Overcoming Biological Barriers in Cancer Therapy: Cell Membrane-Based Nanocarrier Strategies for Precision Delivery

Given the unique capabilities of natural cell membranes, such as prolonged blood circulation and homotypic targeting, extensive research has been devoted to developing cell membrane-inspired nanocarriers for cancer therapy, while most focused on overcoming one or a few biological barriers. In fact, the journey of nanosystems from systemic circulation to tumor cells involves intricate processes, encompassing blood circulation, tissue accumulation, cancer cell targeting, endocytosis, endosomal escape, intracellular trafficking to target sites, and therapeutic action, all of which pose limitations to their clinical translation. This underscores the necessity of meticulously considering these biological barriers in the design of cell membrane-mimetic nanocarriers. In this review, we delineate the functions and applications of diverse types of cell membranes in nanocarrier systems. We elaborate on the biological hurdles encountered at each stage of the biomimetic nanoparticle's odyssey to the target, and comprehensively discuss the obstacles imposed by the tumor microenvironment for precise delivery. Subsequently, we systematically review contemporary cell membrane-based strategies aimed at overcoming these multi-level biological barriers, encompassing hybrid cell membrane (HCM) camouflage, tumor microenvironment remodeling, endosomal/lysosomal escape, multidrug resistance (MDR) reversal, optimization of nanoparticle physicochemical properties, and so on. Finally, we outline potential strategies to accelerate the development of cell membrane-inspired precision nanocarriers and discuss the challenges that must be addressed to enhance their clinical applicability. This review serves as a guide for refining the study of cell membrane-mimetic nanosystems in surmounting in vivo delivery barriers, thereby significantly contributing to advancing the development and application of cell membrane-based nanoparticles in cancer delivery.

Cell-penetrating Peptides as Keys to Endosomal Escape and Intracellular Trafficking in Nanomedicine Delivery

This review article discusses the challenges of delivering cargoes to the cytoplasm, for example, proteins, peptides, and nucleic acids, and the mechanisms involved in endosomal escape. Endocytosis, endosomal maturation, and exocytosis pose significant barriers to effective cytoplasmic delivery. The article explores various endosomal escape mechanisms, such as the proton sponge effect, osmotic lysis, membrane fusion, pore formation, membrane destabilization/ disruption, and vesicle budding and collapse. Additionally, it discusses the role of lysosomes, glycocalyx, and molecular crowding in the cytoplasmic delivery process. Despite the recent advances in nonviral delivery systems, there is still a need to improve cytoplasmic delivery. Strategies such as fusogenic peptides, endosomolytic polymers, and cell-penetrating peptides have shown promise in improving endosomal escape and cytoplasmic delivery. More research is needed to refine these strategies and make them safer and more effective. In conclusion, the article highlights the challenges associated with cytoplasmic delivery and the importance of understanding the mechanisms involved in endosomal escape. A better understanding of these processes could result in the creation of greater effectiveness and safe delivery systems for various cargoes, including proteins, peptides, and nucleic acids.

Matrix-degrading soft-nanoplatform with enhanced tissue penetration for amplifying photodynamic therapeutic efficacy of breast cancer

The dense extracellular matrix (ECM) in the tumor microenvironment forms an abnormal physical barrier, which impedes the delivery and penetration of nanomedicines and hinders their therapeutic efficacy. Herein, we synthesize matrix-degrading soft-nanocapsules composed of human serum albumin (HSA) and hyaluronidase (HAase) for overcoming the obstruction of ECM in the tumor microenvironment. The matrix-degrading human serum albumin/hyaluronidase soft-nanocapsules, referred to as HSA/HAase SNCs, possess a uniform diameter, inward hollow structure, and wrinkled morphology. In vitro biocompatibility results indicate that the HSA/HAase SNCs display no adverse effects on the viability of human umbilical vein endothelial cells (HUVECs), smooth muscle cells (SMCs), and mouse breast cancer (4T1) cells and do not induce hemolysis towards red blood cells (RBCs). The HSA/HAase SNCs exhibit a 1.4-fold increase in tumor cellular uptake compared to the stiff-counterparts and enhanced penetration in 4T1-, mouse colon carcinoma 26- (CT26-), and mouse pancreatic cancer- (PanO2-) multicellular spheroids. Thanks to the advanced biological properties, a photodynamic platform prepared by loading Ce6 in the HSA/HAase SNCs (HSA/HAase@Ce6) shows improved reactive oxygen species production, a stronger killing effect for cancer cells, and deeper penetration in tumor tissues. In vivo experiments show that HSA/HAase@Ce6 effectively inhibits tumor growth in breast cancer mouse models. RNA-seq analysis of the mice that received the treatment of HSA/HAase@Ce6 shows enrichment of signaling pathways associated with ECM-degradation, which demonstrates that the matrix-degrading nanocapsules overcome the ECM-induced physical barriers in tumors. Overall, the matrix-degrading soft-nanoplatform represents a highly promising strategy to overcome ECM-induced physical barriers and enhance the therapeutic efficacy of nanomedicines.

