Fusogenic-oligoarginine peptide-mediated delivery of siRNAs targeting the CIP2A oncogene into oral cancer cells

Non-Viral Carriers for Nucleic Acids Delivery: Fundamentals and Current Applications

Over the past decades, non-viral DNA and RNA delivery systems have been intensively studied as an alternative to viral vectors. Despite the most significant advantage over viruses, such as the lack of immunogenicity and cytotoxicity, the widespread use of non-viral carriers in clinical practice is still limited due to the insufficient efficacy associated with the difficulties of overcoming extracellular and intracellular barriers. Overcoming barriers by non-viral carriers is facilitated by their chemical structure, surface charge, as well as developed modifications. Currently, there are many different forms of non-viral carriers for various applications. This review aimed to summarize recent developments based on the essential requirements for non-viral carriers for gene therapy.

The paradigm of miRNA and siRNA influence in Oral-biome

Short nucleotide sequences like miRNA and siRNA have attracted a lot of interest in Oral-biome investigations. miRNA is a small class of non-coding RNA that regulates gene expression to provide effective regulation of post-transcription. On contrary, siRNA is 21-25 nucleotide dsRNA impairing gene function post-transcriptionally through inhibition of mRNA for homologous dependent gene silencing. This review highlights the application of miRNA in oral biome including oral cancer, dental implants, periodontal diseases, gingival fibroblasts, oral submucous fibrosis, radiation-induced oral mucositis, dental Pulp, and oral lichenoid disease. Moreover, we have also discussed the application of siRNA against the aforementioned disease along with the impact of miRNA and siRNA to the various pathways and molecular effectors pertaining to the dental diseases. The influence of upregulation and downregulation of molecular effector post-treatment with miRNA and siRNA and their impact on the clinical setting has been elucidated. Thus, the mentioned details on application of miRNA and siRNA will provide a novel gateway to the scholars to not only mitigate the long-lasting issue in dentistry but also develop new theragnostic approaches.

Lipid and Peptide-Oligonucleotide Conjugates for Therapeutic Purposes: From Simple Hybrids to Complex Multifunctional Assemblies

Antisense and small interfering RNA (siRNA) oligonucleotides have been recognized as powerful therapeutic compounds for targeting mRNAs and inducing their degradation. However, a major obstacle is that unmodified oligonucleotides are not readily taken up into tissues and are susceptible to degradation by nucleases. For these reasons, the design and preparation of modified DNA/RNA derivatives with better stability and an ability to be produced at large scale with enhanced uptake properties is of vital importance to improve current limitations. In the present study, we review the conjugation of oligonucleotides with lipids and peptides in order to produce oligonucleotide conjugates for therapeutics aiming to develop novel compounds with favorable pharmacokinetics.

From Basic Science to Clinical Practice: The Role of Cancerous Inhibitor of Protein Phosphatase 2A (CIP2A)/p90 in Cancer

Cancerous inhibitor of protein phosphatase 2A (CIP2A), initially reported as a tumor-associated antigen (known as p90), is highly expressed in most solid and hematological tumors. The interaction of CIP2A/p90, protein phosphatase 2A (PP2A), and c-Myc can hinder the function of PP2A toward c-Myc S62 induction, thus stabilizing c-Myc protein, which represents a potential role of CIP2A/p90 in tumorigeneses such as cell proliferation, invasion, and migration, as well as cancer drug resistance. The signaling pathways and regulation networks of CIP2A/p90 are complex and not yet fully understood. Many previous studies have also demonstrated that CIP2A/p90 can be used as a potential therapeutic cancer target. In addition, the autoantibody against CIP2A/p90 in sera may be used as a promising biomarker in the diagnosis of certain types of cancer. In this Review, we focus on recent advances relating to CIP2A/p90 and their implications for future research.

Fusogenic peptide delivery of bioactive siRNAs targeting CSNK2A1 for treatment of ovarian cancer

Ovarian cancer has shown little improvement in survival among advanced-stage patients over the past decade. Current treatment strategies have been largely unsuccessful in treating advanced disease, with many patients experiencing systemic toxicity and drug-resistant metastatic cancer. This study evaluates novel fusogenic peptide carriers delivering short interfering RNA (siRNA) targeting casein kinase II, CSNK2A1, for reducing the aggressiveness of ovarian cancer. The peptides were designed to address two significant barriers to siRNA delivery: insufficient cellular uptake and endosomal entrapment. The three peptide variants developed, DIVA3, DIV3H, and DIV3W, were able to form monodisperse nanoparticle complexes with siRNA and protect siRNAs from serum and RNase degradation. Furthermore, DIV3W demonstrated optimal delivery of bioactive siRNAs into ovarian cancer cells with high cellular uptake efficiency and mediated up to 94% knockdown of CSNK2A1 mRNA compared with non-targeting siRNAs, resulting in decreased cell migration and recolonization in vitro. Intratumoral delivery of DIV3W-siCSNK2A1 complexes to subcutaneous ovarian tumors resulted in reduced CSNK2A1 mRNA and CK2α protein expression after 48 h and reduced tumor growth and migration in a 2-week multi-dosing regimen. These results demonstrate the potential of the DIV3W peptide to deliver bioactive siRNAs and confirms the role of CSNK2A1 in cell-cell communication and proliferation in ovarian cancer.

