Cell Compatible Trimethoprim-Decorated Iron Oxide Nanoparticles Bind Dihydrofolate Reductase for Magnetically Modulating Focal Adhesion of Mammalian Cells

Let's get biophysical - How to get your favorite protein's digits

In these days of information overload and high-throughput analysis, it is easy to lose focus on the study of individual proteins. It is our conjecture that such investigations are still crucially important and offer uniquely penetrative insights. We thus present a discussion of biophysical methods to allow readers to get to know their protein of interest better. Although this perspective is not written with the expert in mind, we hope that for interdisciplinary scientists, or researchers who do not routinely perform biophysical analyses, the content will be helpful and inspiring.

Cage hydrocarbons as linkers in dimeric drug design: Case studies with trimethoprim and tedizolid

The looming threat of a "post-antibiotic era" has been caused by a rapid rise in antibacterial resistance and subsequent depletion of effective antibiotic agents in the clinic. An efficient strategy to address this shortfall lies in the reengineering of pre-existing and commercially available antibiotic drugs. This is exemplified by dimerization, a design concept in which two pharmacophores are covalently linked to form a new chemical entity. The cage hydrocarbons cubane (1), bicyclo[2.2.2]octane (BCO) (2), adamantane (3), and bicyclo[1.1.1]pentane (BCP) (4) present themselves as an attractive family of linkers in this regard. In this report, all four hydrocarbon cages were employed as linkers in a series of dimers based on the commercially available antibiotics trimethoprim and tedizolid. A detailed synthetic roadmap for the protection and deprotection of each pharmacophore is outlined. Several members of the trimethoprim series showed activity on par with that of their trimethoprim progenitor, although this was not the case for the tedizolid series. The design strategy outlined herein highlights the utility of the group as a platform for the rapid and modular construction of future novel antibiotics.

Rapid construction and enhanced vascularization of microtissue using a magnetic control method

Stem cells play critical roles in tissue repair and regeneration. The construction of stem cell-derived microtissue is a promising strategy for transplanting cells into defects to improve tissue regeneration efficiency. However, rapidly constructing larger microtissues and promoting vascularization to ensure the cellular nutrient supply remain major challenges. Here, we have developed a magnetic device to rapidly construct and regulate millimeter-scale microtissues derived from magnetic nanoparticle-labeled cells. When the microtissue was cultured under a specific magnetic field, the shape of the microtissue could be changed. Importantly, cell proliferation was maintained, and angiogenesis was activated in the process of microtissue deformation. We developed a magnetic control method to treat microtissue, and the implanted microtissue showed excellent vascularizationin vivo. In brief, this magnetic control technology provides a promising strategy for vascularized regenerative medicine.

Surface engineering of magnetic iron oxide nanoparticles by polymer grafting: synthesis progress and biomedical applications

Magnetic iron oxide nanoparticles (IONPs) have wide applications in magnetic resonance imaging (MRI), biomedicine, drug delivery, hyperthermia therapy, catalysis, magnetic separation, and others. However, these applications are usually limited by irreversible agglomeration of IONPs in aqueous media because of their dipole-dipole interactions, and their poor stability. A protecting polymeric shell provides IONPs with not only enhanced long-term stability, but also the functionality of polymer shells. Therefore, polymer-grafted IONPs have recently attracted much attention of scientists. In this tutorial review, we will present the current strategies for grafting polymers onto the surface of IONPs, basically including "grafting from" and "grafting to" methods. Available functional groups and chemical reactions, which could be employed to bind polymers onto the IONP surface, are comprehensively summarized. Moreover, the applications of polymer-grafted IONPs will be briefly discussed. Finally, future challenges and perspectives in the synthesis and application of polymer-grafted IONPs will also be discussed.

Regional biomechanical imaging of liver cancer cells

Liver cancer is one of the leading cancers, especially in developing countries. Understanding the biomechanical properties of the liver cancer cells can not only help to elucidate the mechanisms behind the cancer progression, but also provide important information for diagnosis and treatment. At the cellular level, we used well-established atomic force microscopy (AFM) techniques to characterize the heterogeneity of mechanical properties of two different types of human liver cancer cells and a normal liver cell line. Stiffness maps with a resolution of 128x128 were acquired for each cell. The distributions of the indentation moduli of the cells showed significant differences between cancerous cells and healthy controls. Significantly, the variability was even greater amongst different types of cancerous cells. Fitting of the histogram of the effective moduli using a normal distribution function showed the Bel7402 cells were stiffer than the normal cells while HepG2 cells were softer. Morphological analysis of the cell structures also showed a higher cytoskeleton content among the cancerous cells. Results provided a foundation for applying knowledge of cell stiffness heterogeneity to search for tissue-level, early-stage indicators of liver cancer.