Custom-Design of Multi-Stimuli-Responsive Degradable Silica Nanoparticles for Advanced Cancer-Specific Chemotherapy

Chemotherapy is crucial in oncology for combating malignant tumors but often encounters obatacles such as severe adverse effects, drug resistance, and biocompatibility issues. The advantages of degradable silica nanoparticles in tumor diagnosis and treatment lie in their ability to target drug delivery, minimizing toxicity to normal tissues while enhancing therapeutic efficacy. Moreover, their responsiveness to both endogenous and exogenous stimuli opens up new possibilities for integrating multiple treatment modalities. This review scrutinizes the burgeoning utility of degradable silica nanoparticles in combination with chemotherapy and other treatment modalities. Commencing the elucidation of degradable silica synthesis and degradation mechanisms, emphasis is placed on the responsiveness of these materials to endogenous (e.g., pH, redox reactions, hypoxia, and enzymes) and exogenous stimuli (e.g., light and high-intensity focused ultrasound). Moreover, this exploration delves into strategies harnessing degradable silica nanoparticles in chemotherapy alone, coupled with radiotherapy, photothermal therapy, photodynamic therapy, gas therapy, immunotherapy, starvation therapy, and chemodynamic therapy, elucidating multimodal synergies. Concluding with an assessment of advances, challenges, and constraints in oncology, despite hurdles, future investigations are anticipated to augment the role of degradable silica in cancer therapy. These insights can serve as a compass for devising more efficacious combined tumor treatment strategies.

Oxidized Dextran/Chitosan Hydrogel Engineered with Tetrasulfide-Bridged Silica Nanoparticles for Postsurgical Treatment

Tumor recurrence and wound microbial infection after tumor excision are serious threats to patients. Thus, the strategy to supply a sufficient and sustained release of cancer drugs and simultaneously engineer antibacterial properties and satisfactory mechanical strength is highly desired for tumor postsurgical treatment. Herein, A novel double-sensitive composite hydrogel embedded with tetrasulfide-bridged mesoporous silica (4S-MSNs) is developed. The incorporation of 4S-MSNs into oxidized dextran/chitosan hydrogel network, not only enhances the mechanical properties of hydrogels, but also can increase the specificity of drug with dual pH/redox sensitivity, thereby allowing more efficient and safer therapy. Besides, 4S-MSNs hydrogel preserves the favorable physicochemical properties of polysaccharide hydrogel, such as high hydrophilicity, satisfactory antibacterial activity, and excellent biocompatibility. Thus, the prepared 4S-MSNs hydrogel can be served as an efficient strategy for postsurgical bacterial infection and inhibition of tumor recurrence.

Insights into tumor size-dependent nanoparticle accumulation using deformed organosilica nanoprobes

Deformed organosilica nanoprobes (CDPF) exhibit enhanced accumulation within larger tumors, highlighting the pivotal role of the tumor microenvironment in the optimization of nanoparticle-based therapeutic strategies.