Membrane Internalization Mechanisms and Design Strategies of Arginine-Rich Cell-Penetrating Peptides

Cell-penetrating peptides (CPPs) have been discovered to deliver chemical drugs, nucleic acids, and macromolecules to permeate cell membranes, creating a novel route for exogenous substances to enter cells. Up until now, various sequence structures and fundamental action mechanisms of CPPs have been established. Among them, arginine-rich peptides with unique cell penetration properties have attracted substantial scientific attention. Due to the positively charged essential amino acids of the arginine-rich peptides, they can interact with negatively charged drug molecules and cell membranes through non-covalent interaction, including electrostatic interactions. Significantly, the sequence design and the penetrating mechanisms are critical. In this brief synopsis, we summarize the transmembrane processes and mechanisms of arginine-rich peptides; and outline the relationship between the function of arginine-rich peptides and the number of arginine residues, arginine optical isomers, primary sequence, secondary and ternary structures, etc. Taking advantage of the penetration ability, biomedical applications of arginine-rich peptides have been refreshed, including drug/RNA delivery systems, biosensors, and blood-brain barrier (BBB) penetration. Understanding the membrane internalization mechanisms and design strategies of CPPs will expand their potential applications in clinical trials.

MicroRNAs and Their Big Therapeutic Impacts: Delivery Strategies for Cancer Intervention

Three decades have passed from the initial discovery of a microRNA (miRNA) in Caenorhabditis elegans to our current understanding that miRNAs play essential roles in regulating fundamental physiological processes and that their dysregulation can lead to many human pathologies, including cancer. In effect, restoration of miRNA expression or downregulation of aberrantly expressed miRNAs using miRNA mimics or anti-miRNA inhibitors (anti-miRs/antimiRs), respectively, continues to show therapeutic potential for the treatment of cancer. Although the manipulation of miRNA expression presents a promising therapeutic strategy for cancer treatment, it is predominantly reliant on nucleic acid-based molecules for their application, which introduces an array of hurdles, with respect to in vivo delivery. Because naked nucleic acids are quickly degraded and/or removed from the body, they require delivery vectors that can help overcome the many barriers presented upon their administration into the bloodstream. As such, in this review, we discuss the strengths and weaknesses of the current state-of-the-art delivery systems, encompassing viral- and nonviral-based systems, with a specific focus on nonviral nanotechnology-based miRNA delivery platforms, including lipid-, polymer-, inorganic-, and extracellular vesicle-based delivery strategies. Moreover, we also shed light on peptide carriers as an emerging technology that shows great promise in being a highly efficacious delivery platform for miRNA-based cancer therapeutics.

Emerging Approaches for Enabling RNAi Therapeutics

RNA interference (RNAi) is a primitive evolutionary mechanism developed to escape incorporation of foreign genetic material. siRNA has been instrumental in achieving the therapeutic potential of RNAi by theoretically silencing any gene of interest in a reversible and sequence-specific manner. Extrinsically administered siRNA generally needs a delivery vehicle to span across different physiological barriers and load into the RISC complex in the cytoplasm in its functional form to show its efficacy. This review discusses the designing principles and examples of different classes of delivery vehicles that have proved to be efficient in RNAi therapeutics. We also briefly discuss the role of RNAi therapeutics in genetic and rare diseases, epigenetic modifications, immunomodulation and combination modality to inch closer in creating a personalized therapy for metastatic cancer. At the end, we present, strategies and look into the opportunities to develop efficient delivery vehicles for RNAi which can be translated into clinics.

Strategies for improving the safety and RNAi efficacy of noncovalent peptide/siRNA nanocomplexes

In the past decades, the striking development of cationic polypeptides and cell-penetrating peptides (CPPs) tailored for small interfering RNA (siRNA) delivery has been fuelled by the conception of nuclear acid therapy and precision medicine. Owing to their amino acid compositions, inherent secondary structures as well as diverse geometrical shapes, peptides or peptide-containing polymers exhibit good biodegradability, high flexibility, and bio-functional diversity as nonviral siRNA vectors. Also, a variety of noncovalent nanocomplexes could be built via self-assembling and electrostatic interactions between cationic peptides and siRNAs. Although the peptide/siRNA nanocomplex-based RNAi therapies, STP705 and MIR-19, are under clinical trials, a guideline addressing the current bottlenecks of peptide/siRNA nanocomplex delivery is in high demand for future research and development. In this review, we present strategies for improving the safety and RNAi efficacy of noncovalent peptide/siRNA nanocomplexes in the treatment of genetic disorders. Through thorough analysis of those RNAi formulations using different delivery strategies, we seek to shed light on the rationale of peptide design and modification in constructing robust siRNA delivery systems, including targeted and co-delivery systems. Based on this, we provide a timely and comprehensive understanding of how to engineer biocompatible and efficient peptide-based siRNA vectors.

Peptide-based delivery of therapeutics in cancer treatment

Current delivery strategies for cancer therapeutics commonly cause significant systemic side effects due to required high doses of therapeutic, inefficient cellular uptake of drug, and poor cell selectivity. Peptide-based delivery systems have shown the ability to alleviate these issues and can significantly enhance therapeutic loading, delivery, and cancer targetability. Peptide systems can be tailor-made for specific cancer applications. This review describes three peptide classes, targeting, cell penetrating, and fusogenic peptides, as stand-alone nanoparticle systems, conjugations to nanoparticle systems, or as the therapeutic modality. Peptide nanoparticle design, characteristics, and applications are discussed as well as peptide applications in the clinical space.

