Typical and atypical trafficking pathways of Ad5 penton base recombinant protein: implications for gene transfer

Adenovirus-Derived Nano-Capsid Platforms for Targeted Delivery and Penetration of Macromolecules into Resistant and Metastatic Tumors

Macromolecular therapeutics such as nucleic acids, peptides, and proteins have the potential to overcome treatment barriers for cancer. For example, nucleic acid or peptide biologics may offer an alternative strategy for attacking otherwise undruggable therapeutic targets such as transcription factors and similar oncologic drivers. Delivery of biological therapeutics into tumor cells requires a robust system of cell penetration to access therapeutic targets within the cell interior. A highly effective means of accomplishing this may be borrowed from cell-penetrating pathogens such as viruses. In particular, the cell entry function of the adenovirus penton base capsid protein has been effective at penetrating tumor cells for the intracellular deposition of macromolecular therapies and membrane-impermeable drugs. Here, we provide an overview describing the evolution of tumor-targeted penton-base-derived nano-capsids as a framework for discussing the requirements for overcoming key barriers to macromolecular delivery. The development and pre-clinical testing of these proteins for therapeutic delivery has begun to also uncover the elusive mechanism underlying the membrane-penetrating function of the penton base. An understanding of this mechanism may unlock the potential for macromolecular therapeutics to be effectively delivered into cancer cells and to provide a treatment option for tumors resisting current clinical therapies.

Adenovirus Fibers as Ultra-Stable Vehicles for Intracellular Nanoparticle and Protein Delivery

Protein-based carriers are promising vehicles for the intracellular delivery of therapeutics. In this study, we designed and studied adenovirus protein fiber constructs with potential applications as carriers for the delivery of protein and nanoparticle cargoes. We used as a basic structural framework the fibrous shaft segment of the adenovirus fiber protein comprising of residues 61–392, connected to the fibritin foldon trimerization motif at the C-terminal end. A fourteen-amino-acid biotinylation sequence was inserted immediately after the N-terminal, His-tagged end of the construct in order to enable the attachment of a biotin moiety in vivo. We report herein that this His-tag biotinylated construct folds into thermally and protease-stable fibrous nanorods that can be internalized into cells and are not cytotoxic. Moreover, they can bind to proteins and nanoparticles through the biotin–streptavidin interaction and mediate their delivery to cells. We demonstrate that streptavidin-conjugated gold nanoparticles can be transported into NIH3T3 fibroblast and HeLa cancer cell lines. Furthermore, two streptavidin-conjugated model proteins, alkaline phosphatase and horseradish peroxidase can be delivered into the cell cytoplasm in their enzymatically active form. This work is aimed at establishing the proof-of-principle for the rational engineering of diverse functionalities onto the initial protein structural framework and the use of adenovirus fiber-based proteins as nanorods for the delivery of nanoparticles and model proteins. These constructs could constitute a stepping stone for the development of multifunctional and modular fibrous nanorod platforms that can be tailored to applications at the sequence level.

HER3-targeted protein chimera forms endosomolytic capsomeres and self-assembles into stealth nucleocapsids for systemic tumor homing of RNA interference in vivo

RNA interference represents a potent intervention for cancer treatment but requires a robust delivery agent for transporting gene-modulating molecules, such as small interfering RNAs (siRNAs). Although numerous molecular approaches for siRNA delivery are adequate in vitro, delivery to therapeutic targets in vivo is limited by payload integrity, cell targeting, efficient cell uptake, and membrane penetration. We constructed nonviral biomaterials to transport small nucleic acids to cell targets, including tumor cells, on the basis of the self-assembling and cell-penetrating activities of the adenovirus capsid penton base. Our recombinant penton base chimera contains polypeptide domains designed for noncovalent assembly with anionic molecules and tumor homing. Here, structural modeling, molecular dynamics simulations, and functional assays suggest that it forms pentameric units resembling viral capsomeres that assemble into larger capsid-like structures when combined with siRNA cargo. Pentamerization forms a barrel lined with charged residues mediating pH-responsive dissociation and exposing masked domains, providing insight on the endosomolytic mechanism. The therapeutic impact was examined on tumors expressing high levels of HER3/ErbB3 that are resistant to clinical inhibitors. Our findings suggest that our construct may utilize ligand mimicry to avoid host attack and target the siRNA to HER3+ tumors by forming multivalent capsid-like structures.

