Nonviral gene delivery to human breast cancer cells by targeted Ad5 penton proteins

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.

The Adenovirus Dodecahedron: Beyond the Platonic Story

Many geometric forms are found in nature, some of them adhering to mathematical laws or amazing aesthetic rules. One of the best-known examples in microbiology is the icosahedral shape of certain viruses with 20 triangular facets and 12 edges. What is less known, however, is that a complementary object displaying 12 faces and 20 edges called a 'dodecahedron' can be produced in huge amounts during certain adenovirus replication cycles. The decahedron was first described more than 50 years ago in the human adenovirus (HAdV3) viral cycle. Later on, the expression of this recombinant scaffold, combined with improvements in cryo-electron microscopy, made it possible to decipher the structural determinants underlying their architecture. Recently, this particle, which mimics viral entry, was used to fish the long elusive adenovirus receptor, desmoglein-2, which serves as a cellular docking for some adenovirus serotypes. This breakthrough enabled the understanding of the physiological role played by the dodecahedral particles, showing that icosahedral and dodecahedral particles live more than a simple platonic story. All these points are developed in this review, and the potential use of the dodecahedron in therapeutic development is discussed.

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.

Oligonucleotide therapeutics in neurodegenerative diseases

Therapeutics that directly target RNAs are promising for a broad spectrum of disorders, including the neurodegenerative diseases. This is exemplified by the FDA approval of Nusinersen, an antisense oligonucleotide (ASO) therapeutic for spinal muscular atrophy (SMA). RNA targeting therapeutics are currently under development for amyotrophic lateral sclerosis (ALS), Huntington's disease (HD), and spinocerebellar ataxias. We have used an ASO approach toward developing a treatment for spinocerebellar ataxia type 2 (SCA2), for targeting the causative gene ATXN2. We demonstrated that reduction of ATXN2 expression in SCA2 mice treated by intracerebroventicular injection (ICV) of ATXN2 ASO delayed motor phenotype onset, improved the expression of several genes demonstrated abnormally reduced by transcriptomic profiling of SCA2 mice, and restored abnormal Purkinje cell firing frequency in acute cerebellar sections. Here we discuss RNA abnormalities in disease and the prospects of targeting neurodegenerative diseases at the level of RNA control using ASOs and other RNA-targeted therapeutics.

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.

Journey to the Center of the Cell: Current Nanocarrier Design Strategies Targeting Biopharmaceuticals to the Cytoplasm and Nucleus

New biopharmaceutical molecules, potentially able to provide more personalized and effective treatments, are being identified through the advent of advanced synthetic biology strategies, sophisticated chemical synthesis approaches, and new analytical methods to assess biological potency. However, translation of many of these structures has been significantly limited due to the need for more efficient strategies to deliver macromolecular therapeutics to desirable intracellular sites of action. Engineered nanocarriers that encapsulate peptides, proteins, or nucleic acids are generally internalized into target cells via one of several endocytic pathways. These nanostructures, entrapped within endosomes, must navigate the intracellular milieu to orchestrate delivery to the intended destination, typically the cytoplasm or nucleus. For therapeutics active in the cytoplasm, endosomal escape continues to represent a limiting step to effective treatment, since a majority of nanocarriers trapped within endosomes are ultimately marked for enzymatic degradation in lysosomes. Therapeutics active in the nucleus have the added challenges of reaching and penetrating the nuclear envelope, and nuclear delivery remains a preeminent challenge preventing clinical translation of gene therapy applications. Herein, we review cutting-edge peptide- and polymer-based design strategies with the potential to enable significant improvements in biopharmaceutical efficacy through improved intracellular targeting. These strategies often mimic the activities of pathogens, which have developed innate and highly effective mechanisms to penetrate plasma membranes and enter the nucleus of host cells. Understanding these mechanisms has enabled advances in synthetic peptide and polymer design that may ultimately improve intracellular trafficking and bioavailability, leading to increased access to new classes of biotherapeutics.

Biomimetic strategies for targeted nanoparticle delivery

Nanoparticle‐based drug delivery and imaging platforms have become increasingly popular over the past several decades. Among different design parameters that can affect their performance, the incorporation of targeting functionality onto nanoparticle surfaces has been a widely studied subject. Targeted formulations have the ability to improve efficacy and function by positively modulating tissue localization. Many methods exist for creating targeted nanoformulations, including the use of custom biomolecules such as antibodies or aptamers. More recently, a great amount of focus has been placed on biomimetic targeting strategies that leverage targeting interactions found directly in nature. Such strategies, which have been painstakingly selected over time by the process of evolution to maximize functionality, oftentimes enable scientists to forgo the specialized discovery processes associated with many traditional ligands and help to accelerate development of novel nanoparticle formulations. In this review, we categorize and discuss in‐depth recent works in this growing field of bioinspired research.

