Therapeutic siRNAs for dominant genetic skin disorders including pachyonychia congenita

4'-C-Cholesterol/Pyridyl-2'-O-Methyl Uridine-Functionalized siRNA Enhances Stability and Carrier-Free Gene Silencing

Chemical modifications and targeted delivery through the conjugation of small molecules have transformed the potential of siRNA-based therapeutics. These advancements address key challenges, such as poor cellular uptake, low bioavailability, and limited metabolic stability, making siRNA delivery more efficient and clinically viable. Cholesterol-conjugated siRNA enables cellular uptake through lipoprotein pathways without transfection agents. In this study, we reported the synthesis of 4'-C-cholesterol-2'-O-methyl (4'-C-chol-2'-OMe) and 4'-C-methylpyridine-2'-O-methyl (4'-C-Mpy-2'-OMe) uridine conjugates via copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC) and their incorporation at the 3'-overhangs of the siRNA duplex. A single incorporation of 4'-C-chol-2'-OMe or 4'-C-Mpy-2'-OMe uridine marginally increased the stability of the siRNA duplex. In the nuclease resistance assay, 4'-C-Mpy-2'-OMe modification at the penultimate position of the 3'-end of poly dT20 showed significant resistance against snake venom phosphodiesterase (SVPD), 3'-specific exonucleases. Gene silencing activity using anti-Renilla siRNA exhibited enhanced gene silencing activity when a single modification was incorporated at the 3'-overhang of the passenger strand. Similarly, 4'-C-Mpy-2'-OMe modification at the 3'-overhang of the passenger strand in anti-Bcl-2 siRNA showed compatibility to RISC assembly and exhibited effective gene silencing against the endogenous Bcl-2 gene. A molecular modeling study illustrated that the 4'-C-Mpy-2'-OMe uridine at the 3'-overhang of the guide strand shows minimal interaction with the PAZ domain of the hAgo2 protein. The dual incorporation of cholesterol modifications at the 3'-overhang of both strands resulted in 68% and 93% reductions in Renilla luciferase expression at 1000 nM concentration after 48 and 96 h, respectively, in a carrier-free system. This study demonstrated that C4'-cholesterol conjugation provides effective cellular uptake, high nuclease resistance, and prolonged silencing activity in carrier-free mode.

Nucleic Acid Therapy for the Skin

Advances in sequencing technologies have facilitated the identification of the genes and mechanisms for many inherited skin diseases. Although targeted nucleic acid therapeutics for diseases in other organs have begun to be deployed in patients, the goal of precise therapeutics for skin diseases has not yet been realized. First, we review the current and emerging nucleic acid-based gene-editing and delivery modalities. Next, current and emerging viral and nanoparticle vehicles for the delivery of gene therapies are reviewed. Finally, specific skin diseases that could benefit optimally from nucleic acid therapies are highlighted. By adopting the latest technologies and addressing specific barriers related to skin biology, nucleic acid therapeutics have the potential to revolutionize treatments for patients with skin disease.

Pachyonychia Congenita: Clinical Features and Future Treatments

Pachyonychia congenita (PC) is a rare, autosomal dominant inherited disorder of keratinization that is characterized by a triad of focal palmoplantar keratoderma, plantar pain, and hypertrophic nail dystrophy. It can be debilitating, causing significantly impaired mobility. PC is diagnosed clinically alongside identification of a heterozygous pathogenic mutation in one of five keratin genes: KRT6A, KRT6B, KRT6C, KRT16, or KRT17. Each keratin gene mutation is associated with a distinct clinical phenotype, with variable age of onset and additional features, which has allowed classification by genotype. Additional features include pilosebaceous cysts, follicular hyperkeratosis, natal teeth, oral leukokeratosis, hidradenitis suppurativa, itching, and neurovascular structures. Although classed as rare, the prevalence of PC is likely to be underestimated. There is no cure or specific treatment for PC at present. Current treatments are limited to conservative measures to reduce plantar friction and trauma, mechanical debridement, topical treatments, and treatments for associated features or complications, most commonly infection. However, through active research in collaboration with PC Project, a patient-advocacy group, and the International PC Research Registry, a global registry of PC patients, there are now many new potential therapeutic options on the horizon. This review summarizes the clinical features associated with PC and highlights the current and future treatment of its manifestations.

Pachyonychia Congenita Project: Advancing Research and Drug Development through Collaboration

Pachyonychia Congenita Project (PC Project) is an international patient advocacy organization dedicated to patients who suffer from pachyonychia congenita (PC). This condition is a painful and debilitating skin disorder caused by a mutation in one of five keratin genes: KRT6A, KRT6B, KRT6C, KRT16,or KRT17. Through two primary programs, namely the International Pachyonychia Congenita Consortium (IPCC) and the International Pachyonychia Congenita Research Registry (IPCRR), PC Project provides comprehensive patient support and diagnostics while uniting patients, researchers, physicians, and industry partners on a global level to advance research and drug development for meaningful treatments and, ultimately, a cure for PC.

The future of siRNA-mediated approaches to treat von Willebrand disease

INTRODUCTION

The clinical management of the inherited bleeding disorder von Willebrand disease (VWD) focuses on normalizing circulating levels of von Willebrand factor (VWF) and factor VIII (FVIII) to prevent or control bleeding events. The heterogeneous nature of VWD, however, complicates effective disease management and development of universal treatment guidelines.

AREAS COVERED

The current treatment modalities of VWD and their limitations are described and why this prompts the development of new treatment approaches. In particular, RNA-based therapeutics have gained significant interest because of their ability to reversibly alter gene expression with long-term efficacy. In the field of VWD, small-interfering RNAs (siRNAs) have been explored through various strategies to improve disease phenotypes. These different approaches are discussed as well as their potential impact on reshaping the future therapeutic landscape.

EXPERT OPINION

Current treatments for VWD often require frequent intravenous administration of VWF concentrates or desmopressin, with only short-term benefits. Moreover, remaining circulating mutant VWF can cause detrimental effects. Allele-selective siRNA-based therapies could provide more reliable and long-term disease correction by specifically targeting mutant VWF. This approach could be applied to a large part of the population aligning with the growing emphasis on personalized treatment and patient-centered care in VWD management.