Evolution of complexity in non-viral oligonucleotide delivery systems: from gymnotic delivery through bioconjugates to biomimetic nanoparticles

From the early days of research on RNA biology and biochemistry, there was an interest to utilize this knowledge and RNA itself for therapeutic applications. Today, we have a series of oligonucleotide therapeutics on the market and many more in clinical trials. These drugs - exploit different chemistries of oligonucleotides, such as modified DNAs and RNAs, peptide nucleic acids (PNAs) or phosphorodiamidate morpholino oligomers (PMOs), and different mechanisms of action, such as RNA interference (RNAi), targeted RNA degradation, splicing modulation, gene expression and modification. Despite major successes e.g. mRNA vaccines developed against SARS-CoV-2 to control COVID-19 pandemic, development of therapies for other diseases is still limited by inefficient delivery of oligonucleotides to specific tissues and organs and often prohibitive costs for the final drug. This is even more critical when targeting multifactorial disorders and patient-specific biological variations. In this review, we will present the evolution of complexity of oligonucleotide delivery methods with focus on increasing complexity of formulations from gymnotic delivery to bioconjugates and to lipid nanoparticles in respect to developments that will enable application of therapeutic oligonucleotides as drugs in personalized therapies.

Chemistry of Peptide-Oligonucleotide Conjugates: A Review

Peptide-oligonucleotide conjugates (POCs) represent one of the increasingly successful albeit costly approaches to increasing the cellular uptake, tissue delivery, bioavailability, and, thus, overall efficiency of therapeutic nucleic acids, such as, antisense oligonucleotides and small interfering RNAs. This review puts the subject of chemical synthesis of POCs into the wider context of therapeutic oligonucleotides and the problem of nucleic acid drug delivery, cell-penetrating peptide structural types, the mechanisms of their intracellular transport, and the ways of application, which include the formation of non-covalent complexes with oligonucleotides (peptide additives) or covalent conjugation. The main strategies for the synthesis of POCs are viewed in detail, which are conceptually divided into (a) the stepwise solid-phase synthesis approach and (b) post-synthetic conjugation either in solution or on the solid phase, especially by means of various click chemistries. The relative advantages and disadvantages of both strategies are discussed and compared.

Delivery of Various Cargos into Cancer Cells and Tissues via Cell-Penetrating Peptides: A Review of the Last Decade

Cell-penetrating peptides (CPPs), also known as protein transduction domains, are a class of diverse amino acid sequences with the ability to cross cellular membranes. CPPs can deliver several bioactive cargos, including proteins, peptides, nucleic acids and chemotherapeutics, into cells. Ever since their discovery, synthetic and natural CPPs have been utilized in therapeutics delivery, gene editing and cell imaging in fundamental research and clinical experiments. Over the years, CPPs have gained significant attention due to their low cytotoxicity and high transduction efficacy. In the last decade, multiple investigations demonstrated the potential of CPPs as carriers for the delivery of therapeutics to treat various types of cancer. Besides their remarkable efficacy owing to fast and efficient delivery, a crucial benefit of CPP-based cancer treatments is delivering anticancer agents selectively, rather than mediating toxicities toward normal tissues. To obtain a higher therapeutic index and to improve cell and tissue selectivity, CPP-cargo constructions can also be complexed with other agents such as nanocarriers and liposomes to obtain encouraging outcomes. This review summarizes various types of CPPs conjugated to anticancer cargos. Furthermore, we present a brief history of CPP utilization as delivery systems for anticancer agents in the last decade and evaluate several reports on the applications of CPPs in basic research and preclinical studies.

Peptide-Assisted Nucleic Acid Delivery Systems on the Rise

Concerns associated with nanocarriers' therapeutic efficacy and side effects have led to the development of strategies to advance them into targeted and responsive delivery systems. Owing to their bioactivity and biocompatibility, peptides play a key role in these strategies and, thus, have been extensively studied in nanomedicine. Peptide-based nanocarriers, in particular, have burgeoned with advances in purely peptidic structures and in combinations of peptides, both native and modified, with polymers, lipids, and inorganic nanoparticles. In this review, we summarize advances on peptides promoting gene delivery systems. The efficacy of nucleic acid therapies largely depends on cell internalization and the delivery to subcellular organelles. Hence, the review focuses on nanocarriers where peptides are pivotal in ferrying nucleic acids to their site of action, with a special emphasis on peptides that assist anionic, water-soluble nucleic acids in crossing the membrane barriers they encounter on their way to efficient function. In a second part, we address how peptides advance nanoassembly delivery tools, such that they navigate delivery barriers and release their nucleic acid cargo at specific sites in a controlled fashion.

Advancing peptide siRNA-carrier designs through L/D-amino acid stereochemical modifications to enhance gene silencing

The 599 peptide has been previously shown to effectively deliver small interfering RNAs (siRNAs) to cancer cells, inducing targeted-oncogene silencing, with a consequent inhibition of tumor growth. Although effective, this study was undertaken to advance the 599 peptide siRNA-carrier design through L/D-amino acid stereochemical modifications. Consequently, 599 was modified to generate eight different peptide variants, incorporating either different stereochemical patterns of L/D-amino acids or a specific D-amino acid substitution. Upon analysis of the variants, it was observed that these modifications could, in some instances, increase/decrease the binding, nuclease/serum stability, and complex release of siRNAs, as well as influence the gene-silencing efficiencies of the complex. These modifications were also found to affect cellular uptake and intracellular localization patterns of siRNA cargo, with one particular variant capable of mediating binding of siRNAs to specific cellular projections, identified as filopodia. Interestingly, this variant also exhibited the most enhanced gene silencing in comparison to the parent 599 peptide, thus suggesting a possible connection between filopodia binding and enhanced gene silencing. Together, these data demonstrate the utility of peptide stereochemistry, as well as the importance of a key D-amino acid modification, in advancing the 599 carrier design for the enhancement of gene silencing in cancer cells.