Overcoming tumor microenvironment obstacles: Current approaches for boosting nanodrug delivery

In order to achieve targeted delivery of anticancer drugs, efficacy improvement, and side effect reduction, various types of nanoparticles are employed. However, their therapeutic effects are not ideal. This phenomenon is caused by tumor microenvironment abnormalities such as abnormal blood vessels, elevated interstitial fluid pressure, and dense extracellular matrix that affect nanoparticle penetration into the tumor's interstitium. Furthermore, nanoparticle properties including size, charge, and shape affect nanoparticle transport into tumors. This review comprehensively goes over the factors hindering nanoparticle penetration into tumors and describes methods for improving nanoparticle distribution by remodeling the tumor microenvironment and optimizing nanoparticle physicochemical properties. Finally, a critical analysis of future development of nanodrug delivery in oncology is further discussed. STATEMENT OF SIGNIFICANCE: This article reviews the factors that hinder the distribution of nanoparticles in tumors, and describes existing methods and approaches for improving the tumor accumulation from the aspects of remodeling the tumor microenvironment and optimizing the properties of nanoparticles. The description of the existing methods and approaches is followed by highlighting their advantages and disadvantages and put forward possible directions for the future researches. At last, the challenges of improving tumor accumulation in nanomedicines design were also discussed. This review will be of great interest to the broad readers who are committed to delivering nanomedicine for cancer treatment.

Size effect of fluorescent thiol-organosilica particles on their distribution in the mouse spleen

We investigated the distribution of intravenously administered thiol-organosilica particle (thiol-OS) in the spleen to evaluate their size effect in mice. A single administration of particles of thiol-OS containing rhodamine B (Rh) (90, 280, 340, 450, 630, 1110, 1670, and 3030 nm in diameter) was performed. After 24 h, we conducted a combination analysis using histological studies by fluorescent microscopy and quantitative inductively coupled plasma optical emission spectrometry (ICP-OES), which revealed no clear correlation between the particle size and spleen uptake of particle weight and number per tissue weight, and the injection dose. Moreover, Rh with 450 nm diameter (Rh450) showed the highest uptake, and Rh with 340 nm diameter (Rh340) showed the lowest uptake. Histologically, large fluorescent areas in the marginal zone (MZ) and red pulp (RP) of the spleen were observed for all particle sizes, but less in the follicle of white pulp. Using combination analysis using the particle weights of ICP-OES and the fluorescent area, we compared the distributions of each particle in each region. Rh450 had the largest accumulated weight in the MZ and RP. Particles larger than Rh450 showed negative correlations between their sizes and accumulated weight in the MZ and RP. Simultaneous dual administration of particles using Rhs and thiol-OS containing fluorescein (90 nm in diameter) showed the size-dependent difference in cellular distribution and intracellular localization. Immunohistochemical staining against macrophage markers, CD169, and F4/80 showed various colocalization patterns with macrophages that uptook particles, indicating differences in particle uptake in each macrophage may have novel significance.

Design of Disintegrable Nanoassemblies to Release Multiple Small-Sized Nanoparticles

The therapeutic and diagnostic effects of nanoparticles depend on the efficiency of their delivery to targeted tissues, such as tumors. The size of nanoparticles, among other characteristics, plays a crucial role in determining their tissue penetration and retention. Small nanoparticles may penetrate deeper into tumor parenchyma but are poorly retained, whereas large ones are distributed around tumor blood vessels. Thus, compared to smaller individual nanoparticles, assemblies of such nanoparticles due to their larger size are favorable for prolonged blood circulation and enhanced tumor accumulation. Upon reaching the targeted tissues, nanoassemblies may dissociate at the target region and release the smaller nanoparticles, which is beneficial for their distribution at the target site and ultimate clearance. The recent emerging strategy that combines small nanoparticles into larger, biodegradable nanoassemblies has been demonstrated by several groups. This review summarizes a variety of chemical and structural designs for constructing stimuli-responsive disintegrable nanoassemblies as well as their different disassembly routes. These nanoassemblies have been applied as demonstrators in the fields of cancer therapy, antibacterial infection, ischemic stroke recovery, bioimaging, and diagnostics. Finally, we summarize stimuli-responsive mechanisms and their corresponding nanomedicine designing strategies, and discuss potential challenges and barriers towards clinical translation.