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.

Current status of gene therapy for breast cancer: progress and challenges

Breast cancer is characterized by a series of genetic mutations and is therefore ideally placed for gene therapy intervention. The aim of gene therapy is to deliver a nucleic acid-based drug to either correct or destroy the cells harboring the genetic aberration. More recently, cancer gene therapy has evolved to also encompass delivery of RNA interference technologies, as well as cancer DNA vaccines. However, the bottleneck in creating such nucleic acid pharmaceuticals lies in the delivery. Deliverability of DNA is limited as it is prone to circulating nucleases; therefore, numerous strategies have been employed to aid with biological transport. This review will discuss some of the viral and nonviral approaches to breast cancer gene therapy, and present the findings of clinical trials of these therapies in breast cancer patients. Also detailed are some of the most recent developments in nonviral approaches to targeting in breast cancer gene therapy, including transcriptional control, and the development of recombinant, multifunctional bio-inspired systems. Lastly, DNA vaccines for breast cancer are documented, with comment on requirements for successful pharmaceutical product development.

Peptide vectors for gene delivery: from single peptides to multifunctional peptide nanocarriers

The therapeutic use of nucleic acids relies on the availability of sophisticated delivery systems for targeted and intracellular delivery of these molecules. Such a gene delivery should possess essential characteristics to overcome several extracellular and intracellular barriers. Peptides offer an attractive platform for nonviral gene delivery, as several functional peptide classes exist capable of overcoming these barriers. However, none of these functional peptide classes contain all the essential characteristics required to overcome all of the barriers associated with successful gene delivery. Combining functional peptides into multifunctional peptide vectors will be pivotal for improving peptide-based gene delivery systems. By using combinatorial strategies and high-throughput screening, the identification of multifunctional peptide vectors will accelerate the optimization of peptide-based gene delivery systems.

pH shift assembly of adenoviral serotype 5 capsid protein nanosystems for enhanced delivery of nanoparticles, proteins and nucleic acids

Empty adenovirus serotype 5 (Ad5) capsids devoid of viral genome were developed as a novel delivery system for nanoparticles, proteins, and nucleic acids. Ad5 capsids of 110 nm diameter undergo an increase in particle size to 1637 nm in 1mM acetic acid at pH4.0 and then shrink to 60 nm, following pH reversal to 7.4. These pH shifts induced reversible changes in capsid zeta potential and secondary structure and irreversible changes in tertiary structure of capsid proteins. Using pH shift dependent changes in capsid size and structure, 20 nm fluorescent nanoparticles, FITC-BSA, and Alexa Fluor® 488 conjugated siRNA were encapsulated with high efficiency in Ad5 capsids, as confirmed by electron microscopy and/or flow cytometry. HEK cell uptake with capsid delivery system was 7.8-, 7.4-, and 2.9-fold greater for nanoparticles, FITC-BSA, and Alexa-siRNA, respectively, when compared to plain solutes. Physical mixtures of capsids and fluorescent solutes exhibited less capsid associated fluorescence intensity and cell uptake. Further, unlike physical mixture, pH shift assembled Ad5 capsids protected siRNA from RNase degradation. Ad5 capsids before and after pH shift exhibited endolysosomal escape. Thus, empty Ad5 capsids can encapsulate a variety of solutes based on pH shift assembly, resulting in enhanced cellular delivery.

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.

Photoexcitation of tumor-targeted corroles induces singlet oxygen-mediated augmentation of cytotoxicity

The tumor-targeted corrole particle, HerGa, displays preferential toxicity to tumors in vivo and can be tracked via fluorescence for simultaneous detection, imaging, and treatment. We have recently uncovered an additional feature of HerGa in that its cytotoxicity is enhanced by light irradiation. In the present study, we have elucidated the cellular mechanisms for HerGa photoexcitation-mediated cell damage using fluorescence optical imaging. In particular, we found that light irradiation of HerGa produces singlet oxygen, causing mitochondrial damage and cytochrome c release, thus promoting apoptotic cell death. An understanding of the mechanisms of cell death induced by HerGa, particularly under conditions of light-mediated excitation, may direct future efforts in further customizing this nanoparticle for additional therapeutic applications and enhanced potency.

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.