Non-covalent Encapsulation of siRNA with Cell-Penetrating Peptides

SiRNAs may act as selective and potent therapeutics, but poor deliverability in vivo is a limitation. Among the recently proposed vectors, cell-penetrating peptides (CPPs), also referred as protein transduction domains (PTDs), allow siRNA stabilization and increased cellular uptake. This chapter aims to guide scientists in the preparation and characterization of CPP-siRNA complexes, particularly the evaluation of novel CPPs variants for siRNA encapsulation and delivery. Herein, we present a collection of methods to determine CPP-siRNA interaction, encapsulation, stability, conformation, transfection, and silencing efficiency.

Multivalent ions and biomolecules: Attempting a comprehensive perspective

Ions are ubiquitous in nature. They play a key role for many biological processes on the molecular scale, from molecular interactions, to mechanical properties, to folding, to self-organisation and assembly, to reaction equilibria, to signalling, to energy and material transport, to recognition etc. Going beyond monovalent ions to multivalent ions, the effects of the ions are frequently not only stronger (due to the obviously higher charge), but qualitatively different. A typical example is the process of binding of multivalent ions, such as Ca2+ , to a macromolecule and the consequences of this ion binding such as compaction, collapse, potential charge inversion and precipitation of the macromolecule. Here we review these effects and phenomena induced by multivalent ions for biological (macro)molecules, from the "atomistic/molecular" local picture of (potentially specific) interactions to the more global picture of phase behaviour including, e. g., crystallisation, phase separation, oligomerisation etc. Rather than attempting an encyclopedic list of systems, we rather aim for an embracing discussion using typical case studies. We try to cover predominantly three main classes: proteins, nucleic acids, and amphiphilic molecules including interface effects. We do not cover in detail, but make some comparisons to, ion channels, colloidal systems, and synthetic polymers. While there are obvious differences in the behaviour of, and the relevance of multivalent ions for, the three main classes of systems, we also point out analogies. Our attempt of a comprehensive discussion is guided by the idea that there are not only important differences and specific phenomena with regard to the effects of multivalent ions on the main systems, but also important similarities. We hope to bridge physico-chemical mechanisms, concepts of soft matter, and biological observations and connect the different communities further.

Peptide carriers to the rescue: overcoming the barriers to siRNA delivery for cancer treatment

Cancer is a significant health concern worldwide and its clinical treatment presents many challenges. Consequently, much research effort has focused on the development of new anticancer drugs to combat this disease. One area of exploration, in particular, has been in the therapeutic application of RNA interference (RNAi). Although RNAi appears to be an attractive therapeutic tool for the treatment of cancer, one of the primary obstacles towards its pervasive use in the clinic has been cell/tissue type-specific cytosolic delivery of therapeutic small interfering RNA (siRNA) molecules. Consequently, varied drug delivery platforms have been developed and widely explored for siRNA delivery. Among these candidate drug delivery systems, peptides have shown great promise as siRNA carriers due to their varied physiochemical properties and functions, simple formulations, and flexibility in design. In this review, we will focus on distinguishing between the different classes of peptide carriers based on their functions, as well as summarize and discuss the various design strategies and advancements that have been made in circumventing the barriers to siRNA delivery for cancer treatment. Resolution of these challenges by peptide carriers will accelerate the translation of RNAi-based therapies to the clinic.

PP2A: A Promising Biomarker and Therapeutic Target in Endometrial Cancer

Over the last decade, the use of targeted therapies has immensely increased in the treatment of cancer. However, treatment for endometrial carcinomas (ECs) has lagged behind, although potential molecular markers have been identified. This is particularly problematic for the type II ECs, since these aggressive tumors are usually not responsive toward the current standard therapies. Therefore, type II ECs are responsible for most EC-related deaths, indicating the need for new treatment options. Interestingly, molecular analyses of type II ECs have uncovered frequent genetic alterations (up to 40%) in PPP2R1A, encoding the Aα subunit of the tumor suppressive heterotrimeric protein phosphatase type 2A (PP2A). PPP2R1A mutations were also reported in type I ECs and other common gynecologic cancers, albeit at much lower frequencies (0-7%). Nevertheless, PP2A inactivation in the latter cancer types is common via other mechanisms, in particular by increased expression of Cancerous Inhibitor of PP2A (CIP2A) and PP2A Methylesterase-1 (PME-1) proteins. In this review, we discuss the therapeutic potential of direct and indirect PP2A targeting compounds, possibly in combination with other anti-cancer drugs, in EC. Furthermore, we investigate the potential of the PP2A status as a predictive and/or prognostic marker for type I and II ECs.

