Unravelling the in vivo dynamics of liposomes: Insights into biodistribution and cellular membrane interactions

Liposomes, as a colloidal drug delivery system dating back to the 1960s, remain a focal point of extensive research and stand as a highly efficient drug delivery method. The amalgamation of technological and biological advancements has propelled their evolution, elevating them to their current status. The key attributes of biodegradability and biocompatibility have been instrumental in driving substantial progress in liposome development. Demonstrating a remarkable ability to surmount barriers in drug absorption, enhance stability, and achieve targeted distribution within the body, liposomes have become pivotal in pharmaceutical research. In this comprehensive review, we delve into the intricate details of liposomal drug delivery systems, focusing specifically on their pharmacokinetics and cell membrane interactions via fusion, lipid exchange, endocytosis etc. Emphasizing the nuanced impact of various liposomal characteristics, we explore factors such as lipid composition, particle size, surface modifications, charge, dosage, and administration routes. By dissecting the multifaceted interactions between liposomes and biological barriers, including the reticuloendothelial system (RES), opsonization, enhanced permeability and retention (EPR) effect, ATP-binding cassette (ABC) phenomenon, and Complement Activation-Related Pseudoallergy (CARPA) effect, we provide a deeper understanding of liposomal behaviour in vivo. Furthermore, this review addresses the intricate challenges associated with translating liposomal technology into practical applications, offering insights into overcoming these hurdles. Additionally, we provide a comprehensive analysis of the clinical adoption and patent landscape of liposomes across diverse biomedical domains, shedding light on their potential implications for future research and therapeutic developments.

IRGD-modified erythrocyte membrane biomimetic temozolomide nanodots for the treatment of glioblastoma

The crossing of the blood-brain barrier (BBB) for conventional anticancer drugs is still a big challenge in treating glioma. The biomimetic nanoparticle delivery system has attracted increasing attention and has a promising future for crossing the BBB. Herein, we construct a multifunctional biomimetic nanoplatform using the erythrocyte membrane (EM) with the tumor-penetrating peptide iRGD (CRGDK/RGPD/EC) as a delivery, and the inner core loaded with the chemotherapeutic drug temozolomide (TMZ). The resulting biomimetic nanoparticle has perfect biocompatibility and stealth ability, which will provide more chances to escape the reticuloendothelial system (RES) entrapment, and increase the opportunity to enter the tumor site. Moreover, the decorated iRGD has been extensively used to actively targeting and deliver therapeutic agents across the BBB into glioma tissue. We show that this biomimetic delivery of TMZ with a diameter of 22 nm efficiently slowed the growth of glioblastoma multiforme (GBM) and increased the survival rate of the 30 d from 0% to 100%.

A lipo-polymeric hybrid nanosystem with metal enhanced fluorescence for targeted imaging of metastatic breast cancer

Cancer metastasis plays a major role in failure of therapeutic avenues against cancer. Owing to metastasis, nearly 70-80% of stage IV breast cancer patients lose their lives. Nanodrug delivery systems are playing a critical role in the therapy of metastatic cancer in the recent times. This paper reports the enhanced permeation and retention (EPR) based targeting of metastatic breast cancer using a novel nano lipo-polymeric system (PIR-Au NPs). The PIR-Au NPs demonstrated an increase in fluorescence by virtue of surface coating with gold, owing to the metal enhanced fluorescence phenomenon as reported in our earlier reports. Enhanced fluorescence of PIR-Au NPs was observed in murine mammary carcinoma cell line (4T1), as compared to free IR780 or IR780 loaded nanosystems (P-IR NPs), when incubated for same time at same concentrations, indicating its potential application for imaging and an enhanced bioavailability of IR780. Significant cell death was noted with photothermal mediated cytotoxicity in-vitro against breast cancer cells (MCF-7 and 4T1). An enhanced fluorescence was observed in the zebra fish embryos incubated with PIR-Au NPs. The enhanced permeation and retention (EPR) effect was seen with PIR-Au NPs in-vivo. A strong fluorescent signal was recorded in mice injected with PIR-Au NPs. The tumor tissue collected after 72 h, clearly showed a greater fluorescence as compared to other groups, indicating the plasmon enhanced fluorescence. We also demonstrated the EPR-based targeting of the PIR-Au NPs in-vivo by means of photothermal heat. This lipo-polymeric hybrid nanosystem could therefore be successfully applied for image-guided, passive-targeting to achieve maximum therapeutic benefits.