Resistance to receptor-blocking therapies primes tumors as targets for HER3-homing nanobiologics

Resistance to anti-tumor therapeutics is an important clinical problem. Tumor-targeted therapies currently used in the clinic are derived from antibodies or small molecules that mitigate growth factor activity. These have improved therapeutic efficacy and safety compared to traditional treatment modalities but resistance arises in the majority of clinical cases. Targeting such resistance could improve tumor abatement and patient survival. A growing number of such tumors are characterized by prominent expression of the human epidermal growth factor receptor 3 (HER3) on the cell surface. This study presents a “Trojan-Horse” approach to combating these tumors by using a receptor-targeted biocarrier that exploits the HER3 cell surface protein as a portal to sneak therapeutics into tumor cells by mimicking an essential ligand. The biocarrier used here combines several functions within a single fusion protein for mediating targeted cell penetration and non-covalent self-assembly with therapeutic cargo, forming HER3-homing nanobiologics. Importantly, we demonstrate here that these nanobiologics are therapeutically effective in several scenarios of resistance to clinically approved targeted inhibitors of the human EGF receptor family. We also show that such inhibitors heighten efficacy of our nanobiologics on naïve tumors by augmenting HER3 expression. This approach takes advantage of a current clinical problem (i.e. resistance to growth factor inhibition) and uses it to make tumors more susceptible to HER3 nanobiologic treatment. Moreover, we demonstrate a novel approach in addressing drug resistance by taking inhibitors against which resistance arises and re-introducing these as adjuvants, sensitizing tumors to the HER3 nanobiologics described here.

A corrole nanobiologic elicits tissue-activated MRI contrast enhancement and tumor-targeted toxicity

Water-soluble corroles with inherent fluorescence can form stable self-assemblies with tumor-targeted cell penetration proteins, and have been explored as agents for optical imaging and photosensitization of tumors in pre-clinical studies. However, the limited tissue-depth of excitation wavelengths limits their clinical applicability. To examine their utility in more clinically-relevant imaging and therapeutic modalities, here we have explored the use of corroles as contrast enhancing agents for magnetic resonance imaging (MRI), and evaluated their potential for tumor-selective delivery when encapsulated by a tumor-targeted polypeptide. We have found that a manganese-metallated corrole exhibits significant T1 relaxation shortening and MRI contrast enhancement that is blocked by particle formation in solution but yields considerable MRI contrast after tissue uptake. Cell entry but not low pH enables this. Additionally, the corrole elicited tumor-toxicity through the loss of mitochondrial membrane potential and cytoskeletal breakdown when delivered by the targeted polypeptide. The protein-corrole particle (which we call HerMn) exhibited improved therapeutic efficacy compared to current targeted therapies used in the clinic. Taken together with its tumor-preferential biodistribution, our findings indicate that HerMn can facilitate tumor-targeted toxicity after systemic delivery and tumor-selective MR imaging activatable by internalization.

