Limits and challenges in using transport inhibitors to characterize how nano-sized drug carriers enter cells

A Spontaneous Assembling Lipopeptide Nanoconjugate Transporting the Anthracycline Drug N-Benzyladriamycin-14-valerate for Personalized Therapy of Ewing Sarcoma

To meet the current need for a tumor-selective, targeted therapy regimen associated with reduced toxicity, our laboratory has developed a spontaneously assembled nanostructure that resembles high-density lipoproteins (HDLs). These myristoyl-5A (MYR-5A) nanotransporters are designed to safely transport lipophilic pharmaceuticals, including a novel anthracycline drug (N-benzyladriamycin-14-valerate (AD198)). This formulation has been found to enhance the therapeutic efficacy and reduced toxicity of drugs in preclinical studies of 2D and 3D models of Ewing sarcoma (EWS) and cardiomyocytes. Our findings indicate that the MYR-5A/AD198 nanocomplex delivers its payload selectively to cancer cells via the scavenger receptor type B1 (SR-B1), thus providing a solid proof of concept for the development of an improved and highly effective, potentially personalized therapy for EWS while protecting against treatment-associated cardiotoxicity.

Polymer Nanoparticles with 2-HP-β-Cyclodextrin for Enhanced Retention of Uptake into HCE-T Cells

Triamcinolone acetonide (TA), a medium-potency synthetic glucocorticoid, is primarily employed to treat posterior ocular diseases using vitreous injection. This study aimed to design novel ocular nanoformulation drug delivery systems using PLGA carriers to overcome the ocular drug delivery barrier and facilitate effective delivery into the ocular tissues after topical administration. The surface of the PLGA nanodelivery system was made hydrophilic (2-HP-β-CD) through an emulsified solvent volatilization method, followed by system characterization. The mechanism of cellular uptake across the corneal epithelial cell barrier used rhodamine B (Rh-B) to prepare fluorescent probes for delivery systems. The triamcinolone acetonide (TA)-loaded nanodelivery system was validated by in vitro release behavior, isolated corneal permeability, and in vivo atrial hydrodynamics. The results indicated that the fluorescent probes, viz., the Rh-B-(2-HP-β-CD)/PLGA NPs and the drug-loaded TA-(2-HP-β-CD)/PLGA NPs, were within 200 nm in size. Moreover, the system was homogeneous and stable. The in vitro transport mechanism across the epithelial barrier showed that the uptake of nanoparticles was time-dependent and that NPs were actively transported across the epithelial barrier. The in vitro release behavior of the TA-loaded nanodelivery systems revealed that (2-HP-β-CD)/PLGA nanoparticles could prolong the drug release time to up to three times longer than the suspensions. The isolated corneal permeability demonstrated that TA-(2-HP-β-CD)/PLGA NPs could extend the precorneal retention time and boost corneal permeability. Thus, they increased the cumulative release per unit area 7.99-fold at 8 h compared to the suspension. The pharmacokinetics within the aqueous humor showed that (2-HP-β-CD)/PLGA nanoparticles could elevate the bioavailability of the drug, and its Cmax was 51.91 times higher than that of the triamcinolone acetonide aqueous solution. Therefore, (2-HP-β-CD)/PLGA NPs can potentially elevate transmembrane uptake, promote corneal permeability, and improve the bioavailability of drugs inside the aqueous humor. This study provides a foundation for future research on transocular barrier nanoformulations for non-invasive drug delivery.

Evaluation of cell membrane-derived nanoparticles as therapeutic carriers for pancreatic ductal adenocarcinoma using an in vitro tumour stroma model

Here, we fabricated nanoparticles made solely from the membrane of cells found in the pancreatic tumour's microenvironment (TME), like the human MiaPaCa-2 cells and M2-polarized macrophages. The cell membrane-derived nanoparticles (CMNPs) deriving from the MiaPaCa-2 cells (MPC2-CMNPs) were loaded with the chemotherapeutic drug paclitaxel (PTX), and the CMNPs deriving from M2-polarized macrophages (M2-CMNPs) were loaded with the colony-stimulating factor 1 receptor inhibitor, pexidartinib (PXDB). The CMNPs' thorough morphological and physicochemical characterisation was followed by an in-depth study of their targeting ability and the endocytosis pathway involved during their internalisation. An in vitro model of the desmoplastic stroma comprising cancer-associated fibroblast-mimicking cells and M2-polarized macrophages was also developed. The model was characterised by collagen and α-smooth muscle actin (α-SMA) expression (overexpressed in desmoplasia) and was used to assess the CMNPs' ability to cross the stroma and target the tumour cells. Moreover, we assessed the effect of PXDB-loaded M2-CMNPs on the expression of M1 (CD80/CD86) and M2 (CD206/CD209) polarisation markers on activated macrophages. Finally, we evaluated the PTX and PXDB-loaded CMNPs' effect on the viability of all the used TME cell lines alone or in combination. Overall, this pilot study showed the potential of the CMNPs to cross an in vitro stroma model and act synergistically to treat PDAC.

A Comparison of Cellular Uptake Mechanisms, Delivery Efficacy, and Intracellular Fate between Liposomes and Extracellular Vesicles

A key aspect for successful drug delivery via lipid-based nanoparticles is their internalization in target cells. Two prominent examples of such drug delivery systems are artificial phospholipid-based carriers, such as liposomes, and their biological counterparts, the extracellular vesicles (EVs). Despite a wealth of literature, it remains unclear which mechanisms precisely orchestrate nanoparticle-mediated cargo delivery to recipient cells and the subsequent intracellular fate of therapeutic cargo. In this review, internalization mechanisms involved in the uptake of liposomes and EVs by recipient cells are evaluated, also exploring their intracellular fate after intracellular trafficking. Opportunities are highlighted to tweak these internalization mechanisms and intracellular fates to enhance the therapeutic efficacy of these drug delivery systems. Overall, literature to date shows that both liposomes and EVs are predominantly internalized through classical endocytosis mechanisms, sharing a common fate: accumulation inside lysosomes. Studies tackling the differences between liposomes and EVs, with respect to cellular uptake, intracellular delivery and therapy efficacy, remain scarce, despite its importance for the selection of an appropriate drug delivery system. In addition, further exploration of functionalization strategies of both liposomes and EVs represents an important avenue to pursue in order to control internalization and fate, thereby improving therapeutic efficacy.