Development, Characterization and Pharmacological Evaluation of Cannabidiol-Loaded Long Circulating Niosomes

Cannabidiol (CBD) is a promising drug candidate with pleiotropic pharmacological activity, whose low aqueous solubility and unfavorable pharmacokinetics have presented obstacles to its full clinical implementation. The rational design of nanocarriers, including niosomes for CBD encapsulation, can provide a plausible approach to overcoming these limitations. The present study is focused on exploring the feasibility of copolymer-modified niosomes as platforms for systemic delivery of CBD. To confer steric stabilization, the niosomal membranes were grafted with newly synthesized amphiphilic linear or star-shaped 3- and 4-arm star-shaped copolymers based on polyglycidol (PG) and poly(ε-caprolactone) (PCL) blocks. The niosomes were prepared by film hydration method and were characterized by DLS, cryo-TEM, encapsulation efficacy, and in vitro release. Free and formulated cannabidiol were further investigated for cytotoxicity and pro-apoptotic and anti-inflammatory activities in vitro in three human tumor cell lines. The optimal formulation, based on Tween 60:Span60:Chol (3.5:3.5:3 molar ration) modified with 2.5 mol% star-shaped 3-arm copolymer, is characterized by a size of 235 nm, high encapsulation of CBD (94%), and controlled release properties. Niosomal cannabidiol retained the antineoplastic activity of the free agent, but noteworthy superior apoptogenic and inflammatory biomarker-modulating effects were established at equieffective exposure vs. the free drug. Specific alterations in key signaling molecules, implicated in programmed cell death, cancer cell biology, and inflammation, were recorded with the niosomal formulations.

Targeting endothelial permeability in the EPR effect

The characteristics of the primary tumor blood vessels and the tumor microenvironment drive the enhanced permeability and retention (EPR) effect, which confers an advantage towards enhanced delivery of anti-cancer nanomedicine and has shown beneficial effects in preclinical models. Increased vascular permeability is a landmark feature of the tumor vessels and an important driver of the EPR. The main focus of this review is the endothelial regulation of vascular permeability. We discuss current challenges of targeting vascular permeability towards clinical translation and summarize the structural components and mechanisms of endothelial permeability, the principal mediators and signaling players, the targeted approaches that have been used and their outcomes to date. We also critically discuss the effects of the tumor-infiltrating immune cells, their interplay with the tumor vessels and the impact of immune responses on nanomedicine delivery, the impact of anti-angiogenic and tumor-stroma targeting approaches, and desirable nanoparticle design approaches for greater translational benefit.

Innovative Design of Targeted Nanoparticles: Polymer-Drug Conjugates for Enhanced Cancer Therapy

Polymer-drug conjugates (PDCs) have shown great promise in enhancing the efficacy and safety of cancer therapy. These conjugates combine the advantageous properties of both polymers and drugs, leading to improved pharmacokinetics, controlled drug release, and targeted delivery to tumor tissues. This review provides a comprehensive overview of recent developments in PDCs for cancer therapy. First, various types of polymers used in these conjugates are discussed, including synthetic polymers, such as poly(↋-caprolactone) (PCL), D-α-tocopheryl polyethylene glycol (TPGS), and polyethylene glycol (PEG), as well as natural polymers such as hyaluronic acid (HA). The choice of polymer is crucial to achieving desired properties, such as stability, biocompatibility, and controlled drug release. Subsequently, the strategies for conjugating drugs to polymers are explored, including covalent bonding, which enables a stable linkage between the polymer and the drug, ensuring controlled release and minimizing premature drug release. The use of polymers can extend the circulation time of the drug, facilitating enhanced accumulation within tumor tissues through the enhanced permeability and retention (EPR) effect. This, in turn, results in improved drug efficacy and reduced systemic toxicity. Moreover, the importance of tumor-targeting ligands in PDCs is highlighted. Various ligands, such as antibodies, peptides, aptamers, folic acid, herceptin, and HA, can be incorporated into conjugates to selectively deliver the drug to tumor cells, reducing off-target effects and improving therapeutic outcomes. In conclusion, PDCs have emerged as a versatile and effective approach to cancer therapy. Their ability to combine the advantages of polymers and drugs offers enhanced drug delivery, controlled release, and targeted treatment, thereby improving the overall efficacy and safety of cancer therapies. Further research and development in this field has great potential to advance personalized cancer treatment options.

