[Show abstract][Hide abstract] ABSTRACT: Chimeric molecules consisting of peptide nucleic acid (PNA) and lactose have been synthesized to test the hypothesis that lactose moieties can promote cell-specific uptake of PNAs. We find that lactose modified PNAs rapidly enter liver-derived HepG2 cells while unmodified PNAs do not and that lactose modified PNAs can inhibit cellular telomerase.
[Show abstract][Hide abstract] ABSTRACT: Genome sequencing has revealed thousands of novel genes, placing renewed emphasis on chemical approaches for controlling gene expression. Antisense oligomers designed directly from the information generated by sequencing are one option for achieving this control. Here we explore the rules governing the inhibition of gene expression by peptide nucleic acids (PNAs) inside cells. PNAs are a DNA/RNA mimic in which the phosphate deoxyribose backbone has been replaced by uncharged linkages. Binding to complementary sequences is not hindered by electrostatic repulsion and is characterized by high rates of association and elevated affinities. Here we test the hypothesis that the favorable properties of PNAs offer advantages for recognition of mRNA and antisense inhibition of gene expression in vivo. We have targeted 27 PNAs to 18 different sites throughout the 5'-untranslated region (5'-UTR), start site, and coding regions of luciferase mRNA. PNAs were introduced into living cells in culture as PNA-DNA-lipid complexes, providing a convenient high throughput method for cellular delivery. We find that PNAs targeted to the terminus of the 5'-UTR are potent and sequence-specific antisense agents. PNAs fifteen to eighteen bases in length were optimal inhibitors. The introduction of one or two mismatches abolished inhibition, and complementary PNAs targeted to the sense strand were also inactive. In striking contrast to effective inhibition by PNAs directed to the terminal region, PNAs complementary to other sites within the 5'-UTR do not inhibit gene expression. We also observe no inhibition by PNAs complementary to the start site or rest of the coding region, nor do we detect inhibition by PNAs that are highly C/G rich and possess extremely high affinities for their target sequences. Our results suggest that PNAs can block binding of the translation machinery but are less able to block the progress of the ribosome along mRNA. The high specificity of antisense inhibition by PNAs emphasizes both the promise and the challenges for PNAs as antisense agents and provides general guidelines for using PNAs to probe the molecular recognition of biological targets inside cells.
[Show abstract][Hide abstract] ABSTRACT: Telomerase activity, the ability to add telomeric repeats to the ends of chromosomes, has been detected in most immortal cell lines including tumor cells, but is low or absent in most diploid, mortal cells such as those of somatic tissues. Peptide nucleic acids (PNAs), analogs of DNA or RNA which bind to complementary nucleic acids with very high affinity, were co-electroporated into immortal human cells along with a selectable plasmid. Introduction of PNAs inverse-complementary to telomerase RNA effectively inhibited telomerase activity in intact cells, shortened telomeres, reduced colony size, and arrested cell proliferation after a lag period of 5-30 cell generations, consistent with suppression of their 'immortality'. Electroporation of selection plasmid alone had no effect, while PNAs of altered sequence were markedly less effective in each assay. This constitutes the first demonstration of cell growth arrest through telomerase inhibition, upon treatment of intact cells with an exogenous compound which can be efficiently delivered in vivo. The phenotype of telomerase-inhibited transformed cells differs from senescence of normal diploid fibroblasts, but rather resembles the crisis state of incompletely transformed cells.
[Show abstract][Hide abstract] ABSTRACT: Human telomerase has an essential RNA component and is an ideal target for developing rules correlating oligonucleotide chemistry with disruption of biological function. Similarly, peptide nucleic acids (PNAs), DNA analogs that bind complementary sequences with high affinity, are outstanding candidates for inducing phenotypic changes through hybridization.
We identify PNAs directed to nontemplate regions of the telomerase RNA that can overcome RNA secondary structure and inhibit telomerase by intercepting the RNA component prior to holoenzyme assembly. Relative potencies of inhibition delineate putative structural domains. We describe a novel protocol for introducing PNAs into eukaryotic cells and report efficient inhibition of cellular telomerase by PNAs.
PNAs directed to nontemplate regions are a new class of telomerase inhibitor and may contribute to the development of novel antiproliferative agents. The dependence of inhibition by nontemplate-directed PNAs on target sequence suggests that PNAs have great potential for mapping nucleic acid structure and predictably regulating biological processes. Our simple method for introducing PNAs into cells will not only be useful for probing the complex biology surrounding telomere length maintenance but can be broadly applied for controlling gene expression and functional genomics.
[Show abstract][Hide abstract] ABSTRACT: The ability of DNA oligonucleotides, neutral peptide nucleic acids (PNAS), and oligonucleotide conjugates to hybridize to inverted repeat sequences within supercoiled double-stranded DNA by Watson-Crick base-pairing is examined. PNAs and oligonucleotide conjugates initiate and maintain strand invasion under more stringent conditions than do unmodified DNA oligonucleotides. PNAs hybridize rapidly and, once bound, hold open a target site allowing oligonucleotides to base-pair to the displaced strand under conditions that would otherwise preclude hybridization. The ability to manipulate hybridization efficiency through different options for the alteration of oligomer charge should have important implications for optimizing sequence-specific recognition of DNA.
[Show abstract][Hide abstract] ABSTRACT: Chimeric molecules consisting of peptide nucleic acid oligomers (PNAs) and peptides derived from the third helix of the homeodomain of Antennapedia are taken up by mammalian cells in culture. Uptake is independent of orientation and occurs with high efficiency, suggesting that peptide conjugates are a promising strategy for intracellular PNA delivery.