Multimodality imaging in vivo for preclinical assessment of tumor-targeted doxorubicin nanoparticles

This study presents a new multimodal imaging approach that includes high-frequency ultrasound, fluorescence intensity, confocal, and spectral imaging to improve the preclinical evaluation of new therapeutics in vivo. Here we use this approach to assess in vivo the therapeutic efficacy of the novel chemotherapy construct, HerDox during and after treatment. HerDox is comprised of doxorubicin non-covalently assembled in a viral-like particle targeted to HER2+ tumor cells, causing tumor cell death at over 10-fold lower dose compared to the untargeted drug, while sparing the heart. Whereas our initial proof-of-principle studies on HerDox used tumor growth/shrinkage rates as a measure of therapeutic efficacy, here we show that multimodal imaging deployed during and after treatment can supplement traditional modes of tumor monitoring to further characterize the particle in tissues of treated mice. Specifically, we show here that tumor cell apoptosis elicited by HerDox can be monitored in vivo during treatment using high frequency ultrasound imaging, while in situ confocal imaging of excised tumors shows that HerDox indeed penetrated tumor tissue and can be detected at the subcellular level, including in the nucleus, via Dox fluorescence. In addition, ratiometric spectral imaging of the same tumor tissue enables quantitative discrimination of HerDox fluorescence from autofluorescence in situ. In contrast to standard approaches of preclinical assessment, this new method provides multiple/complementary information that may shorten the time required for initial evaluation of in vivo efficacy, thus potentially reducing the time and cost for translating new drug molecules into the clinic.

Investigating photoexcitation-induced mitochondrial damage by chemotherapeutic corroles using multimode optical imaging

We recently reported that a targeted, brightly fluorescent gallium corrole (HerGa) is highly effective for breast tumor detection and treatment. Unlike structurally similar porphryins, HerGa exhibits tumor-targeted toxicity without the need for photoexcitation. We have now examined whether photoexcitation further modulates HerGa toxicity, using multimode optical imaging of live cells, including two-photon excited fluorescence, differential interference contrast (DIC), spectral, and lifetime imaging. Using two-photon excited fluorescence imaging, we observed that light at specific wavelengths augments the HerGa-mediated mitochondrial membrane potential disruption of breast cancer cells in situ. In addition, DIC, spectral, and fluorescence lifetime imaging enabled us to both validate cell damage by HerGa photoexcitation and investigate HerGa internalization, thus allowing optimization of light dose and timing. Our demonstration of HerGa phototoxicity opens the way for development of new methods of cancer intervention using tumor-targeted corroles.

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.

Targeted liposomes to deliver DNA to cells expressing 5-HT receptors

Cell targeted delivery of drugs, including nucleic acids, is known to enhance the therapeutic potential of free drugs. We used serotonin (5-HT) as the targeting ligand to deliver plasmid DNA to cells specifically expressing 5-HT receptor. Our liposomal formulation includes the 5-HT conjugated targeting lipid, a cationic lipid and cholesterol. DNA-binding studies indicate that the targeting 5-HT-lipid binds DNA efficiently. The formulation was tested and found to efficiently deliver DNA into CHO cells stably expressing the human serotonin(1A) receptor (CHO-5-HT(1A)R) compared to control CHO cells. Liposomes without the 5-HT moiety were less efficient in both cell lines. Similar enhancement in transfection efficiency was also observed in human neuroblastoma IMR32 and hepatocellular carcinoma (HepG2) cells. Cell uptake studies using CHO-5-HT(1A)R cells by flow cytometry and confocal microscopy clearly indicated that the targeting liposomes through 5-HT moiety may have a direct role in increasing the cellular uptake of DNA-lipid complexes. To our knowledge this is the first report that demonstrates receptor-targeted nucleic acid delivery into cells expressing 5-HT receptor.

Ratiometric spectral imaging for fast tumor detection and chemotherapy monitoring in vivo

We report a novel in vivo spectral imaging approach to cancer detection and chemotherapy assessment. We describe and characterize a ratiometric spectral imaging and analysis method and evaluate its performance for tumor detection and delineation by quantitatively monitoring the specific accumulation of targeted gallium corrole (HerGa) into HER2-positive (HER2 +) breast tumors. HerGa temporal accumulation in nude mice bearing HER2 + breast tumors was monitored comparatively by a. this new ratiometric imaging and analysis method; b. established (reflectance and fluorescence) spectral imaging; c. more commonly used fluorescence intensity imaging. We also tested the feasibility of HerGa imaging in vivo using the ratiometric spectral imaging method for tumor detection and delineation. Our results show that the new method not only provides better quantitative information than typical spectral imaging, but also better specificity than standard fluorescence intensity imaging, thus allowing enhanced in vivo outlining of tumors and dynamic, quantitative monitoring of targeted chemotherapy agent accumulation into them.