Pachyonychia congenita: pathogenesis of pain and approaches to treatment

Pachyonychia congenita (PC) is an autosomal dominant genodermatosis characterized by a triad of chronic severe plantar pain, focal palmoplantar keratoderma and hypertrophic nail dystrophy. Plantar pain can be debilitating and have a profound impact on quality of life. Current therapeutic options for pain in PC are limited to lifestyle adjustment and mechanical techniques, with a small subgroup of patients benefiting from oral retinoids. This review investigates the pathogenesis of pain in PC and provides a summary of the current and future therapeutic options.

Keratins 6, 16, and 17 in Health and Disease: A Summary of Recent Findings

Keratins 6, 16, and 17 occupy unique positions within the keratin family. These proteins are not commonly found in the healthy, intact epidermis, but their expression increases in response to damage, inflammation, and hereditary skin conditions, as well as cancerous cell transformations and tumor growth. As a result, there is an active investigation into the potential use of these proteins as biomarkers for different pathologies. Recent studies have revealed the role of these keratins in regulating keratinocyte migration, proliferation, and growth, and more recently, their nuclear functions, including their role in maintaining nuclear structure and responding to DNA damage, have also been identified. This review aims to summarize the latest research on keratins 6, 16, and 17, their regulation in the epidermis, and their potential use as biomarkers in various skin conditions.

Effect of a novel siRNA delivery system, siRNA ternary complex, on melanoma lung metastasis

In this study, we determined effects of an anionic siRNA delivery vector, siRNA ternary complex, which is constructed with biodegradable dendrigraft poly-L-lysine (DGL) and γ-polyglutamic acid (γ-PGA) on the melanoma cells and melanoma lung metastasis. The siRNA ternary complex showed high cellular uptake and silencing effect in melanoma cell line B16-F10/Luc cells. After intravenous administration of the siRNA ternary complex, high silencing effect was also observed in the lung of B16-F10/Luc melanoma metastasis model mice. Therefore, we applied vascular endothelial growth factor (VEGF)-siRNA on the siRNA ternary complex and determined the effect on the melanoma lung metastasis. The siRNA ternary complex containing VEGF-siRNA reduced VEGF protein levels significantly in in vitro and in vivo, and the complex successfully inhibited melanoma lung metastasis. This biodegradable and effective siRNA delivery vector, siRNA ternary complex, could be available for clinical trials.

Pachyonychia Congenita: A Research Agenda Leading to New Therapeutic Approaches

Pachyonychia congenita (PC) is a dominantly inherited genetic disorder of cornification. PC stands out among other genodermatoses because despite its rarity, it has been the focus of a very large number of pioneering translational research efforts over the past 2 decades, mostly driven by a patient support organization, the Pachyonychia Congenita Project. These efforts have laid the ground for innovative strategies that may broadly impact approaches to the management of other inherited cutaneous and noncutaneous diseases. This article outlines current avenues of research in PC, expected outcomes, and potential hurdles.

Modified Linear Peptides Effectively Silence STAT-3 in Breast Cancer and Ovarian Cancer Cell Lines

RNA interference (RNAi) has drawn enormous attention as a powerful tool because of its capability to interfere with mRNA and protein production. However, designing a safe and efficient delivery system in RNAi therapeutics remains challenging. Herein, we have designed and synthesized several linear peptides containing tryptophan (W) and arginine (R) residues separated by the β-alanine (βA) spacer and attached to a lipophilic fatty acyl chain, cholesterol, or PEG. The peptide backbone sequences were: Ac-C-βA-βA-W4-βA-βA-R4-CO-NH2 and Ac-K-βA-βA-W4-βA-βA-R4-CO-NH2, with only a difference in N-terminal amino acid. The cysteine side chain in the first sequence was used for the conjugation with PEG2000 and PEG550. Alternatively, the side chain of lysine in the second sequence was used for conjugation with cholesterol or oleic acid. We hypothesized that amphiphilic peptides and optimum fatty acyl chain or PEG could function as an effective siRNA carrier by complementing each structural component's self-assembly and membrane internalization properties. None of the designed peptides showed cytotoxicity up to 10 µM. Serum stability studies suggested that the newly designed peptides efficiently protected siRNA against early degradation by nucleases. Flow cytometry analysis indicated 50-90% cellular uptake of siRNA using the newly developed modified linear peptides (MLPs). Western blot results revealed more than 90% protein downregulation after targeting STAT3 in MDA-MB-231 and SKOV-3 cell lines. In summary, a new peptide class was developed to safely and efficiently deliver siRNA.

Genotype-structurotype-phenotype correlations in pachyonychia congenita patients

Pachyonychia congenita (PC) is a genetic disorder of keratin that presents with nail dystrophy, painful palmoplantar keratoderma, and other clinical manifestations. We investigated genotype-structurotype-phenotype correlations seen with mutations in keratin genes (KRT6A, KRT6B, KRT6C, KRT16, KRT17) and utilized protein structure modeling of high frequency mutations to examine the functional importance of keratin structural domains in PC pathogenesis. Participants of the International PC Research Registry underwent genetic testing and completed a standardized survey on their symptoms. Our results support prior reports associating oral leukokeratosis with KRT6A mutations, and cutaneous cysts, follicular hyperkeratosis, and natal teeth with KRT17 mutations. Painful keratoderma was prominent with KRT6A and KRT16 mutations. Nail involvement was most common in KRT6A and least common in KRT6C patients. Across keratin subtypes, patients with coil 2B mutations had greatest impairment in ambulation, and patients with coil 1A mutations reported more emotional issues. Molecular modeling demonstrated that hotspot missense mutations in PC largely disrupted hydrophobic interactions or surface charge. The former may destabilize keratin dimers/tetramers, while the latter likely interferes with higher-order keratin filament formation. Understanding pathologic alterations in keratin structure improves our knowledge of how PC genotype correlates with clinical phenotype, advancing insight into disease pathogenesis and therapeutic development.

Silencing PCBP2 normalizes desmoplastic stroma and improves the antitumor activity of chemotherapy in pancreatic cancer

Rationale: Dense desmoplastic stroma is a fundamental characteristic of pancreatic ductal adenocarcinoma (PDAC) and comprises up to 80% of the tumor mass. Type I collagen is the major component of the extracellular matrix (ECM), which acts as a barrier to impede the delivery of drugs into the tumor microenvironment. While the strategy to deplete PDAC stroma has failed in clinical trials, normalization of the stroma to allow chemotherapy to kill the tumor cells in the “nest” could be a promising strategy for PDAC therapy. We hypothesize that silencing the poly(rC)-binding protein 2 (αCP2, encoded by the PCBP2 gene) leads to the destabilization and normalization of type I collagen in the PDAC stroma.

