Carrier capability of halloysite nanotubes for the intracellular delivery of antisense PNA targeting mRNA of neuroglobin gene

Peptide nucleic acid (PNA) is a DNA mimic that shows good stability against nucleases and proteases, forming strongly recognized complementary strands of DNA and RNA. However, due to its feeble ability to cross the cellular membrane, PNA activity and its targeting gene action is limited. Halloysite nanotubes (HNTs) are a natural and low-cost aluminosilicate clay. Because of their peculiar ability to cross cellular membrane, HNTs represent a valuable candidate for delivering genetic materials into cells. Herein, two differently charged 12-mer PNAs capable of recognizing as molecular target a 12-mer DNA molecule mimicking a purine-rich tract of neuroglobin were synthetized and loaded onto HNTs by electrostatic attraction interactions. After characterization, the kinetic release was also assessed in media mimicking physiological conditions. Resonance light scattering measurements assessed their ability to bind complementary single-stranded DNA. Furthermore, their intracellular delivery was assessed by confocal laser scanning microscopy on living MCF-7 cells incubated with fluorescence isothiocyanate (FITC)-PNA and HNTs labeled with a probe. The nanomaterials were found to cross cellular membrane and cell nuclei efficiently. Finally, it is worth mentioning that the HNTs/PNA can reduce the level of neuroglobin gene expression, as shown by reverse transcription-quantitative polymerase chain reaction and western blotting analysis.

Exploring the DNA2-PNA heterotriplex formation in targeting the Bcl-2 gene promoter: A structural insight by physico-chemical and microsecond-scale MD investigation

Peptide Nucleic Acids (PNAs) represent a promising tool for gene modulation in anticancer treatment. The uncharged peptidyl backbone and the resistance to chemical and enzymatic degradation make PNAs highly advantageous to form stable hybrid complexes with complementary DNA and RNA strands, providing higher stability than the corresponding natural analogues. Our and other groups' research has successfully shown that tailored PNA sequences can effectively downregulate the expression of human oncogenes using antigene, antisense, or anti-miRNA approaches. Specifically, we identified a seven bases-long PNA sequence, complementary to the longer loop of the main G-quadruplex structure formed by the bcl2midG4 promoter sequence, capable of downregulating the expression of the antiapoptotic Bcl-2 protein and enhancing the anticancer activity of an oncolytic adenovirus. Here, we extended the length of the PNA probe with the aim of including the double-stranded Bcl-2 promoter among the targets of the PNA probe. Our investigation primarily focused on the structural aspects of the resulting DNA2-PNA heterotriplex that were determined by employing conventional and accelerated microsecond-scale molecular dynamics simulations and chemical-physical analysis. Additionally, we conducted preliminary biological experiments using cytotoxicity assays on human A549 and MDA-MB-436 adenocarcinoma cell lines, employing the oncolytic adenovirus delivery strategy.

Exploring a peptide nucleic acid-based antisense approach for CD5 targeting in chronic lymphocytic leukemia

We herein report an innovative antisense approach based on Peptide Nucleic Acids (PNAs) to down-modulate CD5 expression levels in chronic lymphocytic leukemia (CLL). Using bioinformatics tools, we selected a 12-mer tract of the CD5 mRNA as the molecular target and synthesized the complementary and control PNA strands bearing a serine phosphate dipeptide tail to enhance their water solubility and bioavailability. The specific recognition of the 12-mer DNA strand, corresponding to the target mRNA sequence by the complementary PNA strand, was confirmed by non-denaturing polyacrylamide gel electrophoresis, thermal difference spectroscopy, circular dichroism (CD), and CD melting studies. Cytofluorimetric assays and real-time PCR analysis demonstrated the downregulation of CD5 expression due to incubation with the anti-CD5 PNA at RNA and protein levels in Jurkat cell line and peripheral blood mononuclear cells from B-CLL patients. Interestingly, we also observed that transfection with the anti-CD5 PNA increases apoptotic response induced by fludarabine in B-CLL cells. The herein reported results suggest that PNAs could represent a potential candidate for the development of antisense therapeutic agents in CLL.