Analysis of targeted viral protein nanoparticles delivered to HER2+ tumors

The HER2+ tumor-targeted nanoparticle, HerDox, exhibits tumor-preferential accumulation and tumor-growth ablation in an animal model of HER2+ cancer. HerDox is formed by non-covalent self-assembly of a tumor targeted cell penetration protein with the chemotherapy agent, doxorubicin, via a small nucleic acid linker. A combination of electrophilic, intercalation, and oligomerization interactions facilitate self-assembly into round 10-20 nm particles. HerDox exhibits stability in blood as well as in extended storage at different temperatures. Systemic delivery of HerDox in tumor-bearing mice results in tumor-cell death with no detectable adverse effects to non-tumor tissue, including the heart and liver (which undergo marked damage by untargeted doxorubicin). HER2 elevation facilitates targeting to cells expressing the human epidermal growth factor receptor, hence tumors displaying elevated HER2 levels exhibit greater accumulation of HerDox compared to cells expressing lower levels, both in vitro and in vivo. Fluorescence intensity imaging combined with in situ confocal and spectral analysis has allowed us to verify in vivo tumor targeting and tumor cell penetration of HerDox after systemic delivery. Here we detail our methods for assessing tumor targeting via multimode imaging after systemic delivery.

Development of adenovirus capsid proteins for targeted therapeutic delivery

The outer shell of the adenovirus capsid comprises three major types of protein (hexon, penton base and fiber) that perform the majority of functions facilitating the early stages of adenovirus infection. These stages include initial cell-surface binding followed by receptor-mediated endocytosis, endosomal penetration and cytosolic entry, and intracellular trafficking toward the nucleus. Numerous studies have shown that the penton base contributes to several of these steps and have supported the development of this protein into a delivery agent for therapeutic molecules. Studies revealing that the fiber and hexon bear unexpected properties of cell entry and/or nuclear homing have supported the development of these capsid proteins, as well into potential delivery vehicles. This review summarizes the findings to date of the protein-cell activities of these capsid proteins in the absence of the whole virus and their potential for therapeutic application with regard to the delivery of foreign molecules.

Chemotherapy targeting by DNA capture in viral protein particles

AIM

This study tests the hypothesis that DNA intercalation and electrophilic interactions can be exploited to noncovalently assemble doxorubicin in a viral protein nanoparticle designed to target and penetrate tumor cells through ligand-directed delivery. We further test whether this new paradigm of doxorubicin targeting shows therapeutic efficacy and safety in vitro and in vivo.

MATERIALS & METHODS

We tested serum stability, tumor targeting and therapeutic efficacy in vitro and in vivo using biochemical, microscopy and cytotoxicity assays.

RESULTS

Self-assembly formed approximately 10-nm diameter serum-stable nanoparticles that can target and ablate HER2+ tumors at >10× lower dose compared with untargeted doxorubicin, while sparing the heart after intravenous delivery. The targeted nanoparticle tested here allows doxorubicin potency to remain unaltered during assembly, transport and release into target cells,while avoiding peripheral tissue damage and enabling lower, and thus safer, drug dose for tumor killing.

CONCLUSION

This nanoparticle may be an improved alternative to chemical conjugates and signal-blocking antibodies for tumor-targeted treatment.

A mechanistic study of tumor-targeted corrole toxicity

HerGa is a self-assembled tumor-targeted particle that bears both tumor detection and elimination activities in a single, two-component complex (Agadjanian et al. Proc. Natl. Acad. Sci. U.S.A.2009, 106, 6105-6110). Given its multifunctionality, HerGa (composed of the fluorescent cytotoxic corrole macrocycle, S2Ga, noncovalently bound to the tumor-targeted cell penetration protein, HerPBK10) has the potential for high clinical impact, but its mechanism of cell killing remains to be elucidated, and hence is the focus of the present study. Here we show that HerGa requires HerPBK10-mediated cell entry to induce toxicity. HerGa (but not HerPBK10 or S2Ga alone) induced mitochondrial membrane potential disruption and superoxide elevation, which were both prevented by endosomolytic-deficient mutants, indicating that cytosolic exposure is necessary for corrole-mediated cell death. A novel property discovered here is that corrole fluorescence lifetime acts as a pH indicator, broadcasting the intracellular microenvironmental pH during uptake in live cells. This feature in combination with two-photon imaging shows that HerGa undergoes early endosome escape during uptake, avoiding compartments of pH < 6.5. Cytoskeletal disruption accompanied HerGa-mediated mitochondrial changes whereas oxygen scavenging reduced both events. Paclitaxel treatment indicated that HerGa uptake requires dynamic microtubules. Unexpectedly, low pH is insufficient to induce release of the corrole from HerPBK10. Altogether, these studies identify a mechanistic pathway in which early endosomal escape enables HerGa-induced superoxide generation leading to cytoskeletal and mitochondrial damage, thus triggering downstream cell death.