Methods: We develop a micro-flow mixing method to fabricate a peptide-based core-stabilized PCBP2 siRNA nanocomplex to reverse the accumulation of type I collagen in PDAC tumor stroma. Various in vitro studies were performed to evaluate the silencing activity, cellular uptake, serum stability, and tumor penetration of the PCBP2 siRNA nanocomplex. We also investigated the penetration of small molecules in stroma-rich pancreatic cancer spheroids after the treatment with the PCBP2 siRNA nanocomplex. The anti-tumor activity of the PCBP2 siRNA nanocomplex and its combination with gemcitabine was evaluated in an orthotopic stroma-rich pancreatic cancer mouse model.

Results: Silencing the PCBP2 gene using siRNA reverses the accumulation of type I collagen in human pancreatic stellate cells (PSCs) and mouse NIH 3T3 fibroblast cells. The siRNA nanocomplex significantly reduces ECM production and enhances drug penetration through desmoplastic tumor stroma. The combination of gemcitabine with the PCBP2 siRNA nanocomplex markedly suppresses the tumor progression in a desmoplastic PDAC orthotopic mouse model.

Conclusion: This approach provides a new therapeutic avenue to improve the antitumor efficacy of PDAC therapies by normalizing tumor stroma using the PCBP2 siRNA nanocomplex.

Current RNA-based Therapeutics in Clinical Trials

Long-term research on various types of RNAs has led to further understanding of diverse mechanisms, which eventually resulted in the rapid development of RNA-based therapeutics as powerful tools in clinical disease treatment. Some of the developing RNA drugs obey the antisense mechanisms including antisense oligonucleotides, small interfering RNAs, microRNAs, small activating RNAs, and ribozymes. These types of RNAs could be utilized to inhibit/activate gene expression or change splicing to provide functional proteins. In the meantime, some others based on different mechanisms like modified messenger RNAs could replace the dysfunctional endogenous genes to manage some genetic diseases, and aptamers with special three-dimensional structures could bind to specific targets in a high-affinity manner. In addition, the recent most popular CRISPR-Cas technology, consisting of a crucial single guide RNA, could edit DNA directly to generate therapeutic effects. The desired results from recent clinical trials indicated the great potential of RNA-based drugs in the treatment of various diseases, but further studies on improving delivery materials and RNA modifications are required for the novel RNA-based drugs to translate to the clinic. This review focused on the advances and clinical studies of current RNA-based therapeutics, analyzed their challenges and prospects.

Pathophysiology of pachyonychia congenita-associated palmoplantar keratoderma: new insights into skin epithelial homeostasis and avenues for treatment

BACKGROUND

Pachyonychia congenita (PC), a rare genodermatosis, primarily affects ectoderm-derived epithelial appendages and typically includes oral leukokeratosis, nail dystrophy and very painful palmoplantar keratoderma (PPK). PC dramatically impacts quality of life although it does not affect lifespan. PC can arise from mutations in any of the wound-repair-associated keratin genes KRT6A, KRT6B, KRT6C, KRT16 or KRT17. There is no cure for this condition, and current treatment options for PC symptoms are limited and palliative in nature.

OBJECTIVES

This review focuses on recent progress made towards understanding the pathophysiology of PPK lesions, the most prevalent and debilitating of all PC symptoms.

METHODS

We reviewed the relevant literature with a particular focus on the Krt16 null mouse, which spontaneously develops footpad lesions that mimic several aspects of PC-associated PPK.

RESULTS

There are three main stages of progression of PPK-like lesions in Krt16 null mice. Ahead of lesion onset, keratinocytes in the palmoplantar (footpad) skin exhibit specific defects in terminal differentiation, including loss of Krt9 expression. At the time of PPK onset, there is elevated oxidative stress and hypoactive Keap1-Nrf2 signalling. During active PPK, there is a profound defect in the ability of the epidermis to maintain or return to normal homeostasis.

CONCLUSIONS

The progress made suggests new avenues to explore for the treatment of PC-based PPK and deepens our understanding of the mechanisms controlling skin tissue homeostasis. What's already known about this topic? Pachyonychia congenita (PC) is a rare genodermatosis caused by mutations in KRT6A, KRT6B, KRT6C, KRT16 and KRT17, which are normally expressed in skin appendages and induced following injury. Individuals with PC present with multiple clinical symptoms that usually include thickened and dystrophic nails, palmoplantar keratoderma (PPK), glandular cysts and oral leukokeratosis. The study of PC pathophysiology is made challenging because of its low incidence and high complexity. There is no cure or effective treatment for PC. What does this study add? This text reviews recent progress made when studying the pathophysiology of PPK associated with PC. This recent progress points to new possibilities for devising effective therapeutics that may complement current palliative strategies.

Effective In Vivo Topical Delivery of siRNA and Gene Silencing in Intact Corneal Epithelium Using a Modified Cell-Penetrating Peptide

Autosomal dominantly inherited genetic disorders such as corneal dystrophies are amenable to allele-specific gene silencing with small interfering RNA (siRNA). siRNA delivered to the cornea by injection, although effective, is not suitable for a frequent long-term treatment regimen, whereas topical delivery of siRNA to the cornea is hampered by the eye surface's protective mechanisms. Herein we describe an attractive and innovative alternative for topical application using cell-penetrating peptide derivatives capable of complexing siRNA non-covalently and delivering them into the cornea. Through a rational design approach, we modified derivatives of a cell-penetrating peptide, peptide for ocular delivery (POD), already proved to diffuse into the corneal layers. These POD derivatives were able to form siRNA-peptide complexes (polyplexes) of size and ζ-potential similar to those reported able to undergo cellular internalization. Successful cytoplasmic release and gene silencing in vitro was obtained when an endosomal disruptor, chloroquine, was added. A palmitoylated-POD, displaying the best delivery properties, was covalently functionalized with trifluoromethylquinoline, an analog of chloroquine. This modified POD, named trifluoromethylquinoline-palmitoyl-POD (QN-Palm-POD), when complexed with siRNA and topically applied to the eye in vivo, resulted in up to 30% knockdown of luciferase reporter gene expression in the corneal epithelium. The methods developed within represent a valid standardized approach that is ideal for screening of a range of delivery formulations.