Rapid Internalization of Nanoparticles by Human Cells at the Single Particle Level

Nanoparticle uptake by cells has been studied for applications both in nanomedicine and in nanosafety. While the majority of studies have focused on the biological mechanisms underlying particle internalization, less attention has been given to questions of a more quantitative nature, such as how many nanoparticles enter cells and how rapidly they do so. To address this, we exposed human embryonic kidney cells to 40-200 nm carboxylated polystyrene nanoparticles and the particles were observed by live-cell confocal and super-resolution stimulated emission depletion fluorescence microscopy. How long a particle remained at the cell membrane after adsorbing onto it was monitored, distinguishing whether the particle ultimately desorbed again or was internalized by the cell. We found that the majority of particles desorb, but interestingly, most of the particles that are internalized do so within seconds, independently of particle size. As this is faster than typical endocytic mechanisms, we interpret this observation as the particles entering via an endocytic event that is already taking place (as opposed to directly triggering their own uptake) or possibly via an as yet uncharacterized endocytic route. Aside from the rapidly internalizing particles, a minority of particles remain at the membrane for tens of seconds to minutes before desorbing or being internalized. We also followed particles after cell internalization, observing particles that appeared to exit the cell, sometimes as rapidly as within tens of seconds. Overall, our results provide quantitative information about nanoparticle cell internalization times and early trafficking.

PepFect14 mediates the delivery of mRNA into human primary keratinocytes and in vivo

mRNA-based vaccines and candidate therapeutics have great potential in various medical fields. For the delivery of mRNA into target cells and tissues, lipid formulations are often employed. However, this approach could cause the activation of immune responses, making it unsuitable for the treatment of inflammatory conditions. Therefore, alternative delivery systems are highly demanded. In this study, we evaluated the transport efficiency and characteristics of cell-penetrating peptide PepFect14 (PF14) and mRNA nanoparticles in the presence of different additives. Our results show that all PF14-mRNA formulations entered cultured cells, while calcium chloride enhanced the transport and production of the encoded protein in HeLa and HaCaT cell lines, and polysorbate 80 did so in primary human keratinocytes. All formulations had similar physical properties and did not remarkably affect cell viability. By selectively blocking endocytosis pathways, we show that PF14-mRNA nanoparticles primarily entered HeLa cells via macropinocytosis and HaCaT cells via both macropinocytosis and clathrin-mediated endocytosis, while none of the blockers significantly affected the delivery into primary keratinocytes. Finally, subcutaneous injection of PF14-mRNA nanoparticles before inducing mouse irritant contact dermatitis resulted in the expression of a reporter protein without provoking harmful immune responses in the skin. Together, our findings suggest that PF14-mRNA nanoparticles have the potential for developing mRNA-based therapeutics for treating inflammatory skin conditions.

Cargo-Dependent Targeted Cellular Uptake Using Quaternized Starch as a Carrier

The tailored design of drug delivery systems for specific therapeutic agents is a prevailing approach in the field. In this paper, we present a study that highlights the potential of our modified starch, Q-starch, as a universal and adaptable drug delivery carrier for diverse therapeutic agents. We investigate the ability of Q-starch/cargo complexes to target different organelles within the cellular landscape, based on the specific activation sites of therapeutic agents. Plasmid DNA (pDNA), small interfering RNA (siRNA), and phosphatidylinositol (3,4,5)-trisphosphate (PIP3) were chosen as representative therapeutic molecules, acting in the nucleus, cytoplasm, and membrane, respectively. By carrying out comprehensive characterizations, employing dynamic light scattering (DLS), determining the zeta potential, and using cryo-transmitting electron microscopy (cryo-TEM), we reveal the formation of nano-sized, positively charged, and spherical Q-starch complexes. Our results demonstrate that these complexes exhibit efficient cellular uptake, targeting their intended organelles while preserving their physical integrity and functionality. Notably, the intracellular path of the Q-starch/cargo complex is guided by the cargo itself, aligning with its unique biological activity site. This study elucidates the versatility and potency of Q-starch as a versatile drug delivery carrier, paving the way for novel applications offering targeted delivery strategies for potential therapeutic molecules.

Ligand-dependent intracellular trafficking of the G protein-coupled P2Y6 receptor

Endosomal trafficking is intricately linked to G protein-coupled receptors (GPCR) fate and signaling. Extracellular uridine diphosphate (UDP) acts as a signaling molecule by selectively activating the GPCR P2Y₆. Despite the recent interest for this receptor in pathologies, such as gastrointestinal and neurological diseases, there is sparse information on the endosomal trafficking of P2Y₆ receptors in response to its endogenous agonist UDP and synthetic selective agonist 5-iodo-UDP (MRS2693). Confocal microscopy and cell surface ELISA revealed delayed internalization kinetics in response to MRS2693 vs. UDP stimulation in AD293 and HCT116 cells expressing human P2Y₆. Interestingly, UDP induced clathrin-dependent P2Y₆ internalization, whereas receptor stimulation by MRS2693 endocytosis appeared to be associated with a caveolin-dependent mechanism. Internalized P2Y₆ was associated with Rab4, 5, and 7 positive vesicles independent of the agonist. We have measured a higher frequency of receptor expression co-occurrence with Rab11-vesicles, the trans-Golgi network, and lysosomes in response to MRS2693. Interestingly, a higher agonist concentration reversed the delayed P2Y₆ internalization and recycling kinetics in the presence of MRS2693 stimulation without changing its caveolin-dependent internalization. This work showed a ligand-dependent effect affecting the P2Y₆ receptor internalization and endosomal trafficking. These findings could guide the development of bias ligands that could influence P2Y₆ signaling.