New SDS-Based Polyelectrolyte Multicore Nanocarriers for Paclitaxel Delivery-Synthesis, Characterization, and Activity against Breast Cancer Cells

The low distribution of hydrophobic anticancer drugs in patients is one of the biggest limitations during conventional chemotherapy. SDS-based polyelectrolyte multicore nanocarriers (NCs) prepared according to the layer by layer (LbL) procedure can release paclitaxel (PTX), and selectively kill cancer cells. Our main objective was to verify the antitumor properties of PTX-loaded NCs and to examine whether the drug encapsulated in these NCs retained its cytotoxic properties. The cytotoxicity of the prepared nanosystems was tested on MCF-7 and MDA-MB-231 tumour cells and the non-cancerous HMEC-1 cell line in vitro. Confocal microscopy, spectrophotometry, spectrofluorimetry, flow cytometry, and RT PCR techniques were used to define the typical hallmarks of apoptosis. It was demonstrated that PTX encapsulated in the tested NCs exhibited similar cytotoxicity to the free drug, especially in the triple negative breast cancer model. Moreover, SDS/PLL/PTX and SDS/PLL/PGA/PTX significantly reduced DNA synthesis. In addition, PTX-loaded NCs triggered apoptosis and upregulated the transcription of Bax, AIF, cytochrome-c, and caspase-3 mRNA. Our data demonstrate that these novel polyelectrolyte multicore NCs coated with PLL or PLL/PGA are good candidates for delivering PTX. Our discoveries have prominent implications for the possible choice of newly synthesized, SDS-based polyelectrolyte multicore NCs in different anticancer therapeutic applications.

Nanoparticle-based drug delivery systems to enhance cancer immunotherapy in solid tumors

Immunotherapy has developed rapidly in solid tumors, especially in the areas of blocking inhibitory immune checkpoints and adoptive T-cell transfer for immune regulation. Many patients benefit from immunotherapy. However, the response rate of immunotherapy in the overall population are relatively low, which depends on the characteristics of the tumor and individualized patient differences. Moreover, the occurrence of drug resistance and adverse reactions largely limit the development of immunotherapy. Recently, the emergence of nanodrug delivery systems (NDDS) seems to improve the efficacy of immunotherapy by encapsulating drug carriers in nanoparticles to precisely reach the tumor site with high stability and biocompatibility, prolonging the drug cycle of action and greatly reducing the occurrence of toxic side effects. In this paper, we mainly review the advantages of NDDS and the mechanisms that enhance conventional immunotherapy in solid tumors, and summarize the recent advances in NDDS-based therapeutic strategies, which will provide valuable ideas for the development of novel tumor immunotherapy regimen.

Perspectives for Improving the Tumor Targeting of Nanomedicine via the EPR Effect in Clinical Tumors

Over the past few decades, the enhanced permeability and retention (EPR) effect of nanomedicine has been a crucial phenomenon in targeted cancer therapy. Specifically, understanding the EPR effect has been a significant aspect of delivering anticancer agents efficiently to targeted tumors. Although the therapeutic effect has been demonstrated in experimental models using mouse xenografts, the clinical translation of the EPR effect of nanomedicine faces several challenges due to dense extracellular matrix (ECM), high interstitial fluid pressure (IFP) levels, and other factors that arise from tumor heterogeneity and complexity. Therefore, understanding the mechanism of the EPR effect of nanomedicine in clinics is essential to overcome the hurdles of the clinical translation of nanomedicine. This paper introduces the basic mechanism of the EPR effect of nanomedicine, the recently discussed challenges of the EPR effect of nanomedicine, and various strategies of recent nanomedicine to overcome the limitations expected from the patients' tumor microenvironments.

Human solid tumors and clinical relevance of the enhanced permeation and retention effect: a 'golden gate' for nanomedicine in preclinical studies?

