Evaluation of drug penetration with cationic micelles and their penetration mechanism using an in vitro tumor model

The Optimized Lipid-Modified Prodrug for CNV Treatment

Choroidal neovascularization (CNV) is a prevalent cause of vision impairment. The primary treatment for CNV involves intravitreal injections of anti-vascular endothelial growth factor antibodies. Nevertheless, this approach still faces numerous limitations like poor patient compliance, high therapy expenditure and lack of response in some individuals. Herein, a series of anti-neovascularization prodrugs, SU5402 (SU), modified with lipids of varying chain lengths (C12, C16, C20, C24, C28) is synthesized (SU-C12, SU-C16, SU-C20, SU-C24, SU-C28). 1% polyvinyl alcohol (PVA) is used as a stabilizer to create nanoformulations of five prodrugs named SU-C12 NPs, SU-C16 NPs, SU-C20 NPs, SU-C24 NPs, SU-C28 NPs. Among these, SU-C20 NPs significantly prolong the retention of bioactive drug in the eye for up to 70 d. Moreover, SU-C20 NPs demonstrate superior tissue permeability via enhanced cellular endocytosis and exocytosis. With its prolonged retention and improved penetration, SU-C20 NPs reduce the fluorescence intensity of fundus leakage by 42.5% and the fluorescence area by 51.5% in CNV mice after four weeks, effectively inhibiting the progression of CNV. Altogether, small molecule drug SU is innovatively modified to improve its effectiveness for treating fundus neovascular diseases, proposing an alternative therapy for wet age-related macular degeneration (wAMD).

Modulating Intracellular Dynamics for Optimized Intracellular Release and Transcytosis Equilibrium

Active transcytosis-mediated nanomedicine transport presents considerable potential in overcoming diverse delivery barriers, thereby facilitating tumor accumulation and penetration. Nevertheless, the persistent challenge lies in achieving a nuanced equilibrium between intracellular interception for drug release and transcytosis for tumor penetration. In this study, a comprehensive exploration is conducted involving a series of polyglutamine-paclitaxel conjugates featuring distinct hydrophilic/hydrophobic ratios (HHR) and tertiary amine-oxide proportions (TP) (OPGA-PTX). The screening process, meticulously focused on delineating their subcellular distribution, transcytosis capability, and tumor penetration, unveils a particularly promising candidate denoted as OPPX, characterized by an HHR of 10:1 and a TP of 100%. OPPX, distinguished by its rapid cellular internalization through multiple endocytic pathways, selectively engages in trafficking to the Golgi apparatus for transcytosis to facilitate accumulation within and penetration throughout tumor tissues and simultaneously sorted to lysosomes for cathepsin B-activated drug release. This study not only identifies OPPX as an exemplary nanomedicine but also underscores the feasibility of modulating subcellular distribution to optimize the active transport capabilities and intracellular release mechanisms of nanomedicines, providing an alternative approach to designing efficient anticancer nanomedicines.

Orange-derived extracellular vesicles nanodrugs for efficient treatment of ovarian cancer assisted by transcytosis effect

Extracellular vesicles (EVs) have recently received much attention about the application of drug carriers due to their desirable properties such as nano-size, biocompatibility, and high stability. Herein, we demonstrate orange-derived extracellular vesicles (OEV) nanodrugs (DN@OEV) by modifying cRGD-targeted doxorubicin (DOX) nanoparticles (DN) onto the surface of OEV, enabling significantly enhancing tumor accumulation and penetration, thereby efficiently inhibiting the growth of ovarian cancer. The obtained DN@OEV enabled to inducement of greater transcytosis capability in ovarian cancer cells, which presented the average above 10-fold transcytosis effect compared with individual DN. It was found that DN@OEV could trigger receptor-mediated endocytosis to promote early endosome/recycling endosomes pathway for exocytosis and simultaneously reduce degradation in the early endosomes-late endosomes-lysosome pathway, thereby inducing the enhanced transcytosis. In particular, the zombie mouse model bearing orthotopic ovarian cancer further validated DN@OEV presented high accumulation and penetration in tumor tissue by the transcytosis process. Our study indicated the strategy in enhancing transcytosis has significant implications for improving the therapeutic efficacy of the drug delivery system.

Tumor Abnormality-Oriented Nanomedicine Design

Anticancer nanomedicines have been proven effective in mitigating the side effects of chemotherapeutic drugs. However, challenges remain in augmenting their therapeutic efficacy. Nanomedicines responsive to the pathological abnormalities in the tumor microenvironment (TME) are expected to overcome the biological limitations of conventional nanomedicines, enhance the therapeutic efficacies, and further reduce the side effects. This Review aims to quantitate the various pathological abnormalities in the TME, which may serve as unique endogenous stimuli for the design of stimuli-responsive nanomedicines, and to provide a broad and objective perspective on the current understanding of stimuli-responsive nanomedicines for cancer treatment. We dissect the typical transport process and barriers of cancer drug delivery, highlight the key design principles of stimuli-responsive nanomedicines designed to tackle the series of barriers in the typical drug delivery process, and discuss the "all-into-one" and "one-for-all" strategies for integrating the needed properties for nanomedicines. Ultimately, we provide insight into the challenges and future perspectives toward the clinical translation of stimuli-responsive nanomedicines.

Primary Human Pancreatic Cancer Cells Cultivation in Microfluidic Hydrogel Microcapsules for Drug Evaluation

Chemotherapy is an essential postoperative treatment for pancreatic cancer, while due to the lack of effective drug evaluation platforms, the therapeutic outcomes are hampered by tumor heterogeneity among individuals. Here, a novel microfluidic encapsulated and integrated primary pancreatic cancer cells platform is proposed for biomimetic tumor 3D cultivation and clinical drug evaluation. These primary cells are encapsulated into hydrogel microcapsules of carboxymethyl cellulose cores and alginate shells based on a microfluidic electrospray technique. Benefiting from the good monodispersity, stability, and precise dimensional controllability of the technology, the encapsulated cells can proliferate rapidly and spontaneously form 3D tumor spheroids with highly uniform size and good cell viability. By integrating these encapsulated tumor spheroids into a microfluidic chip with concentration gradient channels and culture chambers, dynamic and high-throughput drug evaluation of different chemotherapy regimens could be realized. It is demonstrated that different patient-derived tumor spheroids show different drug sensitivity on-chip, which is significantly consistent with the clinical follow-up study after the operation. The results demonstrate that the microfluidic encapsulated and integrated tumor spheroids platform has great application potential in clinical drug evaluation.