Cellular and Molecular Processes Are Differently Influenced in Primary Neural Cells by Slight Changes in the Physicochemical Properties of Multicore Magnetic Nanoparticles

Herein, we use two exemplary superparamagnetic iron oxide multicore nanoparticles (SPIONs) to illustrate the significant influence of slightly different physicochemical properties on the cellular and molecular processes that define SPION interplay with primary neural cells. Particularly, we have designed two different SPION structures, NFA (i.e., a denser multicore structure accompanied by a slightly less negative surface charge and a higher magnetic response) and NFD (i.e., a larger surface area and more negatively charged), and identified specific biological responses dependent on SPION type, concentration, exposure time, and magnetic actuation. Interestingly, NFA SPIONs display a higher cell uptake, likely driven by their less negative surface and smaller protein corona, more significantly impacting cell viability and complexity. The tight contact of both SPIONs with neural cell membranes results in the significant augmentation of phosphatidylcholine, phosphatidylserine, and sphingomyelin and the reduction of free fatty acids and triacylglycerides for both SPIONs. Nonetheless, NFD induces greater effects on lipids, especially under magnetic actuation, likely indicating a preferential membranal location and/or a tighter interaction with membrane lipids than NFA, in agreement with their lower cell uptake. From a functional perspective, these lipid changes correlate with an increase in plasma membrane fluidity, again larger for more negatively charged nanoparticles (NFD). Finally, the mRNA expression of iron-related genes such as Ireb-2 and Fth-1 remains unaltered, while TfR-1 is only detected in SPION-treated cells. Taken together, these results demonstrate the substantial impact that minor physicochemical differences of nanomaterials may exert in the specific targeting of cellular and molecular processes. A denser multicore structure generated by autoclave-based production is accompanied by a slight difference in surface charge and magnetic properties that become decisive for the biological impact of these SPIONs. Their capacity to markedly modify the lipidic cell content makes them attractive as lipid-targetable nanomedicines.

The steep road to nonviral nanomedicines: Frequent challenges and culprits in designing nanoparticles for gene therapy

The potential of therapeutically loaded nanoparticles (NPs) has been successfully demonstrated during the last decade, with NP-mediated nonviral gene delivery gathering significant attention as highlighted by the broad clinical acceptance of mRNA-based COVID-19 vaccines. A significant barrier to progress in this emerging area is the wild variability of approaches reported in published literature regarding nanoparticle characterizations. Here, we provide a brief overview of the current status and outline important concerns regarding the need for standardized protocols to evaluate NP uptake, NP transfection efficacy, drug dose determination, and variability of nonviral gene delivery systems. Based on these concerns, we propose wide adherence to multimodal, multiparameter, and multistudy analysis of NP systems. Adoption of these proposed approaches will ensure improved transparency, provide a better basis for interlaboratory comparisons, and will simplify judging the significance of new findings in a broader context, all critical requirements for advancing the field of nonviral gene delivery.

Targeting Ultrasmall Gold Nanoparticles with cRGD Peptide Increases the Uptake and Efficacy of Cytotoxic Payload

Cyclic arginyl-glycyl-aspartic acid peptide (cRGD) peptides show a high affinity towards αVβ3 integrin, a receptor overexpressed in many cancers. We aimed to combine the versatility of ultrasmall gold nanoparticles (usGNP) with the target selectivity of cRGD peptide for the directed delivery of a cytotoxic payload in a novel design. usGNPs were synthesized with a modified Brust-Schiffrin method and functionalized via amide coupling and ligand exchange and their uptake, intracellular trafficking, and toxicity were characterized. Our cRGD functionalized usGNPs demonstrated increased cellular uptake by αVβ3 integrin expressing cells, are internalized via clathrin-dependent endocytosis, accumulated in the lysosomes, and when loaded with mertansine led to increased cytotoxicity. Targeting via cRGD functionalization provides a mechanism to improve the efficacy, tolerability, and retention of therapeutic GNPs.

Liposomes Loaded with Amaranth Unsaponifiable Matter and Soybean Lunasin Prevented Melanoma Tumor Development Overexpressing Caspase-3 in an In Vivo Model

The objective of this study was to assess the effectiveness of liposomes loaded with soybean lunasin and amaranth unsaponifiable matter (UM + LunLip) as a source of squalene in the prevention of melanoma skin cancer in an allograft mice model. Tumors were induced by transplanting melanoma B16-F10 cells into the mice. The most effective treatments were those including UM + LunLip, with no difference between the lunasin concentrations (15 or 30 mg/kg body weight); however, these treatments were statistically different from the tumor-bearing untreated control (G3) (p < 0.05). The groups treated with topical application showed significant inhibition (68%, p < 0.05) compared to G3. The groups treated with subcutaneous injections showed significant inhibition (up to 99%, p < 0.05) in G3. During tumor development, UM + LunLip treatments under-expressed Ki-67 (0.2-fold compared to G3), glycogen synthase kinase-3β (0.1-fold compared to G3), and overexpressed caspase-3 (30-fold compared to G3). In addition, larger tumors showed larger necrotic areas (38% with respect to the total tumor) (p < 0.0001). In conclusion, the UM + LunLip treatment was effective when applied either subcutaneously or topically in the melanoma tumor-developing groups, as it slowed down cell proliferation and activated apoptosis.

