will discuss the role of particle size, biodegradability, and mechanical properties in the behavior of the particles in the joint, and the challenges to be addressed in future research.

Tumor Microenvironment Sensitive Nanocarriers for Bioimaging and Therapeutics

The tumor microenvironment (TME), which is composed of cancer cells, stromal cells, immune cells, and extracellular matrices, plays an important role in tumor growth and progression. Thus, targeting the TME using a well-designed nano-drug delivery system is emerging as a promising strategy for the treatment of solid tumors. Compared to normal tissues, the TME presents several distinguishable physiological features such as mildly acidic pH, hypoxia, high level of reactive oxygen species, and overexpression of specific enzymes, that are exploited as stimuli to induce specific changes in the nanocarrier structures, and thereby facilitates target-specific delivery of imaging or chemotherapeutic agents for the early diagnosis or effective treatment, respectively. Recently, smart nanocarriers that respond to more than one stimulus in the TME have also been designed to elicit a more desirable spatiotemporally controlled drug release. This review highlights the recent progress in TME-sensitive nanocarriers designed for more efficient tumor therapy and imaging. In particular, the design strategies, challenges, and critical considerations involved in the fabrication of TME-sensitive nanocarriers, along with their in vitro and in vivo evaluations are discussed.

On the road to smart biomaterials for bone research: definitions, concepts, advances, and outlook

The demand for biomaterials that promote the repair, replacement, or restoration of hard and soft tissues continues to grow as the population ages. Traditionally, smart biomaterials have been thought as those that respond to stimuli. However, the continuous evolution of the field warrants a fresh look at the concept of smartness of biomaterials. This review presents a redefinition of the term "Smart Biomaterial" and discusses recent advances in and applications of smart biomaterials for hard tissue restoration and regeneration. To clarify the use of the term "smart biomaterials", we propose four degrees of smartness according to the level of interaction of the biomaterials with the bio-environment and the biological/cellular responses they elicit, defining these materials as inert, active, responsive, and autonomous. Then, we present an up-to-date survey of applications of smart biomaterials for hard tissues, based on the materials' responses (external and internal stimuli) and their use as immune-modulatory biomaterials. Finally, we discuss the limitations and obstacles to the translation from basic research (bench) to clinical utilization that is required for the development of clinically relevant applications of these technologies.

Core-Cross-linked Fluorescent Worm-Like Micelles for Glucose-Mediated Drug Delivery

We herein report the fabrication of core-crosslinked, fluorescent, and surface-functionalized worm-like block copolymer micelles as drug delivery vehicles. The polyether-based diblock terpolymer [allyl-poly(ethylene oxide)-block-poly(2-ethylhexyl glycidyl ether-co-furfuryl glycidyl ether)] was synthesized via anionic ring opening polymerization, and self-assembly in water as a selective solvent led to the formation of long filomicelles. Subsequent cross-linking was realized using hydrophobic bismaleimides as well as a designed fluorescent cross-linker for thermally induced Diels-Alder reactions with the furfuryl units incorporated in the hydrophobic block of the diblock terpolymer. As a fluorescent cross-linker, we synthesized and incorporated a cyanine 5-based bismaleimide in the cross-linking process, which can be used for fluorescence tracking of the particles. Furthermore, we covalently attached glucose to the allyl end groups present on the surface of the micelles to investigate active glucose-mediated transport into suitable cell lines. First studies in 2D as well as 3D cell culture models suggest a glucose-dependent uptake of the particles into cells despite their unusually large size compared to other nanoparticle systems used in drug delivery.

Recent Advancements in Stimuli Responsive Drug Delivery Platforms for Active and Passive Cancer Targeting

The tumor-specific targeting of chemotherapeutic agents for specific necrosis of cancer cells without affecting the normal cells poses a great challenge for researchers and scientists. Though extensive research has been carried out to investigate chemotherapy-based targeted drug delivery, the identification of the most promising strategy capable of bypassing non-specific cytotoxicity is still a major concern. Recent advancements in the arena of onco-targeted therapies have enabled safe and effective tumor-specific localization through stimuli-responsive drug delivery systems. Owing to their promising characteristic features, stimuli-responsive drug delivery platforms have revolutionized the chemotherapy-based treatments with added benefits of enhanced bioavailability and selective cytotoxicity of cancer cells compared to the conventional modalities. The insensitivity of stimuli-responsive drug delivery platforms when exposed to normal cells prevents the release of cytotoxic drugs into the normal cells and therefore alleviates the off-target events associated with chemotherapy. Contrastingly, they showed amplified sensitivity and triggered release of chemotherapeutic payload when internalized into the tumor microenvironment causing maximum cytotoxic responses and the induction of cancer cell necrosis. This review focuses on the physical stimuli-responsive drug delivery systems and chemical stimuli-responsive drug delivery systems for triggered cancer chemotherapy through active and/or passive targeting. Moreover, the review also provided a brief insight into the molecular dynamic simulations associated with stimuli-based tumor targeting.