The association of viral proteins with host cell dynein components during virus infection

After fusion with the cellular plasma membrane or endosomal membranes, viral particles are generally too large to diffuse freely within the crowded cytoplasm environment. Thus, they will never reach the cell nucleus or the perinuclear areas where replication or reverse transcription usually takes place. It has been proposed that many unrelated viruses are transported along microtubules in a retrograde manner using the cellular dynein machinery or, at least, some dynein components. A putative employment of the dynein motor in a dynein‐mediated transport has been suggested from experiments in which viral capsid proteins were used as bait in yeast two‐hybrid screens using libraries composed of cellular proteins and dynein‐associated chains were retrieved as virus‐interacting proteins. In most cases DYNLL1, DYNLT1 or DYNLRB1 were identified as the dynein chains that interact with viral proteins. The importance of these dynein–virus interactions has been supported, in principle, by the observation that in some cases the dynein‐interacting motifs of viral proteins altered by site‐directed mutagenesis result in non‐infective virions. Furthermore, overexpression of p50 dynamitin, which blocks the dynein–dynactin interaction, or incubation of infected cells with peptides that compete with viral polypeptides for dynein binding have been shown to alter the viral retrograde transport. Still, it remains to be proved that dynein light chains can bind simultaneously to incoming virions and to the dynein motor for retrograde transport to take place. In this review, we will analyse the association of viral proteins with dynein polypeptides and its implications for viral infection.

Block in entry of enteric adenovirus type 41 in HEK293 cells

Human species F adenoviruses, HAdV-40 and HAdV-41, display characteristic gut tropism in vivo as well as poor infectivity in cell culture. To address the hypothesis that poor infectivity of HAdV-40/41 reflects a partial block prior to genome delivery, the internalization and trafficking of HAdV-41, HAdV-5 (species C) and HAdV-35 (species B) were compared in 293 (human embryonic kidney) cells, which complement E1B function in HAdV-40/41, and in A549 (lung epithelial) cells. Unlike fluorescently labeled HAdV-5 virions which were transported towards the nucleus and HAdV-35 virions which colocalized with LAMP-1, HAdV-41 virions appeared to be scattered throughout the cytoplasm but did not colocalize with markers of late endosomes/lysosomes (cathepsin B, LAMP-1) or with caveolin 1. Fluorescent dextran was released from vesicles in only 10% of HAd41-infected cells that took up dextran, compared to 70% of HAdV-5-infected cells, suggesting inefficient disruption of endosomes by HAdV-41 or uptake of HAdV-41 virions into a different compartment than HAdV-5 virions. Quantitative transmission electron microscopy, which showed greater binding of HAdV-41 virions to 293 cells than to A549 cells, identified a major block in uptake of HAdV-41 virions from the surface of both cell lines. More than 80% of virions remained on the surface 60 min p.i. and as late as 4h p.i. In contrast to HAdV-5 and HAdV-35 virions, which associated mostly with clathrin-coated pits, HAdV-41 virions associated mostly with caveolar-like invaginations and, to a lesser extent, with larger non-clathrin-coated pits, suggesting internalization by pathways other than clathrin-mediated endocytosis.

Time-series nasal epithelial transcriptomics during natural pollen exposure in healthy subjects and allergic patients

BACKGROUND

The role of epithelium has recently awakened interest in the studies of type I hypersensitivity.

OBJECTIVE

We analysed the nasal transcriptomics epithelial response to natural birch pollen exposure in a time series manner.