Synthesis of magnetite hybrid nanocomplexes to eliminate bacteria and enhance biofilm disruption

Bacteria can increase drug resistance by forming bacterial biofilms. Once the biofilm is formed, it becomes difficult to remove or kill the related bacteria completely by antibiotics and other antibacterial agents because these antibacterial agents cannot easily break through the biofilm matrix barrier and reach the internal bacteria. Therefore, we synthesized magnetite hybrid nanocomplexes that can penetrate and disrupt bacterial biofilms. The obtained nanocomposites are composed of multinucleated iron oxides and Ag seeds. The outer iron oxides can help the internal Ag nanoparticles penetrate the bacterial biofilms, hence killing the internal bacteria and disrupting the biofilms. We took advantage of E. coli and P. aeruginosa bacteria to test the antibacterial properties of the magnetite hybrid nanocomplexes. When planktonic E. coli and P. aeruginosa bacteria were incubated with 100 μg mL-1 magnetite hybrid nanocomplexes for 30 min, almost all the bacteria were killed. When the obtained biofilms of E. coli and P. aeruginosa were treated with magnetite hybrid nanocomplexes (10 μg mL-1 and 100 μg mL-1), the survival of E. coli and P. aeruginosa biofilms with a magnetic field showed a big decrease compared with that without a magnetic field. Therefore, the as-synthesized nanocomposites have promising potential as antimicrobial agents for killing bacteria and disrupting biofilms in the presence of a magnetic field, and thus should be further studied for a wide range of antibacterial applications.

Non-viral nanocarriers for intracellular delivery of microRNA therapeutics

MicroRNAs are small regulatory noncoding RNAs that regulate various biological processes. Herein, we will present the development of the strategies for intracellular miRNAs delivery, and specially focus on the rational designed routes, their mechanisms of action, as well as potential therapeutics used in the host cells orin vivostudies.

Using porous magnetic iron oxide nanomaterials as a facile photoporation nanoplatform for macromolecular delivery

The intracellular delivery of exogenous macromolecules such as functional proteins, antibodies, polysaccharides and nucleic acids into living cells for biomedical applications is of great interest. Even though great efforts have been devoted to this task, universal delivery systems that provide excellent intracellular delivery performance combined with easy cell recovery are urgently needed. Magnetic iron oxide nanoparticles show promising potential for various biomedical applications because of their advantages such as high biocompatibility and cost-effectiveness. Herein, a new facile platform for macromolecular delivery was developed based on the photothermal properties of porous magnetic iron oxide nanoparticles (P-MNPs). The near-infrared radiation (NIR) absorption behavior of P-MNPs remarkably facilitates the delivery of macromolecules into cells while maintaining high cell viability. Furthermore, the assistance of polycationic polyethylenimine improves the efficiency of DNA delivery. Most importantly, the cells could be easily recovered after macromolecular delivery by trypsinization, which is of great significance for further practical application of the delivery system. The facile and cost-effective platform proposed in this work provides a new avenue for the utilization of P-MNPs in macromolecular delivery.

Multifunctional Magnetic Mesoporous Silica Nanoagents for in vivo Enzyme-Responsive Drug Delivery and MR Imaging

In this study, we report novel multifunctional nanoagents for in vivo enzyme-responsive anticancer drug delivery and magnetic resonance imaging (MRI), based on mesoporous silica coated iron oxide nanoparticles (Fe3O4@MSNs). The anticancer drug, DOX, was encapsulated in the porous cavities with a MMP-2 enzyme responsive peptide being covalently linked to the nanoparticles surface. The in vitro experiment results indicated that the enzyme responsive nanoagents own high specificity for controlled drug release in the cell line with high MMP-2 expression. Furthermore, the targeted delivery of the nanoagents to the tumor site purpose has been successfully achieved through magnet-guided nanocarrier accumulation by utilizing the magnetic properties of the Fe3O4 nanocores, which resulted in efficient inhibition of the tumor growth. Additionally, these novel nanoagents can also be used as MRI agent for the real-time diagnosis the tumor treatment process of living animals. Taking the advantages of high specificity, controllable drug release and real-time MRI imaging, we believe these multifunctional nanoagents could also be used as a general platform for the design of stimulus-responsive multifunctional nanomaterials for the aim of accurate diagnosis and efficient treatment of other diseases.