Head and Neck Cancer Treatments from Chemotherapy to Magnetic Systems: Perspectives and Challenges

BACKGROUND

Cancer is one of the diseases causing society's fears as a stigma of death and pain. Head and Neck Squamous Cell Carcinoma (HNSCC) is a group of malignant neoplasms of different locations in this region of the human body. It is one of the leading causes of morbidity and mortality in Brazil, because these malignant neoplasias, in most cases, are diagnosed in late phases. Surgical excision, chemotherapy and radiotherapy encompass the forefront of antineoplastic therapy; however, the numerous side effects associated with these therapeutic modalities are well known. Some treatments present enough potential to help or replace conventional treatments, such as Magnetic Hyperthermia and Photodynamic Therapy. Such approaches require the development of new materials at the nanoscale, able to carry out the loading of their active components while presenting characteristics of biocompatibility mandatory for biomedical applications.

OBJECTIVE

This work aims to make a bibliographical review of HNSCC treatments. Recent techniques proven effective in other types of cancer were highlighted and raised discussion and reflections on current methods and possibilities of enhancing the treatment of HNSCC.

METHOD

The study was based on a bibliometric research between the years 2008 and 2019 using the following keywords: Cancer, Head and Neck Cancer, Chemotherapy, Radiotherapy, Photodynamic Therapy, and Hyperthermia.

RESULTS

A total of 5.151.725 articles were found, 3.712.670 about cancer, 175.470 on Head and Neck Cancer, 398.736 on Radiotherapy, 760.497 on Chemotherapy, 53.830 on Hyperthermia, and 50.522 on Photodynamic Therapy.

CONCLUSION

The analysis shows that there is still much room for expanding research, especially for alternative therapies since most of the studies still focus on conventional treatments and on the quest to overcome their side effects. The scientific community needs to keep looking for more effective therapies generating fewer side effects for the patient. Currently, the so-called alternative therapies are being used in combination with the conventional ones, but the association of these new therapies shows great potential, in other types of cancer, to improve the treatment efficacy.

Stimulus-responsive nanocarriers for targeted drug delivery

Cancer is a multifactorial disease that involves unique tumor microenvironment (TEM) and abnormal organs with complex structures.

Esterase-Responsive Polypeptide Vesicles as Fast-Response and Sustained-Release Nanocompartments for Fibroblast-Exempt Drug Delivery

Enzyme-responsive polypeptide vesicles have attracted considerable attention for precision theranostics because of their biocompatibility, biodegradability, and unique secondary conformation transition triggered by the catalytic actions of enzymes. These promising potentials of polypeptide vesicles could be limited in a drug delivery system by the very slow enzyme diffusion rate into vesicles that could reduce the efficacy of the drug. On the other hand, stimuli-responsive polymeric vesicles that respond to stimuli can undergo microstructure destruction for the burst release of drugs, which would penetrate through the membrane of dead cells and the tumor extracellular matrix, inducing acute toxicity to neighboring cells. Here, we designed amphiphilic PEG-polypeptide copolymers containing esterase-labile carbamate-caged primary amines. It was found that the diblock can self-assemble into vesicular structures. Esterase-triggered self-immolative decaging reactions could quickly release the primary amine moiety of monomers that can undergo an amidation reaction for transition of the bilayer of vesicles from hydrophobic to partially hydrophilic. This esterase-responsive process retains the nanostructure of vesicles but permeabilizes the vesicle membrane, which can afford the sustained release of encapsulating drugs. These esterase-responsive polypeptide vesicles mediate selective cytotoxicity in cancer cells with high esterase expression over normal fibroblasts with low esterase, enabling the potent anticancer chemotherapy with minimized side effects.