Assisting PNA transport through cystic fibrosis human airway epithelia with biodegradable hybrid lipid-polymer nanoparticles

Cystic fibrosis (CF) is characterized by an airway obstruction caused by a thick mucus due to a malfunctioning Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) protein. The sticky mucus restricts drugs in reaching target cells limiting the efficiency of treatments. The development of new approaches to enhance drug delivery to the lungs represents CF treatment's main challenge. In this work, we report the production and characterization of hybrid core–shell nanoparticles (hNPs) comprising a PLGA core and a dipalmitoylphosphatidylcholine (DPPC) shell engineered for inhalation. We loaded hNPs with a 7-mer peptide nucleic acid (PNA) previously considered for its ability to modulate the post-transcriptional regulation of the CFTR gene. We also investigated the in vitro release kinetics of hNPs and their efficacy in PNA delivery across the human epithelial airway barrier using an ex vivo model based on human primary nasal epithelial cells (HNEC) from CF patients. Confocal analyses and hNPs transport assay demonstrated the ability of hNPs to overcome the mucus barrier and release their PNA cargo within the cytoplasm, where it can exert its biological function.

The Multifaceted Roles of MicroRNAs in Cystic Fibrosis

Cystic fibrosis (CF) is a lifelong disorder affecting 1 in 3500 live births worldwide. It is a monogenetic autosomal recessive disease caused by loss-of-function mutations in the gene encoding the chloride channel cystic fibrosis transmembrane conductance regulator (CFTR), the impairment of which leads to ionic disequilibria in exocrine organs. This translates into a chronic multisystemic disease characterized by airway obstruction, respiratory infections, and pancreatic insufficiency as well as hepatobiliary and gastrointestinal dysfunction. Molecular characterization of the mutational heterogeneity of CFTR (affected by more than 2000 variants) improved the understanding and management of CF. However, these CFTR variants are linked to different clinical manifestations and phenotypes, and they affect response to treatments. Expanding evidence suggests that multisystemic disease affects CF pathology via impairing either CFTR or proteins regulated by CFTR. Thus, altering the expression of miRNAs in vivo could constitute an appealing strategy for developing new CF therapies. In this review, we will first describe the pathophysiology and clinical management of CF. Then, we will summarize the current knowledge on altered miRNAs in CF patients, with a focus on the miRNAs involved in the deregulation of CFTR and in the modulation of inflammation. We will highlight recent findings on the potential utility of measuring circulating miRNAs in CF as diagnostic, prognostic, and predictive biomarkers. Finally, we will provide an overview on potential miRNA-based therapeutic approaches.

Peptide Nucleic Acid-Functionalized Adenoviral Vectors Targeting G-Quadruplexes in the P1 Promoter of Bcl-2 Proto-Oncogene: A New Tool for Gene Modulation in Anticancer Therapy

The B-cell lymphoma 2 (Bcl-2) gene encodes for an antiapoptotic protein associated with the onset of many human tumors. Several oligonucleotides (ONs) and ON analogues are under study as potential tools to counteract the Bcl-2 expression. Among these are Peptide Nucleic Acids (PNAs). The absence of charges on PNA backbones allows the formation of PNA/DNA complexes provided with higher stability than the corresponding natural DNA/DNA counterparts. To date, the use of PNAs in antigene or antisense strategies is strongly limited by their inability to efficiently cross the cellular membranes. With the aim of downregulating the expression of Bcl-2, we propose here a novel antigene approach which uses oncolytic adenoviral vectors (OAds) as a new cancer cell-targeted PNA delivery system. The ability of oncolytic Ad5D24 vectors to selectively infect and kill cancer cells was exploited to transfect with high efficiency and selectivity a short cytosine-rich PNA complementary to the longest loop of the main G-quadruplex formed by the 23-base-long bcl2midG4 sequence located 52-30 bp upstream of the P1 promoter of Bcl-2 gene. Physico-chemical and biological investigations confirmed the ability of the PNA-conjugated Ad5D24 vectors to load and transfect their PNA cargo into human A549 and MDA-MB-436 cancer cell lines, as well as the synergistic (OAd+PNA) cytotoxic effect against the same cell lines. This approach holds promise for safer chemotherapy because of reduced toxicity to healthy tissues and organs.

Potential of Peptide Nucleic Acids in Future Therapeutic Applications

Peptide nucleic acids (PNA) are synthetic analog of DNA with a repeating N-(2-aminoethyl)-glycine peptide backbone connected to purine and pyrimidine nucleobases via a linker. Considering the unique properties of PNA, including resistance to enzymatic digestion, higher biostability combined with great hybridization affinity toward DNA and RNA, it has attracted great attention toward PNA- based technology as a promising approach for gene alteration. However, an important challenge in utilizing PNA is poor intracellular uptake. Therefore, some strategies have been developed to enhance the delivery of PNA in order to reach cognate site. Although PNAs primarily demonstrated to act as an antisense and antigene agents for inhibition of transcription and translation of target genes, more therapeutic applications such as splicing modulation and gene editing are also used to produce specific genome modifications. Hence, several approaches based on PNAs technology have been designed for these purposes. This review briefly presents the properties and characteristics of PNA as well as different gene modulation mechanisms. Thereafter, current status of successful therapeutic applications of PNA as gene therapeutic intervention in different research areas with special interest in medical application in particular, anti-cancer therapy are discussed. Then it focuses on possible use of PNA as anti-mir agent and PNA-based strategies against clinically important bacteria.