METHODS

Human nasal epithelial cell swabs were collected from birch pollen allergic patients and healthy controls in winter season. In addition, four specimens at weekly intervals were collected from the same subjects during natural birch pollen exposure in spring and transcriptomic analyses were performed.

RESULTS

The nasal epithelium of healthy subjects responded vigorously to allergen exposure. The immune response was a dominating category of this response. Notably, the healthy subjects did not display any clinical symptoms regardless of this response detected by transcriptomic analysis. Concomitantly, the epithelium of allergic subjects responded also, but with a different set of responders. In allergic patients the regulation of dyneins, the molecular motors of intracellular transport dominated. This further supports our previous hypothesis that the birch pollen exposure results in an active uptake of allergen into the epithelium only in allergic subjects but not in healthy controls.

CONCLUSION

We showed that birch pollen allergen causes a defence response in healthy subjects, but not in allergic subjects. Instead, allergic patients actively transport pollen allergen through the epithelium to tissue mast cells. Our study showed that new hypotheses can arise from the application of discovery driven methodologies. To understand complex multifactorial diseases, such as type I hypersensitivity, this kind of hypotheses might be worth further analyses.

Viral vectors: from virology to transgene expression

In the late 1970s, it was predicted that gene therapy would be applied to humans within a decade. However, despite some success, gene therapy has still not become a routine practise in medicine. In this review, we will examine the problems, both experimental and clinical, associated with the use of viral material for transgenic insertion. We shall also discuss the development of viral vectors involving the most important vector types derived from retroviruses, adenoviruses, herpes simplex viruses and adeno-associated viruses.

Adenoviruses: update on structure and function

Adenoviruses have been studied intensively for over 50 years as models of virus-cell interactions and latterly as gene vectors. With the advent of more sophisticated structural analysis techniques the disposition of most of the 13 structural proteins have been defined to a reasonable level. This review seeks to describe the functional properties of these proteins and shows that they all have a part to play in deciding the outcome of an infection and act at every level of the virus's path through the host cell. They are primarily involved in the induction of the different arms of the immune system and a better understanding of their overall properties should lead to more effective ways of combating virus infections.

Peptide-assisted traffic engineering for nonviral gene therapy

Many of the challenges facing nonviral gene therapy, to make it as effective as the viral-based version, have yet to be overcome. The technology possesses sufficient biosafety advantages to make the construction of 'artificial viruses' a worthwhile undertaking. The impact of vehicle architecture on traffic regulation, and the convergence of several intracellular pathways in late endosomes, indicates that the particular intracellular route might be less relevant than formerly believed. Proper functional tuning of artificial viruses by the use of full proteins or protein stretches, and especially, the incorporation of membrane-active peptides, would improve transgene expression levels and convert artificial viruses into powerful tools for gene medicine.

Adenovirus dodecahedron cell attachment and entry are mediated by heparan sulfate and integrins and vary along the cell cycle

The adenovirus penton base is a strategic protein involved in the virus internalisation pathway through interaction between its RGD sequences and integrin. In some human adenovirus serotypes, this pentameric protein features the ability of interacting together by twelve, leading to the formation of a symmetric nanoparticle called dodecahedron (Dd). This non-infectious adenovirus-like particle exhibiting sixty RGD sequences interacts with integrin but also with heparan sulfate proteoglycans (HSPGs) expressed at the cell surface. In this study, we discriminate the respective importance of HSPGs and integrin on human adenovirus serotype 3 dodecahedron attachment and entry. Using different cell lines and a specific integrin inhibitor, we have determined that HSPGs are mainly responsible for particle attachment to the cell surface, favouring a strictly required interaction with integrin that triggers internalisation. No other receptors are involved in Dd entry and integrins on their own can mediate the particle entry in HSPGs-deficient cells. Moreover, integrin recognition by Dd is highly susceptible to cations and particularly to manganese that enhances particle binding by 4- to 7-fold compared to calcium. Interestingly, investigations on Dd receptors along the cell cycle revealed an enhanced particle targeting to mitotic cells and a loss of internalisation at this stage. This phenomenon observed with both HeLa- and HSPGs-deficient cells, depends on integrin remodelling during mitosis. This provides new clues for the use of this adenovirus nanoparticle as a delivery vector and sheds light on the integrin and HSPGs relationship in both resting and dividing cells.