Synthesis of Monodispersed Hollow Mesoporous Organosilica and Silica Nanoparticles with Controllable Shell Thickness Using Soft and Hard Templates

Hollow mesoporous nanoparticles with controllable size (less than 100 nm) are desired as drug-delivery carriers. Herein, we report the synthesis of monodispersed hollow mesoporous organosilica (HMOS) and hollow mesoporous silica (HMS) nanoparticles using soft and hard templating methods. HMOS shells, with 1,2-bis(triethoxysilyl)ethane (BTEE) as the precursor and hexadecyltrimethylammonium bromide and sodium dodecyl sulfate (SDS) as the soft templates, were formed on monodispersed silica nanoparticles (SNPs), which were used as the hard templates. HMOS and HMS nanoparticles were obtained by removing the SNPs after three rounds of ammonia dialysis. The hollow size of HMOS can be tuned by changing the size of the SNPs. By using SNPs with a size of 36.5 nm, hollow spaces of approximately 20 nm connected the surface through narrow pores (<5 nm). Mesopores of approximately 12 nm were formed by the surfactant micelles. Additionally, the interparticle space in HMOS and HMS was approximately 12 nm. The shell thicknesses of HMOS and HMS could be tuned in the range of 5-9 nm by changing the BTEE amount. Moreover, the amount of surfactant used varied the porous structure. The HMOS with a thickness of 5 nm exhibited a Brunauer-Emmett-Teller (BET) surface area of 268 m²/g and a total pore volume of 1.14 cm³/g. Meanwhile, HMS demonstrated a BET surface area of 553 m²/g and a total pore volume of 1.82 cm³/g while maintaining a hollow structure. HMOS displayed a high loading capacity for ibuprofen (3009 mg/g), and its drug release system showed a sustained-release property. Therefore, the HMOS preparation using hard and soft templates proposed herein can control the hollow size and shell thickness for drug-delivery applications.

Folic acid-modified disulfiram/Zn-IRMOF3 nanoparticles for oral cancer therapy by inhibiting ALDH1A1+ cancer stem cells

The repurposing of old drugs can reduce the cost of drug development and speed up the availability of drugs for clinical use. Disulfiram (DSF) is an approved drug for alcohol abuse. In recent years, it has been established that DSF exerts an antitumor effect via targeted inhibition of ALDH1+ cancer stem cells (CSCs). However, due to its metal ion dependence, easy hydrolysis and low availability, the clinical application of DSF is limited. Previous studies have also shown that Zn²⁺ can inhibit CSCs. Accordingly, we developed a novel metal organic framework (IRMOF3)-Zn²⁺, and DSF was incorporated in the IRMOF3. Folic acid (FA) was subsequently loaded on the surface yielding IRMOF3 (IRMOF3-DSF-FA) for targeted therapy of tumors. The nanoscale IRMOF3-DSF-FA exhibited a high loading capacity, good biocompatibility and strong cell uptake capacity, which could provide metal ions, target tumor tissues and inhibit ALDH1+ CSCs. In vivo experiments showed that IRMOF3-DSF-FA could significantly inhibit the growth of CSCs and tumors, with no significant vital organ damage during treatment. Accordingly, IRMOF3-DSF-FA has great prospects for application as a DSF carrier, opening new horizons for targeted therapy of oral cancer.

Intelligent Pore Switch of Hollow Mesoporous Organosilica Nanoparticles for High Contrast Magnetic Resonance Imaging and Tumor-Specific Chemotherapy

Hollow mesoporous organosilica nanoparticles (HMONs) are widely considered as a promising drug nanocarrier, but the loaded drugs can easily leak from HMONs, resulting in the considerably decreased drug loading capacity and increased biosafety risk. This study reports the smart use of core/shell Fe₃O₄/Gd₂O₃ (FG) hybrid nanoparticles as a gatekeeper to block the pores of HMONs, which can yield an unreported large loading content (up to 20.4%) of DOX. The conjugation of RGD dimer (R2) onto the DOX-loaded HMON with FG capping (D@HMON@FG@R2) allowed for active tumor-targeted delivery. The aggregated FG in D@HMON@FG@R2 could darken the normal tissue surrounding the tumor due to the high r₂ value (253.7 mM^-1 s^-1) and high r₂/r₁ ratio (19.13), and the intratumorally released FG as a result of reducibility-triggered HMON degradation could brighten the tumor because of the high r₁ value (20.1 mM^-1 s^-1) and low r₂/r₁ ratio (7.01), which contributed to high contrast magnetic resonance imaging (MRI) for guiding highly efficient tumor-specific DOX release and chemotherapy.