Charge-conversional click polyprodrug nanomedicine for targeted and synergistic cancer therapy

Polyprodrug nanomedicines hold great potential for combating tumors. However, the functionalization of polyprodrug nanomedicines to improve therapeutic efficacy is restricted by conventional polymerization methods. Herein, we fabricated a charge-conversional click polyprodrug nanomedicine system by metal-free azide-alkyne cycloaddition click polymerization (AACCP) for targeted and synergistic cancer therapy. Specifically, Pt(IV) prodrug-backboned diazide monomer, DMC prodrug-pendent diazide monomer, dialkyne-terminated PEG monomer and azide-modified folate were click polymerized to obtain the target polyprodrug (P1). P1 could self-assemble into nano-micelles (1-NM), where PEG was the hydrophilic shell with folate on the surface, Pt(IV) and DMC prodrugs as the hydrophobic core. Taking advantage of PEGylation and folate-mediated tumor cell targeting, 1-NM achieved prolonged blood circulation time and high tumor accumulation efficiency. Tumor acidic microenvironment-responsive cleavage and cascade activation of pendant DMC prodrug induced surface charge conversion of 1-NM from negative to positive, which promoted tumor penetration and cellular internalization of the remaining 1-NM. After internalization into tumor cells, the reduction-responsive activation of Pt(IV) prodrug to Pt(II) further showed synergetic effect with DMC for enhanced apoptosis. This first designed charge-conversional click polyprodrug nanomedicine exhibited targeted and synergistic efficacy to suppress tumor proliferation in living mice bearing human ovarian tumor model.

Tuning the Endocytosis of Hybrid Micelles through Spatial Regulation of Cationic Groups

The ability of nanocarriers to enter tumor cells can be enhanced by positive surface charge. Nonetheless, the relationship between the spatial distributions of cationic groups and the endocytosis and tumor penetration of nanocarriers remains largely elusive. Here, using quaternary ammonium salt (QAS) as a model cationic group, a series of hybrid micelles (HMs) bearing QAS with different spatial distributions were prepared from star-shaped polymers with well-defined molecular architectures. The structural characteristics of HM, such as spatial location of QAS and local poly(ethylene glycol) (PEG) density near QAS, were investigated by both experimental techniques and dissipative particle dynamics (DPD) simulation. We show that the drug carriers with QAS extending to the micellar outer space allows QAS to facilitate cell surface binding with minimized hindrance, resulting in greatly enhanced endocytosis compared with nanocarriers with QAS attached onto the micellar surface or shielded by a PEG corona. This study offers cues for future development of tumor-penetrating drug delivery systems.

Transcytosis-enabled active extravasation of tumor nanomedicine

Extravasation is the first step for nanomedicines in circulation to reach targeted solid tumors. Traditional nanomedicines have been designed to extravasate into tumor interstitium through the interendothelial gaps previously assumed rich in tumor blood vessels, i.e., the enhanced permeability and retention (EPR) effect. While the EPR effect has been validated in animal xenograft tumor models, accumulating evidence implies that the EPR effect is very limited and highly heterogeneous in human tumors, leading to highly unpredictable and inefficient extravasation and thus limited therapeutic efficacy of nanomedicines, including those approved in clinics. Enabling EPR-independent extravasation is the key to develop new generation of nanomedicine with enhanced efficacy. Transcytosis of tumor endothelial cells can confer nanomedicines to actively extravasate into solid tumors without relying on the EPR effect. Here, we review and prospectthe development of transcytosis-inducing nanomedicines, in hope of providing instructive insights for design of nanomedicines that can undergo selective transcellular transport across tumor endothelial cells, and thus inspiring the development of next-generation nanomedicines for clinical translation.

Current Strategies for the Treatment of Hepatocellular Carcinoma by Modulating the Tumor Microenvironment via Nano-Delivery Systems: A Review

Liver cancer remains a global health challenge with a projected incidence of over one million cases by 2025. Hepatocellular carcinoma (HCC) is a common primary liver cancer, accounting for about 90% of all liver cancer cases. The tumor microenvironment (TME) is the internal and external environment for tumor development, which plays an important role in tumorigenesis, immune escape and treatment resistance. Knowing that TME is a unique setting for HCC tumorigenesis, exploration of strategies to modulate TME has attracted increasing attention. Among them, the use of nano-delivery systems to deliver therapeutic agents to regulate TME components has shown great potential. TME-modulating nanoparticles have the advantages of protecting therapeutic agents from degradation, enhancing the ability of targeting HCC and reducing systemic toxicity. In this article, we summarize the TME components associated with HCC, including cancer-associated fibroblasts (CAFs), extracellular matrix (ECM), endothelial cells and immune cells, discuss their impact on the HCC progression, and highlight recent studies on nano-delivery systems that modulate these components. Finally, we also discuss opportunities and challenges in this field.