Development of Novel Therapeutic Agents by Inhibition of Oncogenic MicroRNAs

MicroRNAs (miRs, miRNAs) are regulatory small noncoding RNAs, with their roles already confirmed to be important for post-transcriptional regulation of gene expression affecting cell physiology and disease development. Upregulation of a cancer-causing miRNA, known as oncogenic miRNA, has been found in many types of cancers and, therefore, represents a potential new class of targets for therapeutic inhibition. Several strategies have been developed in recent years to inhibit oncogenic miRNAs. Among them is a direct approach that targets mature oncogenic miRNA with an antisense sequence known as antimiR, which could be an oligonucleotide or miRNA sponge. In contrast, an indirect approach is to block the biogenesis of miRNA by genome editing using the CRISPR/Cas9 system or a small molecule inhibitor. The development of these inhibitors is straightforward but involves significant scientific and therapeutic challenges that need to be resolved. In this review, we summarize recent relevant studies on the development of miRNA inhibitors against cancer.

Peptide Nucleic Acids as miRNA Target Protectors for the Treatment of Cystic Fibrosis

Cystic Fibrosis (CF) is one of the most common life shortening conditions in Caucasians. CF is caused by mutations in the CF Transmembrane Conductance Regulator (CFTR) gene which result in reduced or altered CFTR functionality. Several microRNAs (miRNAs) downregulate the expression of CFTR, thus causing or exacerbating the symptoms of CF. In this context, the design of anti-miRNA agents represents a valid functional tool, but its translation to the clinic might lead to unpredictable side effects because of the interference with the expression of other genes regulated by the same miRNAs. Herein, for the first time, is proposed the use of peptide nucleic acids (PNAs) to protect specific sequences in the 3’UTR (untranslated region) of the CFTR messenger RNA (mRNA) by action of miRNAs. Two PNAs (7 and 13 bases long) carrying the tetrapeptide Gly-SerP-SerP-Gly at their C-end, fully complementary to the 3’UTR sequence recognized by miR-509-3p, have been synthesized and the structural features of target PNA/RNA heteroduplexes have been investigated by spectroscopic and molecular dynamics studies. The co-transfection of the pLuc-CFTR-3´UTR vector with different combinations of PNAs, miR-509-3p, and controls in A549 cells demonstrated the ability of the longer PNA to rescue the luciferase activity by up to 70% of the control, thus supporting the use of suitable PNAs to counteract the reduction in the CFTR expression.

Synthesis and label free characterization of a bimolecular PNA homo quadruplex

BACKGROUND

G-quadruplex DNA is involved in many physiological and pathological processes. Both clinical and experimental studies on DNA G-quadruplexes are slowed down by their enzymatic instability. In this frame, more stable chemically modified analogs are needed.

METHODS

The bis-end-linked-(gggt)₂ PNA molecule (BEL-PNA) was synthesized using in solution and solid phase synthetic approaches. Quadruplex formation was assessed by circular dichroism (CD) and surface enhanced Raman scattering (SERS).

RESULTS

An unprecedented bimolecular PNA homo quadruplex is here reported. To achieve this goal, we developed a bifunctional linker that once functionalized with gggt PNA strands and annealed in K⁺ buffer allowed the obtainment of a PNA homo quadruplex. The identification of the strong SERS band at ~1481cm^-1, attributable to vibrations involving the quadruplex diagnostic Hoogsteen type hydrogen bonds, confirmed the formation of the PNA homo quadruplex.

CONCLUSIONS

By tethering two G-rich PNA strands to the two ends of a suitable bifunctional linker it is possible to obtain bimolecular PNA homo quadruplexes after annealing in K⁺-containing buffers. The formation of such CD-unfriendly complexes can be monitored, even at low concentrations, by using the SERS technique.

GENERAL SIGNIFICANCE

Given the importance of DNA G-quadruplexes in medicine and nanotechnology, the obtainment of G-quadruplex analogs provided with enhanced enzymatic stability, and their monitoring by highly sensitive label-free techniques are of the highest importance. This article is part of a Special Issue entitled "G-quadruplex" Guest Editor: Dr. Concetta Giancola and Dr. Daniela Montesarchio.