Self-transformation synthesis of hierarchically porous benzene-bridged organosilica nanoparticles for efficient drug delivery

Herein, a feasible outside-in hydrothermal self-transformation strategy is presented to fabricate hierarchically porous benzene-bridged organosilica nanoparticles (HPBONs), and detailed mechanistic investigations were performed to study the formation of hierarchically porous nanostructures. The obtained HPBONs consisted of a mesoporous core (2.3 nm) and a large mesoporous flocculent shell (12.6 nm), which corresponded to an overall diameter of ∼ 200 nm and good water dispersibility, respectively. Owing to the unique hierarchically porous structure and high surface area (877 m²/g), HPBONs showed a high coloading capacity for the hydrophilic drug doxorubicin (DOX) and the hydrophobic photosensitizer chlorin e6 (Ce6) (355 µg/mg, 38 µg/mg, respectively) and acid-responsive DOX drug release (42.62%), leading to precise chemo-photodynamic therapy in vitro, as the cytotoxicity assay revealed 70% killing of breast cancer (MCF-7) cells. This research provides a new method to construct hierarchically porous organosilica-based nanodelivery systems.

Rapid pH-responsive self-disintegrating nanoassemblies balance tumor accumulation and penetration for enhanced anti-breast cancer therapy

The dilemma of tumor accumulation and deep penetration has always been a barrier in antitumor therapy. Stimuli-responsive size changeable drug delivery systems provide possible solutions. Nevertheless, the low size-shrinkage efficiency limited the antitumor effects. In this study, an instant pH-responsive size shrinkable nanoassemblies named self-aggregated DOX@HA-CD (SA-DOX@HA-CD) was formulated using small-sized hyaluronic acid modified carbon dots (HA-CD) as monomers, which could self-aggregate into raspberry-like structure via hydrophobicity force in neutral pH and rapidly disassemble into shotgun-like DOX-loaded CD monomer in simulated tumor microenvironment (pH 6.5), owing to the transformation in electrical charge and hydrophobicity/hydrophilicity of this system. The transmission electron microscopy showed that the clustered SA-DOX@HA-CD had a diameter of ~150 nm, and thoroughly disassembled into ~30 nm nanoparticles in response to acidic environment. The disassemble efficiency was approximately 100%. Attributed to this property, SA-DOX@HA-CD led to enhanced cellular internalization and accumulation in 4T1 cells in simulated tumor microenvironment, as well as deep tumor penetration in 3D tumor spheroid model. Besides, the imine bond between DOX and HA-CD endowed DOX with pH-responsive release profile in the acidic lysosome environment. Furthermore, in the orthotopic 4T1 tumor-bearing mouse model, SA-DOX@HA-CD demonstrated higher tumor accumulation than non-aggregated DOX-HA-CD. Meanwhile, in response to the acid tumor microenvironment, the dissociated DOX-HA achieved deep tumor penetration, which consequently resulted in 2.5-fold higher antitumor efficiency. The formulation of self-aggregated SA-DOX@HA-CD provides a simple and effective alternative to prepare pH-responsive size-shrinkable nanodrug delivery systems. STATEMENT OF SIGNIFICANCE: The heterogeneity of tumor vasculature and the high tumor interstitial pressure lead to the barriers in tumor accumulation and deep penetration, which calls for opposite properties (e.g. size) of drug delivery systems. To address this dilemma, various size changeable nanoparticles have been developed utilizing special features of tumor microenvironment, such as pH, enzyme and reactive oxygen species. Nevertheless, the current strategies face the problems of incomplete hydrolysis of chemical bonds or insufficient enzyme degradation, which result in only partial size shrinkage, hindering the tumor deep penetration effects. Here we developed a self-assembled nanocluster, which could respond to acidic pH rapidly and thoroughly disassemble into small nanodots due to the alteration of hydrophobicity/hydrophilicity/charge, leading to approximately 100% dissociation. This strategy provides a new concept for design of size changeable drug delivery systems.

