Current Gene Therapy (v.17, #2)

Smart Micro/Nano-robotic Systems for Gene Delivery by Alireza Pedram, Hossein Nejat Pishkenari (73-79).
Background: Small scale robotics have attracted growing attention for the prospect of targeting and accessing cell-sized sites, necessary for high precision biomedical applications and drug/gene delivery. The loss of controlled gene therapy, inducing systemic side effects and reduced therapeutic efficiency, can be settled utilizing these intelligent carriers.

Methods: Newly proposed solutions for the main challenges of control, power supplying, gene release and final carrier extraction/degradation have shifted these smart miniature robots to the point of being employed for practical applications of transferring oligonucleotides (pDNA, siRNA, mRNA, etc.) in near future.

Conclusion: In this paper, different scenarios and their endeavors to address the vital working demands and steps, in particular, carrier attachment and release, cell internalization, manipulation concerns as well as actuation systems are discussed.This review highlights some promising experimental results showing controlled gene release of robotic systems in comparison with current non-specific gene delivery methods.

Background: Successful gene delivery requires overcoming both systemic and intracellular obstacles before the nucleic acid cargo can successfully reach its tissue and subcellular target location.

Materials & Methods: Non-viral mechanisms to enable targeting while avoiding off-target delivery have arisen via biological, chemical, and physical engineering strategies.

Discussion: Herein we will discuss the physical parameters in particle design that promote tissue- and cell-targeted delivery of genetic cargo. We will discuss systemic concerns, such as circulation, tissue localization, and clearance, as well as cell-scale obstacles, such as cellular uptake and nucleic acid packaging.

Conclusion: In particular, we will focus on engineering particle shape and size in order to enhance delivery and promote precise targeting. We will also address methods to program or change particle shape in situ using environmentally triggered cues.

Lipid Nanoparticles as Potential Gene Therapeutic Delivery Systems for Oral Administration by Golnar Dorraj, Juan Jose Carreras, Hugo Nunez, Issam Abushammala, Ana Melero (89-104).
Background: Gene therapy has experimented an increasing attention in the last decades, due to its enormous potential applications in the medical field. It can be defined as the use of genes or genetic material (DNA, RNA, oligonucleotides) to treat or prevent a disease state, generally a geneticbased one.

Application: Other applications, like treating viral, bacterial or parasite infections or development of vaccines are gaining also interest. Efficient gene therapy is mainly dependent on the ability of the highly labile genetic material to reach the therapeutic target. For this purpose, different delivery systems have been designed and extensively investigated. Nanoparticles offer a broad range of possibilities in design, being prepared using biocompatible and biodegradable excipients, being therefore generally considered as safe.

Conclusion: Oral delivery of the genetic material is also a great challenge, due to the complexity of this specific biological barrier. Special attention to all the intrinsic hazards for gene delivery due to the barrier must be taken into account during the particle design process. Particle design will also allow targeting to specific sites of the gastrointestinal tract. Solid lipid nanoparticles have been extensively studied in the oral drug delivery field, and also in gene delivery through other administration routes, but still not explored in oral gene delivery. In this manuscript, design considerations and particle-cell interaction mechanisms will be extensively reviewed, focusing on the oral route to encourage the scientific community to explore these valuable carriers for oral gene delivery.

Delivering siRNA with Dendrimers: In Vivo Applications by Victoria Leiro, Sofia Duque Santos, Ana Paula Pego (105-119).
Over the last decades, gene therapy has emerged as a pioneering therapeutic approach to treat or prevent several diseases. Among the explored strategies, the short-term silencing of protein coding genes mediated by siRNAs has a good therapeutic potential in a clinical setting.

However, the widespread use of siRNA will require the development of clinically suitable, safe and effective vehicles with the ability to complex and deliver siRNA into target cells with minimal toxicity. Lately, dendrimers have gained considerable attention as non-viral vectors in nucleic acid delivery due to their unique structural characteristics (globular, well defined and highly branched structure, multivalency, low polydispersity and tunable nanosize), along with their relevant capacity to complex and protect nucleic acids in compact nanostructures, which can be functionalized with targeting moieties in order to get cell specificity.