Designing Enzyme-responsive Biomaterials

Enzymes are a class of protein that catalyze a wide range of chemical reactions, including the cleavage of specific peptide bonds. They are expressed in all cell types, play vital roles in tissue development and homeostasis, and in many diseases, such as cancer. Enzymatic activity is tightly controlled through the use of inactive pro-enzymes, endogenous inhibitors and spatial localization. Since the presence of specific enzymes is often correlated with biological processes, and these proteins can directly modify biomolecules, they are an ideal biological input for cell-responsive biomaterials. These materials include both natural and synthetic polymers, cross-linked hydrogels and self-assembled peptide nanostructures. Within these systems enzymatic activity has been used to induce biodegradation, release therapeutic agents and for disease diagnosis. As technological advancements increase our ability to quantify the expression and nanoscale organization of proteins in cells and tissues, as well as the synthesis of increasingly complex and well-defined biomaterials, enzyme-responsive biomaterials are poised to play vital roles in the future of biomedicine.

Possible contribution of sialic acid to the enhanced tumor targeting efficiency of nanoparticles engineered with doxorubicin

Doxorubicin (DOX)-engineered poly(lactic-co-glycolic acid) (PLGA) nanoparticles (NPs) including phloretin (PHL) were designed and the feasible contribution of sialic acid (SA) to the improved tumor targeting and penetration capabilities was elucidated in lung adenocarcinoma models. DOX has been clinically used as liposomal formulations after its introduction to the inner side of vehicles, however DOX is anchored in the outer surface of PLGA NPs for improved tumor penetration by interactions with SA in this study. DOX (positively charged at physiological pH) was adsorbed onto the negatively charged PLGA NPs via electrostatic interactions and consequent binding of SA (negatively charged at physiological pH) to DOX located in NPs was also elucidated. DOX layer in DOX@PLGA NPs rendered improved endocytosis and partial contribution of SA (expressed in cancer cells) to that endocytosis was demonstrated. DOX@PLGA/PHL NPs provided enhanced antiproliferation potentials in A549 cells rather than single agent (DOX or PHL)-installed NPs. In addition, DOX-SA interactions seemed to play critical roles in tumor infiltration and accumulation of DOX@PLGA NPs in A549 tumor-xenografted mouse model. All these findings support the novel use of DOX which is used for the surface engineering of NPs for improved tumor targeting and penetration.

Bioresponsive drug delivery systems for the treatment of inflammatory diseases

Inflammation is intimately related to the pathogenesis of numerous acute and chronic diseases like cardiovascular disease, inflammatory bowel disease, rheumatoid arthritis, and neurodegenerative diseases. Therefore anti-inflammatory therapy is a very promising strategy for the prevention and treatment of these inflammatory diseases. To overcome the shortcomings of existing anti-inflammatory agents and their traditional formulations, such as nonspecific tissue distribution and uncontrolled drug release, bioresponsive drug delivery systems have received much attention in recent years. In this review, we first provide a brief introduction of the pathogenesis of inflammation, with an emphasis on representative inflammatory cells and mediators in inflammatory microenvironments that serve as pathological fundamentals for rational design of bioresponsive carriers. Then we discuss different materials and delivery systems responsive to inflammation-associated biochemical signals, such as pH, reactive oxygen species, and specific enzymes. Also, applications of various bioresponsive drug delivery systems in the treatment of typical acute and chronic inflammatory diseases are described. Finally, crucial challenges in the future development and clinical translation of bioresponsive anti-inflammatory drug delivery systems are highlighted.

Recent Advances in Stimuli-Responsive Platforms for Cancer Immunotherapy

Immunotherapy has attracted significant interest because of its tremendous potential in cancer therapy. The recent advances in the identification of cancer-associated neoantigens, chimeric antigen receptor (CAR) T-cell and immune checkpoint blockade (ICB), have revolutionized the field of cancer immunotherapy. Cancer immunotherapeutic agents typically exhibit strong immune activation or inhibition activity, thereby inducing robust biological effect even when administered at a small dosage. However, in most cases, cancer immunotherapeutic targets are not cancer specific. Some of them are also expressed in nonmalignant normal tissues and the undesired release of the cancer immunotherapeutic agents into these normal tissues may lead to severe side effects. Thus, the on-demand release of the cancer immunotherapeutic agents into the target site is critical to achieving efficient antitumor immune responses while minimizing the side effects.In this Account, we introduce the recent progress of our group and others on the development of stimuli-responsive platforms for cancer immunotherapy. Stimuli-responsive platforms have been constructed for on-demand release of payloads in a temporally and spatially controllable manner. First, we give a brief introduction to the endogenous and exogenous stimuli that are employed to trigger the release of cancer immunotherapeutic agents. The chemical design strategies to construct the specific stimuli-responsive delivery systems are highlighted. Moreover, the recently developed representative stimuli-responsive platforms for the delivery of immune checkpoint inhibitors, indoleamine 2,3-dioxygenase (IDO) inhibitors, stimulator of interferon genes (STING) agonists, and near-infrared photoimmunotherapy (NIR-PIT) agents are discussed in detail. Meanwhile, we summarize the general chemical design for constructing stimuli-responsive delivery platforms targeting immune targets at distinct locations. Lastly, the probable issues on the clinical translation of these stimuli-responsive platforms for cancer immunotherapy are outlined. Since we are still on the way of exploring the immune system and optimizing the chemical design of biomaterials, we hope the information in this account can provide some valuable references for the development of optimal cancer immunotherapeutics.