Nanocarriers passively accumulate in solid tumors through irregular wide fenestrations in neovasculature and increased retention due to poor lymphatic drainage, a phenomenon termed the enhanced permeation and retention (EPR) effect. Although several preclinical reports have described the role of EPR in nanomedicine, its role in human solid tumor is obscure. There are several distinct factors for tumors in mice versus humans, including size, heterogeneity and nanomedicine pharmacokinetics. This review focuses on preclinical and clinical studies demonstrating the role of the EPR effect and passive targeting. The article illustrates the gaps that limit clinical effectiveness of the EPR effect and elaborates strategies to boost its efficiency, relaying future clinical outcomes for designing clinically applicable EPR-based nanomedicine.

pH-Responsive Poly(ethylene glycol)-b-poly(2-vinylpyridine) Micelles for the Triggered Release of Therapeutics

The use of pH-responsive polymeric micelles is a promising approach to afford the targeted, pH-mediated delivery of hydrophobic drugs within the low-pH tumour milieu and intracellular organelles of cancer cells. However, even for a common pH-responsive polymeric micelle system-e.g., those utilising poly(ethylene glycol)-b-poly(2-vinylpyridine) (PEG-b-PVP) diblock copolymers-there is a lack of available data describing the compatibility of hydrophobic drugs, as well as the relationships between copolymer microstructure and drug compatibility. Furthermore, synthesis of the constituent pH-responsive copolymers generally requires complex temperature control or degassing procedures that limit their accessibility. Herein we report the facile synthesis of a series of diblock copolymers via visible-light-mediated photocontrolled reversible addition-fragmentation chain-transfer polymerisation, with a constant PEG block length (90 repeat units (RUs)) and varying PVP block lengths (46-235 RUs). All copolymers exhibited narrow dispersity values (Đ ≤ 1.23) and formed polymeric micelles with low polydispersity index (PDI) values (typically <0.20) at physiological pH (7.4), within a suitable size range for passive tumour targeting (<130 nm). The encapsulation and release of three hydrophobic drugs (cyclin-dependent kinase inhibitor (CDKI)-73, gossypol, and doxorubicin) were investigated in vitro at pH 7.4-4.5 to simulate drug release within the tumour milieu and cancer cell endosome. Marked differences in drug encapsulation and release were observed when the PVP block length was increased from 86 to 235 RUs. With a PVP block length of 235 RUs, the micelles exhibited differing encapsulation and release properties for each drug. Minimal release was observed for doxorubicin (10%, pH 4.5) and CDKI-73 exhibited moderate release (77%, pH 4.5), whereas gossypol exhibited the best combination of encapsulation efficiency (83%) and release (91% pH 4.5) overall. These data demonstrate the drug selectivity of the PVP core, where both the block molecular weight and hydrophobicity of the core (and accordingly the hydrophobicity of the drug) have a significant effect on drug encapsulation and release. These systems remain a promising means of achieving targeted, pH-responsive drug delivery-albeit for select, compatible hydrophobic drugs-which warrants their further investigation to develop and evaluate clinically relevant micelle systems.

Influence of lung cancer model characteristics on tumor targeting behavior of nanodrugs

Evidence is mounting that there is a significant gap between the antitumor efficacy of nanodrugs in preclinical mouse tumor models and in clinical human tumors, and that differences in tumor models are likely to be responsible for this gap. Herein, we investigated the enhanced permeability and retention (EPR) effect in mouse lung cancer models with different tumor growth rates, volumes and locations, and analyzed the nanodrug tumor targeting behaviors limited by tumor vascular pathophysiological characteristics in various tumor models. The results showed that the fast-growing tumors were characterized by lower vascular tight junctions, leading to higher vascular paracellular transport activity and nanodrug tumor accumulation. The paracellular transport activity increased with the growth of tumor, but the vascular density and transcellular transport activity decreased, and as a result, the average tumor accumulation of passive targeting nanodrugs decreased. Orthotopic tumors were rich in blood vessels, but had low vascular transcellular and paracellular transport activities, making it difficult for nanodrug accumulation in orthotopic tumors via passive targeting strategies. The antitumor efficacy of passive targeting nanodrugs in various lung cancer-bearing mice validated the aforementioned nanodrug accumulation behavior, and nanodrugs based on the angiogenesis-tumor sequential targeting strategy achieved obviously improved efficacy in orthotopic lung cancer-bearing mice. These results suggest that the EPR effect varies in different tumor models and should not be used as a universal targeting strategy for antitumor nanodrugs. Besides, attention should be paid to the animal tumor models in the evaluation of nanodrugs so as to avoid exaggerating the antitumor efficacy.