CRISPR/Cas9 gene editing for genodermatoses: progress and perspectives

Genodermatoses constitute a clinically heterogeneous group of devastating genetic skin disorders. Currently, therapy options are largely limited to symptomatic treatments and although significant advances have been made in ex vivo gene therapy strategies, various limitations remain. However, the recent technical transformation of the genome editing field promises to overcome the hurdles associated with conventional gene addition approaches. In this review, we discuss the need for developing novel treatments and describe the current status of gene editing for genodermatoses, focusing on a severe blistering disease called epidermolysis bullosa (EB), for which significant progress has been made. Initial research utilized engineered nucleases such as transcription activator-like effector nucleases and meganucleases. However, over the last few years, clustered regularly interspaced short palindromic repeats/CRISPR-associated protein 9 (CRISPR/Cas9) have upstaged older generation gene editing tools. We examine different strategies for CRISPR/Cas9 application that can be employed depending on the type and position of the mutation as well as the mode of its inheritance. Promising developments in the field of base editing opens new avenues for precise correction of single base substitutions, common in EB and other genodermatoses. We also address the potential limitations and challenges such as safety concerns and delivery efficiency. This review gives an insight into the future of gene editing technologies for genodermatoses.

Current status and future perspectives of gold nanoparticle vectors for siRNA delivery

Discovering the vast therapeutic potential of siRNA opened up new clinical research areas focussing on a number of diseases and applications; however significant problems with siRNA stability and delivery have hindered its clinical applicability. As a result, interest in the development of practical siRNA delivery systems has grown in recent years. Of the numerous siRNA delivery strategies currently on offer, gold nanoparticles (AuNPs) stand out thanks to their biocompatibility and capacity to protect siRNA against degradation; not to mention the versatility offered by their tuneable shape, size and optical properties. Herein this review provides a complete summary of the methodologies for functionalizing AuNPs with siRNA, paying singular attention to the AuNP shape, size and surface coating, since these key factors heavily influence cellular interaction, internalization and, ultimately, the efficacy of the hybrid particle. The most noteworthy hybridization strategies have been highlighted along with the most innovative and outstanding in vivo studies with a view to increasing clinical interest in the use of AuNPs as siRNA nanocarriers.

ASPsiRNA: A Resource of ASP-siRNAs Having Therapeutic Potential for Human Genetic Disorders and Algorithm for Prediction of Their Inhibitory Efficacy

Allele-specific siRNAs (ASP-siRNAs) have emerged as promising therapeutic molecules owing to their selectivity to inhibit the mutant allele or associated single-nucleotide polymorphisms (SNPs) sparing the expression of the wild-type counterpart. Thus, a dedicated bioinformatics platform encompassing updated ASP-siRNAs and an algorithm for the prediction of their inhibitory efficacy will be helpful in tackling currently intractable genetic disorders. In the present study, we have developed the ASPsiRNA resource (http://crdd.osdd.net/servers/aspsirna/) covering three components viz (i) ASPsiDb, (ii) ASPsiPred, and (iii) analysis tools like ASP-siOffTar. ASPsiDb is a manually curated database harboring 4543 (including 422 chemically modified) ASP-siRNAs targeting 78 unique genes involved in 51 different diseases. It furnishes comprehensive information from experimental studies on ASP-siRNAs along with multidimensional genetic and clinical information for numerous mutations. ASPsiPred is a two-layered algorithm to predict efficacy of ASP-siRNAs for fully complementary mutant (Eff^mut) and wild-type allele (Eff^wild) with one mismatch by ASPsiPred^SVM and ASPsiPred^matrix, respectively. In ASPsiPred^SVM, 922 unique ASP-siRNAs with experimentally validated quantitative Eff^mut were used. During 10-fold cross-validation (10nCV) employing various sequence features on the training/testing dataset (T737), the best predictive model achieved a maximum Pearson’s correlation coefficient (PCC) of 0.71. Further, the accuracy of the classifier to predict Eff^mut against novel genes was assessed by leave one target out cross-validation approach (LOTOCV). ASPsiPred^matrix was constructed from rule-based studies describing the effect of single siRNA:mRNA mismatches on the efficacy at 19 different locations of siRNA. Thus, ASPsiRNA encompasses the first database, prediction algorithm, and off-target analysis tool that is expected to accelerate research in the field of RNAi-based therapeutics for human genetic diseases.

Non-Invasive Intravital Imaging of siRNA-Mediated Mutant Keratin Gene Repression in Skin

PURPOSE

Small interfering RNAs (siRNAs) specifically and potently inhibit target gene expression. Pachyonychia congenita (PC) is a skin disorder caused by mutations in genes encoding keratin (K) 6a/b, K16, and K17, resulting in faulty intermediate filaments. A siRNA targeting a single nucleotide, PC-relevant mutation inhibits K6a expression and has been evaluated in the clinic with encouraging results.

PROCEDURES

To better understand the pathophysiology of PC, and develop a model system to study siRNA delivery and visualize efficacy in skin, wild type (WT) and mutant K6a complementary DNAs (cDNAs) were fused to either enhanced green fluorescent protein or tandem tomato fluorescent protein cDNA to allow covisualization of mutant and WT K6a expression in mouse footpad skin using a dual fluorescence in vivo confocal imaging system equipped with 488 and 532 nm lasers.

RESULTS

Expression of mutant K6a/reporter resulted in visualization of keratin aggregates, while expression of WT K6a/reporter led to incorporation into filaments. Addition of mutant K6a-specific siRNA resulted in inhibition of mutant, but not WT, K6a/reporter expression.

CONCLUSIONS

Intravital imaging offers subcellular resolution for tracking functional activity of siRNA in real time and enables detailed analyses of therapeutic effects in individual mice to facilitate development of nucleic acid-based therapeutics for skin disorders.