PEGylated Liposomes Accumulate in the Areas Relevant to Skin Toxicities via Passive Extravasation across "Leaky" Endothelium

PEGylated liposome is the cornerstone platform for modern drug delivery. Unfortunately, as exemplified by PEGylated liposomal doxorubicin (aka Doxil), altered doxorubicin pharmacokinetics causes off-target accumulation in the skin, including the palms and feet, leading to severe dose-limiting toxicity. In addition to Doxil, other nanoparticles and PEGylated liposomes exhibit significant deposition in the skin, but mechanisms of accumulation are poorly understood. Using ex vivo imaging and ex vivo confocal microscopy, we show that PEGylated liposomes in mice accumulate predominantly in the areas subject to mechanical stress/pressure. Blood vessels in foot skin appear to be especially leaky, exhibiting burst-like extravasations. Using high-resolution confocal microscopy and liposomes labeled with different dyes in the membrane and/or interior, two modes of extravasation were observed: (1) as intact liposomes; (2) as separated liposomal components. On the other hand, stable cross-linked iron oxide nanoworms extravasated only as intact nanoparticles. There was no colocalization between liposomes and exosomal marker CD81, excluding the role of exocytosis. Also, in situ perfusion of formalin-fixed foot skin with labeled liposomes revealed that the extravasation is mediated by passive, energy-independent diffusion and not by leukocyte "hitchhiking". These findings improve our understanding of extravasation pathways of nanocarriers in the areas relevant to skin pathologies and could lead to strategies to prevent and treat liposome-induced skin toxicities.

A tumor-penetrable drug nanococktail made from human histones for interventional nucleus-targeted chemophotothermal therapy of drug-resistant tumors

Nanoparticle-based chemophotothermal therapy (CPT) is a promising treatment for multidrug resistant tumors. In this study, a drug nanococktail of DIR825@histone was developed by employing doxorubicin (DOX), NIR dye IR825 and human histones for interventional nucleus-targeted CPT of multidrug resistant tumors with an interventional laser. After localized intervention, DIR825@histone penetrated tumor tissues by transcytosis, efficiently entered tumor cells and targeted the cell nuclei. DIR825@histone also exhibited good photothermal performance and thermal-triggered drug release. Efficient multidrug resistant tumor inhibition was achieved by enhanced CPT sensitization and MDR reversion via nuclear targeting. Moreover, an interventional laser assisted DIR825@histone in inhibiting multidrug resistant tumors by promoting the sufficient delivery of laser energy inside the tumor while reducing skin injury. Therefore, DIR825@histone together with this interventional nucleus-targeted CPT strategy holds great promise for treating multidrug resistant tumors.

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Proposing an interventional nucleus-targeted chemophotothermal therapy (CPT) for treating MDR tumors

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Using natural human histones for the first time to fabricate nucleus-targeted nanococktails.

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The nanococktail can penetrate tumor tissues by transcytosis, efficiently enter tumor cells and target the cell nuclei.

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Highly improved intracellular MDR reversion and less heat shock response in drug-resistant tumor cells can be achieved by nucleus-targeted chemophotothermal therapy.

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The combination of the nucleus-targeted DIR825@histone and interventional laser harvested the best therapeutic outcomes against drug-resistant tumor.

Preparation of Cationic Amphiphilic Nanoparticles with Modified Chitosan Derivatives for Doxorubicin Delivery

Polymeric micelle-like nanoparticles have demonstrated effectiveness for the delivery of some poorly soluble or hydrophobic anticancer drugs. In this study, a hydrophobic moiety, deoxycholic acid (DCA) was first bonded on a polysaccharide, chitosan (CS), for the preparation of amphiphilic chitosan (CS-DCA), which was further modified with a cationic glycidyltrimethylammounium chloride (GTMAC) to form a novel soluble chitosan derivative (HT-CS-DCA). The cationic amphiphilic HT-CS-DCA was easily self-assembled to micelle-like nanoparticles about 200 nm with narrow size distribution (PDI 0.08–0.18). The zeta potential of nanoparticles was in the range of 14 to 24 mV, indicating higher positive charges. Then, doxorubicin (DOX), an anticancer drug with poor solubility, was entrapped into HT-CS-DCA nanoparticles. The DOX release test was performed in PBS (pH 7.4) at 37 °C, and the results showed that there was no significant burst release in the first two hours, and the cumulative release increased steadily and slowly in the following hours. HT-CS-DCA nanoparticles loaded with DOX could easily enter into MCF-7 cells, as observed by a confocal microscope. As a result, DOX-loaded HT-CS-DCA nanoparticles demonstrated a significant inhibition activity on MCF-7 growth without obvious cellular toxicity in comparison with blank nanoparticles. Therefore, the anticancer efficacy of these cationic HT-CS-DCA nanoparticles showed great promise for the delivery of DOX in cancer therapy.

Interface-sensitized prodrug nanoaggregate as an effective in situ antitumor vaccine

In situ antitumor vaccines have been widely explored as an effective strategy to inhibit tumor growth by stimulating antitumor immune responses. Herein, we reported a simple and effective in situ antitumor vaccine, which was prepared by co-assembling cationic lipids (DOTAP) with the disulfide bond-linked lipid-drug conjugates of camptothecin and resiquimod. The resulting vaccine had a rod-sharped morphology with nanoscale sizes (average hydrodynamic diameter of ∼163.7 nm) and positively-charged interfaces (zeta potential ∼ +36.2 mV). The interfacial cationization of nanoaggregate resulted in 1000 folds faster redox-responsive drug release than that of unmodified ones, which induced a much more potent in vivo antitumor immune by accelerating the glutathione-responsive drug release at the tumor site. Such cationic lipid-drug nanoaggregates displayed many benefits, such as high co-loading capacity, simple preparation process, and wide applicability, which would serve as a promising new approach to design effective in situ antitumor vaccines.

Polymeric micelles in drug delivery: An insight of the techniques for their characterization and assessment in biorelevant conditions

Polymeric micelles, i.e. aggregation colloids formed in solution by self-assembling of amphiphilic polymers, represent an innovative tool to overcome several issues related to drug administration, from the low water-solubility to the poor drug permeability across biological barriers. With respect to other nanocarriers, polymeric micelles generally display smaller size, easier preparation and sterilization processes, and good solubilization properties, unfortunately associated with a lower stability in biological fluids and a more complicated characterization. Particularly challenging is the study of their interaction with the biological environment, essential to predict the real in vivo behavior after administration. In this review, after a general presentation on micelles features and properties, different characterization techniques are discussed, from the ones used for the determination of micelles basic characteristics (critical micellar concentration, size, surface charge, morphology) to the more complex approaches used to figure out micelles kinetic stability, drug release and behavior in the presence of biological substrates (fluids, cells and tissues). The techniques presented (such as dynamic light scattering, AFM, cryo-TEM, X-ray scattering, FRET, symmetrical flow field-flow fractionation (AF4) and density ultracentrifugation), each one with their own advantages and limitations, can be combined to achieve a deeper comprehension of polymeric micelles in vivo behavior. The set-up and validation of adequate methods for micelles description represent the essential starting point for their development and clinical success.