Manipulating cell fate: dynamic control of cell behaviors on functional platforms

We review the recent advances and new horizons in the dynamic control of cell behaviors on functional platforms and their applications.

Glucose-6-Phosphate-Functionalized Magnetic Microsphere as Novel Hydrophilic Probe for Specific Capture of N-Linked Glycopeptides

Developing cost-effective approaches based on hydrophilic interaction liquid chromatography (HILIC) has been the main tendency for low-abundance glycopeptides capture before LC-MS/MS analysis. Carbohydrates with outstanding biocompatibility and hydrophilicity are ubiquitous in the kingdoms of animal and plant and could be a wonderful choice as functional groups for glycopeptides enrichment. In this work, glucose-6-phosphate, as one of the indispensable cogs in pivotal metabolic wheels of life, was chosen as functionalized groups to be grafted onto the surface of Fe₃O₄ microspheres via one-step surface fabrication strategy. The acquired hydrophilic Fe₃O₄@G6P microspheres showed superior enrichment performance for glycopeptides with high sensitivity (0.5 fmol/μL) and high selectivity (1:100) and good repeatability (10 times at least). Furthermore, the Fe₃O₄@G6P microspheres also exhibited enrichment ability for glycopeptides in different biosamples. A total of 243 glycopeptides assigned to 92 glycoproteins and 183 glycopeptides corresponding to 74 different glycoproteins was identified from merely 2 μL of serum and saliva, respectively.

Iron oxide nanoclusters for T 1 magnetic resonance imaging of non-human primates

Iron-oxide-based contrast agents for magnetic resonance imaging (MRI) had been clinically approved in the United States and Europe, yet most of these nanoparticle products were discontinued owing to failures to meet rigorous clinical requirements. Significant advances have been made in the synthesis of magnetic nanoparticles and their biomedical applications, but several major challenges remain for their clinical translation, in particular large-scale and reproducible synthesis, systematic toxicity assessment, and their preclinical evaluation in MRI of large animals. Here, we report the results of a toxicity study of iron oxide nanoclusters of uniform size in large animal models, including beagle dogs and the more clinically relevant macaques. We also show that iron oxide nanoclusters can be used as T ₁ MRI contrast agents for high-resolution magnetic resonance angiography in beagle dogs and macaques, and that dynamic MRI enables the detection of cerebral ischaemia in these large animals. Iron oxide nanoclusters show clinical potential as next-generation MRI contrast agents.

Click Synthesis of Hydrophilic Maltose-Functionalized Iron Oxide Magnetic Nanoparticles Based on Dopamine Anchors for Highly Selective Enrichment of Glycopeptides

The development of methods to isolate and enrich low-abundance glycopeptides from biological samples is crucial to glycoproteomics. Herein, we present an easy and one-step surface modification strategy to prepare hydrophilic maltose functionalized Fe3O4 nanoparticles (NPs). First, based on the chelation of the catechol ligand with iron atoms, azido-terminated dopamine (DA) derivative was assembled on the surface of magnetic Fe3O4 nanoparticles by sonication. Second, the hydrophilic maltose-functionalized Fe3O4 (Fe3O4-DA-Maltose) NPs were obtained via copper(I)-catalyzed azide-alkyne cycloaddition (click chemistry). The morphology, structure, and composition of Fe3O4-DA-Maltose NPs were investigated by Fourier transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM), X-ray powder diffraction (XRD), X-ray photoelectron spectrometer (XPS), and vibrating sample magnetometer (VSM). Meanwhile, hydrophilicity of the obtained NPs was evaluated by water contact angle measurement. The hydrophilic Fe3O4-DA-Maltose NPs were applied in isolation and enrichment of glycopeptides from horseradish peroxidase (HRP), immunoglobulin (IgG) digests. The MALDI-TOF mass spectrometric analysis indicated that the novel NPs exhibited high detection sensitivity in enrichment from HRP digests at concentration as low as 0.05 ng μL(-1), a large binding capacity up to 43 mg g(-1), and good recovery for glycopeptides enrichment (85-110%). Moreover, the Fe3O4-DA-Maltose NPs were applied to enrich glycopeptides from human renal mesangial cells (HRMC) for identification of N-glycosylation sites. Finally, we identified 115 different N-linked glycopeptides, representing 93 gene products and 124 glycosylation sites in HRMC.