Controlling Nanoparticle Uptake in Innate Immune Cells with Heparosan Polysaccharides

We used heparosan (HEP) polysaccharides for controlling nanoparticle delivery to innate immune cells. Our results show that HEP-coated nanoparticles were endocytosed in a time-dependent manner by innate immune cells via both clathrin-mediated and macropinocytosis pathways. Upon endocytosis, we observed HEP-coated nanoparticles in intracellular vesicles and the cytoplasm, demonstrating the potential for nanoparticle escape from intracellular vesicles. Competition with other glycosaminoglycan types inhibited the endocytosis of HEP-coated nanoparticles only partially. We further found that nanoparticle uptake into innate immune cells can be controlled by more than 3 orders of magnitude via systematically varying the HEP surface density. Our results suggest a substantial potential for HEP-coated nanoparticles to target innate immune cells for efficient intracellular delivery, including into the cytoplasm. This HEP nanoparticle surface engineering technology may be broadly used to develop efficient nanoscale devices for drug and gene delivery as well as possibly for gene editing and immuno-engineering applications.

Probing the Intracellular Delivery of Nanoparticles into Hard-to-Transfect Cells

Hard-to-transfect cells are cells that are known to present special difficulties in intracellular delivery of exogenous entities. However, the special transport behaviors underlying the special delivery problem in these cells have so far not been examined carefully. Here, we combine single-particle motion analysis, cell biology studies, and mathematical modeling to investigate nanoparticle transport in bone marrow-derived mesenchymal stem cells (BMSCs), a technologically important type of hard-to-transfect cells. Tat peptide-conjugated quantum dots (QDs-Tat) were used as the model nanoparticles. Two different yet complementary single-particle methods, namely, pair-correlation function and single-particle tracking, were conducted on the same cell samples and on the same viewing stage of a confocal microscope. Our results reveal significant differences in each individual step of transport of QDs-Tat in BMSCs vs a commonly used model cell line, HeLa cells. Single-particle motion analysis demonstrates that vesicle escape and cytoplasmic diffusion are dramatically more difficult in BMSCs than in HeLa cells. Cell biology studies show that BMSCs use different biological pathways for the cellular uptake, vesicular transport, and exocytosis of QDs-Tat than HeLa cells. A reaction-diffusion-advection model is employed to mathematically integrate the individual steps of cellular transport and can be used to predict and design nanoparticle delivery in BMSCs. This work provides dissective, quantitative, and mechanistic understandings of nanoparticle transport in BMSCs. The investigative methods described in this work can help to guide the tailored design of nanoparticle-based delivery in specific types and subtypes of hard-to-transfect cells.

Cell-surface glycosaminoglycans regulate the cellular uptake of charged polystyrene nanoparticles

Engineered nanoparticles approaching the cell body will first encounter and interact with cell-surface glycosaminoglycans (GAGs) before reaching the plasma membrane and becoming internalized. However, how surface GAGs may regulate the cellular entry of nanoparticles remains poorly understood. Herein, it is shown that the surface GAGs of Chinese hamster ovary cells perform as a charge-based barrier against the cellular internalization of anionic polystyrene nanoparticles (PS NPs). In contrast, cationic PS NPs interact favorably with the surface GAGs and thereby are efficiently internalized. Anionic PS NPs eventually reaching the plasma membrane bind to scavenger receptors and are endocytosed by clathrin-mediated and lipid raft/cholesterol-dependent mechanisms, whereas cationic PS NPs are primarily internalized via clathrin-mediated endocytosis and macropinocytosis. Upon the enzymatic shedding of surface GAGs, the uptake of anionic PS NPs increases while that of cationic PS NPs is dramatically reduced. Interestingly, the diminished uptake of cationic PS NPs is observed only when heparan sulfate, but not chondroitin sulfate, is cleaved from the cell surface. Heparan sulfate therefore serves as anchors/first receptors to facilitate the cellular entry of cationic PS NPs. These findings contribute to advance the basic science of nanoparticle endocytosis while also having important implications for the use of engineered nanocarriers as intracellular drug-delivery systems.

Mechanisms of Uptake and Membrane Curvature Generation for the Internalization of Silica Nanoparticles by Cells

Nanosized drug carriers enter cells via active mechanisms of endocytosis but the pathways involved are often not clarified. Cells possess several mechanisms to generate membrane curvature during uptake. However, the mechanisms of membrane curvature generation for nanoparticle uptake have not been explored so far. Here, we combined different methods to characterize how silica nanoparticles with a human serum corona enter cells. In these conditions, silica nanoparticles are internalized via the LDL receptor (LDLR). We demonstrate that despite the interaction with LDLR, uptake is not clathrin-mediated, as usually observed for this receptor. Additionally, silencing the expression of different proteins involved in clathrin-independent mechanisms and several BAR-domain proteins known to generate membrane curvature strongly reduces nanoparticle uptake. Thus, nanosized objects targeted to specific receptors, such as here LDLR, can enter cells via different mechanisms than their endogenous ligands. Additionally, nanoparticles may trigger alternative mechanisms of membrane curvature generation for their internalization.

Drug Targeting and Nanomedicine: Lessons Learned from Liver Targeting and Opportunities for Drug Innovation

Drug targeting and nanomedicine are different strategies for improving the delivery of drugs to their target. Several antibodies, immuno-drug conjugates and nanomedicines are already approved and used in clinics, demonstrating the potential of such approaches, including the recent examples of the DNA- and RNA-based vaccines against COVID-19 infections. Nevertheless, targeting remains a major challenge in drug delivery and different aspects of how these objects are processed at organism and cell level still remain unclear, hampering the further development of efficient targeted drugs. In this review, we compare properties and advantages of smaller targeted drug constructs on the one hand, and larger nanomedicines carrying higher drug payload on the other hand. With examples from ongoing research in our Department and experiences from drug delivery to liver fibrosis, we illustrate opportunities in drug targeting and nanomedicine and current challenges that the field needs to address in order to further improve their success.