Prodrug Nanomedicine Inhibits Chemotherapy-Induced Proliferative Burst by Altering the Deleterious Intercellular Communication

Chemotherapy is one of the most commonly used clinical antitumor strategies. However, the therapy-induced proliferative burst, which always accompanies drug resistance and metastasis, has become a major obstacle during treatment. Except for some endogenous cellular or genetic mechanisms and some microenvironmental selection pressures, the intercellular connections in the tumor microenvironment (TME) are also thought to be the driving force for the acquired drug resistance and proliferative burst. Even though some pathway inhibitors or cell exempting strategies could be applied to partially avoid these unwanted communications, the complexity of the TME and the limited knowledge about those unknown detrimental connections might greatly compromise the efforts. Therefore, a more broad-spectrum strategy is urgently needed to relieve the drug-induced burst proliferation during various treatments. In this article, based on the possible discrepancies in metabolic activity between cells with different growth rates, several ester-bond-based prodrugs were synthesized. After screening, 7-ethyl-10-hyodroxycamptothecin-based prodrug nanoparticles were found to efficiently overcome the paclitaxel resistance, to selectively act on the malignantly proliferated drug-resistant cells and, furthermore, to greatly diminish the proliferative effect of common cytotoxic agents by blocking the detrimental intercellular connections. With the discriminating ability against malignant proliferating cells, the as-prepared prodrug nanomedicine exhibited significant anticancer efficacy against both drug-sensitive and drug-resistant tumor models, either by itself or by combining with highly potent nonselective chemotherapeutics. This work provides a different perspective and a possible solution for the treatment of therapy-induced burst proliferation.

Dual variable of drug loaded micelles in both particle and electrical charge on gastric cancer treatment

Gastric cancer is a malignant tumour characterised by the uncontrolled cell growth. The incidence and mortality of gastric cancer remain high for the invasion and metastasis. We are urgently seeking a risk-free and effective treatment strategy for gastric cancer. In this study, paclitaxel and tetrandrine were encapsulated in the inner core of micelles, and DSPE-PEG₂₀₀₀-CPP and HA were modified on the micellar surface. HA/CPP modified paclitaxel plus tetrandrine micelles had a suitable particle size (90 nm) for permeating tumour tissue. The zeta potential of the targeting micelles was 8.37 mV after hydrolysis by HAase solution. Results of in vitro experiments indicated that HA/CPP modified paclitaxel plus tetrandrine micelles + HAase could enhance the intracellular uptake, inhibit the formation of neovascularization, block the process of EMT and destroy the invasion and metastasis. In vivo assays indicated that HA/CPP modified paclitaxel plus tetrandrine micelles could be selectively accumulated into tumour sites and exhibited the strong antitumor activity with negligible toxicity. These results suggested that HA/CPP modified paclitaxel plus tetrandrine micelles might provide a new strategy for treating gastric cancer.

Transcytosis - An effective targeting strategy that is complementary to "EPR effect" for pancreatic cancer nano drug delivery

Numerous nano drug delivery systems have been developed for preclinical cancer research in the past 15 years with the hope for a fundamental change in oncology. The robust nanotherapeutic research has yielded early-stage clinical products as exemplified by the FDA-approved nano formulations (Abraxane® for paclitaxel and Onyvide® for irinotecan) for the treatment of solid tumors, including pancreatic ductal adenocarcinoma (PDAC). It is generally believed that enhanced permeability and retention (EPR) plays a key role in nanocarriers' accumulation in preclinical tumor models and is a clinically relevant phenomenon in certain cancer types. However, use of EPR effect as an across-the-board explanation for nanoparticle tumor access is likely over-simplified, particularly in the stroma rich solid tumors such as PDAC. Recently, ample evidences including our own data showed that it is possible to use transcytosis as a major mechanism for PDAC drug delivery. In this mini-review, we summarize the key studies that discuss how transcytosis can be employed to enhance EPR effect in PDAC, and potentially, other cancer malignancies. We also mentioned other vasculature engineering approaches that work beyond the classic EPR effect.

Stable, Bioresponsive, and Macrophage-Evading Polyurethane Micelles Containing an Anionic Tripeptide Chain Extender

Polymeric nanocarriers have been extensively used in medicinal applications for drug delivery. However, intravenous nanocarriers circulating in the blood will be rapidly cleared from the mononuclear macrophage system. The surface physicochemical characterizations of nanocarriers are the primary factors to determine their fate in vivo, such as evading the reticuloendothelial system, exhibiting long blood circulation times, and accumulating in the targeted site. In this work, we develop a series of polyurethane micelles containing segments of an anionic tripeptide, hydrophilic mPEG, and disulfide bonds. It is found that the long hydrophilic mPEG can shield the micellar surface and have a synergistic effect with the negatively charged tripeptide to minimize macrophage phagocytosis. Meanwhile, the disulfide bond can rapidly respond to the intracellular reduction environment, leading to the acceleration of drug release and improvement of the therapeutic effect. Our results verify that these anionic polyurethane micelles hold great potential in the development of the stealth immune system and controllable intracellular drug transporters.