Multimode Optical Imaging for Translational Chemotherapy: In Vivo Tumor Detection and Delineation by Targeted Gallium Corroles

We report the feasibility of tumor detection and delineation in vivo using multimode optical imaging of targeted gallium corrole (HerGa). HerGa is highly effective for targeted HER2+ tumor elimination in vivo, and it emits intense fluorescence. These unique characteristics of HerGa prompted us to investigate the potential of HerGa for tumor detection and delineation, by performing multimode optical imaging ex vivo and in vivo; the imaging modes included fluorescence intensity, spectral (including ratiometric), lifetime, and two-photon excited fluorescence, using our custom-built imaging system. While fluorescence intensity imaging provided information about tumor targeting capacity and tumor retention of HerGa, ratiometric spectral imaging offered more quantitative and specific information about HerGa location and accumulation. Most importantly, the fluorescence lifetime imaging of HerGa allowed us to discriminate between tumor and non-tumor regions by fluorescence lifetime differences. Finally, two-photon excited fluorescence images provided highly resolved and thus topologically detailed information around the tumor regions where HerGa accumulates. Taken together, the results shown in this report suggest the feasibility of tumor detection and delineation by multimode optical imaging of HerGa, and fluorescent chemotherapy agents in general. Specifically, the multimode optical imaging can offer complementary and even synergetic information simultaneously in the tumor detection and delineation by HerGa, thus enhancing contrast.

Structure prediction and validation of an affibody engineered for cell-specific nucleic acid targeting

Cell-penetrating peptides comprising cloned epitopes that contribute to membrane transduction, DNA-binding and cell targeting functions are known to facilitate nucleic acid delivery. Using the ITASSER software, we predicted the 3-D structure of a well characterized and efficient transfecting cell-penetrating peptide, namely TAT-Mu and its derivative TAT-Mu-AF protein that harbors a targeting ligand, the HER2-binding affibody. Our model predicts TAT-Mu-AF fusion protein as primarily comprising α-helices. The affibody in TAT-Mu-AF is predicted as a 3-helical domain that is distinct from the TAT-Mu domain. Its positioning in three-dimensional structure is oriented in a manner that possibly favors interactions with receptor and facilitates transport to the target site. The linker region between TAT-Mu and the affibody is also predicted as a helix that is likely to stabilize the overall fold of the TAT-Mu-AF complex. Further, the evaluation of secondary structure of the designed TAT-Mu-AF fusion protein by circular dichroism is in support of our predictions.

Plasmid DNA delivery into MDA-MB-453 cells mediated by recombinant Her-NLS fusion protein

A major rate-limiting step in nonviral gene delivery is the entry of nucleic acids across various membrane barriers and eventually into the nucleus where it must be transcribed. Cell-penetrating peptides and proteins are employed to generate formulations that overcome these challenges to facilitate DNA delivery into cells efficiently. However, these are limited by their inability to deliver nucleic acids selectively due to lack of specificity because they deliver to both cancer and normal cells. In this study, through modular design, we generated a recombinant fusion protein designated as Her-nuclear localization sequence (Her-NLS), where heregulin-α (Her), a targeting moiety, was cloned in frame with cationic NLS peptide to obtain a cell-specific targeting biomolecule for nucleic acid delivery. The heregulin-α₁ isoform possesses the epidermal growth factor-like domain and binds to HER2/3 heterodimers which are overexpressed in certain breast cancers. Purified recombinant Her-NLS fusion protein binds plasmid DNA and specifically transfects MDA-MB-453 cells overexpressing the epidermal growth factor receptors HER2/3 in vitro. The approach described would also permit replacement of heregulin ligand with other targeting moieties that would be suited to cell-specific nucleic acid delivery mediated via receptor-ligand interactions.

Tumor detection and elimination by a targeted gallium corrole

Sulfonated gallium(III) corroles are intensely fluorescent macrocyclic compounds that spontaneously assemble with carrier proteins to undergo cell entry. We report in vivo imaging and therapeutic efficacy of a tumor-targeted corrole noncovalently assembled with a heregulin-modified protein directed at the human epidermal growth factor receptor (HER). Systemic delivery of this protein-corrole complex results in tumor accumulation, which can be visualized in vivo owing to intensely red corrole fluorescence. Targeted delivery in vivo leads to tumor cell death while normal tissue is spared. These findings contrast with the effects of doxorubicin, which can elicit cardiac damage during therapy and required direct intratumoral injection to yield similar levels of tumor shrinkage compared with the systemically delivered corrole. The targeted complex ablated tumors at >5 times a lower dose than untargeted systemic doxorubicin, and the corrole did not damage heart tissue. Complexes remained intact in serum and the carrier protein elicited no detectable immunogenicity. The sulfonated gallium(III) corrole functions both for tumor detection and intervention with safety and targeting advantages over standard chemotherapeutic agents.