Recent advances in construction of small molecule-based fluorophore-drug conjugates

As a powerful tool to advance drug discovery, molecular imaging may provide new insights into the process of drug effect and therapy at cellular and molecular levels. When compared with other detection methods, fluorescence-based strategies are highly attractive and can be used to illuminate pathways of drugs' transport, with multi-color capacity, high specificity and good sensitivity. The conjugates of fluorescent molecules and therapeutic agents create exciting avenues for real-time monitoring of drug delivery and distribution, both in vitro and in vivo. In this short review, we discuss recent developments of small molecule-based fluorophore-drug conjugates, including non-cleavable and cleavable ones, that are capable of visualizing drug delivery.

Approaches for the synthesis of o-nitrobenzyl and coumarin linkers for use in photocleavable biomaterials and bioconjugates and their biomedical applications

Photocleavable biomaterials and bioconjugates are particularly interesting because light sources are easy to obtain and the responsiveness of materials is convenient to control. In recent years, various photocleavable biomaterials and bioconjugates have been synthesized for the control of payload release, regulation of biomolecule activity, 3D cell culture, and investigation of molecular mechanisms. Photocleavable linkers are crucial components of photocleavable biomaterials, which significantly influence the photoresponsive capabilities of materials. Photosensitive molecules, such as o-nitrobenzyls and coumarins, have been extensively developed as photocleavable linkers. In the present review, we provide comprehensive knowledge regarding the synthetic strategies of o-nitrobenzyl and coumarin derived linkers with various functional groups and their applications for the construction of photocleavable biomaterials and bioconjugates. Finally, the biomedical applications of o-nitrobenzyl and coumarin-based photocleavable biomaterials and bioconjugates will be summarized and discussed.

Caspase-Activated Oligonucleotide Probe

Light-activated ("caged") oligonucleotides provide a strategy for modulating the activity of antisense oligos, siRNA, miRNA, aptamers, DNAzymes, and mRNA-capturing probes with high spatiotemporal resolution. However, the near-UV and visible wavelengths that promote these bond-breaking reactions poorly penetrate living tissue, which limits some biological applications. To address this issue, we describe the first example of a protease-activated oligonucleotide probe, capable of reporting on caspase-3 during cellular apoptosis. The 2'-F RNA-peptide substrate-peptide nucleic acid (PNA) hairpin structure was generated in 30% yield in a single bioconjugation step.

Nanomedicine and chemotherapeutics drug delivery: challenges and opportunities

Cancer is considered as one of the biggest threats to humans worldwide. Researchers suggest that tumour is not just a single mass, it comprises cancerous cells surrounded by noncancerous cells such as immune cells, adipocytes and cancer stem cells (CSCs) in the extracellular matrix (ECM) containing distinct components such as proteins, glycoproteins and enzymes; thus tumour microenvironment (TME) is partially complex. Multiple interactions happen in the dynamic microenvironment (ME) lead to an acidic, hypoxic and stiff ME that is considered as one of the major contributors to cancer progression and metastasis. Furthermore, TME involves in drug resistance mechanisms and affects enhanced permeability and retention (EPR) in tumours. In such a scenario, the first step to accomplish satisfying results is the identification and recognition of this ME. Then designing proper drug delivery systems can perform selectively towards cancerous cells. In this way, several targeting and stimuli/enzyme responsive drug delivery systems have been designed. More importantly, it is necessary to design a drug delivery system that can penetrate deeper into the tumours, efficiently and selectively. Various drug delivery systems such as exosomes and size-switchable nanocarriers (NCs) could decrease side effects and increase tumour treatment results by selective accumulation in tumours. In this review, TME features, current drug delivery approaches, challenges and promising strategies towards cancer treatment are discussed.