HPMA copolymer conjugated 5-aminolevulinic acid exhibits superior efficacy for photodynamic therapy with tumor-responsive and targeting properties

In this study, we developed a nanoformulation of 5-aminolevulinic acid (5-ALA) for tumor-targeted photodynamic therapy, in which 5-ALA was conjugated with a biocompatible polymer N-(2-hydroxypropyl)methacrylamide (HPMA) through the hydrazone bond, i.e., P-ALA. P-ALA behaves as the nano-sized molecule with an average size of 5.5 nm in aqueous solution. P-ALA shows a largely increased release rate in acidic pH than physiological pH, suggesting the rapid release profile in acidic tumor environment. P-ALA did not show apparent cytotoxicity up to 0.1 mg/ml, however, under light irradiation, remarkable cell death was induced with the IC₅₀ of 20-30 μg/ml. More importantly, we found significantly higher tumor accumulation of P-ALA than 5-ALA which benefit from its nano-size by taking advantage of the enhanced permeability and retention (EPR) effect. Consequently, P-ALA exhibited much improved in vivo antitumor efficacy without any apparent side effects. We thus anticipate the application of P-ALA as a nano-designed photosensitizer for anticancer photodynamic therapy.

Effect of Cellular and Microenvironmental Multidrug Resistance on Tumor-Targeted Drug Delivery in Triple-Negative Breast cancer

Multidrug resistance (MDR) reduces the efficacy of chemotherapy. Besides inducing the expression of drug efflux pumps, chemotherapy treatment alters the composition of the tumor microenvironment (TME), thereby potentially limiting tumor-directed drug delivery. To study the impact of MDR signaling in cancer cells on TME remodeling and nanomedicine delivery, we generated multidrug-resistant 4T1 triple-negative breast cancer (TNBC) cells by exposing sensitive 4T1 cells to gradually increasing doxorubicin concentrations. In 2D and 3D cell cultures, resistant 4T1 cells are presented with a more mesenchymal phenotype and produced increased amounts of collagen. While sensitive and resistant 4T1 cells showed similar tumor growth kinetics in vivo, the TME of resistant tumors was enriched in collagen and fibronectin. Vascular perfusion was also significantly increased. Fluorophore-labeled polymeric (∼10 nm) and liposomal (∼100 nm) drug carriers were administered to mice with resistant and sensitive tumors. Their tumor accumulation and penetration were studied using multimodal and multiscale optical imaging. At the whole tumor level, polymers accumulate more efficiently in resistant than in sensitive tumors. For liposomes, the trend was similar, but the differences in tumor accumulation were insignificant. At the individual blood vessel level, both polymers and liposomes were less able to extravasate out of the vasculature and penetrate the interstitium in resistant tumors. In a final in vivo efficacy study, we observed a stronger inhibitory effect of cellular and microenvironmental MDR on liposomal doxorubicin performance than free doxorubicin. These results exemplify that besides classical cellular MDR, microenvironmental drug resistance features should be considered when aiming to target and treat multidrug-resistant tumors more efficiently.

Dual-targeting of brain tumors with nanovesicles

The delivery of chemotherapies to brain tumors faces the difficult task of crossing the blood-brain barrier (BBB).^1-4 The brain capillary endothelial cells (BCECs) along with other cell lines, such as astrocytes and pericytes, form the BBB. This highly selective semipermeable barrier separates the blood from the brain parenchyma. The BBB controls the movement of drug molecules in a selective manner⁵ and maintains central nervous system (CNS) homeostasis. Depending on the properties of drugs such as their hydrophilic-lipophilic balance (HLB), some can cross the BBB through passive diffusion.⁶ However, this approach alone has not led to successful drug developments due to low net diffusion rates and systemic toxicity. Although the use of nanomedicine has been proposed to overcome these drawbacks, many recent studies still rely on the so-called 'enhanced permeability and retention (EPR)' effect though there is a realization in the field of drug delivery that EPR effect may not be sufficient for successful drug delivery to brain tumors. Since, compared to many other solid tumors, brain tumors pose additional challenges such as more restrictive blood-tumor barrier as well as the well-developed lymphatic drainage, the selection of functional moieties on the nanocarriers under consideration must be carried out with care to propose better solutions to this challenge.