Intelligent biosynthetic nanobiomaterials (IBNs) for hyperthermic gene delivery

PURPOSE

Intelligent biosynthetic nanobiomaterials (IBNs) were constructed as recombinant diblock copolymers, notated as K8-ELP(1-60), containing a cationic oligolysine (VGK8G) and a thermosensitive elastin-like polypeptide (ELP) block with 60 repetitive pentapeptide units [(VPGXG)60; X is Val, Ala and Gly in a 5:2:3 ratio].

METHODS

K8-ELP(1-60) was synthesized by recursive directional ligation for DNA oligomerization. Purity and molecular weight of K8-ELP(1-60) were confirmed by SDS-PAGE and mass spectrometry. DNA polyplexes were prepared from K8-ELP(1-60) and pGL3-Control (pGL3-C) plasmid DNA (pDNA) and stability was evaluated by gel retardation, DLS, and DNA displacement with heparin. Thermal transition profiles were studied by measuring the turbidity change at 350 nm and the polyplexes were used to transfect MCF-7 cells with a concomitant cytotoxicity assay.

RESULTS

SDS-PAGE and MALDI-TOF studies showed highly pure copolymers at the desired molecular weight. K8-ELP(1-60) condensed pDNA at a cation to anion (N/P) ratio above 0.25 with a tight distribution of particle size ranging from 115.5-32.4 nm with increasing N/P ratio. Thermal transition temperatures of K8-ELP(1-60)/pDNA and K8-ELP(1-60) alone were 44.9 and 71.5 degrees C, respectively. K8-ELP(1-60)/pDNA complexes successfully transduced MCF-7 cells with qualitative expression of enhanced green fluorescent protein (EGFP) and minimal cytotoxicity compared to branched poly(ethyleneimine) controls.

CONCLUSIONS

K8-ELP(1-60) was successfully designed and purified through recombinant means with efficient and stable condensation of pDNA at N/P ratios>0.25 and polyplex particle size<115 nm. MCF-7 cells successfully expressed EGFP with minimal cytotoxicity compared to positive controls; moreover, polyplexes retained sharp, thermotransitive kinetics within a narrow Tt range at clinically relevant hyperthermic temperatures, where the decrease of Tt was due to the increased hydrophobicity upon charge neutralization.

Current status of gene delivery and gene therapy in lacrimal gland using viral vectors

Gene delivery is one of the biggest challenges in the field of gene therapy. It involves the efficient transfer of transgenes into somatic cells for therapeutic purposes. A few major drawbacks in gene delivery include inefficient gene transfer and lack of sustained transgene expression. However, the classical method of using viral vectors for gene transfer has circumvented some of these issues. Several kinds of viruses, including retrovirus, adenovirus, adeno-associated virus, and herpes simplex virus, have been manipulated for use in gene transfer and gene therapy applications. The transfer of genetic material into lacrimal epithelial cells and tissues, both in vitro and in vivo, has been critical for the study of tear secretory mechanisms and autoimmunity of the lacrimal gland. These studies will help in the development of therapeutic interventions for autoimmune disorders such as Sjögren's syndrome and dry eye syndromes which are associated with lacrimal dysfunction. These studies are also critical for future endeavors which utilize the lacrimal gland as a reservoir for the production of therapeutic factors which can be released in tears, providing treatment for diseases of the cornea and posterior segment. This review will discuss the developments related to gene delivery and gene therapy in the lacrimal gland using several viral vector systems.

Protein transduction into human cells by adenovirus dodecahedron using WW domains as universal adaptors

BACKGROUND

Direct protein transduction is a recent technique that involves use of peptide vectors. In this study, we demonstrate that adenovirus dodecahedron (Dd), a virus-like particle devoid of DNA and able to penetrate cells with high efficiency, can be used as a vector for protein delivery.

METHODS

Taking advantage of Dd interaction with structural domains called WW, we have elaborated a universal adaptor to attach a protein of interest to this vector.

RESULTS

A tandem of three WW structural domains derived from the Nedd4 protein enables the formation of stable complexes with Dd, without impairing its endocytosis efficiency. Our protein of interest fused to the triple WW linker is delivered by the dodecahedron in 100% of cells in culture with on average more than ten million molecules per cell.

