Disulfide and thioether linked cytochrome c-oligoarginine conjugates in HeLa cells

A BODIPY-embedding miltefosine analog linked to cell-penetrating Tat(48-60) peptide favors intracellular delivery and visualization of the antiparasitic drug

Therapeutic application of many drugs is often hampered by poor or denied access to intracellular targets. A case in point is miltefosine (MT), an orally active antiparasitic drug, which becomes ineffective when parasites develop dysfunctional uptake systems. We report here the synthesis of a fluorescent BODIPY-embedding MT analogue with appropriate thiol functionalization allowing linkage to the cell-penetrating Tat(48-60) peptide through disulfide or thioether linkages. The resulting constructs are efficiently internalized into the otherwise MT-invulnerable R40 Leishmania strain, resulting in fast parasite killing, and hence successful avoidance of the resistance. In the disulfide-linked conjugate, an additional fluoro tag on the Tat moiety allows to monitor its reductive cleavage within the cytoplasm. Terminally differentiated cells such as peritoneal macrophages, impervious to MT unless infected by Leishmania, can uptake the drug in its Tat-conjugated form. The results afford proof-of-principle for using CPP vectors to avert drug resistance in parasites, and/or for tackling leishmaniasis by modulating macrophage uptake.

Engineering cytochrome-modified silica nanoparticles to induce programmed cell death

A low native membrane permeability and ineffective access to the cellular cytosol, together with aggressive proteolytic degradation, often severely hampers the practical application of any therapeutic protein or antibody. Through engineering the charging profile of mesoporous silica nanoparticles, cellular uptake and subsequent subcellular distribution can be controlled. We show herein that programmed cell death can subsequently be induced across a population of cancer cells with remarkable efficacy on conjugating a specific caspase-cascade-activating cytochrome to such cytosol-accessing particles.

Delivery of chemically glycosylated cytochrome c immobilized in mesoporous silica nanoparticles induces apoptosis in HeLa cancer cells

Cytochrome c (Cyt c) is a small mitochondrial heme protein involved in the intrinsic apoptotic pathway. Once Cyt c is released into the cytosol, the caspase mediated apoptosis cascade is activated resulting in programmed cell death. Herein, we explore the covalent immobilization of Cyt c into mesoporous silica nanoparticles (MSN) to generate a smart delivery system for intracellular drug delivery to cancer cells aiming at affording subsequent cell death. Cyt c was modified with sulfosuccinimidyl-6-[3'-(2-pyridyldithio)-propionamido] hexanoate (SPDP) and incorporated into SH-functionalized MSN by thiol-disulfide interchange. Unfortunately, the delivery of Cyt c from the MSN was not efficient in inducing apoptosis in human cervical cancer HeLa cells. We tested whether chemical Cyt c glycosylation could be useful in overcoming the efficacy problems by potentially improving Cyt c thermodynamic stability and reducing proteolytic degradation. Cyt c lysine residues were modified with lactose at a lactose-to-protein molar ratio of 3.7 ± 0.9 using mono(lactosylamido)-mono(succinimidyl) suberate linker chemistry. Circular dichroism (CD) spectra demonstrated that part of the activity loss of Cyt c was due to conformational changes upon its modification with the SPDP linker. These conformational changes were prevented in the glycoconjugate. In agreement with the unfolding of Cyt c by the linker, a proteolytic assay demonstrated that the Cyt c-SPDP conjugate was more susceptible to proteolysis than Cyt c. Attachment of the four lactose molecules reversed this increased susceptibility and protected Cyt c from proteolytic degradation. Furthermore, a cell-free caspase-3 assay revealed 47% and 87% of relative caspase activation by Cyt c-SPDP and the Cyt c-lactose bioconjugate, respectively, when compared to Cyt c. This again demonstrates the efficiency of the glycosylation to improve maintaining Cyt c structure and thus function. To test for cytotoxicity, HeLa cells were incubated with Cyt c loaded MSN at different Cyt c concentrations (12.5, 25.0, and 37.5 μg/mL) for 24-72 h and cellular metabolic activity determined by a cell proliferation assay. While MSN-SPDP-Cyt c did not induced cell death, the Cyt c-lactose bioconjugate induced significant cell death after 72 h, reducing HeLa cell viability to 67% and 45% at the 25 μg/mL and 37.5 μg/mL concentrations, respectively. Confocal microscopy confirmed that the MSN immobilized Cyt c-lactose bioconjugate was internalized by HeLa cells and that the bioconjugate was capable of endosomal escape. The results clearly demonstrate that chemical glycosylation stabilized Cyt c upon formulation of a smart drug delivery system and upon delivery into cancer cells and highlight the general potential of chemical protein glycosylation to improve the stability of protein drugs.

Efficient delivery of p53 and cytochrome c by supramolecular assembly of a dendritic multi-domain delivery system

Versatile nanocarrier systems facilitating uptake of exogenous proteins are highly alluring in evaluating these proteins for therapeutic applications. The self-assembly of an efficient nano-sized protein transporter consisting of three different entities is presented: A streptavidin protein core functioning as an adapter, second generation polyamidoamine dendrons for facilitating cell uptake as well as two different therapeutic proteins (tumor suppressor p53 or pro-apoptotic cytochrome c as cargo). Well-defined dendrons containing a biotin core are prepared and display no cytotoxic behavior upon conjugation to streptavidin. The integration of biotinylated human recombinant p53 (B-p53) into the three component system allows excellent internalization into HeLa, A549 and SaOS osteosarcoma cells monitored via confocal microscopy, immunoblot analysis and co-localization studies. In addition, the conjugation of B-p53 to dendronized streptavidin preserves its specific DNA-binding in vitro, and its delivery into SaOS cells impairs cell viability with concomitant activation of caspases 3 and 7. The versatility of this system is further exhibited by the significant enhancement of the pro-apoptotic effects of internalized cytochrome c which is analyzed by flow cytometry and cell viability assays. These results demonstrate that the "bio-click" self-assembly of biotinylated dendrons and proteins on a streptavidin adapter yields a stable supramolecular complex. This efficient bionanotransporter provides an attractive platform for mediating the delivery of functional proteins of interest into living mammalian cells in a facile and rapid way.