Effect of Hypertension on EPR effect Induced by Polymer Nanomicelles in Renal Cell Carcinoma in vitro

Objective

To investigate the effect of hypertension on the (enhanced permeability and retention, EPR) effect induced by polymer nanomicelles in renal cell carcinoma in vitro.

Methods

A total of 80 patients with renal cell carcinoma treated at the Department of Urology Surgery in the Dept. of Urology of the Affiliated Hospital of Hebei University from Oct. 2019 to Oct. 2020, were analyzed retrospectively. The hypertension group (experimental group) included 40 patients, and the normal blood pressure group (control group) included 40 patients. The diagnosis of renal clear cell carcinoma was confirmed by preoperative auxiliary examinations, such as ultrasonography and CT combined with postoperative pathological analysis. All patients underwent laparoscopic radical nephrectomy for renal cell carcinoma. Polymer nanomicelles (loaded with prolonium iodide) were perfused into the resected kidney specimens within the specified time. The iodine enrichment of polymer nanomicelles in renal tumors was assessed by CT scanning. The peak EPR effect and the time to the peak were statistically compared between the two groups.

Results

No significant differences were found in age, sex, location of kidney disease, tumor location or tumor size between the two groups (p> 0.05). The peak (χ̄±S) of the EPR effect in experimental group was 3.60±0.95 ug/cm3 and 3.01±0.96 ug/cm3 in control group, respectively. There was significant difference between the two groups (p< 0.05). The time to the peak of the EPR effect was 3.76±0.75 h in experimental group and 3.82±0.93 hour in control group, respectively. No statistically significant difference was found in the time to the peak of the EPR effect between the two groups (p> 0.05).

Conclusion

Hypertension has a certain effect on the EPR effect induced by polymer nanomicelles in renal cell carcinoma in vitro.

Supermagnetic Human Serum Albumin (HSA) Nanoparticles and PLGA-Based Doxorubicin Nanoformulation: A Duet for Selective Nanotherapy

Predicting the ability of nanoparticles (NP) to access the tumor is key to the success of chemotherapy using nanotherapeutics. In the present study, the ability of the dual NP-based theranostic system to accumulate in the tumor was evaluated in vivo using intravital microscopy (IVM) and MRI. The system consisted of model therapeutic doxorubicin-loaded poly(lactide-co-glycolide) NP (Dox-PLGA NP) and novel hybrid Ce^3/4+-doped maghemite NP encapsulated within the HSA matrix (hMNP) as a supermagnetic MRI contrasting agent. Both NP types had similar sizes of ~100 nm and negative surface potentials. The level of the hMNP and PLGA NP co-distribution in the same regions of interest (ROI, ~2500 µm²) was assessed by IVM in mice bearing the 4T1-mScarlet murine mammary carcinoma at different intervals between the NP injections. In all cases, both NP types penetrated into the same tumoral/peritumoral regions by neutrophil-assisted extravasation through vascular micro- and macroleakages. The maximum tumor contrasting in MRI scans was obtained 5 h after hMNP injection/1 h after PLGA NP injection; the co-distribution level at this time reached 78%. Together with high contrasting properties of the hMNP, these data indicate that the hMNP and PLGA NPs are suitable theranostic companions. Thus, analysis of the co-distribution level appears to be a useful tool for evaluation of the dual nanoparticle theranostics, whereas assessment of the leakage areas helps to reveal the tumors potentially responsive to nanotherapeutics.

The tumor EPR effect for cancer drug delivery: Current status, limitations, and alternatives

Over the past three decades, the enhanced permeability and retention (EPR) effect has been considered the basis of tumor-targeted drug delivery. Various cancer nanomedicines, including macromolecular drugs, have been designed to utilize this mechanism for preferential extravasation and accumulation in solid tumors. However, such nanomedicines have not yet achieved convincing therapeutic benefits in clinics. Increasing evidence suggests that the EPR effect is over-represented in human tumors, especially in metastatic tumors. This review covers the evolution of the concept, the heterogeneity and limitation of the EPR effect in clinical realities, and prospects for alternative strategies independent of the EPR effect.