Assays to Study Consequences of Cytoplasmic Intermediate Filament Mutations: The Case of Epidermal Keratins

The discovery of the causative link between keratin mutations and a growing number of human diseases opened the way for a better understanding of the function of the whole intermediate filament families of cytoskeleton proteins. This chapter describes analytical approaches to identification and interpretation of the consequences of keratin mutations, from the clinical and diagnostic level to cells in tissue culture. Intermediate filament pathologies can be accurately diagnosed from skin biopsies and DNA samples. The Human Intermediate Filament Database collates reported mutations in intermediate filament genes and their diseases, and can help clinicians to establish accurate diagnoses, leading to disease stratification for genetic counseling, optimal care delivery, and future mutation-aligned new therapies. Looking at the best-studied keratinopathy, epidermolysis bullosa simplex, the generation of cell lines mimicking keratinopathies is described, in which tagged mutant keratins facilitate live-cell imaging to make use of today's powerful enhanced light microscopy modalities. Cell stress assays such as cell spreading and cell migration in scratch wound assays can interrogate the consequences of the compromised cytoskeletal network. Application of extrinsic stresses, such as heat, osmotic, or mechanical stress, can enhance the differentiation of mutant keratin cells from wild-type cells. To bring the experiments to the next level, 3D organotypic human cultures can be generated, and even grafted onto the backs of immunodeficient mice for greater in vivo relevance. While development of these assays has focused on mutant K5/K14 cells, the approaches are often applicable to mutations in other intermediate filaments, reinforcing fundamental commonalities in spite of diverse clinical pathologies.

Diphencyprone Treatment of Alopecia Areata: Postulated Mechanism of Action and Prospects for Therapeutic Synergy with RNA Interference

Diphencyprone (DPCP) is a potent topical sensitizing agent that has been used since the late 1970s by physicians for the treatment of alopecia areata (AA), viral warts (human papillomavirus) and cutaneous metastases of melanoma. Although to date the compound is not approved as a drug by the FDA or EMA, physicians have continued to use DPCP because of its proven effects in these dermatological conditions. The use of the drug has been highly variable because of differences in compounding, and as a result, the literature reports vary widely in the concentrations used for sensitization and challenge treatment with DPCP. The efficacy of DPCP has generally been ascribed to immunological reactions by the host. Inducing inflammation with a contact sensitizer is counterintuitive to treating AA, an autoimmune disorder. We have hypothesized that the body's attempt to downregulate the inflammation caused by the contact sensitizer may also ameliorate AA. Studies using microarray and miRNA profiling may provide information about how DPCP induces inflammation in human skin at different times. Gene targets and microRNAs identified through these data may be modulated by an RNA interference approach to enhance DPCP efficacy and response rates. In addition, this approach may result in the discovery and development of drugs that are more potent and selective for the treatment of AA.

Imaging Functional Nucleic Acid Delivery to Skin

Monogenic skin diseases arise from well-defined single gene mutations, and in some cases a single point mutation. As the target cells are superficial, these diseases are ideally suited for treatment by nucleic acid-based therapies as well as monitoring through a variety of noninvasive imaging technologies. Despite the accessibility of the skin, there remain formidable barriers for functional delivery of nucleic acids to the target cells within the dermis and epidermis. These barriers include the stratum corneum and the layered structure of the skin, as well as more locally, the cellular, endosomal and nuclear membranes. A wide range of technologies for traversing these barriers has been described and moderate success has been reported for several approaches. The lessons learned from these studies include the need for combinations of approaches to facilitate nucleic acid delivery across these skin barriers and then functional delivery across the cellular and nuclear membranes for expression (e.g., reporter genes, DNA oligonucleotides or shRNA) or into the cytoplasm for regulation (e.g., siRNA, miRNA, antisense oligos). The tools for topical delivery that have been evaluated include chemical, physical and electrical methods, and the development and testing of each of these approaches has been greatly enabled by imaging tools. These techniques allow delivery and real time monitoring of reporter genes, therapeutic nucleic acids and also triplex nucleic acids for gene editing. Optical imaging is comprised of a number of modalities based on properties of light-tissue interaction (e.g., scattering, autofluorescence, and reflectance), the interaction of light with specific molecules (e.g., absorbtion, fluorescence), or enzymatic reactions that produce light (bioluminescence). Optical imaging technologies operate over a range of scales from macroscopic to microscopic and if necessary, nanoscopic, and thus can be used to assess nucleic acid delivery to organs, regions, cells and even subcellular structures. Here we describe the animal models, reporter genes, imaging approaches and general strategies for delivery of nucleic acids to cells in the skin for local expression (e.g., plasmid DNA) or gene silencing (e.g., siRNA) with the intent of developing nucleic acid-based therapies to treat diseases of the skin.

Nucleic acid delivery into skin for the treatment of skin disease: Proofs-of-concept, potential impact, and remaining challenges

Nucleic acids (NAs) hold significant potential for the treatment of several diseases. Topical delivery of NAs for the treatment of skin diseases is especially advantageous since it bypasses the challenges associated with systemic administration which suffers from enzymatic degradation, systemic toxicity and lack of targeting to skin. However, the skin's protective barrier function limits the delivery of NAs into skin after topical application. Here, we highlight strategies for enhancing delivery of NAs into skin, and provide evidence that translation of topical NA therapies could have a transformative impact on the treatment of skin diseases.

Gene Silencing in Skin After Deposition of Self-Delivery siRNA With a Motorized Microneedle Array Device

Despite the development of potent siRNAs that effectively target genes responsible for skin disorders, translation to the clinic has been hampered by inefficient delivery through the stratum corneum barrier and into the live cells of the epidermis. Although hypodermic needles can be used to transport siRNA through the stratum corneum, this approach is limited by pain caused by the injection and the small volume of tissue that can be accessed by each injection. The use of microneedle arrays is a less painful method for siRNA delivery, but restricted payload capacity limits this approach to highly potent molecules. To address these challenges, a commercially available motorized microneedle array skin delivery device was evaluated. This device combines the positive elements of both hypodermic needles and microneedle array technologies with little or no pain to the patient. Application of fluorescently tagged self-delivery (sd)-siRNA to both human and murine skin resulted in distribution throughout the treated skin. In addition, efficient silencing (78% average reduction) of reporter gene expression was achieved in a transgenic fluorescent reporter mouse skin model. These results indicate that this device effectively delivers functional sd-siRNA with an efficiency that predicts successful clinical translation.