RNA interference: new mechanistic and biochemical insights with application in oral cancer therapy

Over the last few decades, the incidence of oral cancer has gradually increased, due to the negative influence of environmental factors and also abnormalities within the genome. The main issues in oral cancer treatment consist in surpassing resistance and recurrence. However, continuous discovery of altered signaling pathways in these tumors provides valuable information for the identification of novel gene candidates targeted in personalized therapy. RNA interference (RNAi) is a natural mechanism that involves small interfering RNA (siRNA); this can be exploited in biomedical research by using natural or synthetic constructs for activation of the mechanism. Synthetic siRNA transcripts were developed as a versatile class of molecular tools that have a diverse range of programmable roles, being involved in the regulation of several biological processes, thereby providing the perspective of an alternative option to classical treatment. In this review, we summarize the latest information related to the application of siRNA in oral malignancy together with molecular aspects of the technology and also the perspective upon the delivery system. Also, the emergence of newer technologies such as clustered regularly interspaced short palindromic repeats/Cas9 or transcription activator-like effector nucleases in comparison with the RNAi approach is discussed in this paper.

Cell-Penetrating Peptides to Enhance Delivery of Oligonucleotide-Based Therapeutics

The promise of nucleic acid based oligonucleotides as effective genetic therapies has been held back by their low bioavailability and poor cellular uptake to target tissues upon systemic administration. One such strategy to improve upon delivery is the use of short cell-penetrating peptides (CPPs) that can be either directly attached to their cargo through covalent linkages or through the formation of noncovalent nanoparticle complexes that can facilitate cellular uptake. In this review, we will highlight recent proof-of-principle studies that have utilized both of these strategies to improve nucleic acid delivery and discuss the prospects for translation of this approach for clinical application.

Dual peptide-mediated targeted delivery of bioactive siRNAs to oral cancer cells in vivo

OBJECTIVES

Despite significant advances in cancer treatment, the prognosis for oral cancer remains poor in comparison to other cancer types, including breast, skin, and prostate. As a result, more effective therapeutic modalities are needed for the treatment of oral cancer. Consequently, in the present study, we examined the feasibility of using a dual peptide carrier approach, combining an epidermal growth factor receptor (EGFR)-targeting peptide with an endosome-disruptive peptide, to mediate targeted delivery of small interfering RNAs (siRNAs) into EGFR-overexpressing oral cancer cells and induce silencing of the targeted oncogene, cancerous inhibitor of protein phosphatase 2A (CIP2A).

MATERIALS AND METHODS

Fluorescence microscopy, real-time PCR, Western blot analysis, and in vivo bioimaging of mice containing orthotopic xenograft tumors were used to examine the ability of the dual peptide carrier to mediate specific delivery of bioactive siRNAs into EGFR-overexpressing oral cancer cells/tissues.

RESULTS

Co-complexation of the EGFR-targeting peptide, GE11R9, with the endosome-disruptive 599 peptide facilitated the specific uptake of siRNAs into oral cancer cells overexpressing EGFR in vitro with optimal gene silencing observed at a 60:30:1 (GE11R9:599:siRNA) molar ratio. Furthermore, when administered systemically to mice bearing xenograft oral tumors, this dual peptide complex mediated increased targeted delivery of siRNAs into tumor tissues in comparison to the 599 peptide alone and significantly enhanced CIP2A silencing.

CONCLUSION

Herein we provide the first report demonstrating the clinical potential of a dual peptide strategy for siRNA-based therapeutics by synergistically mediating the effective targeting and delivery of bioactive siRNAs into EGFR-overexpressing oral cancer cells.

Delivery of gene targeting siRNAs to breast cancer cells using a multifunctional peptide complex that promotes both targeted delivery and endosomal release

RNA interference has been used to dissect the importance of individual gene products in various human disease processes, including cancer. Small-interfering RNA, or siRNA, is one of the tools utilized in this regard, but specially-designed delivery agents are required to allow the siRNA to gain optimal access to the cell interior. Our laboratory has utilized two different siRNA-binding delivery peptides containing a polyarginine core, and modified by myristoylation and targeting motifs (iRGD or Lyp-1). A third peptide was designed to assist with endosomal release. Various ratios of the peptides and siRNA were combined and assayed for the ability to form stable complexes, and optimized ratios were determined. The complexes were found to form particles, with the majority having a diameter of 100-300 nm, as visualized by electron microscopy. These siRNA complexes have enhanced protection from nucleases present in serum, as compared to "naked" unprotected siRNA. The particles were internalized by the cells and could be detected in the cell cytoplasm by confocal fluorescence microscopy. In functional assays, peptide/siRNA complexes were shown to cause the knock down of corresponding targeted proteins. The peptide with the LyP-1 targeting motif was more effective at knockdown in MDA-MB-231 breast cancer cells than the peptide with the iRGD motif. Inclusion of the endosomal release peptide in the complexes greatly enhanced the peptide/siRNA effects. Peptide/siRNA complexes simultaneously targeting Stat3 and c-Myc caused a marked reduction in anchorage-independent growth, a property correlated with tumorigenicity. This study demonstrates the ability of a peptide-based siRNA-delivery system to deliver siRNA into breast cancer cells and cause both protein knockdown and suppression of the malignant phenotype. Such peptide complexes are likely to become highly useful siRNA-delivery vehicles for the characterization, and potentially for the treatment, of human cancer.

Functional peptides for siRNA delivery

siRNA is considered as a potent therapeutic agent because of its high specificity and efficiency in suppressing genes that are overexpressed during disease development. For nearly two decades, a significant amount of efforts has been dedicated to bringing the siRNA technology into clinical uses. However, only limited success has been achieved to date, largely due to the lack of a cell type-specific, safe, and efficient delivery technology to carry siRNA into the target cells' cytosol where RNA interference takes place. Among the emerging candidate nanocarriers for siRNA delivery, peptides have gained popularity because of their structural and functional diversity. A variety of peptides have been discovered for their ability to translocate siRNA into living cells via different mechanisms such as direct penetration through the cellular membrane, endocytosis-mediated cell entry followed by endosomolysis, and receptor-mediated uptake. This review is focused on the multiple roles played by peptides in siRNA delivery, such as membrane penetration, endosome disruption, targeting, as well as the combination of these functionalities.