Extracellular matrix degrading enzyme with stroma-targeting peptides enhance the penetration of liposomes into tumors

Various anti-tumor nanomedicines have been developed based on the enhanced permeability and retention effect. However, the dense extracellular matrix (ECM) in tumors remains a major barrier for the delivery and accumulation of nanoparticles into tumors. While ECM-degrading enzymes, such as collagenase, hyaluronidase, and bromelain, have been used to facilitate the accumulation of nanoparticles, serious side effects arising from the current non-tumor-specific delivery methods limit their clinical applications. Here, we report targeted delivery of bromelain into tumor tissues through its covalent attachment to a hyaluronic acid (HA)-peptide conjugate with tumor ECM targeting ability. The ECM targeting peptide, collagen type IV-binding peptide (C4BP), was chosen from six candidate-peptides based on their ability to bind to frozen sections of triple-negative breast cancer, 4T1 tumor ex vivo. The HA- C4BP conjugate showed a significant increase in tumor accumulation in 4T1-bearing mice after intravenous administration compared to unmodified HA. We further demonstrated that the systemic administration of bromelain conjugated C4BP-HA (C4BP-HA-Bro) potentiates the anti-tumor efficacy of liposomal doxorubicin. C4BP-HA-Bro decreased the number and length of collagen fibers and improved the distribution of doxorubicin within the tumor. No infusion reaction was noted after delivery of C4BP-HA-Bro. C4BP-HA thus offers a potential for effective and safe delivery of bromelain for improved intratumoral delivery of therapeutics.

Poly(Styrene-Co-Maleic Acid)-Conjugated 6-Aminofluorescein and Rhodamine Micelle as Macromolecular Fluorescent Probes for Micro-Tumors Detection and Imaging

Styrene-co-maleic acid (SMA) copolymer was evaluated as a polymer platform to conjugate with two fluorescent dyes, i.e., 6-aminofluorescein (AF) and Rhodamine (Rho); which spontaneously self-assembles in an aqueous medium and forms a micelle through a non-covalent interaction. These SMA-dye conjugates showed the nanosized micelle formation through dynamic light scattering (DLS) with discrete distributions having mean particle sizes of 135.3 nm, and 190.9 nm for SMA-AF, and SMA-Rho, respectively. The apparent molecular weight of the micelle was evaluated using Sephadex G-100 gel chromatography and it was found that the 49.3 kDa, and 28.7 kDa for SMA-AF, and SMA-Rho, respectively. Moreover, the biodistribution study showed the selective accumulation of the SMA-dye conjugates in the tumor of mice. Taken together, the SMA-dye conjugated micelles appear in high concentrations in the tumor by utilizing the enhanced permeability and retention (EPR) effect of the tumor-targeted delivery. These results indicate that SMA-dye conjugates have the advanced potential as macromolecular fluorescent probes for microtumor imaging by means of a photodynamic diagnosis.

Prediction the clinical EPR effect of nanoparticles in patient-derived xenograft models

Many preclinically tested nanoparticles in existing animal models fail to be directly translated into clinical applications because of their poor resemblance to human cancer. Herein, the enhanced permeation and retention (EPR) effect of glycol chitosan nanoparticles (CNPs) in different tumor microenvironments (TMEs) was compared using different pancreatic tumor models, including pancreatic cancer cell line (BxPC3), patient-derived cancer cell (PDC), and patient-derived xenograft (PDX) models. CNPs were intravenously injected into different tumor models, and their accumulation efficiency was evaluated using non-invasive near-infrared fluorescence (NIRF) imaging. In particular, differences in angiogenic vessel density, collagen matrix, and hyaluronic acid content in tumor tissues of the BxPC3, PDC, and PDX models greatly affected the tumor-targeting efficiency of CNPs. In addition, different PDX models were established using different tumor tissues of patients to predict the clinical EPR effect of CNPs in inter-patient TMEs, wherein the gene expression levels of PECAM1, COL4A1, and HAS1 in human tumor tissues were observed to be closely related to the EPR effect of CNPs in PDX models. The results suggested that the PDX models could mimic inter-patient TMEs with different blood vessel structures and extracellular matrix (ECM) content that critically affect the tumor-targeting ability of CNPs in different pancreatic PDX models. This study provides a better understanding of the heterogeneity and complexity of inter-patient TMEs that can predict the response of various nanoparticles in individual tumors for personalized cancer therapy.