A real-time assay for cell-penetrating peptide-mediated delivery of molecular cargos

Cell-penetrating peptides (CPPs) are capable of transporting molecules to which they are tethered across cellular membranes. Unsurprisingly, CPPs have attracted attention for their potential drug delivery applications, but several technical hurdles remain to be overcome. Chief among them is the so-called 'endosomal escape problem,' i.e. the propensity of CPP-cargo molecules to be endocytosed but remain entrapped in endosomes rather than reaching the cytosol. Previously, a CPP fused to calmodulin that bound calmodulin binding site-containing cargos was shown to efficiently deliver cargos to the cytoplasm, effectively overcoming the endosomal escape problem. The CPP-adaptor, "TAT-CaM," evinces delivery at nM concentrations and more rapidly than we had previously been able to measure. To better understand the kinetics and mechanism of CPP-adaptor-mediated cargo delivery, a real-time cell penetrating assay was developed in which a flow chamber containing cultured cells was installed on the stage of a confocal microscope to allow for observation ab initio. Also examined in this study was an improved CPP-adaptor that utilizes naked mole rat (Heterocephalus glaber) calmodulin in place of human and results in superior internalization, likely due to its lesser net negative charge. Adaptor-cargo complexes were delivered into the flow chamber and fluorescence intensity in the midpoint of baby hamster kidney cells was measured as a function of time. Delivery of 400 nM cargo was observed within seven minutes and fluorescence continued to increase linearly as a function of time. Cargo-only control experiments showed that the minimal uptake which occurred independently of the CPP-adaptor resulted in punctate localization consistent with endosomal entrapment. A distance analysis was performed for cell-penetration experiments in which CPP-adaptor-delivered cargo showing wider dispersions throughout cells as compared to an analogous covalently-bound CPP-cargo. Small molecule endocytosis inhibitors did not have significant effects upon delivery. The real-time assay is an improvement upon static endpoint assays and should be informative in a broad array of applications.

Uptake of Upconverting Nanoparticles by Breast Cancer Cells: Surface Coating versus the Protein Corona

Fluorophores with multifunctional properties known as rare-earth-doped nanoparticles (RENPs) are promising candidates for bioimaging, therapy, and drug delivery. When applied in vivo, these nanoparticles (NPs) have to retain long blood-circulation time, bypass elimination by phagocytic cells, and successfully arrive at the target area. Usually, NPs in a biological medium are exposed to proteins, which form the so-called "protein corona" (PC) around the NPs and influence their targeted delivery and accumulation in cells and tissues. Different surface coatings change the PC size and composition, subsequently deciding the fate of the NPs. Thus, detailed studies on the PC are of utmost importance to determine the most suitable NP surface modification for biomedical use. When it comes to RENPs, these studies are particularly scarce. Here, we investigate the PC composition and its impact on the cellular uptake of citrate-, SiO₂-, and phospholipid micelle-coated RENPs (LiYF₄:Yb³⁺,Tm³⁺). We observed that the PC of citrate- and phospholipid-coated RENPs is relatively stable and similar in the adsorbed protein composition, while the PC of SiO₂-coated RENPs is larger and highly dynamic. Moreover, biocompatibility, accumulation, and cytotoxicity of various RENPs in cancer cells have been evaluated. On the basis of the cellular imaging, supported by the inhibition studies, it was revealed that RENPs are internalized by endocytosis and that specific endocytic routes are PC composition dependent. Overall, these results are essential to fill the gaps in the fundamental understanding of the nano-biointeractions of RENPs, pertinent for their envisioned application in biomedicine.

Intracellular delivery of oxaliplatin conjugate via cell penetrating peptide for the treatment of colorectal carcinoma in vitro and in vivo

Pt-based drugs are one of the main active agents in colorectal cancer treatment. However, drug resistance and dose-dependent side effects are the main barriers that restrict their clinical applications. As an alternative approach to these issues, we designed and synthesized a cell penetrating peptide (CPP) octaarginine-oxaliplatin conjugate that quickly and successfully delivered oxaliplatin into colon cancer cells. The CPP octaarginine is a well-studied cationic peptide that can play a role as a drug delivery vector. In this work, an octaarginine CPP (RRRRRRRR) was conjugated with oxaliplatin via a specific heterobifunctional linker. The in vitro studies showed the conjugate had affinity toward mitochondria inside cells and the MTT assay confirmed that conjugate is active in low micromolar range against colon cancer cells, requiring much lower concentrations than the oxaliplatin alone to reach IC₅₀. More importantly, in the in vivo mouse study, the conjugate effectively inhibited tumor growth and showed considerably high antitumor activity, demonstrating the conjugate can perform well in vivo. This strategy may offer a new approach for designing oxaliplatin derivatives or prodrugs with remarkable therapeutic capabilities.

Dynamic interactions and intracellular fate of label-free, thin graphene oxide sheets within mammalian cells: role of lateral sheet size

Graphene oxide (GO) holds great potential for biomedical applications, however fundamental understanding of the way it interacts with biological systems is still lacking even though it is essential for successful clinical translation. In this study, we exploit intrinsic fluorescent properties of thin GO sheets to establish the relationship between lateral dimensions of the material, its cellular uptake mechanisms and intracellular fate over time. Label-free GO with distinct lateral dimensions, small (s-GO) and ultra-small (us-GO) were thoroughly characterised both in water and in biologically relevant cell culture medium. Interactions of the material with a range of non-phagocytic mammalian cell lines (BEAS-2B, NIH/3T3, HaCaT, 293T) were studied using a combination of complementary analytical techniques (confocal microscopy, flow cytometry and TEM). The uptake mechanism was initially interrogated using a range of pharmaceutical inhibitors and validated using polystyrene beads of different diameters (0.1 and 1 μm). Subsequently, RNA-Seq was used to follow the changes in the uptake mechanism used to internalize s-GO flakes over time. Regardless of lateral dimensions, both types of GO were found to interact with the plasma membrane and to be internalized by a panel of cell lines studied. However, s-GO was internalized mainly via macropinocytosis while us-GO was mainly internalized via clathrin- and caveolae-mediated endocytosis. Importantly, we report the shift from macropinocytosis to clathrin-dependent endocytosis in the uptake of s-GO at 24 h, mediated by upregulation of mTORC1/2 pathway. Finally, we show that both s-GO and us-GO terminate in lysosomal compartments for up to 48 h. Our results offer an insight into the mechanism of interaction of GO with non-phagocytic cell lines over time that can be exploited for the design of biomedically-applicable 2D transport systems.