Intricately structured mesoporous organosilica nanoparticles: synthesis strategies and biomedical applications

Intricately structured mesoporous organosilica nanoparticles (IMONs) are being increasingly studied from their synthesis strategies to their use in biomedical applications, because of their distinctive hierarchical structures, excellent physicochemical features and satisfactory biological properties. This minireview is the first to summarize recently developed IMONs, including yolk-shell-structured nanoparticles, multi-shelled hollow spheres, deformable nanocapsules, Janus nanostructures and virus-like bionic-structured nanocarriers, and describe the corresponding formation mechanisms and recent evolution of the strategies used to synthesize these kinds of IMONs. Structure-dependent biomedical applications, such as multidrug delivery, bioimaging, synergistic therapy and biocatalysis, are also discussed. Finally, we provide an outlook for IMONs ranging from their structural control to synthesis strategies and ending with their use in biomedical applications.

Gas-Stabilizing Sub-100 nm Mesoporous Silica Nanoparticles for Ultrasound Theranostics

Recent studies have demonstrated that gas-stabilizing particles can generate cavitating micron-sized bubbles when exposed to ultrasound, offering excellent application potential, including ultrasound imaging, drug delivery, and tumor ablation. However, the majority of the reported gas-stabilizing particles are relatively large (>200 nm), and smaller particles require high acoustic pressures to promote cavitation. Here, this paper reports the preparation of sub-100 nm gas-stabilizing nanoparticles (GSNs) that can initiate cavitation at low acoustic intensities, which can be delivered using a conventional medical ultrasound imaging system. The highly echogenic GSNs (F127-hMSN) were prepared by carefully engineering the surfaces of ∼50 nm mesoporous silica nanoparticles. It was demonstrated that the F127-hMSNs could be continuously imaged with ultrasound in buffer or biological solutions or agarose phantoms for up to 20 min. Also, the F127-hMSN can be stored in phosphate-buffered saline for at least a month with no loss in ultrasound responsiveness. The particles significantly degraded when diluted in simulated body fluids, indicating possible biodegradation of the F127-hMSNs in vivo. Furthermore, at ultrasound imaging conditions, F127-hMSNs did not cause detectable cell death, supporting the potential safety of these particles. Finally, strong cavitation activity generation by the F127-hMSNs under high-intensity focused ultrasound insonation was demonstrated and applied to effectively ablate cancer cells.

Barriers and Strategies of Cationic Liposomes for Cancer Gene Therapy

Cationic liposomes (CLs) have been regarded as the most promising gene delivery vectors for decades with the advantages of excellent biodegradability, biocompatibility, and high nucleic acid encapsulation efficiency. However, the clinical use of CLs in cancer gene therapy is limited because of many uncertain factors in vivo. Extracellular barriers such as opsonization, rapid clearance by the reticuloendothelial system and poor tumor penetration, and intracellular barriers, including endosomal/lysosomal entrapped network and restricted diffusion to the nucleus, make CLs not the ideal vector for transferring extrinsic genes in the body. However, the obstacles in achieving productive therapeutic effects of nucleic acids can be addressed by tailoring the properties of CLs, which are influenced by lipid compositions and surface modification. This review focuses on the physiological barriers of CLs against cancer gene therapy and the effects of lipid compositions on governing transfection efficiency, and it briefly discusses the impacts of particle size, membrane charge density, and surface modification on the fate of CLs in vivo, which may provide guidance for their preclinical studies.

Hyaluronic acid-coated metal-organic frameworks benefit the ROS-mediated apoptosis and amplified anticancer activity of artesunate

Artesunate (AS), as an effective new tumour treatment drug, induces cancer cell death based on high intracellular reactive oxygen species (ROS) produced by interacting with ferrous ions. However, the relatively low intracellular ferrous iron ion concentrations and the low efficiency of ROS generation limit its clinical application. Herein, we developed a metal-organic framework-Fe²⁺ (MOF), and AS was loaded in the MOF and then coated with hyaluronic acid (HA) on the surface of the MOF (HA@MOF-AS) for targeted and enhanced cancer treatment. HA@MOF-AS has high loading efficiency, good monodispersity, biocompatibility, strong cell uptake capacity and high intracellular ROS production, and it can target tumour tissues. In addition, in vivo anticancer studies have shown that HA@MOF-AS not only has high accumulation in tumours but also significantly inhibits tumour growth without significant damage to major organs. Therefore, HA@MOF-AS has excellent potential and may open a new approach for targeted cancer treatment.