Development of cholesteryl peptide micelles for siRNA delivery

Despite the rapid progress in the siRNA field, developing a safe and efficient delivery system of siRNA remains to be an obstacle in the therapeutical application of siRNA. The purpose of this study is to develop an efficient peptide-based siRNA delivery system for cancer therapy. To this end, cholesterol was conjugated to a series of peptides composed of lysine and histidine residues. The resultant cholesteryl peptides were characterized, and their potential for siRNA delivery was evaluated. Our results indicate that short peptides (11-21 mer) composed of various numbers of lysine and histidine residues alone are not sufficient to mediate efficient siRNA delivery. However, the amphiphilic cholesteryl peptides can self-assemble to form a micelle-like structure in aqueous solutions, which significantly promotes the siRNA condensation capability of the peptides. The cholesteryl peptides form stable complex with siRNA and effectively protect siRNA from degradation in rat serum up to three days. Furthermore, the cholesteryl peptides efficiently transfect siRNA into different cancer cells and trigger potent gene silencing effect, whereas peptides without cholesterol modification cannot deliver siRNA into the cells. In addition, one of the cholesteryl peptides Chol-H3K2s displays comparable cellular uptake and gene silencing effect but less cytotoxicity compared with branched polyethylenimine (bPEI) and Lipofectamine-2000. Our results reveal that the cholesteryl peptides possess great potential as an efficient siRNA delivery system.

Noninvasive delivery of siRNA and plasmid DNA into skin by fractional ablation: erbium:YAG laser versus CO₂ laser

The present study was conducted to evaluate the impacts of fractional erbium (Er):YAG and CO2 lasers on skin permeation of small interfering (si)RNA and plasmid (p)DNA vectors. In vitro skin delivery was determined with a Franz diffusion cell. In vivo absorption was investigated by observing fluorescence and confocal microscopic imaging. Fractional laser-mediated ablation of the skin resulted in significant enhancement of dextran and siRNA penetration. Respective fluxes of dextran (10 kDa) and siRNA, which had similar molecular size, with Er:YAG laser irradiation at 5 J/cm(2) were 56- and 11-fold superior to that of intact skin. The respective permeation extents of dextran and siRNA by the CO2 laser at 4 mJ/400 spots were 42- and 12-fold greater than that of untreated skin. Fluorescence and confocal images showed increased fluorescence intensities and penetration depths of siRNA and pDNA delivery. According to an examination of the follicular permeant amount and fluorescence microscopy, hair follicles were important deposition areas for fractional laser-assisted delivery, with the Er:YAG modality revealing higher follicular siRNA selectivity than the CO2 modality. This is the first report of siRNA and pDNA penetrating the skin with a sufficient amount and depth with the assistance of fractional lasers.

Silencing human genetic diseases with oligonucleotide-based therapies

RNA interference is an endogenous mechanism present in most eukaryotic cells that enables degradation of specific mRNAs. Pharmacological exploitation of this mechanism for therapeutic purposes attracted a whole amount of attention in its initial years, but was later hampered due to difficulties in delivery of the pharmacological agents to the appropriate organ or tissue. Advances in recent years have to a certain level started to address this specific issue. Genetic diseases are caused by aberrations in gene sequences or structure; these particular abnormalities are in theory easily addressable by RNAi therapeutics. Sequencing of the human genome has largely contributed to the identification of alterations responsible for genetic conditions, thus facilitating the design of compounds that can address these diseases. This review addresses the currently on-going programs with the aim of developing RNAi and other antisense compounds for the treatment of genetic conditions and the pros and cons that these products may encounter along the way. The authors have focused on those programs that have reached clinical trials or are very close to do so.

Best treatment practices for pachyonychia congenita

BACKGROUND

Numerous therapeutic modalities have been proposed to treat the manifestations of pachyonychia congenita (PC). While research hopes lie with molecular therapies, patients are in need of answers regarding the efficacy of conventional treatments.

AIM OF THE STUDY

To determine patients' experience and preferences regarding conventional treatments for PC.

METHODS

The study population included 120 PC patients from 20 countries. The study was based on a patient survey developed by physicians and researchers from the International Pachyonychia Congenita Consortium and conducted via the internet. Using an effectiveness scale of 1 to 5, the patients were asked to grade treatments for different manifestations, including keratoderma, cysts, follicular hyperkeratosis, fingernail and toenail involvement.

RESULTS

Patients reported surgical treatments being most effective for cysts and mechanical treatments the most effective conventional therapeutic approach for all other investigated manifestations. The other conventional medical treatments were found to be non-effective to only slightly effective. Among patients with keratoderma, older people were more likely to report beneficial effect from mechanical treatments (P = 0.04), topical retinoids (P = 0.04) and topical steroids (P = 0.02). Likewise, females were more inclined to report filing and grinding beneficial than males (P = 0.02). Finally, carriers of KRT16 and KRT6a were more likely to benefit from keratolytics than carriers of mutations in KRT17 (P = 0.04).

CONCLUSIONS

None of the currently available therapeutic options for PC are ideal, although they provide some relief, with mechanical/surgical options being preferred over medical therapies. These results emphasize the need for more efficient and targeted therapies.

Delivery systems and local administration routes for therapeutic siRNA

With the increasing number of studies proposing new and optimal delivery strategies for the efficacious silencing of gene-related diseases by the local administration of siRNAs, the present review aims to provide a broad overview of the most important and latest developments of non-viral siRNA delivery systems for local administration. Moreover, the main disease targets for the local delivery of siRNA to specific tissues or organs, including the skin, the lung, the eye, the nervous system, the digestive system and the vagina, were explored.

Allele-specific siRNA silencing for the common keratin 12 founder mutation in Meesmann epithelial corneal dystrophy

PURPOSE

To identify an allele-specific short interfering RNA (siRNA), against the common KRT12 mutation Arg135Thr in Meesmann epithelial corneal dystrophy (MECD) as a personalized approach to treatment.

METHODS

siRNAs against the K12 Arg135Thr mutation were evaluated using a dual luciferase reporter gene assay and the most potent and specific siRNAs were further screened by Western blot. Off-target effects on related keratins were assessed and immunological stimulation of TLR3 was evaluated by RT-PCR. A modified 5' rapid amplification of cDNA ends method was used to confirm siRNA-mediated mutant knockdown. Allele discrimination was confirmed by quantitative infrared immunoblotting.