Enzyme-activatable polymer-drug conjugate augments tumour penetration and treatment efficacy

A tumour microenvironment imposes barriers to the passive diffusion of molecules, which renders tumour penetration an unresolved obstacle to an effective anticancer drug delivery. Here, we present a γ-glutamyl transpeptidase-responsive camptothecin-polymer conjugate that actively infiltrates throughout the tumour tissue through transcytosis. When the conjugate passes on the luminal endothelial cells of the tumour blood vessels or extravasates into the tumour interstitium, the overexpressed γ-glutamyl transpeptidase on the cell membrane cleaves the γ-glutamyl moieties of the conjugate to generate positively charged primary amines. The resulting cationic conjugate undergoes caveolae-mediated endocytosis and transcytosis, which enables transendothelial and transcellular transport and a relatively uniform distribution throughout the tumour. The conjugate showed a potent antitumour activity in mouse models that led to the eradication of small solid tumours (~100 mm³) and regression of large established tumours with clinically relevant sizes (~500 mm³), and significantly extended the survival of orthotopic pancreatic tumour-bearing mice compared to that with the first-line chemotherapeutic drug gemcitabine.

Chain-Length- and Saturation-Tuned Mechanics of Fluid Nanovesicles Direct Tumor Delivery

Small unilamellar vesicles (SUVs), ubiquitous in organisms, play key and active roles in various biological processes. Although the physical properties of the constituent lipid molecules (i.e., the acyl chain length and saturation) are known to affect the mechanical properties of SUVs and consequently regulate their biological behaviors and functions, the underlying mechanism remains elusive. Here, we combined theoretical modeling and experimental investigation to probe the mechanical behaviors of SUVs with different lipid compositions. The membrane bending rigidity of SUVs increased with increasing chain length and saturation, resulting in differences in the vesicle rigidity and deformable capacity. Furthermore, we tested the tumor delivery capacity of liposomes with low, intermediate, and high rigidity as typical models for SUVs. Interestingly, liposomes with intermediate rigidity exhibited better tumor extracellular matrix diffusion and multicellular spheroid (MCS) penetration and retention than that of their stiffer or softer counterparts, contributing to improved tumor suppression. Stiff SUVs had superior cellular internalization capacity but intermediate tumor delivery efficacy. Stimulated emission depletion microscopy directly showed that the optimal formulation was able to transform to a rod-like shape in MCSs, which stimulated fast transport in tumor tissues. In contrast, stiff liposomes hardly deformed, whereas soft liposomes changed their shape irregularly, which slowed their MCS penetration. Our findings introduce special perspectives from which to map the detailed mechanical properties of SUVs with different compositions, provide clues for understanding the biological functions of SUVs, and suggest that liposome mechanics may be a design parameter for enhancing drug delivery.

"Navigate-dock-activate" anti-tumor strategy: Tumor micromilieu charge-switchable, hierarchically activated nanoplatform with ultrarapid tumor-tropic accumulation for trackable photothermal/chemotherapy

The delivery of therapeutics into tumors remains a challenge in nanoparticle-mediated drug delivery. However, effective therapies such as photothermal therapy (PTT) are limited by quick systemic clearance and non-specific biodistribution. Anti-tumor strategies tailored to accommodate both tumor accumulation/retention and cellular internalization under a single platform would be a promising strategy. This work demonstrates a hierarchical activating strategy that would exhibit enhanced circulation and rapid tumor-tropism as well as facilitate tumor penetration, followed by tumor-specific drug release to realize trackable photothermal/chemotherapy. Methods: We engineered a lithocholic acid-conjugated disulfide-linked polyethyleneimine micelle (LAPMi) loaded with paclitaxel (LAPMi-PTX, L), followed by the electrostatic adsorption of indocyanine green (ICG, I) on LAPMI-PTX and subsequently coated them with thermosensitive DPPC and DSPE-PEG-NH₂ lipids (L), producing Lipid/ICG/LAPMi-PTX (LIL-PTX) nanoparticles (NPs). The characteristics of NPs, including physicochemical characterization, photothermal & pH responsiveness, cell uptake, tumor spheroid penetration, anti-tumor efficacy and hierarchical activation of LIL-PTX NPs were investigated in vitro and in vivo by using CT26 cell line. The anti-metastatic potential of LIL-PTX NPs were demonstrated using 4T1 orthotopic tumor model. Results: The NPs synthesized possessed charge switchability in the mildly acidic pH, and were laser- and pH-responsive. Dual stimuli-responsive nature of LIL-PTX NPs improved the disposition of therapeutics to the tumor, reflected by enhanced intracellular uptake, tumor spheroid penetration and in vitro cytotoxicity studies. LIL-PTX NPs readily switched its surface charge from neutral to positive upon reaching the tumor milieu, thus resulting in rapid tumor tropism and accumulation. Under near-infrared laser irradiation, the thermosensitive lipids on LIL-PTX NPs were deshielded, and the tumor-penetrating LAPMi-PTX was subsequently exposed to the tumor milieu, thus resulting in enhanced intracellular internalization. Next, LAPMi-PTX evaded the endo-lysosomes, thereby releasing the PTX through the degradation of LAPMi mediated by intracellular GSH in the tumor. LIL-PTX NPs significantly improved the therapy by eradicating primary tumors completely and suppressing their subsequent lung metastasis. Conclusion: The improved therapeutic index is due to enhanced passive targeting by rapid tumor-tropic accumulation and tumor penetration by laser-driven exposure of LAPMi, thereby improving the therapeutic delivery for image-guided photothermal/chemotherapy.

Challenges and Recent Progress in Oral Drug Delivery Systems for Biopharmaceuticals

Routes of drug administration and the corresponding physicochemical characteristics of a given route play significant roles in therapeutic efficacy and short term/long term biological effects. Each delivery method has favorable aspects and limitations, each requiring a specific delivery vehicles design. Among various routes, oral delivery has been recognized as the most attractive method, mainly due to its potential for solid formulations with long shelf life, sustained delivery, ease of administration and intensified immune response. At the same time, a few challenges exist in oral delivery, which have been the main research focus in the field in the past few years. The present work concisely reviews different administration routes as well as the advantages and disadvantages of each method, highlighting why oral delivery is currently the most promising approach. Subsequently, the present work discusses the main obstacles for oral systems and explains the most recent solutions proposed to deal with each issue.