Here, we present an overview of the state-of-the-art of the most significant and recent advances on the use of dendrimers as siRNA delivery vectors, with particular focus on the in vivo applications. We will cover the use of different dendrimers, distinct administration routes, toxicity issues, as well as the target tissue or disease, highlighting the potential of dendrimers as nanocarriers for therapeutic and biomedical applications.

Phage-Mediated Gene Therapy by Zeinab Hosseinidoust (120-126).
Background: Bacteriophages (bacterial viruses) have long been under investigation as vectors for gene therapy. Similar to other viral vectors, the phage coat proteins have evolved over millions of years to protect the viral genome from degradation post injection, offering protection for the valuable therapeutic sequence.

Materials and Methods: However, what sets phage apart from other viral gene delivery vectors is their safety for human use and the relative ease by which foreign molecules can be expressed on the phage outer surface, enabling highly targeted gene delivery. The latter property also makes phage a popular choice for gene therapy target discovery through directed evolution. Although promising, phage-mediated gene therapy faces several outstanding challenges, the most notable being lower gene delivery efficiency compared to animal viruses, vector stability, and nondesirable immune stimulation.

Result: This review presents a critical review of promises and challenges of employing phage as gene delivery vehicles as well as an introduction to the concept of phage-based microbiome therapy as the new frontier and perhaps the most promising application of phage-based gene therapy.

Cell therapy using mesenchymal stem cells (MSCs) is a powerful tool for the treatment of various diseases and injuries. Still, important limitations including the large amounts of cells required for application in vivo and the age-related decline in lifespan, proliferation, and potency may hinder the use of MSCs in patients. In this regard, gene therapy may offer strong approaches to optimize the use of MSCs for regenerative medicine. Diverse nonviral and viral gene vehicles have been manipulated to genetically modify MSCs, among which the highly effective and relatively safe recombinant adeno-associated viral (rAAV) vectors that emerged as the preferred gene delivery system to treat human disorders. Yet, clinical adaptation of such gene vehicles may be limited by several hurdles, including the possibility of dissemination to nontarget sites and the presence of immune and toxic responses in the host organism that may impair their therapeutic actions. The use of smart biomaterials acting as interfaces to enhance the temporal and spatial presentation of therapeutic agents in the target place and/or acting as scaffolding for MSC growth is an innovative, valuable approach to overcome these shortcomings that else restrain the efficacy of such potent cell populations. Here, we provide an overview on the most recent tissue engineering approaches based on the use of biomaterials acting as vehicles for rAAV vectors to target MSCs directly in the recipient (in vivo strategy) or as supportive matrices for rAAV-modified MSCs for indirect cell reimplantation (ex vivo strategy) as means to activate the reparative processes in tissues of the musculoskeletal system.

Recent Advances in Skin Penetration Enhancers for Transdermal Gene and Drug Delivery by Morteza Amjadi, Babak Mostaghaci, Metin Sitti (139-146).
There is a growing interest in transdermal delivery systems because of their noninvasive, targeted, and on-demand delivery of gene and drugs. However, efficient penetration of therapeutic compounds into the skin is still challenging largely due to the impermeability of the outermost layer of the skin, known as stratum corneum. Recently, there have been major research activities to enhance the skin penetration depth of pharmacological agents. This article reviews recent advances in the development of various strategies for skin penetration enhancement. We show that approaches such as ultrasound waves, laser, and microneedle patches have successfully been employed to physically disrupt the stratum corneum structure for enhanced transdermal delivery. Rather than physical approaches, several non-physical route have also been utilized for efficient transdermal delivery across the skin barrier. Finally, we discuss some clinical applications of transdermal delivery systems for gene and drug delivery. This paper shows that transdermal delivery devices can potentially function for diverse healthcare and medical applications while further investigations are still necessary for more efficient skin penetration of gene and drugs.