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.

Trileucine residues in a ligand-CPP-based siRNA delivery platform improve endosomal escape of siRNA

siRNA entrapment within endosomes is a significant problem encountered with siRNA delivery platforms that co-opt receptor-mediated entry pathways. Attachment of a cell-penetrating peptide (CPP), such as nona-arginine (9R) to a cell receptor-binding ligand like the Rabies virus glycoprotein, RVG, allows effective siRNA delivery to the cytoplasm by non-endocytic pathways, but a significant amount of siRNA complexes also enters the cell by ligand-induced receptor endocytosis and remain localized in endosomes. Here, we report that the incorporation of trileucine (3 Leu) residues as an endo-osmolytic moiety in the peptide improves endosomal escape and intracellular delivery of siRNA. The trileucine motif did not affect early non-endosomal mechanism of cytoplasmic siRNA delivery but enhanced target gene silencing by >20% only beyond 24 h of transfection when siRNA delivery is mostly through the endocytic route and siRNA trapped in the endosomes at later stages were subject to release into cytoplasm. The mechanism may involve endosomal membrane disruption as trileucine residues lysed RBCs selectively under endosomal pH conditions. Interestingly <3 Leu or >3 Leu residues were not as effective, suggesting that 3 Leu residues are useful for enhancing cytoplasmic delivery of siRNA routed through endosomes.

Virus-inspired nucleic acid delivery system: Linking virus and viral mimicry

Targeted delivery of nucleic acids into disease sites of human body has been attempted for decades, but both viral and non-viral vectors are yet to meet our expectations. Safety concerns and low delivery efficiency are the main limitations of viral and non-viral vectors, respectively. The structure of viruses is both ordered and dynamic, and is believed to be the key for effective transfection. Detailed understanding of the physical properties of viruses, their interaction with cellular components, and responses towards cellular environments leading to transfection would inspire the development of safe and effective non-viral vectors. To this goal, this review systematically summarizes distinctive features of viruses that are implied for efficient nucleic acid delivery but not yet fully explored in current non-viral vectors. The assembly and disassembly of viral structures, presentation of viral ligands, and the subcellular targeting of viruses are emphasized. Moreover, we describe the current development of cationic material-based viral mimicry (CVM) and structural viral mimicry (SVM) in these aspects. In light of the discrepancy, we identify future opportunities for rational design of viral mimics for the efficient delivery of DNA and RNA.

Cationic cell-penetrating peptides as vehicles for siRNA delivery

RNA interference mediated gene silencing has tremendous applicability in fields ranging from basic biological research to clinical therapy. However, delivery of siRNA across the cell membrane into the cytoplasm, where the RNA silencing machinery is located, is a significant hurdle in most primary cells. Cell-penetrating peptides (CPPs), peptides that possess an intrinsic ability to translocate across cell membranes, have been explored as a means to achieve cellular delivery of siRNA. Approaches using CPPs by themselves or through incorporation into other siRNA delivery platforms have been investigated with the intent of improving cytoplasmic delivery. Here, we review the utilization of CPPs for siRNA delivery with a focus on strategies developed to enhance cellular uptake, endosomal escape and cytoplasmic localization of CPP/siRNA complexes.

Cancerous Inhibitor of PP2A Silencing Inhibits Proliferation and Promotes Apoptosis in Human Multiple Myeloma Cells

Multiple myeloma is the second most prevalent type of blood cancer, representing approximately 1% of all cancers and 2% of all cancer deaths. There is therefore a strong need to identify critical targets in multiple myeloma neoplasia and progression. Cancerous inhibitor of PP2A (CIP2A) is a human oncoprotein that regulates cancer cell viability and anchorage-independent growth and induces apoptosis. The present study investigated CIP2A function in the human multiple myeloma cell lines RPMI-8226 and NCI-H929 to determine whether it can serve as a potential therapeutic target. CIP2A was silenced in the cells by transfection of short interfering RNA and cell proliferation and apoptosis were evaluated by a tetrazolium salt-based assay and flow cytometry, respectively. CIP2A knockdown inhibited proliferation and induced apoptosis in RPMI-8226 and NCI-H929 cells and decreased the phosphorylation of phosphoinositide 3-kinase (PI3K) p85, AKT1, and mammalian target of rapamycin (mTOR) without affecting total protein levels. Treatment of CIP2A-depletion cells with insulin-like growth factor 1 decreased the effects of CIP2A inhibition on cell viability and apoptosis. These results indicate that CIP2A modulates myeloma cell proliferation and apoptosis via PI3K/AKT/mTOR signaling and suggest that it can potentially serve as a drug target for the treatment of multiple myeloma.