Ectoenzyme switches the surface of magnetic nanoparticles for selective binding of cancer cells

Enzymatic switch, such as phosphorylation and dephosphorylation of proteins, is the most important mechanism for cellular signal transductions. Inspired by Nature and encouraged by our recent unexpected observation of the dephosphorylation of d-tyrosine phosphate-contain small peptides, we modify the surface of magnetic nanoparticles (MNP) with d-tyrosine phosphate that is a substrate of alkaline phosphatase (ALP). Our studies find that ALP is able to remove the phosphate groups from the magnetic nanoparticles. Most importantly, placental alkaline phosphatase (ALPP), an ectoenzyme that locates on cell surface with catalytic domains outside the plasma membrane and is overexpressed on many cancer cells, dephosphorylate the d-tyrosine phosphates on the surface of the magnetic nanoparticle and enable the magnetic nanoparticles to adhere selectively to the cancer cells, such as HeLa cells. Unlikely commonly used antibodies, the selectivity of the magnetic nanoparticles to cancer cells originates from the enzymatic reaction catalyzed by ALPP. The use of enzymatic reaction to modulate the surface of various nanostructures may lead to a general method to broadly target cancer cells without relying on specific ligand-receptor interactions (e.g., antibodies). This work, thus, illustrates a fundamentally new concept to allow cells to actively engineer the surface of colloids materials, such as magnetic nanoparticles, for various applications.

Design, synthesis, and application of the trimethoprim-based chemical tag for live-cell imaging

Over the past decade, chemical tags have been developed to complement the use of fluorescent proteins in live-cell imaging. Chemical tags retain the specificity of protein labeling achieved with fluorescent proteins through genetic encoding, but provide smaller, more robust tags and modular use of organic fluorophores with high photon output and tailored functionalities. The trimethoprim-based chemical tag (TMP-tag) was initially developed based on the high affinity interaction between E. coli dihydrofolate reductase and the antibiotic trimethoprim and was subsequently rendered covalent and fluorogenic via proximity-induced protein labeling reactions. To date, the TMP-tag is one of the few chemical tags that enable intracellular protein labeling and high-resolution live-cell imaging. Here we describe the general design, chemical synthesis, and application of TMP-tag for live-cell imaging. Alternate protocols for synthesizing and using the covalent and the fluorogenic TMP-tags are also included.

Advances in chemical labeling of proteins in living cells

The pursuit of quantitative biological information via imaging requires robust labeling approaches that can be used in multiple applications and with a variety of detectable colors and properties. In addition to conventional fluorescent proteins, chemists and biologists have come together to provide a range of approaches that combine dye chemistry with the convenience of genetic targeting. This hybrid-tagging approach amalgamates the rational design of properties available through synthetic dye chemistry with the robust biological targeting available with genetic encoding. In this review, we discuss the current range of approaches that have been exploited for dye targeting or for targeting and activation and some of the recent applications that are uniquely permitted by these hybrid-tagging approaches.

Multidentate block-copolymer-stabilized ultrasmall superparamagnetic iron oxide nanoparticles with enhanced colloidal stability for magnetic resonance imaging

Ultrasmall superparamagnetic iron oxide nanoparticles (USPIOs) with diameters <5 nm hold great promise as T1-positive contrast agents for in vivo magnetic resonance imaging. However, control of the surface chemistry of USPIOs to ensure individual colloidal USPIOs with a ligand monolayer and to impart biocompatibility and enhanced colloidal stability is essential for successful clinical applications. Herein, an effective and versatile strategy enabling the development of aqueous colloidal USPIOs stabilized with well-defined multidentate block copolymers (MDBCs) is reported. The multifunctional MDBCs are designed to consist of an anchoring block possessing pendant carboxylates as multidentate anchoring groups strongly bound to USPIO surfaces and a hydrophilic block having pendant hydrophilic oligo(ethylene oxide) chains to confer water dispersibility and biocompatibility. The surface of USPIOs is saturated with multiple anchoring groups of MDBCs, thus exhibiting excellent long-term colloidal stability as well as enhanced colloidal stability at biologically relevant electrolyte, pH, and temperature conditions. Furthermore, relaxometric properties as well as in vitro and in vivo MR imaging results demonstrate that the MDBC-stabilized USPIO colloids hold great potential as an effective T1 contrast agent.