Non-viral Delivery Systems for Breast Cancer Gene Therapy by Golnaz Vaseghi, Laleh Rafiee, Shaghayegh Haghjooy Javanmard (147-153).
Introduction: The ever-evolving field of gene therapy promises several innovative treatments for cancer. Advances in genetic modification of tumor cells and micro environment have led to the development of more effective therapeutic strategies with fewer side effects.

Materials & Methods: The development of effective delivery system challenges, remains. Non-viral vectors are interesting due to their bio-safety and their ability to transfer different types of nucleic acids. Examples of these techniques are the use of oligonucleoides, liposomes, nanoparticles, inorganic material, and engineered stem cells.

Conclusion: In this review, we focus on recent advances in the intracellular delivery of DNA and siRNA to the cancer cells with emphasis on breast cancer.

The restless endeavors revealing the molecular pathways underlying many neurodegenerative diseases and brain tumors have paved the way for the introduction of the selective exogenous gene-based therapeutics. The implicated active biomolecules encompass mainly negatively-charged nucleic acids ranging from DNA, mRNA, non-coding RNAs (small-interfering RNA, siRNA, and microRNA, miRNA), to antisense oligonucleotides. They selectively interfere with the genes translational and/or transcriptional processes.

Although many reviews previously addressed brain targeting, a thorough correlation between the molecular properties of these biomacromolecules, the nature of blood brain barrier (BBB) in the accompanying pathological condition, the intracellular targets, as well as the design of the delivery system which will transport the bioactive cargo to the target cells attempting efficient delivery to the active sites in the brain will be appraised.

In this review, we will further discuss the tremendous advances in non-viral gene delivery nanosystems currently investigated (starting from self-assembled nanoplexes using cationic polymers or lipids and going through liposomes, aptamers, polymersomes, exosomes, dendrimers and nanoparticles). Unlike previous reviews on this topic, functionalization strategies of the nanocarriers promoting either surface receptor binding or intracellular targeting of the cranial cells will be highlighted, with special emphasis on tailoring smart nanomedicines according to the CNS disease condition. In addition, newly-developed evaluation approaches, cell culture models studying BBB permeability and manipulation of the barrier function of the brain via focused ultrasound will be addressed.

Potential Gene Therapy Towards Treating Neurodegenerative Disea ses Employing Polymeric Nanosystems by Prachi Bangde, Sonal Atale, Anomitra Dey, Ashish Pandit, Prajakta Dandekar, Ratnesh Jain (170-183).
Background: Recent integrated approaches involving nanotechnology and gene therapy have accelerated development of efficient drug delivery to the central nervous system (CNS). Neurodegenerative disorders are closely associated with genetic inheritance and mutation.

Materials: Nanotechnology has allowed effective engineering of various such polymeric structures. Moreover, availability of a wide array of polymeric materials has enabled fabrication of biocompatible and biodegradable delivery vehicles. Our manuscript focuses on the ideal features and properties of polymeric nanoparticles that have enabled successful gene therapy for neurodegenerative disorders, as well as the challenges that are posing difficulties in their practical application. We have highlighted these aspects through examples of polymeric nanoparticles that have exhibited therapeutic promise in the treatment of neurological disorders and mutations.

Methods: Complete cure of these diseases is a challenging task and gene therapy appears as a realistic approach for their treatment. Gene therapy allows effective replacement or suppression of faulty genes, thereby increasing chances for neuron survival and repair. However, successful delivery of naked genetic material to CNS faces severe obstacles due to possible degradation and restricted transportation of these biological entities across the blood brain barrier (BBB). Structurally, the BBB is composed of several tight junctions, making the membrane highly selective towards the entry of molecules.

Conclusion: In order to target BBB for treating neurodegenerative diseases, it is essential to develop a tailor-made system that may not only cross this barrier, but also effectively modulate the expression of disease-causing genes. Stabilization of therapeutic genes and their effective, targeted delivery may be possible using polymeric nanoparticles as carriers.