Solid lipid nanoparticles modified with stearic acid-octaarginine for oral administration of insulin

The aim of this study was to design and characterize solid lipid nanoparticles (SLNs) modified with stearic acid–octaarginine (SA-R₈) as carriers for oral administration of insulin (SA-R ₈-Ins-SLNs). The SLNs were prepared by spontaneous emulsion solvent diffusion methods. The mean particle size, zeta potential, drug loading, and encapsulation efficiency of the SA-R₈-Ins-SLNs were 162 nm, 29.87 mV, 3.19%, and 76.54%, respectively. The zeta potential of the SLNs changed dramatically, from −32.13 mV to 29.87 mV, by binding the positively charged SA-R₈. Morphological studies of SA-R₈-Ins-SLNs using transmission electron microscopy showed that they were spherical. In vitro, a degradation experiment by enzymes showed that SLNs and SA-R₈ could partially protect insulin from proteolysis. Compared to the insulin solution, the SA-R₈-Ins-SLNs increased the Caco-2 cell’s internalization by up to 18.44 times. In the in vivo studies, a significant hypoglycemic effect in diabetic rats over controls was obtained, with a SA-R₈-Ins-SLN pharmacological availability value of 13.86 ± 0.79. These results demonstrate that SA-R₈-modified SLNs promote the oral absorption of insulin.

Defeating Leishmania resistance to miltefosine (hexadecylphosphocholine) by peptide-mediated drug smuggling: a proof of mechanism for trypanosomatid chemotherapy

Miltefosine (hexadecylphosphocholine, HePC), the first orally active drug successful against leishmaniasis, is especially active on the visceral form of the disease. Resistance mechanisms are almost exclusively associated to dysfunction in HePC uptake systems. In order to evade the requirements of its cognate receptor/translocator, HePC-resistant Leishmania donovani parasites (R40 strain) were challenged with constructs consisting of an ω-thiol-functionalized HePC analogue conjugated to the cell-penetrating peptide (CPP) Tat(48-60), either through a disulfide or a thioether bond. The conjugates enter and kill both promastigote and intracellular amastigote forms of the R40 strain. Intracellular release of HePC by reduction of the disulfide-based conjugate was confirmed by means of double tagging at both the CPP (Quasar 670) and HePC (BODIPY) moieties. Scission of the conjugate, however, is not mandatory, as the metabolically more stable thioether conjugate retained substantial activity. The disulfide conjugate is highly active on the bloodstream form of Trypanosoma b. brucei, naturally resistant to HePC. Our results provide proof-of-mechanism for the use of CPP conjugates to avert drug resistance by faulty drug accumulation in parasites, as well as the possibility to extend chemotherapy into other parasites intrinsically devoid of membrane translocation systems.

Comparison of cationic and amphipathic cell penetrating peptides for siRNA delivery and efficacy

Cell penetrating peptides (CPPs) are short strands of arginine- and/or lysine-rich peptides (<30 amino acids) that use their cationic nature for efficient intracellular accumulation. CPPs have been used for small interfering RNA (siRNA) delivery by direct complexation with the siRNA anionic phosphate backbone. During this process, however, part of the CPP cationic charges are neutralized, and the resultant loss of free positive charges may substantially compromise CPP's internalization capabilities and eventually reduce siRNA delivery efficiency. The purpose of this study was to design a novel type of polyplex for siRNA delivery to overcome the CPP neutralization issue. This novel polyplex consists of three components: siRNA, 21mer oligolysine (K21) chemically modified to incorporate CPP conjugation sites (K21-PDP), and CPP delivery moiety. The siRNA was first neutralized by cationic charges of K21-PDP to form a polyplex. Then a cationic (hexaarginine, R6) or an amphipathic (model amphipathic peptide, MAP) CPP was conjugated to the polyplex. Agarose gel shift assays indicated that the siRNA could be released from the polyplex after K21-PDP degradation or polyplex dilution. Furthermore, the total intracellular internalization of these two CPP-polyplexes was studied. Compared with R6-polyplex, MAP-polyplex exhibited 170- and 600-fold greater uptake of fluorescently labeled siRNA at 1 and 6 h post-transfection, respectively. MAP-polyplex also exhibited comparable GFP silencing effects as Lipofectamine 2000 complex in Huh7.5 cells stably transfected to express GFP-light chain 3 protein, whereas R6-polyplex did not demonstrate significant silencing activity. Further studies indicated that the K21-PDP-siRNA polyplex formation and conjugation of MAP to the polyplex were essential for siRNA polyplex uptake and gene silencing. MAP-polyplex was also shown to be unaffected by the presence of 10% FBS during transfection. In addition, MAP-polyplex uptake was dependent on vesicle formation and fusion due to 70 and 54% loss of uptake at 4 and 16 °C, respectively, compared to incubation at 37 °C. Therefore, the amphipathic CPP is a more suitable carrier moiety for delivery of siRNA polyplex.