RESULTS

The lead siRNA, with an IC(50) of thirty picomolar, showed no keratin off-target effects or activation of TLR3 in the concentration ranges tested. We confirmed siRNA-mediated knockdown by the presence of K12 mRNA fragments cleaved at the predicted site. A dual tag infrared immunoblot showed knockdown to be allele-specific, with 70% to 80% silencing of the mutant protein.

CONCLUSIONS

A potent allele-specific siRNA against the K12 Arg135Thr mutation was identified. In combination with efficient eyedrop formulation delivery, this would represent a personalized medicine approach, aimed at preventing the pathology associated with MECD and other ocular surface pathologies with dominant-negative or gain-of-function pathomechanisms.

Gene silencing following siRNA delivery to skin via coated steel microneedles: In vitro and in vivo proof-of-concept

The development of siRNA-based gene silencing therapies has significant potential for effectively treating debilitating genetic, hyper-proliferative or malignant skin conditions caused by aberrant gene expression. To be efficacious and widely accepted by physicians and patients, therapeutic siRNAs must access the viable skin layers in a stable and functional form, preferably without painful administration. In this study we explore the use of minimally-invasive steel microneedle devices to effectively deliver siRNA into skin. A simple, yet precise microneedle coating method permitted reproducible loading of siRNA onto individual microneedles. Following recovery from the microneedle surface, lamin A/C siRNA retained full activity, as demonstrated by significant reduction in lamin A/C mRNA levels and reduced lamin A/C protein in HaCaT keratinocyte cells. However, lamin A/C siRNA pre-complexed with a commercial lipid-based transfection reagent (siRNA lipoplex) was less functional following microneedle coating. As Accell-modified "self-delivery" siRNA targeted against CD44 also retained functionality after microneedle coating, this form of siRNA was used in subsequent in vivo studies, where gene silencing was determined in a transgenic reporter mouse skin model. Self-delivery siRNA targeting the reporter (luciferase/GFP) gene was coated onto microneedles and delivered to mouse footpad. Quantification of reporter mRNA and intravital imaging of reporter expression in the outer skin layers confirmed functional in vivo gene silencing following microneedle delivery of siRNA. The use of coated metal microneedles represents a new, simple, minimally-invasive, patient-friendly and potentially self-administrable method for the delivery of therapeutic nucleic acids to the skin.

Nanoparticle-based delivery of small interfering RNA: challenges for cancer therapy

During recent decades there have been remarkable advances and profound changes in cancer therapy. Many therapeutic strategies learned at the bench, including monoclonal antibodies and small molecule inhibitors, have been used at the bedside, leading to important successes. One of the most important advances in biology has been the discovery that small interfering RNA (siRNA) is able to regulate the expression of genes, by a phenomenon known as RNA interference (RNAi). RNAi is one of the most rapidly growing fields of research in biology and therapeutics. Much research effort has gone into the application of this new discovery in the treatment of various diseases, including cancer. However, even though these molecules may have potential and strong utility, some limitations make their clinical application difficult, including delivery problems, side effects due to off-target actions, disturbance of physiological functions of the cellular machinery involved in gene silencing, and induction of the innate immune response. Many researchers have attempted to overcome these limitations and to improve the safety of potential RNAi-based therapeutics. Nanoparticles, which are nanostructured entities with tunable size, shape, and surface, as well as biological behavior, provide an ideal opportunity to modify current treatment regimens in a substantial way. These nanoparticles could be designed to surmount one or more of the barriers encountered by siRNA. Nanoparticle drug formulations afford the chance to improve drug bioavailability, exploiting superior tissue permeability, payload protection, and the “stealth” features of these entities. The main aims of this review are: to explain the siRNA mechanism with regard to potential applications in siRNA-based cancer therapy; to discuss the possible usefulness of nanoparticle-based delivery of certain molecules for overcoming present therapeutic limitations; to review the ongoing relevant clinical research with its pitfalls and promises; and to evaluate critically future perspectives and challenges in siRNA-based cancer therapy.

Progress towards genetic and pharmacological therapies for keratin genodermatoses: current perspective and future promise

Hereditary keratin disorders of the skin and its appendages comprise a large group of clinically heterogeneous disfiguring blistering and ichthyotic diseases, primarily characterized by the loss of tissue integrity, blistering and hyperkeratosis in severely affected tissues. Pathogenic mutations in keratins cause these afflictions. Typically, these mutations in concert with characteristic features have formed the basis for improved disease diagnosis, prognosis and most recently therapy development. Examples include epidermolysis bullosa simplex, keratinopathic ichthyosis, pachyonychia congenita and several other tissue-specific hereditary keratinopathies. Understanding the molecular and genetic events underlying skin dysfunction has initiated alternative treatment approaches that may provide novel therapeutic opportunities for affected patients. Animal and in vitro disease modelling studies have shed more light on molecular pathogenesis, further defining the role of keratins in disease processes and promoting the translational development of new gene and pharmacological therapeutic strategies. Given that the molecular basis for these monogenic disorders is well established, gene therapy and drug discovery targeting pharmacological compounds with the ability to reinforce the compromised cytoskeleton may lead to promising new therapeutic strategies for treating hereditary keratinopathies. In this review, we will summarize and discuss recent advances in the preclinical and clinical modelling and development of gene, natural product, pharmacological and protein-based therapies for these disorders, highlighting the feasibility of new approaches for translational clinical therapy.

Inhibition of CD44 gene expression in human skin models, using self-delivery short interfering RNA administered by dissolvable microneedle arrays

Treatment of skin disorders with short interfering RNA (siRNA)-based therapeutics requires the development of effective delivery methodologies that reach target cells in affected tissues. Successful delivery of functional siRNA to the epidermis requires (1) crossing the stratum corneum, (2) transfer across the keratinocyte membrane, followed by (3) incorporation into the RNA-induced silencing complex. We have previously demonstrated that treatment with microneedle arrays loaded with self-delivery siRNA (sd-siRNA) can achieve inhibition of reporter gene expression in a transgenic mouse model. Furthermore, treatment of human cultured epidermal equivalents with sd-siRNA resulted in inhibition of target gene expression. Here, we demonstrate inhibition of CD44, a gene that is uniformly expressed throughout the epidermis, by sd-siRNA both in vitro (cultured human epidermal skin equivalents) and in vivo (full-thickness human skin equivalents xenografted on immunocompromised mice). Treatment of human skin equivalents with CD44 sd-siRNA markedly decreased CD44 mRNA levels, which led to a reduction of the target protein as confirmed by immunodetection in epidermal equivalent sections with a CD44-specific antibody. Taken together, these results demonstrate that sd-siRNA, delivered by microneedle arrays, can reduce expression of a targeted endogenous gene in a human skin xenograft model.