Self-Targeting of Carbon Dots into the Cell Nucleus: Diverse Mechanisms of Toxicity in NIH/3T3 and L929 Cells

It is important to understand the nanomaterials intracellular trafficking and distribution and investigate their targeting into the nuclear area in the living cells. In our previous study, we firstly observed penetration of nonmodified positively charged carbon dots decorated with quaternary ammonium groups (QCDs) into the nucleus of mouse NIH/3T3 fibroblasts. Thus, in this work, we focused on deeper study of QCDs distribution inside two healthy mouse NIH/3T3 and L929 cell lines by fluorescence microspectroscopy and performed a comprehensive cytotoxic and DNA damage measurements. Real-time penetration of QCDs across the plasma cell membrane was recorded, concentration dependent uptake was determined and endocytic pathways were characterized. We found out that the QCDs concentration of 200 µg/mL is close to saturation and subsequently, NIH/3T3 had a different cell cycle profile, however, no significant changes in viability (not even in the case with QCDs in the nuclei) and DNA damage. In the case of L929, the presence of QCDs in the nucleus evoked a cellular death. Intranuclear environment of NIH/3T3 cells affected fluorescent properties of QCDs and evoked fluorescence blue shifts. Studying the intracellular interactions with CDs is essential for development of future applications such as DNA sensing, because CDs as DNA probes have not yet been developed.

Anti-Inflammatory Effect and Cellular Uptake Mechanism of Carbon Nanodots in in Human Microvascular Endothelial Cells

Cardiovascular disease (CVD) has become an increasingly important topic in the field of medical research due to the steadily increasing rates of mortality caused by this disease. With recent advancements in nanotechnology, a push for new, novel treatments for CVD utilizing these new materials has begun. Carbon Nanodots (CNDs), are a new form of nanoparticles that have been coveted due to the green synthesis method, biocompatibility, fluorescent capabilities and potential anti-antioxidant properties. With much research pouring into CNDs being used as bioimaging and drug delivery tools, few studies have been completed on their anti-inflammatory potential, especially in the cardiovascular system. CVD begins initially by endothelial cell inflammation. The cause of this inflammation can come from many sources; one being tumor necrosis factor (TNF-α), which can not only trigger inflammation but prolong its existence by causing a storm of pro-inflammatory cytokines. This study investigated the ability of CNDs to attenuate TNF-α induced inflammation in human microvascular endothelial cells (HMEC-1). Results show that CNDs at non-cytotoxic concentrations reduce the expression of pro-inflammatory genes, mainly Interleukin-8 (IL-8), and interleukin 1 beta (IL-1β). The uptake of CNDs by HMEC-1s was examined. Results from the studies involving channel blockers and endocytosis disruptors suggest that uptake takes place by endocytosis. These findings provide insights on the interaction CNDs and endothelial cells undergoing TNF-α induced cellular inflammation.

Understanding nanoparticle endocytosis to improve targeting strategies in nanomedicine

Nanoparticles (NPs) have attracted considerable attention in various fields, such as cosmetics, the food industry, material design, and nanomedicine. In particular, the fast-moving field of nanomedicine takes advantage of features of NPs for the detection and treatment of different types of cancer, fibrosis, inflammation, arthritis as well as neurodegenerative and gastrointestinal diseases. To this end, a detailed understanding of the NP uptake mechanisms by cells and intracellular localization is essential for safe and efficient therapeutic applications. In the first part of this review, we describe the several endocytic pathways involved in the internalization of NPs and we discuss the impact of the physicochemical properties of NPs on this process. In addition, the potential challenges of using various inhibitors, endocytic markers and genetic approaches to study endocytosis are addressed along with the principal (semi) quantification methods of NP uptake. The second part focuses on synthetic and bio-inspired substances, which can stimulate or decrease the cellular uptake of NPs. This approach could be interesting in nanomedicine where a high accumulation of drugs in the target cells is desirable and clearance by immune cells is to be avoided. This review contributes to an improved understanding of NP endocytic pathways and reveals potential substances, which can be used in nanomedicine to improve NP delivery.

Unmasking CSF protein corona: Effect on targeting capacity of nanoparticles

Among biological fluids, cerebrospinal fluid (CSF) not only protects and support brain, but also plays a pivotal role in intracerebral interaction of various nano-drug carriers. However, it is still uncertain how protein corona from CSF affects the targeting capability of functionalized nanoparticles (NPs). So, two types of polystyrene NPs, including PEGylated polystyrene NPs (PN) and transferrin (Tf)-modified PN (PT), were used to obtain protein corona-coated NPs, by incubating with CSF in vivo and in vitro. Strikingly, both the corona-coated NPs recovered in vivo and in vitro completely lost their active targeting characteristics towards bEnd.3 and C6 cells. Charge-, clathrin- and energy-mediated endocytosis contributed to the improved uptake efficiency of PT, whereas this enhancement in uptake of PT was disappeared after the formation of CSF protein corona. Moreover, serum albumin, which were found both in vivo and in vitro CSF corona, could mediate and facilitate the internalization of corona-coated NPs. Overall, these results have distinctly confirmed that the formation of CSF protein corona could cause the loss of active targeting specificity by shielding the targeting groups on the surface of polystyrene NPs and alter their cellular uptake by other non-specific internalization pathways.