Liposome-mediated cellular delivery of active gp91(phox)

Background

Gp91^phox is a transmembrane protein and the catalytic core of the NADPH oxidase complex of neutrophils. Lack of this protein causes chronic granulomatous disease (CGD), a rare genetic disorder characterized by severe and recurrent infections due to the incapacity of phagocytes to kill microorganisms.

Methodology

Here we optimize a prokaryotic cell-free expression system to produce integral mammalian membrane proteins.

Conclusions

Using this system, we over-express truncated forms of the gp91^phox protein under soluble form in the presence of detergents or lipids resulting in active proteins with a “native-like” conformation. All the proteins exhibit diaphorase activity in the presence of cytosolic factors (p67^phox, p47^phox, p40^phox and Rac) and arachidonic acid. We also produce proteoliposomes containing gp91^phox protein and demonstrate that these proteins exhibit activities similar to their cellular counterpart. The proteoliposomes induce rapid cellular delivery and relocation of recombinant gp91^phox proteins to the plasma membrane. Our data support the concept of cell-free expression technology for producing recombinant proteoliposomes and their use for functional and structural studies or protein therapy by complementing deficient cells in gp91^phox protein.

"Alternative" endocytic mechanisms exploited by pathogens: new avenues for therapeutic delivery?

Some pathogens utilize unique routes to enter cells that may evade the intracellular barriers encountered by the typical clathrin-mediated endocytic pathway. Retrograde transport and caveolar uptake are among the better characterized pathways, as alternatives to clathrin-mediated endocytosis, that are known to facilitate entry of pathogens and potential delivery agents. Recent characterization of the trafficking mechanisms of prion proteins and certain bacteria may present new paradigms for strategizing improvements in therapeutic spread and retention of therapy. This review will provide an overview of such endocytic pathways, and discuss current and future possibilities in using these routes as a means to improve therapeutic delivery.

Novel fiber-dependent entry mechanism for adenovirus serotype 5 in lacrimal acini

The established mechanism for infection of most cells with adenovirus serotype 5 (Ad5) involves fiber capsid protein binding to coxsackievirus-adenovirus receptor (CAR) at the cell surface, followed by penton base capsid protein binding to alpha(v) integrins, which triggers clathrin-mediated endocytosis of the virus. Here we determined the identity of the capsid proteins responsible for mediating Ad5 entry into the acinar epithelial cells of the lacrimal gland. Ad5 transduction of primary rabbit lacrimal acinar cells was inhibited by excess Ad5 fiber or knob (terminal region of the fiber) but not excess penton base. Investigation of the interactions of recombinant Ad5 penton base, fiber, and knob with lacrimal acini revealed that the penton base capsid protein remained surface associated, while the knob domain of the fiber capsid protein was rapidly internalized. Introduction of rabbit CAR-specific small interfering RNA (siRNA) into lacrimal acini under conditions that reduced intracellular CAR mRNA significantly inhibited Ad5 transduction, in contrast to a control (nonspecific) siRNA. Preincubation of Ad5 with excess heparin or pretreatment of acini with a heparinase cocktail each inhibited Ad5 transduction by a separate and apparently additive mechanism. Functional and imaging studies revealed that Ad5, fiber, and knob, but not penton base, stimulated macropinocytosis in acini and that inhibition of macropinocytosis significantly reduced Ad5 transduction of acini. However, inhibition of macropinocytosis did not reduce Ad5 uptake. We propose that internalization of Ad5 into lacrimal acini is through a novel fiber-dependent mechanism that includes CAR and heparan sulfate glycosaminoglycans and that the subsequent intracellular trafficking of Ad5 is enhanced by fiber-induced macropinocytosis.