Egg Component-Composited Inverse Opal Particles for Synergistic Drug Delivery

Microparticles have a demonstrated value in drug delivery systems. The attempts to develop this technology focus on the generation of functional microparticles by using innovative but accessible materials. Here, we present egg component-composited microparticles with a hybrid inverse opal structure for synergistic drug delivery. The egg component inverse opal particles were produced by using egg yolk to negatively replicate colloid crystal bead templates. Because of their huge specific surface areas, abundant nanopores, and complex nanochannels of the inverse opal structure, the resultant egg yolk particles could be loaded with different kinds of drugs, such as hydrophobic camptothecin (CPT), by simply immersing them into the corresponding drug solutions. Attractively, additional drugs, such as the hydrophilic doxorubicin (DOX), could also be encapsulated into the particles through the secondary filling of the drug-doped egg white hydrogel into the egg yolk inverse opal scaffolds, which realized the synergistic drug delivery for the particles. It was demonstrated that the egg-derived inverse opal particles were with large quantity and lasting releasing for the CPT and DOX codelivery, and thus could significantly reduce cell viability, and enhance therapeutic efficacy in treating cancer cells. These features of the egg component-composited inverse opal microparticles indicated that they are ideal microcarriers for drug delivery.

Programmed 'triple-mode' anti-tumor therapy: Improving peritoneal retention, tumor penetration and activatable drug release properties for effective inhibition of peritoneal carcinomatosis

Peritoneal carcinomatosis (PC) is a fatal condition arising in the gastrointestinal tract. PC patients administered drugs locally in the tumor region, such as in intraperitoneal chemotherapy (IPCh), suffer from low drug retention time and tumor penetration. Herein, we synthesized a lithocholic acid (LCA)-conjugated disulfide-linked polyethyleneimine (ssPEI) micelle (LAPMi) nanoconstruct by covalently conjugating ssPEI and LCA, thereby forming positive charged nanomicellar structures loaded with paclitaxel (PTX) (LAPMi-PTX) for IPCh. The incorporation of a positive surface charge aided in prolonging the peritoneal retention time, presumably via ascites-induced protein corona formation, and the subsequent size expansion caused resistance against undesired clearance through lymphatic openings. Furthermore, preferential tumor penetration by LAPMi-PTX is attributable to the permeation-enhancing properties of LCA, and the subsequent tumor activatable drug release was induced by the presence of disulfide linkages. By integrating these properties, LAPMi exhibited prolonged peritoneal residence time, enhanced tumor permeation and chemotherapeutic effect evidenced by in vitro, tumor spheroid and in vivo studies. Importantly, our strategy enabled significant PC inhibition and increased the overall survival rate of tumor-bearing mice. In conclusion, we provided a new paradigm of intractable PC treatment by enabling the prolonged residence time of the nanoconstruct, thereby enhancing tumor penetration and anti-tumor therapy.

Size shrinkable drug delivery nanosystems and priming the tumor microenvironment for deep intratumoral penetration of nanoparticles

The penetration of nanomedicine into solid tumor still constitutes a great challenge for cancer therapy, which lead to the failure of thorough clearance of tumor cells. Aiming at solving this issue, lots of encouraging progress has been made in the development of multistage nanoparticles triggered by various stimuli in the past few years. Besides, the therapeutical effects of nanoagents are also greatly impacted by the complex tumor microenvironment, and remodeling tumor microenvironment has become another important approach for promoting nanoparticles penetration. In this review, we summarize and analyze recent research progress and challenges in promoting nanoparticle penetration based on two kinds of different strategies, which include size shrinkable nanoparticles and priming tumor microenvironments. Especially, many recent reported multi-strategy approaches based on particle size reduction in conjugated with other therapeutic strategies are discussed. And we expect to provide some useful enlightenments and proposals on nanotechnology-based drug delivery systems for more effective therapy of solid tumors.

Multifunctional hybrid micelles with tunable active targeting and acid/phosphatase-stimulated drug release for enhanced tumor suppression

Therapeutic efficacy of conventional single PEGylated polymeric micelles is significantly reduced by limited endocytosis and intracellular drug release. To improve drug delivery efficiency, poly (ethylene glycol)-block-poly (l-lactic acid)/(Arg-Gly-Asp-Phe)-poly (aminoethyl ethylene phosphate)-block-poly (l-lactic acid) (PEG-PLLA/RGDF-PAEEP-PLLA) hybrid micelles with tunable active targeting and acid/phosphatase-stimulated drug release are developed. The optimized hybrid micelles with 6 wt % of RGDF have favorable in vitro and in vivo activities. The hybrid micelles could temporarily shield the targeting efficacy of RGDF at pH 7.4 due to the steric effect exerted by concealment of RGDF peptides in the PEG corona, which strongly decreases the clearance by mononuclear phagocyte system and consequently improves the tumor accumulation. Inside the solid tumor with a lower acidic pH, the hybrid micelles restore the active tumor targeting property with exposed RGDF on the surface of the micelles because of the increased protonation and stretching degree of PAEEP blocks. RGDF-mediated endocytosis improves the tumor cell uptake. The hybrid micelles would also enhance intracellular drug release because of the hydrolysis of the acid/phosphatase-sensitivity of PAEEP blocks in endo/lysosome. Systemic administration of the hybrid micelles significantly inhibits tumor growth by 96% due to the integration of enhanced circulation time, tumor accumulation, cell uptake and intracellular drug release.