Versatility of peptide nucleic acids (PNAs): role in chemical biology, drug discovery, and origins of life

This review briefly discussed nomenclature, synthesis, chemistry, and biophysical properties of a plethora of PNA derivatives reported since the discovery of aegPNA. Different synthetic methods and structural analogs of PNA synthesized till date were also discussed. An insight was gained into various chemical, physical, and biological properties of PNA which make it preferable over all other classes of modified nucleic acid analogs. Thereafter, various approaches with special attention to the practical constraints, characteristics, and inherent drawbacks leading to the delay in the development of PNA as gene therapeutic drug were outlined. An explicit account of the successful application of PNA in different areas of research such as antisense and antigene strategies, diagnostics, molecular probes, and so forth was described along with the current status of PNA as gene therapeutic drug. Further, the plausibility of the existence of PNA and its role in primordial chemistry, that is, origin of life was explored in an endeavor to comprehend the mystery and open up its deepest secrets ever engaging and challenging the human intellect. We finally concluded it with a discussion on the future prospects of PNA technology in the field of therapeutics, diagnostics, and origin of life.

Synthetic approaches to nucleopeptides containing all four nucleobases, and nucleic acid-binding studies on a mixed-sequence nucleo-oligolysine

In this article we describe two solid-phase synthetic routes to obtain a nucleo-oligolysine α-peptide containing all four natural nucleobases.

In this article we describe two solid-phase synthetic routes to obtain a nucleo-oligolysine α-peptide containing all four natural nucleobases. The first one is based on the oligomerization of the nucleobase-containing monomers, easily synthesized as herein described. The second strategy has the advantage of avoiding the solution synthesis of the monomeric building blocks, leading to the final nucleopeptide by direct solid-phase couplings of the suitably protected nucleobases with the free amino groups on the growing peptide chain still anchored to the resin. Both strategies are general and can be applied to the synthesis of nucleopeptides having backbones formed by any other diamino acid moiety decorated with the four nucleobases. We also report the CD and UV studies on the hybridization properties of the obtained nucleopeptide, containing all four nucleobases on alternate lysines in the sequence, towards complementary DNA and RNA strands. The nucleo-oligolysine with a mixed-base sequence did not prove to bind complementary DNA, but was able to recognize the complementary RNA forming a complex with a higher melting temperature than that of the corresponding RNA/RNA natural duplex and comparable with that of the analogous PNA/RNA system.

Congenital diarrhoeal disorders: advances in this evolving web of inherited enteropathies

Congenital diarrhoeal disorders (CDDs) represent an evolving web of rare chronic enteropathies, with a typical onset early in life. In many of these conditions, severe chronic diarrhoea represents the primary clinical manifestation, whereas in others diarrhoea is only a component of a more complex multi-organ or systemic disorder. Typically, within the first days of life, diarrhoea leads to a life-threatening condition highlighted by severe dehydration and serum electrolyte abnormalities. Thus, in the vast majority of cases appropriate therapy must be started immediately to prevent dehydration and long-term, sometimes severe, complications. The number of well-characterized disorders attributed to CDDs has gradually increased over the past several years, and many new genes have been identified and functionally related to CDDs, opening new diagnostic and therapeutic perspectives. Molecular analysis has changed the diagnostic scenario in CDDs, and led to a reduction in invasive and expensive procedures. Major advances have been made in terms of pathogenesis, enabling a better understanding not only of these rare conditions but also of more common diseases mechanisms.

Exploitation of a very small peptide nucleic acid as a new inhibitor of miR-509-3p involved in the regulation of cystic fibrosis disease-gene expression

Computational techniques, and in particular molecular dynamics (MD) simulations, have been successfully used as a complementary technique to predict and analyse the structural behaviour of nucleic acids, including peptide nucleic acid- (PNA-) RNA hybrids. This study shows that a 7-base long PNA complementary to the seed region of miR-509-3p, one of the miRNAs involved in the posttranscriptional regulation of the CFTR disease-gene of Cystic Fibrosis, and bearing suitable functionalization at its N- and C-ends aimed at improving its resistance to nucleases and cellular uptake, is able to revert the expression of the luciferase gene containing the 3′UTR of the gene in A549 human lung cancer cells, in agreement with the MD results that pointed at the formation of a stable RNA/PNA heteroduplex notwithstanding the short sequence of the latter. The here reported results widen the interest towards the use of small PNAs as effective anti-miRNA agents.