Recent Advances in Nanocarrier-Assisted Therapeutics Delivery Systems

Nanotechnologies have attracted increasing attention in their application in medicine, especially in the development of new drug delivery systems. With the help of nano-sized carriers, drugs can reach specific diseased areas, prolonging therapeutic efficacy while decreasing undesired side-effects. In addition, recent nanotechnological advances, such as surface stabilization and stimuli-responsive functionalization have also significantly improved the targeting capacity and therapeutic efficacy of the nanocarrier assisted drug delivery system. In this review, we evaluate recent advances in the development of different nanocarriers and their applications in therapeutics delivery.

Efficient enzyme-activated therapy based on the different locations of protein and prodrug in nanoMOFs

Enzyme-activated prodrug therapy (EAPT) is an effective cancer treatment strategy able to transport non-toxic prodrugs and subsequently convert them into drugs at specific times and locations. However, due to the limitation of easy biodegradability and the membrane-impermeable characteristic of exogenous enzymes, there is a need to exploit suitable carriers for the effective protection and simultaneous delivery of activating enzymes into cancer cells. Herein, hierarchically porous MOFs were employed for the loading of enzyme and prodrug in a single nanocarrier thanks to their different cavity sizes. The simple loading process allows entrapping of horseradish peroxidase (HRP) and a monocarboxyl-containing indole-3-acetic acid (IAA) prodrug with high loading capacities in different spaces, which keeps the catalytic activity of the enzyme perfectly intact and avoids the premature activation of the prodrug. The encapsulated HRP and IAA exhibit sustained and synchronized release behaviors. Compared to the native HRP enzyme, the current MOF nanocarriers not only facilitate enzyme delivery into cellular lysosomes and subsequent endosomal escape, but also effectively release enzyme and prodrug in the intracellular environment within 48 h. Eventually, HRP and IAA loaded MOF nanocarriers cause significant cell death with a low IC₅₀ of 4.2 mg L^-1, while the IAA prodrug alone is non-toxic even at high concentrations. Thus, hierarchically porous MOFs might offer a promising platform for EAPT with a highly consistent spatiotemporal distribution of enzymes and prodrugs in target tissues.

Dendrimer grafted persistent luminescent nanoplatform for aptamer guided tumor imaging and acid-responsive drug delivery

Theranostic nano-drug delivery systems are promising candidates for early diagnosis and treatment of tumors. However, it is a great challenge to achieve accurate intracellular delivery and stimuli-responsive drug release with the enhanced anti-tumor effects and reduced side effects. Herein we report the fabrication of polyamide-amine (PAMAM) dendrimer grafted persistent luminescence nanoparticles (PLNPs) via in situ growth of PAMAM on the surface of PLNPs and its application in targeted bioimaging and drug delivery. The developed PLNPs-PAMAM possesses strong renewable near-infrared persistent luminescence for imaging and gives abundant terminal groups for further functionalization. Aptamer AS1411 coupled to the PLNPs-PAMAM surface can specifically bind to the over-expressed nucleolin on the membrane of tumor cells and improve the intracellular accumulation of the nanoparticles. Doxorubicin (DOX) is loaded on PLNPs-PAMAM by a pH-sensitive hydrazine, can be specifically released in the intracellular acid environment, leading to apoptosis of HeLa tumor cells and inhibition of tumor growth. The as-prepared smart drug delivery nanoplatform with persistent luminescence, PLNPs-PAMAM-AS1411/DOX, shows a good application prospect for precise cancer theranostics.

Nanomedicine to target multidrug resistant tumors

Nanomedicine employs nanotechnologies to develop innovative applications, and more specifically nano-objects in the field of human health, through exploitation of the physical, chemical and biological properties of materials at the nanoscale. The use of nanovehicles capable of transporting and releasing the active therapeutic payload into target cells, particularly in the case of cancer or inflammatory diseases, can also enhance diagnosis. Therefore, nanomedicines improve the benefit/risk ratio of drugs by increasing their bioavailability, selectivity, and efficacy in the target tissue, while reducing the necessary doses and hence diminishing untoward toxicity to healthy tissues. Overcoming multidrug resistance (MDR) to antitumor agents is a central goal of cancer research and therapeutics, making it possible to treat these diseases more accurately and effectively. The adaptability of nanomedicines e.g. modulation of their components, surface functionalization, encapsulation of various active therapeutics as well as the possibility of combining several treatments using a single nanoparticle platform, are characteristics which are perfectly poised to address classical chemoresistance, a major obstacle towards curative cancer therapy. In this review, we discuss an assortment of nanomedicines along with those that should be developed in order to surmount cancer MDR; these include exosomes, natural compounds, lipid nanocapsules, prodrug self-assemblies, and gold nanoparticles.