Fusogenic-oligoarginine peptide-mediated silencing of the CIP2A oncogene suppresses oral cancer tumor growth in vivo

Intracellular delivery and endosomal escape of functional small interfering RNAs (siRNAs) remain major barriers limiting the clinical translation of RNA interference (RNAi)-based therapeutics. Recently, we demonstrated that a cell-penetrating endosome-disruptive peptide we synthesized, termed 599, enhanced the intracellular delivery and bioavailability of siRNAs designed to target the CIP2A oncoprotein (siCIP2A) into oral cancer cells and consequently inhibited oral cancer cell invasiveness and anchorage-independent growth in vitro. Thus, to further assess the therapeutic potential of the 599 peptide in mediating RNAi-based therapeutics for oral cancer and its prospective applicability in clinical settings, the objective of the current study was to determine whether intratumoral dosing of the 599 peptide-siCIP2A complex could induce silencing of CIP2A and consequently impair tumor growth using a xenograft oral cancer mouse model. Our results demonstrate that the 599 peptide is able to protect siRNAs from degradation by serum and ribonucleases in vitro and upon intratumoral injection in vivo, confirming the stability of the 599 peptide-siRNA complex and its potential for therapeutic utility. Moreover, 599 peptide-mediated delivery of siCIP2A to tumor tissue induces CIP2A silencing without any associated toxicity, consequently resulting in reduction of the mitotic index and significant inhibition of tumor growth. Together, these data suggest that the 599 peptide carrier is a clinically effective mediator of RNAi-based cancer therapeutics.

Micellar carriers for the delivery of multiple therapeutic agents

Multi-drug therapy is described as a simultaneous or sequential administration of two or more drugs with similar or different mechanisms of action and is recognized as a more efficient solution to combat successfully, various ailments. Polymeric micelles (PMs) are self-assemblies of block copolymers providing numerous opportunities for drug delivery. To date various micellar formulations were studied for delivery of drugs, nutraceuticals and genes; a few of them are in clinical trials. It was observed that there is an immense need for the development of PMs embedding multiple therapeutic agents to combat various ailments, including cancers, HIV/AIDS, malaria, multiple sclerosis, hypertension, infectious diseases, cardiovascular and metabolic diseases, immune disorders and many psychiatric disorders. Several combinations of drug-drug, drug-nutraceutical, drug-gene and drug-siRNA explored to date are detailed in this review, with a special emphasis on their potential and future perspectives. A summary of various preparation methods, characterization techniques and applications of PMs are also provided. This review presents a holistic approach on multi-drug delivery using micellar carriers and emphasizes on the development of therapeutic hybrids embedding novel combinations for safer and effective therapy.

Cell-penetrating peptides: strategies for anticancer treatment

Cell-penetrating peptides (CPP) provide an efficient strategy for the intracellular delivery of bioactive molecules in various biomedical applications. This review focuses on recent advances in the use of CPPs to deliver anticancer therapeutics and imaging reagents to cancer cells, along with CPP contributions to novel tumor-targeting techniques. CPPs are now used extensively to deliver a variety of therapeutics, despite lacking cell specificity and having a short duration of action. Resolution of these shortcomings to enable increased cancer cell and/or tumor specificity could improve CPP-based drug delivery strategies, expand combined drug delivery possibilities, and strengthen future clinical applications of these peptides.

A novel chimeric peptide with antimicrobial activity

Beta-lactamase-mediated bacterial drug resistance exacerbates the prognosis of infectious diseases, which are sometimes treated with co-administration of beta-lactam type antibiotics and beta-lactamase inhibitors. Antimicrobial peptides are promising broad-spectrum alternatives to conventional antibiotics in this era of evolving bacterial resistance. Peptides based on the Ala46-Tyr51 beta-hairpin loop of beta-lactamase inhibitory protein (BLIP) have been previously shown to inhibit beta-lactamase. Here, our goal was to modify this peptide for improved beta-lactamase inhibition and cellular uptake. Motivated by the cell-penetrating pVEC sequence, which includes a hydrophobic stretch at its N-terminus, our approach involved the addition of LLIIL residues to the inhibitory peptide N-terminus to facilitate uptake. Activity measurements of the peptide based on the 45-53 loop of BLIP for enhanced inhibition verified that the peptide was a competitive beta-lactamase inhibitor with a K(i) value of 58 μM. Incubation of beta-lactam-resistant cells with peptide decreased the number of viable cells, while it had no effect on beta-lactamase-free cells, indicating that this peptide had antimicrobial activity via beta-lactamase inhibition. To elucidate the molecular mechanism by which this peptide moves across the membrane, steered molecular dynamics simulations were carried out. We propose that addition of hydrophobic residues to the N-terminus of the peptide affords a promising strategy in the design of novel antimicrobial peptides not only against beta-lactamase but also for other intracellular targets.

Attachment of cell-binding ligands to arginine-rich cell-penetrating peptides enables cytosolic translocation of complexed siRNA

Cell-penetrating peptides (CPPs), such as nona-arginine (9R), poorly translocate siRNA into cells. Our studies demonstrate that attaching 9R to ligands that bind cell surface receptors quantitatively increases siRNA uptake and importantly, allows functional delivery of complexed siRNA. The mechanism involved accumulation of ligand-9R:siRNA microparticles on the cell membrane, which induced transient membrane inversion at the site of ligand-9R binding and rapid siRNA translocation into the cytoplasm. siRNA release also occurred late after endocytosis when the ligand was attached to the L isoform of 9R, but not the protease-resistant 9DR, prolonging mRNA knockdown. This critically depended on endosomal proteolytic activity, implying that partial CPP degradation is required for endosome-to-cytosol translocation. The data demonstrate that ligand attachment renders simple polycationic CPPs effective for siRNA delivery by restoring their intrinsic property of translocation.

