Crystallization and preliminary X-ray analysis of a PNA-DNA complex

Efficient Gene Therapy of Pancreatic Cancer via a Peptide Nucleic Acid (PNA)-Loaded Layered Double Hydroxides (LDH) Nanoplatform

Pancreatic ductal adenocarcinoma (PDAC) is one of the deadliest malignant tumors with extremely poor prognosis due to the later stage diagnosis when surgical resection is no longer applicable. Alternatively, the traditional gene therapy which drives pancreatic cancer cells into an inactive state and inhibiting the proliferation and metastasis, presents potentials to safely inhibit pancreatic cancer progression, but unfortunately has received limited success to date. Here, an efficient gene therapy of pancreatic cancer is shown via a peptide nucleic acid (PNA)-loaded layered double hydroxides (LDHs) nanoplatform. Compared with the traditional DNA- or RNA-based gene therapies, the gene therapy using PNA features great advantages in recognizing and hybridizing with the target mutant sequences to form PNA-DNA hybrids with significantly enhanced stability due to the absence of electrostatic repulsion, and the constrained flexibility of the polyamide backbone. Moreover, ultrasmall LDHs are engineered to load PNA and the obtained PNA-loaded LDH platform (LDHs/PNA) is capable of efficiently and selectively targeting the intranuclear mutant sequences thanks to the proton sponge effect. Treatments with LDHs/PNA demonstrate markedly inhibited growth of pancreatic cancer xenografts via a cancer cell proliferation suppression mechanism. The results demonstrate the great potentials of LDHs/PNA as a highly promising gene therapy agent for PDAC.

Detection of PCR products using PNA strand invasion

The unique ability of homopyrimidine peptide nucleic acid (PNA) to strand invade homopurine sites of duplex DNA offers a potential alternative to existing techniques for rapid detection of PCR products. From gel shift studies, PNA was found to specifically strand invade homopurine sites that had been incorporated into an amplicon during the PCR cycle. This was achieved by adding a homopyrimidine sequence to the 5'-terminus of a PCR primer. The position of the strand invasion sites at the termini of the DNA duplex offers kinetic advantages for PNA strand invasion, since the termini of DNA duplexes are known to be unwound. This unwound state was demonstrated using a novel assay that determined single-stranded regions within the amplicon. The presence of the PNA moiety in strand invasion complexes was confirmed by a novel electroblot, an Enzyme Linked Nucleic Acid assay and by an increase in stability as demonstrated by T(m)studies with the Idaho RapidCycler. Since the strand invasion sites can be controlled through selection of the homopurine sequence there is great flexibility for designing strand invasion motifs unique to a particular PCR amplicon, thus providing a huge potential for differentiating and detecting multiplex PCR products.

Hairpin-forming peptide nucleic acid oligomers

A series of partially self-complementary peptide nucleic acid (PNA) oligomers was prepared. Examination of their melting behavior, circular dichroism spectra, and fluorescence properties reveals that these PNA oligomers exist as stem-loop ("hairpin") structures. Fluorescence is readily observed in hairpins containing a covalently linked, emissive acridine derivative which is, at least partially, intercalated in the duplex region of the PNA hairpin. The acridine fluorescence is quenched when an anthraquinone derivative is covalently attached to the PNA so that it is bound near the acridine in the hairpin structure. Acridine fluorescence is restored in hairpins containing both the anthraquinone and the acridine by increasing the temperature and melting the structure to its linear form or by opening the hairpin through formation of a hybrid duplex with complementary DNA. The latter process may form the basis for development of selective and sensitive DNA assays.