Strategies for persistent retention of macromolecules and nanoparticles in the blood circulation

The enhanced permeability and retention (EPR) effect has been the gold standard in developing drug delivery systems for passive tumor targeting. Although the importance of this concept remains unchanged, some controversies have arisen. In this review, various strategies for tumor targeting using macromolecules and nanoparticles based on the EPR effect are discussed from the viewpoint of pharmacokinetics. Overall, such strategies seek to retain therapeutic material in the blood circulation, which is a key factor for successful targeting. Strategies using macromolecules, including antibody-drug conjugates, serum albumin-based delivery systems, PEGylated recombinant proteins, and stealth liposomes as well as nanoparticle-based strategies such as those based on lipid nanoparticles, and polymeric micelles, have been discussed. The feasibility of small extracellular vesicles, a new class of nanosized delivery carriers, is also discussed.

The role of size in PEGylated liposomal doxorubicin biodistribution and anti-tumour activity

The size of nanoliposome‐encapsulated drugs significantly affects their therapeutic efficacy, biodistribution, targeting ability, and toxicity profile for the cancer treatment. In the present study, the biodistribution and anti‐tumoral activity of PEGylated liposomal Doxorubicin (PLD) formulations with different sizes were investigated. First, 100, 200, and 400 nm PLDs were prepared by remote loading procedure and characterised for their size, zeta potential, encapsulation efficacy, and release properties. Then, in vitro cellular uptake and cytotoxicity were studied by flow cytometry and MTT assay, and compared with commercially available PLD Caelyx^®. In vivo studies were applied on BALB/c mice bearing C26 colon carcinoma. The cytotoxicity and cellular uptake tests did not demonstrate any statistically significant differences between PLDs. The biodistribution results showed that Caelyx^® and 100 nm liposomal formulations had the most doxorubicin (Dox) accumulation in the tumour tissue and, as a result, considerably suppressed tumour growth compared with 200 and 400 nm PLDs. In contrast, larger nanoparticles (200 and 400 nm formulations) had more accumulation in the liver and spleen. This study revealed that 90 nm Caelyx^® biodistribution profile led to the stronger anti‐tumour activity of the drug and hence significant survival extension, and showed the importance of vesicle size in the targeting of nanoparticles to the tumour microenvironment for the treatment of cancer.

Ultrasonic Microbubble Cavitation Enhanced Tissue Permeability and Drug Diffusion in Solid Tumor Therapy

Chemotherapy has an essential role not only in advanced solid tumor therapy intervention but also in society’s health at large. Chemoresistance, however, seriously restricts the efficiency and sensitivity of chemotherapeutic agents, representing a significant threat to patients’ quality of life and life expectancy. How to reverse chemoresistance, improve efficacy sensitization response, and reduce adverse side effects need to be tackled urgently. Recently, studies on the effect of ultrasonic microbubble cavitation on enhanced tissue permeability and retention (EPR) have attracted the attention of researchers. Compared with the traditional targeted drug delivery regimen, the microbubble cavitation effect, which can be used to enhance the EPR effect, has the advantages of less trauma, low cost, and good sensitization effect, and has significant application prospects. This article reviews the research progress of ultrasound-mediated microbubble cavitation in the treatment of solid tumors and discusses its mechanism of action to provide new ideas for better treatment strategies.

Navigations of the targeting pathway of nanomedicines towards tumor

INTRODUCTION

Nanomedicines (NMs) have emerged as a promising approach for revolutionizing cancer treatment outcomes, mainly due to their benefits in the tumor targeted delivery of therapeutics. The preferential accumulation of NMs in tumor has been widely verified by macroscopical technologies. Accordingly, several classic and emerging targeting mechanisms have been proposed to support the tumor-specific delivery of NMs. The targeting mechanism has been a topic of intensive interest and controversy in the field of NMs development. Especially, the mechanisms by which NMs target tumor remain elusive.

AREA COVERED

This topical review mainly discussed the evolution of the targeting mechanisms, crucial issues associated with each mechanism, and confused debates among the mechanisms. The targeting mechanisms of tumor-specific NMs discussed here include the enhanced permeability and retention (EPR) effect, protein corona-mediated targeting delivery, circulating cell mediated transportation, and transcytosis.

EXPERT OPINION

It is of great significance for ultimate clinical translation to have more comprehensive considerations on the mechanism driving the pathway of NMs toward tumors. Our thoughts in this review are expected to provide comprehensive understanding on the mechanisms and elicit thorough explorations on new mechanism to renovate the knowledge framework of NMs delivery.