Inhibitor mediated protein degradation

The discovery of drugs that cause the degradation of their target proteins has been largely serendipitous. Here we report that the tert-butyl carbamate-protected arginine (Boc(3)Arg) moiety provides a general strategy for the design of degradation-inducing inhibitors. The covalent inactivators ethacrynic acid and thiobenzofurazan cause the specific degradation of glutathione-S-transferase when linked to Boc(3)Arg. Similarly, the degradation of dihydrofolate reductase is induced when cells are treated with the noncovalent inhibitor trimethoprim linked to Boc(3)Arg. Degradation is rapid and robust, with 30%-80% of these abundant target proteins consumed within 1.3-5 hr. The proteasome is required for Boc(3)Arg-mediated degradation, but ATP is not necessary and the ubiquitin pathways do not appear to be involved. These results suggest that the Boc(3)Arg moiety may provide a general strategy to construct inhibitors that induce targeted protein degradation.

Second-generation covalent TMP-tag for live cell imaging

Chemical tags are now viable alternatives to fluorescent proteins for labeling proteins in living cells with organic fluorophores that have improved brightness and other specialized properties. Recently, we successfully rendered our TMP-tag covalent with a proximity-induced reaction between the protein tag and the ligand-fluorophore label. This initial design, however, suffered from slow in vitro labeling kinetics and limited live cell protein labeling. Thus, here we report a second-generation covalent TMP-tag that has a fast labeling half-life and can readily label a variety of intracellular proteins in living cells. Specifically, we designed an acrylamide-trimethoprim-fluorophore (A-TMP-fluorophore v2.0) electrophile with an optimized linker for fast reaction with a cysteine (Cys) nucleophile engineered just outside the TMP-binding pocket of Escherichia coli dihydrofolate reductase (eDHFR) and developed an efficient chemical synthesis for routine production of a variety of A-TMP-probe v2.0 labels. We then screened a panel of eDHFR:Cys variants and identified eDHFR:L28C as having an 8-min half-life for reaction with A-TMP-biotin v2.0 in vitro. Finally, we demonstrated live cell imaging of various cellular protein targets with A-TMP-fluorescein, A-TMP-Dapoxyl, and A-TMP-Atto655. With its robustness, this second-generation covalent TMP-tag adds to the limited number of chemical tags that can be used to covalently label intracellular proteins efficiently in living cells. Moreover, the success of this second-generation design further validates proximity-induced reactivity and organic chemistry as tools not only for chemical tag engineering but also more broadly for synthetic biology.

Protein oriented ligation on nanoparticles exploiting O6-alkylguanine-DNA transferase (SNAP) genetically encoded fusion

A bimodular genetic fusion comprising a delivery module (scFv) and a capture module (SNAP) is proposed as a novel strategy for the site-specific covalent conjugation of targeting peptides to nanoparticles. An scFv mutant selective for HER2 tumor antigen is chosen as the targeting ligand. SNAP-scFv is immobilized on magnetofluorescent nanoparticles and its targeting efficiency against HER2-positive cells is assessed by flow cytometry and immunofluorescence.