CONCLUSION

These data demonstrate the great potential of adenovirus dodecahedron in combination with WW domains as a protein transduction vector.

Intracellular trafficking of nonviral vectors

Nonviral vectors continue to be attractive alternatives to viruses due to their low toxicity and immunogenicity, lack of pathogenicity, and ease of pharmacologic production. However, nonviral vectors also continue to suffer from relatively low levels of gene transfer compared to viruses, thus the drive to improve these vectors continues. Many studies on vector-cell interactions have reported that nonviral vectors bind and enter cells efficiently, but yield low gene expression, thus directing our attention to the intracellular trafficking of these vectors to understand where the obstacles occur. Here, we will review nonviral vector trafficking pathways, which will be considered here as the steps from cell binding to nuclear delivery. Studies on the intracellular trafficking of nonviral vectors has given us valuable insights into the barriers these vectors must overcome to mediate efficient gene transfer. Importantly, we will highlight the different approaches used by researchers to overcome certain trafficking barriers to gene transfer, many of which incorporate components from biological systems that have naturally evolved the capacity to overcome such obstacles. The tools used to study trafficking pathways will also be discussed.

Specific delivery of corroles to cells via noncovalent conjugates with viral proteins

PURPOSE

Corroles are amphiphilic macrocycles that can bind and transport metal ions, and thus may be toxic to cells. We predicted that anionic corroles would poorly enter cells due to the negatively charged cell membrane, but could be ideal tumor-targeted drugs if appropriate carriers enabled delivery into tumor cells. In this work, we test the hypothesis that recombinant cell penetrating proteins of the adenovirus (Ad) capsid form noncovalent conjugates with corroles to facilitate target-specific delivery and cell death.

METHODS

Corroles mixed with recombinant proteins were tested for conjugate assembly, cell penetration, stability, targeted binding, and cell killing in vitro.

RESULTS

Sulfonated corroles entered cells only with carrier proteins, and formed stable complexes with recombinant Ad capsid proteins. ErbB receptor-targeted conjugates were cytotoxic to ErbB2-positive but not ErbB2-negative breast cancer cells, whereas molar equivalents of free corrole had no effect on these cells.

CONCLUSIONS

Sulfonated corroles are cytotoxic to ErbB2-positive breast cancer cells when delivered by a targeted cell penetrating protein. The relatively low dose required to accomplish this compared to untargeted compounds suggests that corroles may lend themselves to targeted therapy. Importantly, the amphiphilicity of corroles enables a unique approach to bioconjugate formation whereby the carrier and drug form a stable complex by noncovalent assembly.

Enhanced gene delivery to PC12 cells by a cationic polypeptide

Targeted gene delivery to diseased subtypes of neurons will be beneficial to the success of gene therapy of neurological disorders. We designed a recombinant cationic polypeptide to facilitate gene delivery to neuronal-like PC12 cells that express the nerve growth factor (NGF) receptors. The recombinant polypeptide was composed of a targeting moiety derived from loop 4-containing hairpin motif of NGF and a DNA-binding moiety of 10-lysine sequence and expressed in Escherichia coli. It activated NGF receptor, TrkA and its downstream signaling pathways in PC12 and promoted the survival of neuronally differentiated PC12 cells deprived of serum. The polypeptide could also bind plasmid DNA and enhance polycation-mediated gene delivery in NGF receptor-expressing PC12 cells, but not in COS7 cells lacking NGF receptors. The enhancement of gene transfer in PC12 was inhibited by pretreatment of free, unbound polypeptides, suggesting a NGF-receptor-specific effect of the polypeptide. These observations demonstrated the concept of using receptor-mediated mechanism for targeted gene delivery to neurons.

The structure of the human adenovirus 2 penton

The adenovirus penton, a noncovalent complex of the pentameric penton base and trimeric fiber proteins, comprises the vertices of the adenovirus capsid and contains all necessary components for viral attachment and internalization. The 3.3 A resolution crystal structure of human adenovirus 2 (hAd2) penton base shows that the monomer has a basal jellyroll domain and a distal irregular domain formed by two long insertions, a similar topology to the adenovirus hexon. The Arg-Gly-Asp (RGD) motif, required for interactions with cellular integrins, occurs on a flexible surface loop. The complex of penton base with bound N-terminal fiber peptide, determined at 3.5 A resolution, shows that the universal fiber motif FNPVYPY binds at the interface of adjacent penton base monomers and results in a localized structural rearrangement in the insertion domain of the penton base. These results give insight into the structure and assembly of the adenovirus capsid and will be of use for gene-therapy applications.