Progress toward in vivo use of siRNAs-II

RNA interference (RNAi) has been extensively employed for in vivo research since its use was first demonstrated in mammalian cells 10 years ago. Design rules have improved, and it is now routinely possible to obtain reagents that suppress expression of any gene desired. At the same time, increased understanding of the molecular basis of unwanted side effects has led to the development of chemical modification strategies that mitigate these concerns. Delivery remains the single greatest hurdle to widespread adoption of in vivo RNAi methods. However, exciting advances have been made and new delivery systems under development may help to overcome these barriers. This review discusses advances in RNAi biochemistry and biology that impact in vivo use and provides an overview of select publications that demonstrate interesting applications of these principles. Emphasis is placed on work with synthetic, small interfering RNAs (siRNAs) published since the first installment of this review which appeared in 2006.

Development of allele-specific therapeutic siRNA in Meesmann epithelial corneal dystrophy

Background

Meesmann epithelial corneal dystrophy (MECD) is an inherited eye disorder caused by dominant-negative mutations in either keratins K3 or K12, leading to mechanical fragility of the anterior corneal epithelium, the outermost covering of the eye. Typically, patients suffer from lifelong irritation of the eye and/or photophobia but rarely lose visual acuity; however, some individuals are severely affected, with corneal scarring requiring transplant surgery. At present no treatment exists which addresses the underlying pathology of corneal dystrophy. The aim of this study was to design and assess the efficacy and potency of an allele-specific siRNA approach as a future treatment for MECD.

Methods and Findings

We studied a family with a consistently severe phenotype where all affected persons were shown to carry heterozygous missense mutation Leu132Pro in the KRT12 gene. Using a cell-culture assay of keratin filament formation, mutation Leu132Pro was shown to be significantly more disruptive than the most common mutation, Arg135Thr, which is associated with typical, mild MECD. A siRNA sequence walk identified a number of potent inhibitors for the mutant allele, which had no appreciable effect on wild-type K12. The most specific and potent inhibitors were shown to completely block mutant K12 protein expression with negligible effect on wild-type K12 or other closely related keratins. Cells transfected with wild-type K12-EGFP construct show a predominantly normal keratin filament formation with only 5% aggregate formation, while transfection with mutant K12-EGFP construct resulted in a significantly higher percentage of keratin aggregates (41.75%; p<0.001 with 95% confidence limits). The lead siRNA inhibitor significantly rescued the ability to form keratin filaments (74.75% of the cells contained normal keratin filaments; p<0.001 with 95% confidence limits).

Conclusions

This study demonstrates that it is feasible to design highly potent siRNA against mutant alleles with single-nucleotide specificity for future treatment of MECD.

Visualization of plasmid delivery to keratinocytes in mouse and human epidermis

The accessibility of skin makes it an ideal target organ for nucleic acid-based therapeutics; however, effective patient-friendly delivery remains a major obstacle to clinical utility. A variety of limited and inefficient methods of delivering nucleic acids to keratinocytes have been demonstrated; further advances will require well-characterized reagents, rapid noninvasive assays of delivery, and well-developed skin model systems. Using intravital fluorescence and bioluminescence imaging and a standard set of reporter plasmids we demonstrate transfection of cells in mouse and human xenograft skin using intradermal injection and two microneedle array delivery systems. Reporter gene expression could be detected in individual keratinocytes, in real-time, in both mouse skin as well as human skin xenografts. These studies revealed that non-invasive intravital imaging can be used as a guide for developing gene delivery tools, establishing a benchmark for comparative testing of nucleic acid skin delivery technologies.

Development of allele-specific therapeutic siRNA for keratin 5 mutations in epidermolysis bullosa simplex

Epidermolysis bullosa simplex (EBS) is an incurable, inherited skin-blistering disorder predominantly caused by dominant-negative mutations in the genes encoding keratins K5 or K14. RNA interference, particularly in the form of small interfering RNA (siRNA), offers a potential therapy route for EBS and related keratin disorders by selectively silencing the mutant allele. Here, using a systemic screening system based on a luciferase reporter gene assay, we have developed mutant-specific siRNAs for two independent EBS-causing missense mutations in the K5 gene (p.Ser181Pro and p.Asn193Lys). The specificity of the allele-specific inhibitors identified in the screen was subsequently confirmed at the protein level, where the lead inhibitors were shown to strongly knock down the expression of mutant proteins with negligible effect on wild-type K5 expression. In a cell-based model system, the lead inhibitors were able to significantly reverse the cytoskeletal aggregation phenotype. Overall, this approach shows promise for the treatment of EBS and paves the way for future clinical trials.

Keratin disorders: from gene to therapy

The term 'keratin' is generally accepted to refer to the epithelial keratins of soft and hard epithelial tissues such as: skin, cornea, hair and nail. Since their initial characterization, the total number of mammalian keratins has increased to 54, including 28 type I and 26 type II keratins. Inherited defects that weaken the keratin load-bearing cytoskeleton produce phenotypes characterized by fragility of specific subsets of epithelial tissues. The vast majority of mutations are either missense or small in-frame in-del mutations and disease severity often relates to the position of the mutation in relation to the rod domain. The most complex epithelial structure in humans, the hair follicle, contains trichocyte ('hard') keratin filaments and approximately half of the 54 functional human keratin genes are trichocyte keratins. So far, only four of these have been linked to human genetic disorders: monilethrix, hair-nail ectodermal dysplasia, pseudofolliculitis barbae and woolly hair, while the majority of the hair keratins remain unlinked to human phenotypes. Keratin disorders are a classical group of dominant-negative genetic disorders, representing a large healthcare burden, especially within dermatology. Recent advances in RNA interference therapeutics, particularly in the form of small-interfering RNAs, represent a potential therapy route for keratin disorders through selectively silencing the mutant allele. To date, mutant-specific siRNAs for epidermolysis bullosa simplex, pachyonychia congenita and Messmann epithelial corneal dystrophy-causing missense mutations have been developed and proven to have unprecedented specificity and potency. This could herald the dawn of a new era in translational medical research applied to genetics.