The importance of spheroids in analyzing nanomedicine efficacy

The use of nanomedicines for cancer treatment holds a great potential due to their improved efficacy and safety. During the nanomedicine preclinical in vitro evaluation stage, these are mainly tested on cell culture monolayers. However, these 2D models are an unrealistic representation of the in vivo tumors, leading to an inaccurate screening of the candidate formulations. To address this problem, spheroids are emerging as an additional tool to validate the efficacy of new therapeutics due to the ability of these 3D in vitro cancer models to mimic the key features displayed by in vivo solid tumors. In this review, the application of spheroids for the evaluation of nanomedicines' physicochemical properties and therapeutic efficacy is discussed.

Gelated Vorinostat with inner-lysosome triggered release for tumor-targeting chemotherapy

Histonedeacetylase inhibitor (HDACi) has great potential in targeted antitumor therapy by inhibiting tumor migration, invasion, and metastasis. As one of the typical HDACis, vorinostat (Suberoylanilide Hydroxamic Acid, SAHA) was approved as a therapeutic agent for cancer therapy, however, challenges remain due to their poor solubility, short half-life and low efficiency in cellular penetration. Considering the disadvantages of usual drug carriers, folate and vorinostat bound BSA nanogel (FVBN)was fabricated to implement higher solubility, stability, cellular uptake, and lipase-responsive release. With good dispersion and stability, FVBN significantly increased the cellular uptake of vorinostat through folate-mediated endocytosis. FVBN exhibited comparable cytotoxicity with free SAHA, and the growth of tumor cells was blocked in G1/G0 phase just like SAHA performed in cell cycle arrest tests. Moreover, FVBN not only effectively inhibited the growth of melanoma but also observably prevented pulmonary metastasis of melanoma. In the experiment against nude mice bearing solid ovarian cancer, FVBN showed excellent antitumor effect without liver damage, demonstrating the superiority of gelated and inner-lysosome triggered release strategies to the free SAHA, and it is promising to expand the scope of application of HDACi in clinical cancer therapy.

Potential drug delivery nanosystems for improving tumor penetration

Nanosystems, as one of the most important drug delivery systems, play a crucial rule in tumor therapy. However, the deep tumor penetration is retarded by the tumor physiological factors and nanomedicine properties. In this review, we firstly elaborate the factors which impact tumor penetration, including the tumor physiological factors and nanomedicine properties. Then, the latest and potential drug delivery nanosystems for improving tumor penetration are summarized and analyzed in detail. Moreover, recent combination therapies for improving penetration are described to enhance penetration. Finally, we summarize the typical clinical therapies of potential drug delivery nanosystems.

Overview of stimuli-responsive mesoporous organosilica nanocarriers for drug delivery

The application of nanomaterials is regarded nowadays as a highly promising approach for overcoming the limitations of the currently available cancer treatments, contributing for the creation of more effective, precise, and safer therapies. In the last years, organosilica nanoparticles arisen as alternatives to the most common mesoporous silica nanoparticles. The organosilica nanoparticles combine the advantages of the mesoporous silica, such as structural stability and mesoporous structure, with the increased biocompatibility and biodegradability of organic materials. Therefore, the variety of organic bridges that can be incorporated into the silica matrix allowed the development of new and exciting compositions, properties, and functions for improving the therapeutic effectiveness of the anticancer nanomedicines. In this review, the strategies that have been explored to create stimuli-responsive organosilica-based drug delivery systems are highlighted, describing the practical approaches and mechanisms controlling the drug release. Additionally, the organosilica nanoparticles surface modifications aimed for increasing the blood circulation time and the tumor targeting are also described.