Nonviral gene delivery systems: From simple transfection agents to artificial viruses

The introduction of nucleic acids into cells for therapeutic intervention is greatly impeded by the size and charge of these molecules and therefore requires sophisticated vectors that facilitate cellular uptake. Both viral and nonviral vectors have been developed for this purpose, each with their own advantages and shortcomings. The engineering of artificial viruses by dismantling virus particles or incorporating viral features into nonviral vectors represents a novel strategy to combine "the best of both worlds".:

The Ad5 fiber mediates nonviral gene transfer in the absence of the whole virus, utilizing a novel cell entry pathway

The interesting discovery reported here that soluble adenovirus serotype 5 (Ad5) fiber proteins enter cells without the virus was a serendipitous result during our development of Ad5 capsid proteins as nonviral gene transfer vectors. The Ad5 capsid fiber and penton proteins mediate infection. The fiber docks to a noninternalizing cell surface protein called the coxsackievirus-Ad receptor (CAR), followed by penton binding to integrins, triggering integrin-mediated endocytosis of the virus. In our previous work, we assembled the nonviral complex, 3PO, which utilized the penton to mediate gene transfer through integrin binding and endocytosis. Here, we tested whether incorporating the fiber targets 3PO to CAR, thus recapitulating the Ad5 infection pathway. As CAR is not an endocytic receptor, we were surprised to find that the fiber alone, without the penton, enabled gene transfer by binding CAR, but internalizing through an unknown mechanism. We show here that the fiber distributes to the nucleus and cytoplasm after temperature-independent uptake, whereas the penton accumulates around the nucleus after temperature-dependent uptake. Fiber uptake by HeLa cells is also actin-dependent, requires the fiber tail/shaft region, and is largely inhibited by heparin. This study raises the possibility that alternative pathways may enable both viral and nonviral cell entry.

Phosphatidylinositol 3-kinase and Akt effectors mediate insulin-like growth factor-I neuroprotection in dorsal root ganglia neurons

Insulin-like growth factor-I (IGF-I) protects neurons of the peripheral nervous system from apoptosis, but the underlying signaling pathways are not well understood. We studied IGF-I mediated signaling in embryonic dorsal root ganglia (DRG) neurons. DRG neurons express IGF-I receptors (IGF-IR), and IGF-I activates the phosphatidylinositol 3-kinase (PI3K)/Akt pathway. High glucose exposure induces apoptosis, which is inhibited by IGF-I through the PI3K/Akt pathway. IGF-I stimulation of the PI3K/Akt pathway phosphorylates three known Akt effectors: the survival transcription factor cyclic AMP response element binding protein (CREB) and the pro-apoptotic effector proteins glycogen synthase kinase-3beta (GSK-3beta) and forkhead (FKHR). IGF-I regulates survival at the nuclear level through accumulation of phospho-Akt in DRG neuronal nuclei, increased CREB-mediated transcription, and nuclear exclusion of FKHR. High glucose increases expression of the pro-apoptotic Bcl protein Bim (a transcriptional target of FKHR). However, IGF-I does not regulate Bim or anti-apoptotic Bcl-xL protein expression levels, which suggests that IGF-I neuroprotection is not through regulation of their expression. High glucose also induces loss of the initiator caspase-9 and increases caspase-3 cleavage, effects blocked by IGF-I. These data suggest that IGF-I prevents apoptosis in DRG neurons by regulating PI3K/Akt pathway effectors, including GSK-3beta, CREB, and FKHR, and by blocking caspase activation.

Modular protein engineering for non-viral gene therapy

Despite the recognized potential of viral vectors for gene therapy, growing biological concerns are prompting the exploration of safer, non-viral vectors to deliver therapeutic nucleic acids. In this context, recombinant proteins can be bioproduced on a large scale, without the need for further in vitro modifications, being free of known or suspected biohazards. For these vehicles to act as efficient gene-delivery devices, they must perform relevant functions that mimic those of viruses; namely, nucleic acid condensation, targeted cell attachment and internalization, endosomal escape and nuclear transfer. Modular engineering enables the construction of chimeric polypeptides in which selected domains, potentially from different origins, provide the required activities. An equilibrate combination and spatial distribution of such partner elements has generated promising prototypes, able to deliver expressible DNA to tissue culture but also to specific cell-types in whole organisms.