Magnetic nanoparticles for the manipulation of proteins and cells

In the rapidly developing areas of nanobiotechnology, magnetic nanoparticles (MNPs) are one type of the most well-established nanomaterials because of their biocompatibility and the potential applications as alternative contrast enhancing agents for magnetic resonance imaging (MRI). While the development of MNPs as alternative contrast agents for MRI application has moved quickly to testing in animal models and clinical trials, other applications of biofunctional MNPs have been explored extensively at the stage of qualitative or conceptual demonstration. In this critical review, we summarize the development of two straightforward applications of biofunctional MNPs--manipulating proteins and manipulating cells--in the last five years or so and hope to provide a relatively comprehensive assessment that may help the future developments. Specifically, we start with the examination of the strategy for the surface functionalization of MNPs because the applications of MNPs essentially depend on the molecular interactions between the functional molecules on the MNPs and the intended biological targets. Then, we discuss the use of MNPs for manipulating proteins since protein interactions are critical for biological functions. Afterwards, we evaluate the development of the use of MNPs to manipulate cells because the response of MNPs to a magnetic field offers a unique way to modulate cellular behavior in a non-contact or "remote" mode (i.e. the magnet exerts force on the cells without direct contact). Finally, we provide a perspective on the future directions and challenges in the development of MNPs for these two applications. By reviewing the examples of the design and applications of biofunctional MNPs, we hope that this article will provide a reference point for the future development of MNPs that address the present challenges and lead to new opportunities in nanomedicine and nanobiotechnology (137 references).

Multidentate catechol-based polyethylene glycol oligomers provide enhanced stability and biocompatibility to iron oxide nanoparticles

We have designed, prepared, and tested a new set of multidentate catechol- and polyethylene glycol (PEG)-derivatized oligomers, OligoPEG-Dopa, as ligands that exhibit strong affinity to iron oxide nanocrystals. The ligands consist of a short poly(acrylic acid) backbone laterally appended with several catechol anchoring groups and several terminally functionalized PEG moieties to promote affinity to aqueous media and to allow further coupling to target molecules (bio and others). These multicoordinating PEGylated oligomers were prepared using a relatively simple chemical strategy based on N,N'-dicyclohexylcarbodiimide (DCC) and N-(3-dimethylaminopropyl)-N'-ethylcarbodiimide (EDC) condensation. The ability of these catechol-functionalized oligomers to impart long-term colloidal stability to the nanoparticles is compared to other control ligands, namely, oligomers presenting several carboxyl groups and monodentate ligands presenting either one catechol or one carboxyl group. We found that the OligoPEG-Dopa ligands provide rapid ligand exchange, and the resulting nanoparticles exhibit greatly enhanced colloidal stability over a broad pH range and in the presence of excess electrolytes; stability is notably improved compared to non-catechol presenting molecular or oligomer ligands. By inserting controllable fractions of azide-terminated PEG moieties, the nanoparticles (NPs) become reactive to complementary functionalities via azide-alkyne cycloaddition (Click), which opens up the possibility of biological targeting of such stable NPs. In particular, we tested the Click coupling of azide-functionalized nanoparticles to an alkyne-modified dye. We also measured the MRI T(2) contrast of the OligoPEG-capped Fe(3)O(4) nanoparticles and applied MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay to test the potential cytotoxicity of these NPs to live cells; we found no measurable toxicity to live cells.

Cellular uptake and fate of PEGylated gold nanoparticles is dependent on both cell-penetration peptides and particle size

Numerous studies have examined how the cellular delivery of gold nanoparticles (AuNPs) is influenced by different physical and chemical characteristics; however, the complex relationship between AuNP size, uptake efficiency and intracellular localization remains only partially understood. Here we examine the cellular uptake of a series of AuNPs ranging in diameter from 2.4 to 89 nm that are synthesized and made soluble with poly(ethylene glycol)-functionalized dithiolane ligands terminating in either carboxyl or methoxy groups and covalently conjugated to cell penetrating peptides. Following synthesis, extensive physical characterization of the AuNPs was performed with UV-vis absorption, gel electrophoresis, zeta potential, dynamic light scattering, and high resolution transmission electron microscopy. Uptake efficiency and intracellular localization of the AuNP-peptide conjugates in a model COS-1 cell line were probed with a combination of silver staining, fluorescent counterstaining, and dual mode fluorescence coupled to nonfluorescent scattering. Our findings show that AuNP cellular uptake is directly dependent on the surface display of the cell-penetrating peptide and that the ultimate intracellular destination is further determined by AuNP diameter. The smallest 2.4 nm AuNPs were found to localize in the nucleus, while intermediate 5.5 and 8.2 nm particles were partially delivered into the cytoplasm, showing a primarily perinuclear fate along with a portion of the nanoparticles appearing to remain at the membrane. The 16 nm and larger AuNPs did not enter the cells and were located at the cellular periphery. A preliminary assessment of cytotoxicity demonstrated minimal effects on cellular viability following peptide-mediated uptake.