Targeted MMP-2 responsive chimeric polymersomes for therapy against colorectal cancer

In the current study, polyethylene glycol (PEG) was linked to polylactide (PLA) through the synthetic peptide PVGLIG which can be selectively cleaved by the tumor-associated matrix metalloproteinase 2 (MMP-2) enzyme. The synthesized chimeric triblock polymer of PEG-b-PVGLIG-PLA was implemented to form nanoscale self-assemble chimeric polymersomes. The hydrophobic SN38 was loaded into polymersomes with 70.3% ± 3.0% encapsulation efficiency demonstrating monodispersed spherical morphologies with 172 ± 30 nm dimension. The prepared chimeric polymersomal formulation provided controlled release of SN38 at physiological condition while illustrating seven-folds higher release rate when exposed to MMP-2 enzyme. At the next stage, AS1411 aptamer was conjugated onto the surface of MMP-2 responsive polymersomal formulation in order to provide guided drug delivery against nucleolin positive cells. In vitro cellular toxicity assay against C26 cell line (nucleolin positive) demonstrated significantly higher toxicity of targeted formulation in comparison with non-targeted one in low SN38 concentrations (0.15-1.25 μg/mL). In vivo study in mice bearing subcutaneous C26 tumor showed higher therapeutic index for MMP-2 responsive chimeric polymersomal formulation of SN38 in comparison with non-responsive one. On the other hand, AS1411 aptamer-targeted MMP-2 responsive chimeric polymersomal formulation exhibited highest therapeutic index compared to other groups. It could be concluded that the targeted chimeric polymersomes bearing both cleavable peptide sequence between their blocks and targeting ligand on their surface, provide favorable characteristics as an ideal delivery system against cancer.

Tumor microenvironment-induced structure changing drug/gene delivery system for overcoming delivery-associated challenges

Nano-drug/gene delivery systems (DDS) are powerful weapons for the targeted delivery of various therapeutic molecules in treatment of tumors. Nano systems are being extensively investigated for drug and gene delivery applications because of their exceptional ability to protect the payload from degradation in vivo, prolong circulation of the nanoparticles (NPs), realize controlled release of the contents, reduce side effects, and enhance targeted delivery among others. However, the specific properties required for a DDS vary at different phase of the complex delivery process, and these requirements are often conflicting, including the surface charge, particle size, and stability of DDS, which severely reduces the efficiency of the drug/gene delivery. Therefore, researchers have attempted to fabricate structure, size, or charge changeable DDS by introducing various tumor microenvironment (TME) stimuli-responsive elements into the DDS to meet the varying requirements at different phases of the delivery process, thus improving drug/gene delivery efficiency. This paper summarizes the most recent developments in TME stimuli-responsive DDS and addresses the aforementioned challenges.

pH-sensitive CuS@Cu2S@Au nanoparticles as a drug delivery system for the chemotherapy against colon cancer

pH-sensitive CuS@Cu2S@Au nanoparticles (NPs) are successfully prepared by sacrificing template method. The NPs are of hollow structure, which is certified by transmission electron microscopy (TEM). The CuS@Cu2S@Au NPs can be used as carriers for doxorubicin (DOX). The DOX loaded NPs exhibit pH-sensitive release of the drug, which are prospective as controllable drug delivery system. Besides, relative to the high toxicity and lethality of the free DOX, the time-dependent release of drug from the NPs is more suitable for the long-time and lasting treatment for colon cancer. The CuS@Cu2S@Au NPs with good biocompatibility are promising biomaterials in the application of biomedical and tissue engineering fields.

Glutathione- and light-controlled generation of singlet oxygen for triggering drug release in mesoporous silica nanoparticles

An activatable phthalocyanine-based photosensitiser and a singlet-oxygen-triggered doxorubicin releasing system have been incorporated into mesoporous silica nanoparticles, which can release the encapsulated doxorubicin in a controllable manner.

“Smart” self-assembled structures: toward intelligent dual responsive drug delivery systems

In the current review, we summarized the polymer and peptide-based schizophrenic copolymers which could form micellar and vesicular (polymersome) systems providing novel structures with beneficial applications.