CIP2A cooperates with H-Ras to promote epithelial-mesenchymal transition in cervical-cancer progression

The oncoprotein Cancerous Inhibitor of PP2A (CIP2A) has been reported to interact with Protein phosphatase 2 (PP2A) to stabilize c-Myc and prevent its degradation, and high expression levels of CIP2A have been proved to be related to poor clinical outcomes in multiple cancers. Here, we not only proved that the expression of CIP2A is positively correlated with lymph-node metastasis and cervical-cancer progression, but also revealed a close correlation between the protein's expression and the expression levels of two core epithelial-to-mesenchymal transition (EMT) markers, Vimentin and Snail. In addition, we manipulated CIP2A expression to regulate EMT conversion and employed a pull-down assay, mass-spectrometric (MS) peptide sequencing, as well as bilateral co-immunoprecipitation to identify potentially interacting proteins in cervical-cancer cells. In this study, we proposed and successfully proved, for the first time, that CIP2A physically associates with H-Ras, which leads to the activation of the MEK/ERK signaling pathway and promotes EMT and cervical-cancer progression. Based on our observations and prior findings that CIP2A participates in c-Myc regulation, we conjecture that CIP2A may be a potentially promising molecular target for the adoptive therapy of human cancer.

Identification and characterization of Dicer1e, a Dicer1 protein variant, in oral cancer cells

Background

The human dicer1 gene has been predicted to produce several mRNA variants that encode truncated Dicer1 proteins of varying lengths. One of these Dicer1 variants, Dicer1e, was recently found to be differentially expressed in breast cancer cells. Because the expression and function of the Dicer1e protein variant has not been well characterized and the underlying molecular mechanisms for the development of oral squamous cell carcinomas (OSCCs) are poorly understood, the present study sought to characterize the biological role of Dicer1e and determine its relationship, if any, to OSCC pathogenesis.

Methods

Western blot analyses were used to examine Dicer1e expression levels in a panel of oral cancer cells/tissues and during epithelial-mesenchymal transition (EMT), followed by 5′/3′-RACE analyses to obtain the full-length Dicer1e transcript. Biochemical fractionation and indirect immunofluorescent studies were performed to determine the cellular localization of Dicer1e and the effects of Dicer1e silencing on cancer cell proliferation, clonogenicity, and drug sensitivity were also assessed.

Results

Dicer1e protein levels were found to be overexpressed in OSCC cell lines of epithelial phenotype and in OSCC tissues with its levels downregulated during EMT. Moreover, the Dicer1e protein was observed to predominantly localize in the nucleus. 5′/3′-RACE analyses confirmed the presence of the Dicer1e transcript and silencing of Dicer1e impaired both cancer cell proliferation and clonogenicity by inducing either apoptosis and/or G2/M cell cycle arrest. Lastly, Dicer1e knockdown enhanced the chemosensitivity of oral cancer cells to cisplatin.

Conclusion

The expression levels of Dicer1e influence the pathogenesis of oral cancer cells and alter their response to chemosensitivity, thus supporting the importance of Dicer1e as a therapeutic target for OSCCs.

Electronic supplementary material

The online version of this article (doi:10.1186/1476-4598-13-190) contains supplementary material, which is available to authorized users.

Oncogenic nexus of cancerous inhibitor of protein phosphatase 2A (CIP2A): an oncoprotein with many hands

Oncoprotein CIP2A a Cancerous Inhibitor of PP2A forms an "oncogenic nexus" by virtue of its control on PP2A and MYC stabilization in cancer cells. The expression and prognostic function of CIP2A in different solid tumors including colorectal carcinoma, head and neck cancers, gastric cancers, lung carcinoma, cholangiocarcinoma, esophageal cancers, pancreatic carcinoma, brain cancers, breast carcinoma, bladder cancers, ovarian carcinoma, renal cell carcinomas, tongue cancers, cervical carcinoma, prostate cancers, and oral carcinoma as well as a number of hematological malignancies are just beginning to emerge. Herein, we reviewed the recent progress in our understanding of (1) how an "oncogenic nexus" of CIP2A participates in the tumorigenic transformation of cells and (2) how we can prospect/view the clinical relevance of CIP2A in the context of cancer therapy. The review will try to understand the role of CIP2A (a) as a biomarker in cancers and evaluate the prognostic value of CIP2A in different cancers (b) as a therapeutic target in cancers and (c) in drug response and developing chemo-resistance in cancers.

Nanoparticle-mediated systemic delivery of siRNA for treatment of cancers and viral infections

RNA interference (RNAi) is an endogenous post-transcriptional gene regulatory mechanism, where non-coding, double-stranded RNA molecules interfere with the expression of certain genes in order to silence it. Since its discovery, this phenomenon has evolved as powerful technology to diagnose and treat diseases at cellular and molecular levels. With a lot of attention, short interfering RNA (siRNA) therapeutics has brought a great hope for treatment of various undruggable diseases, including genetic diseases, cancer, and resistant viral infections. However, the challenge of their systemic delivery and on how they are integrated to exhibit the desired properties and functions remains a key bottleneck for realizing its full potential. Nanoparticles are currently well known to exhibit a number of unique properties that could be strategically tailored into new advanced siRNA delivery systems. This review summarizes the various nanoparticulate systems developed so far in the literature for systemic delivery of siRNA, which include silica and silicon-based nanoparticles, metal and metal oxides nanoparticles, carbon nanotubes, graphene, dendrimers, polymers, cyclodextrins, lipids, hydrogels, and semiconductor nanocrystals. Challenges and barriers to the delivery of siRNA and the role of different nanoparticles to surmount these challenges are also included in the review.