Differences in surface chemistry of iron oxide nanoparticles result in different routes of internalization

The efficient entry of nanotechnology-based pharmaceuticals into target cells is highly desired to reach high therapeutic efficiency while minimizing the side effects. Despite intensive research, the impact of the surface coating on the mechanism of nanoparticle uptake is not sufficiently understood yet. Herein, we present a mechanistic study of cellular internalization pathways of two magnetic iron oxide nanoparticles (MNPs) differing in surface chemistry into A549 cells. The MNP uptake was investigated in the presence of different inhibitors of endocytosis and monitored by spectroscopic and imaging techniques. The results revealed that the route of MNP entry into cells strongly depends on the surface chemistry of the MNPs. While serum bovine albumin-coated MNPs entered the cells via clathrin-mediated endocytosis (CME), caveolin-mediated endocytosis (CavME) or lipid rafts were preferentially involved in the internalization of polyethylene glycol-coated MNPs. Our data indicate that surface engineering can contribute to an enhanced delivery efficiency of nanoparticles.

Uptake and Intracellular Trafficking Studies of Multiple Dye-Doped Core-Shell Silica Nanoparticles in Lymphoid and Myeloid Cells

Introduction

Since most biologically active macromolecules are natural nanostructures, operating in the same scale of biomolecules gives the great advantage to enhance the interaction with cellular components. Noteworthy efforts in nanotechnology, particularly in biomedical and pharmaceutical fields, have propelled a high number of studies on the biological effects of nanomaterials. Moreover, the determination of specific physicochemical properties of nanomaterials is crucial for the evaluation and design of novel safe and efficient therapeutics and diagnostic tools. In this in vitro study, we report a physicochemical characterisation of fluorescent silica nanoparticles (NPs), interacting with biological models (U937 and PBMC cells), describing the specific triggered biologic response.

Methods

Flow Cytometric and Confocal analyses are the main method platforms. However TEM, NTA, DLS, and chemical procedures to synthesize NPs were employed.

Results

NT_B700 NPs, employed in this study, are fluorescent core-shell silica nanoparticles, synthesized through a micelle-assisted method, where the fluorescence energy transfer process, known as FRET, occurs at a high efficiency rate. Using flow cytometry and confocal microscopy, we observed that NT_B700 NP uptake seemed to be a rapid, concentration-, energy- and cell type-dependent process, which did not induce significant cytotoxic effects. We did not observe a preferred route of internalization, although their size and the possible aggregated state could influence their extrusion. At this level of analysis, our investigation focuses on lysosome and mitochondria pathways, highlighting that both are involved in NP co-localization. Despite the main mitochondria localization, NPs did not induce a significant increase of intracellular ROS, known inductors of apoptosis, during the time course of analyses. Finally, both lymphoid and myeloid cells are able to release NPs, essential to their biosafety.

Discussion

These data allow to consider NT_B700 NPs a promising platform for future development of a multifunctional system, by combining imaging and localized therapeutic applications in a unique tool.

Key principles and methods for studying the endocytosis of biological and nanoparticle therapeutics

Endocytosis is a critical step in the process by which many therapeutic nanomedicines reach their intracellular targets. Our understanding of cellular uptake mechanisms has developed substantially in the past five years. However, these advances in cell biology have not fully translated to the nanoscience and therapeutics literature. Misconceptions surrounding the role of different endocytic pathways and how to study these pathways are hindering progress in developing improved nanoparticle therapies. Here, we summarize the latest insights into cellular uptake mechanisms and pathways. We highlight limitations of current systems to study endocytosis, particularly problems with non-specific inhibitors. We also summarize alternative genetic approaches to robustly probe these pathways and discuss the need to understand how cells endocytose particles in vivo. We hope that this critical assessment of the current methods used in studying nanoparticle uptake will guide future studies at the interface of cell biology and nanomedicine.

Strategies for Delivering Nanoparticles across Tumor Blood Vessels

Nanoparticle transport across tumor blood vessels is a key step in nanoparticle delivery to solid tumors. However, the specific pathways and mechanisms of this nanoparticle delivery process are not fully understood. Here, the biological and physical characteristics of the tumor vasculature and the tumor microenvironment are explored and how these features affect nanoparticle transport across tumor blood vessels is discussed. The biological and physical methods to deliver nanoparticles into tumors are reviewed and paracellular and transcellular nanoparticle transport pathways are explored. Understanding the underlying pathways and mechanisms of nanoparticle tumor delivery will inform the engineering of safer and more effective nanomedicines for clinical translation.

Nanoparticles Incorporating a Fluorescence Turn-on Reporter for Real-Time Drug Release Monitoring, a Chemoenhancer and a Stealth Agent: Poseidon's Trident against Cancer?

The rate and extent of drug release under physiological conditions is a key factor influencing the therapeutic activity of a formulation. Real-time detection of drug release by conventional pharmacokinetics approaches is confounded by low sensitivity, particularly in the case of tissue-targeted novel drug delivery systems, where low concentrations of the drug reach systemic circulation. We present a novel fluorescence turn-on platform for real-time monitoring of drug release from nanoparticles based on reversible fluorescence quenching in fluorescein esters. Fluorescein-conjugated carbon nanotubes (CNTs) were esterified with methotrexate in solution and solid phase, followed by supramolecular functionalization with a chemoenhancer (suramin) or/and a stealth agent (dextran sulfate). Suramin was found to increase the cytotoxicity of methotrexate in A549 cells. On the other hand, dextran sulfate exhibited no effect on cytotoxicity or cellular uptake of CNTs by A549 cells, while a decrease in cellular uptake of CNTs and cytotoxicity of methotrexate was observed in macrophages (RAW 264.7 cells). Similar results were also obtained when CNTs were replaced with graphene. Docking studies revealed that the conjugates are not internalized by folate receptors/transporters. Further, docking and molecular dynamics studies revealed the conjugates do not exhibit affinity toward the methotrexate target, dihydrofolate reductase. Molecular dynamics studies also revealed that distinct features of dextran-CNT and suramin-CNT interactions, characterized by π-π interactions between CNTs and dextran/suramin. Our study provides a simple, cost-effective, and scalable method for the synthesis of nanoparticles conferred with the ability to monitor drug release in real-time. This method could also be extended to other drugs and other types of nanoparticles.