Microarray transfection analysis of transcriptional regulation by cAMP-dependent protein kinase

A wide variety of bioinformatic tools have been described to characterize potential transcriptional regulatory mechanisms based on genomic sequence analysis and microarray hybridization studies. However, these regulatory mechanisms are still experimentally verified using transient transfection methods. Current transfection methods are limited both by their large scale and by the low level of efficiency for certain cell types. Our goals were to develop a microarray-based transfection method that could be optimized for different cell types and that would be useful in reporter assays of transcriptional regulation. Here we describe a novel transfection method, termed STEP (surface transfection and expression protocol), which employs microarray-based DNA transfection of adherent cells in the functional analysis of transcriptional regulation. In STEP, recombinant proteins with biological activities designed to enhance transfection are complexed with expression vector DNAs prior to spotting on microscope slides. The recombinant proteins used in STEP complexes can be varied to increase the efficiency for different cell types. We demonstrate that STEP efficiently transfects both supercoiled plasmids and PCR-generated linear expression cassettes. A co-transfection assay using effector expression vectors encoding the cAMP-dependent protein kinase (PKA), as well as reporter vectors containing PKA-regulated promoters, showed that STEP transfection allows detection and quantitation of transcriptional regulation by this protein kinase. Because bioinformatic studies often result in the identification of many putative regulatory elements and signaling pathways, this approach should be of utility in high-throughput functional genomic studies of transcriptional regulation.

Endocytosis of adenovirus and adenovirus capsid proteins

Key proteins of the icosahedral-shaped adenovirus (Ad) capsid mediate infection, and interact with cellular proteins to coordinate stepwise events of cell entry that produce successful gene transfer. Infection is mediated predominantly by the penton and fiber capsid proteins. The fiber initiates cell binding while the penton binds integrin coreceptors, triggering integrin-mediated endocytosis. Penton integrin signaling precedes viral escape from the endosomal vesicle. After cell binding, the virus undergoes stepwise disassembly of the capsid, shedding proteins during cell entry. Intracellular trafficking of the remaining capsid shell is mediated by the interaction of naked particles with the cytoskeleton. The capsid translocates toward the nucleus, with the majority of capsid proteins accumulating at the nuclear periphery, while viral DNA and associated protein VII are extruded through the nuclear pore. This discussion will encompass the current knowledge on Ad cell entry and trafficking, with an emphasis on the contribution of Ad capsid proteins to these processes. A greater understanding of the highly effective Ad cell entry pathway may lend itself to the development of safer drug and gene delivery alternatives utilizing similar pathways.

Targeting of Synthetic Gene Delivery Systems

Safe, efficient, and specific delivery of therapeutic genes remains an important bottleneck for the development of gene therapy. Synthetic, nonviral systems have a unique pharmaceutical profile with potential advantages for certain applications. Targeting of the synthetic vector improves the specificity of gene medicines through a modulation of the carriers' biodistribution, thus creating a dose differential between healthy tissue and the target site. The biodistribution of current carrier systems is being influenced to a large extent by intrinsic physicochemical characteristics, such as charge and size. Consequently, such nonspecific interactions can interfere with specific targeting, for example, by ligands. Therefore, a carrier complex should ideally be inert, that is, free from intrinsic properties that would bias its distribution away from the target site. Strategies such as coating of DNA carrier complexes with hydrophilic polymers have been used to mask some of these intrinsic targeting effects and avoid nonspecific interactions. Preexisting endogenous ligand-receptor interactions have frequently been used for targeting to certain cell types or tumours. Recently exogenous ligands have been derived from microorganisms or, like antibodies or phage-derived peptides, developed de novo. In animal models, such synthetic vectors have targeted remote sites such as a tumour. Furthermore, the therapeutic proof of the concept has been demonstrated for fitting combinations of synthetic vectors and therapeutic gene.

Adenovirus dodecahedron allows large multimeric protein transduction in human cells

Adenovirus dodecahedron is a virus-like particle composed of only two viral proteins of human adenovirus serotype 3 that are responsible for virus attachment and internalization. We show here that this dodecameric particle, devoid of genetic information, efficiently penetrates human cells and can deliver large multimeric proteins such as immunoglobulins.

Using GFP--ligand fusions to measure receptor-mediated endocytosis in living cells

Recombinant DNA technology has enabled the production of many types of chimeric proteins containing heterologous functional domains that have served a variety of useful capacities for cell biology research. Among proteins gaining wide use as a fusion partner is Aequorea victoria green fluorescent protein (GFP). GFP has been employed by numerous groups as a reporter gene for cell transfection and as an autofluorescent tag by recombinant fusion to foreign sequences. Here we describe the use of GFP as a tag for ligands, and provide examples of how purified recombinant GFP-ligand fusion proteins may be used to detect ligand-receptor interactions, including receptor-mediated endocytosis. Both its utility and limitations are discussed.