Programmed drug delivery system based on optimized "size decrease and hydrophilicity/hydrophobicity transformation" for enhanced hepatocellular carcinoma therapy of doxorubicin

Requirements on drug delivery systems to surmount a complex series of pathophysiological barriers bear "cascading contradictions", especially size and hydrophilicity/hydrophobicity contradiction. Herein, a programmed drug delivery system (GNPs-Dox-Lac) based on optimized "size decrease and hydrophilicity/hydrophobicity transformation" was developed by combination the gelatin nanoparticle (GNPs) and prodrug Doxorubicin-Lactose (Dox-Lac). The results showed that GNPs-Dox-Lac (133.3 nm) were kinetically stable in blood circulation and inclined to accumulate at the tumor site. Then the degradation of the GNPs triggered by tumor extracellular matrix metalloproteinase-2 (MMP2) led to the release of prodrug Dox-Lac (Mw 898 Da) to facilitate the tumor tissue penetration and cellular uptake. Last, pH-responsive disassociation of Dox-Lac in tumor cells resulted in the free Dox (Mw 543 Da) release to induce toxicity. As expected, GNPs-Dox-Lac achieved superior tumor inhibition rate of 90.8% with low toxicity in vivo, suggesting its potential for enhanced hepatocellular carcinoma (HCC) therapy of doxorubicin in future.

The Effects of Biological Fluids on Colloidal Stability and siRNA Delivery of a pH-Responsive Micellar Nanoparticle Delivery System

Nanoparticles (NPs) interact with complex protein milieus in biological fluids, and these interactions have profound effects on NP physicochemical properties and function. Surprisingly, most studies neglect the impact of these interactions, especially with respect to NP-mediated siRNA delivery. Here, the effects of serum on colloidal stability and siRNA delivery of a pH-responsive micellar NP delivery system were characterized. Results show cationic NP-siRNA complexes aggregate in ≥2% serum in buffer, but are stable in serum-free media. Furthermore, nonaggregated NP-siRNA delivered in serum-free media result in 4-fold greater siRNA uptake in vitro, compared to aggregated NP-siRNA. Interestingly, pH-responsive membrane lysis behavior, which is required for endosomal escape, and NP-siRNA dissociation, necessary for gene knockdown, are significantly reduced in serum. Consistent with these data, nonaggregated NP-siRNA in serum-free conditions result in highly efficient gene silencing, even at doses as low as 5 nM siRNA. NP-siRNA diameter was measured at albumin and IgG levels mimicking biological fluids. Neither albumin nor IgG alone induces NP-siRNA aggregation, implicating other serum proteins in NP colloidal instability. Finally, as a proof-of-principle that stability is maintained in established in vivo models, transmission electron microscopy reveals NP-siRNA are taken up by ductal epithelial cells in a nonaggregated state when injected retroductally into mouse salivary glands in vivo. Overall, this study shows serum-induced NP-siRNA aggregation significantly diminishes efficiency of siRNA delivery by reducing uptake, pH-responsive membrane lysis activity, and NP-siRNA dissociation. Moreover, these results highlight the importance of local NP-mediated drug delivery and are broadly applicable to other drug delivery systems.

Intelligent "Peptide-Gathering Mechanical Arm" Tames Wild "Trojan-Horse" Peptides for the Controlled Delivery of Cancer Nanotherapeutics

Cell-penetrating peptides (CPPs), also called "Trojan-Horse" peptides, have been used for facilitating intracellular delivery of numerous diverse cargoes and even nanocarriers. However, the lack of targeting specificity ("wildness" or nonselectivity) of CPP-nanocarriers remains an intractable challenge for many in vivo applications. In this work, we used an intelligent "peptide-gathering mechanical arm" (Int PMA) to curb CPPs' wildness and enhance the selectivity of R₉-liposome-based cargo delivery for tumor targeting. The peptide NGR, serving as a cell-targeting peptide for anchoring, and peptide PLGLAG, serving as a substrate peptide for deanchoring, were embedded in the Int PMA motif. The Int PMA construct was designed to be sensitive to tumor microenvironmental stimuli, including aminopeptidase N (CD13) and matrix metalloproteinases (MMP-2/9). Moreover, Int PMA could be specifically recognized by tumor tissues via CD13-mediated anchoring and released for cell entry by MMP-2/9-mediated deanchoring. To test the Int PMA design, a series of experiments were conducted in vitro and in vivo. Functional conjugates Int PMA-R₉-poly(ethylene glycol) (PEG)₂₀₀₀-distearoylphosphatidyl-ethanolamine (DSPE) and R₉-PEG₂₀₀₀-DSPE were synthesized by Michael addition reaction and were characterized by thin-layer chromatography and matrix-assisted laser desorption ionization-time-of-flight mass spectrometry. The Int PMA-R₉-modified doxorubicin-loaded liposomes (Int PMA-R₉-Lip-DOX) exhibited a proper particle diameter (approximately 155 nm) with in vitro sustained release characteristics. Cleavage assay showed that Int PMA-R₉ peptide molecules could be cleaved by MMP-2/9 for completion of deanchoring. Flow cytometry and confocal microscopy studies indicated that Int PMA-R₉-Lip-DOX can respond to both endogenous and exogenous stimuli in the presence/absence of excess MMP-2/9 and MMP-2/9 inhibitor (GM6001) and effectively function under competitive receptor-binding conditions. Moreover, Int PMA-R₉-Lip-DOX generated more significant subcellular dispersions that were especially evident within endoplasmic reticulum (ER) and Golgi apparatus. Notably, Int PMA-R₉-Lip-DOX could induce enhanced apoptosis, during which caspase 3/7 might be activated. In addition, Int PMA-R₉-Lip-DOX displayed enhanced in vitro and in vivo antitumor efficacy versus "wild" R₉-Lip-DOX. On the basis of investigations at the molecular level, cellular level, and animals' level, the control of Int PMA was effective and promoted selective delivery of R₉-liposome cargo to the target site and reduced nonspecific uptake. This Int PMA-controlled strategy based on aminopeptidase-guided anchoring and protease-triggered deanchoring effectively curbed the wildness of CPPs and bolstered their effectiveness for in vivo delivery of nanotherapeutics. The specific nanocarrier delivery system used here could be adapted using a variety of intelligent designs based on combinations of multifunctional peptides that would specifically and preferentially bind to tumors versus nontumor tissues for tumor-localized accumulation in vivo. Thus, CPPs have a strong advantage for the development of intelligent nanomedicines for targeted tumor therapy.