Comparison of the uptake mechanisms of zwitterionic and negatively charged liposomes by HeLa cells

Zwitterionic molecules are used as an alternative to PEGylation to reduce protein adsorption on nanocarriers. Nonetheless, little is known on the effect of zwitterionic modifications on the mechanisms cells use for nanocarrier uptake. In this study, the uptake mechanism of liposomes containing zwitterionic or negatively charged lipids was characterized using pharmacological inhibitors and RNA interference on HeLa cells to block endocytosis. As expected, introducing zwitterionic lipids reduced protein adsorption in serum, as well as uptake efficiency. Blocking clathrin-mediated endocytosis strongly decreased the uptake of the negatively charged liposomes, but not the zwitterionic ones. Additionally, inhibition of macropinocytosis reduced uptake of both liposomes, but blocking actin polymerization had effects only on the negatively charged ones. Overall, the results clearly indicated that the two liposomes were internalized by HeLa cells using different pathways. Thus, introducing zwitterionic lipids affects not only protein adsorption and uptake efficiency, but also the mechanisms of liposome uptake by cells.

Thermosensitive nanoparticle of mPEG-PTMC for oligopeptide delivery into osteoclast precursors

Transmembrane delivery of biomolecules through nanoparticles plays an important role in targeted therapy. Here, we designed a simple nanoparticle for the delivery of model peptide drug into primary osteoclast precursor cells (bone marrow macrophages) by thermosensitive and biodegradable diblock copolymer monomethoxy poly(ethylene glycol)-block-poly(trimethylene carbonate). The model peptide drug was encapsulated into the nanoparticle by dropping the drug carrier dissolved in dimethylsulfoxide solvent into water containing poly(vinyl alcohol) to achieve temperature response nanoparticles. Through size analysis, we found that the nanoparticles possessed a temperature-sensitive property between 30°C and 40°C. Moreover, flow cytometry and spectrofluorimetry analysis indicated that nanoparticle systems underwent significant cellular uptake. In addition, the evaluation of cell biology showed that nanoparticles have excellent biocompatibility. Thus, the results indicated that the temperature-sensitive nanoparticles have potential application value for targeted delivery of oligopeptide in the treatment process of osteoarthritis.

Preparation of electrospray ALG/PDA-PVP nanocomposites and their application in cancer therapy

In this study, sodium alginate (ALG)/poly dopamine (PDA)-polyvinylpyrrolidone (PVP) nanocomposites was synthesized via a one-step electrostatic spraying method. The spinning solution of ALG and dopamine was electrostatically sprayed into an alkaline solution of PVP, calcium chloride and tris buffer (pH = 8.5), in which the gelation of ALG and the polymerization of dopamine could be simultaneously triggered. PDA hence produced possesses a high photothermal conversion efficiency, while the PVP that was facilely conjugated onto the surface of nanocomposites improves the colloidal stability and compatibility of the material. Moreover, the ALG renders the nanocomposite excellent drug (doxorubicine, DOX) loading capacity. Promisingly, the temperature increment during the PTT process could promote the DOX release, thus enhancing its therapeutic effect. The in vitro/in vivo biosafety and tumor treatment experiments further corroborate that the ALG/PDA-PVP nanocomposites have remarkable biocompatibility and synergism for tumor hyperthermia and chemotherapy. Consequently, such a one-step electrospray strategy provides a new way for designing nanomaterials and is expected to significantly promote the development of organic photothermal therapeutic agents with excellent bio-compatibility.

Interactions at the cell membrane and pathways of internalization of nano-sized materials for nanomedicine

Nano-sized materials have great potential as drug carriers for nanomedicine applications. Thanks to their size, they can exploit the cellular machinery to enter cells and be trafficked intracellularly, thus they can be used to overcome some of the cellular barriers to drug delivery. Nano-sized drug carriers of very different properties can be prepared, and their surface can be modified by the addition of targeting moieties to recognize specific cells. However, it is still difficult to understand how the material properties affect the subsequent interactions and outcomes at cellular level. As a consequence of this, designing targeted drugs remains a major challenge in drug delivery. Within this context, we discuss the current understanding of the initial steps in the interactions of nano-sized materials with cells in relation to nanomedicine applications. In particular, we focus on the difficult interplay between the initial adhesion of nano-sized materials to the cell surface, the potential recognition by cell receptors, and the subsequent mechanisms cells use to internalize them. The factors affecting these initial events are discussed. Then, we briefly describe the different pathways of endocytosis in cells and illustrate with some examples the challenges in understanding how nanomaterial properties, such as size, charge, and shape, affect the mechanisms cells use for their internalization. Technical difficulties in characterizing these mechanisms are presented. A better understanding of the first interactions of nano-sized materials with cells will help to design nanomedicines with improved targeting.

Corona Composition Can Affect the Mechanisms Cells Use to Internalize Nanoparticles

Nanosized objects, such as nanoparticles and other drug carriers used in nanomedicine, once in contact with biological environments are modified by adsorption of biomolecules on their surface. The presence of this corona strongly affects the following interactions at cell and organism levels. It has been shown that corona proteins can be recognized by cell receptors. However, it is not known whether the composition of this acquired layer can also affect the mechanisms nanoparticles use to enter cells. This is of particular importance when considering that the same nanoparticles can form different coronas for instance in vitro when exposed to cells in different serum amounts or in vivo depending on the exposure or administration route. Thus, in this work, different coronas were formed on 50 nm silica by exposing them to different serum concentrations. The uptake efficiency in HeLa cells was compared, and the uptake mechanisms were characterized using transport inhibitors and RNA interference. The results showed that the nanoparticles were internalized by cells via different mechanisms when different coronas were formed, and only for one corona condition was uptake mediated by the LDL receptor. This suggested that coronas of different composition can be recognized differently by cell receptors, and this in turn leads to internalization via different mechanisms. Similar studies were performed using other cells, including A549 cells and primary HUVEC, and different nanoparticles, namely 100 nm liposomes and 200 nm silica. Overall, the results confirmed that the corona composition can affect the mechanisms of nanoparticle uptake by cells.