Microfluidic generation of egg-derived protein microcarriers for 3D cell culture and drug delivery

Microcarriers have a demonstrated value for biomedical applications, in particular for drug delivery and three-dimensional cell culture. Attempts to develop this technique tend to focus on the fabrication of functional microparticles by using convenient methods with innovative but accessible materials. Inspired by the process of boiling eggs in everyday life, which causes the solidification of egg proteins, we present a new microfluidic "cooking" approach for the generation of egg-derived microcarriers for cell culture and drug delivery. As the egg emulsion droplets are formed with exquisite precision during the microfluidic emulsification, the resultant egg microcarriers present highly monodisperse and uniform morphologies at the size range of hundred microns to one millimeter. Benefiting from the excellent biocompatibility of the egg protein components, the obtained microcarriers showed good performances of cell adherence and growth. In addition, after a freezing treatment, the egg microcarriers were shown to have interconnected porous structures throughout their whole sphere, could absorb and load different kinds of drugs or other active molecules, and work as microcarrier-based delivery systems. These features point to the potential value of the microfluidic egg microcarriers in biomedicine.

Enhancing Tumor Penetration of Nanomedicines

Tumor-targeted nanomedicines have been extensively applied to alter the drawbacks and enhance the efficacy of chemotherapeutics. Despite the large number of preclinical nanomedicine studies showing initial success, their therapeutic benefit in the clinic has been rather modest, which is partially due to the inefficient tumor penetration caused by the tumor microenvironment (high density of cells and extracellular matrix, increased interstitial fluid pressure). Furthermore, tumor penetration of nanomedicines is significantly influenced by physicochemical characteristics, such as size, surface chemistry, and shape. The effect of size on tumor penetration has been exploited to design nanomedicines with switchable size to tackle this challenge. Moreover, several pharmacological and physical approaches have been developed to enhance the tumor penetration of nanomedicines, by penetration-promoting ligands, intratumoral drug release, and modulating the tumor microenvironment and vasculature. Overall, these efforts have resulted in nanomedicines with better tumor penetration properties and with enhanced therapeutic efficacy. Future research should be directed to penetration-promoting strategies with broad applicability and with high translational potential.

Positively Charged Combinatory Drug Delivery Systems against Multi-Drug-Resistant Breast Cancer: Beyond the Drug Combination

The formation and development of cancer is usually accompanied by angiogenesis and is related to multiple pathways. The inhibition of one pathway by monotherapy might result in the occurrence of drug resistance, tumor relapse, or metastasis. Thus, a combinatory therapeutic system that targets several independent pathways simultaneously is preferred for the treatment. To this end, we prepared combinatory drug delivery systems consisting of cytotoxic drug SN38, pro-apoptotic KLAK peptide, and survivin siRNA with high drug loading capacity and reductive responsiveness for the treatment of multi-drug-resistant (MDR) cancer. With the help of positive charge and the synergistic effect of different drug, the combinatory systems inhibited the growth of doxorubicin-resistant breast cancer cells (MCF-7/ADR) efficiently. Interestingly, the systems without siRNA showed more superior in vivo anticancer efficacy than those with siRNA which exhibited enhanced in vitro cytotoxicity and pro-apoptotic ability. This phenomenon could be attributed to the preferential tumor accumulation, strong tumor penetration, and excellent tumor vasculature targeting ability of the combinatory micelles of SN38 and KLAK. As a result, a combinatory multitarget therapeutic system with positive charge induced tumor accumulation and vasculature targeting which can simultaneously inhibit the growth of both tumor cell and tumor vasculature was established. This work also enlightened us to the fact that the design of combinatory drug delivery systems is not just a matter of simple drug combination. Besides the cytotoxicity and pro-apoptotic ability, tumor accumulation, tumor penetration, or vascular targeting may also influence the eventual antitumor effect of the combinatory system.

Modality of tumor endothelial VEGFR2 silencing-mediated improvement in intratumoral distribution of lipid nanoparticles

The vascular endothelial growth factor (VEGF)-mediated enhancement in vascular permeability is considered to be a major factor in tumor-targeting delivery via the enhanced permeability and retention (EPR) effect. We previously reported that the silencing of the endothelial VEGF receptor (VEGFR2) by a liposomal siRNA system (RGD-MEND) resulted in an enhanced intratumoral distribution of polyethylene glycol (PEG)-modified liposomes (LPs) in a renal cell carcinoma, a type of hypervascularized cancer, although the inhibition of VEGF signaling would be expected to decrease the permeability of the tumor vasculature. We herein report that the enhancement in the intratumoral distribution of LPs by VEGFR2 inhibition was dependent on the vascular type of the tumor (stroma vessel type; SV and tumor vessel type; TV). In the case of TV-type tumors (renal cell carcinoma and hepatocellular carcinoma), inhibiting VEGFR2 improved intratumoral distribution, while no effect was found in the case of SV-type tumors (colorectal cancer). Moreover, through a comparison of the intratumoral distribution of LPs with a variety of physical properties (100nm vs 400nm, neutral vs negative vs positive), VEGFR2 inhibition was found to alter the tumor microenvironment, including heparan sulfate proteoglycans (HSPGs). In addition, the results regarding the effect of the size of nanoparticles indicated that VEGFR2 inhibition improved the penetration of nanoparticles through the vessel wall, but not via permeability, suggesting the involvement of an unknown mechanism. Our findings suggest that a combination of anti-angiogenic therapy and delivery via the EPR effect would be useful in certain cases, and that altering the tumor microenvironment by VEGFR2 blockade has a drastic effect on the intratumoral distribution of nanoparticles.

A promising strategy for improved solubilization of ionic drugs simply by electrostatic pushing

Addition of soluble salts to the SDS-bound phenosafranin induces electrostatic pushing of the probe within the micellar interior from its initial location at the micelle–water interface.