Genetic medicine--when will it come to the drugstore?

Synthesis and biological properties of sequence-specific DNA-alkylating pyrrole-imidazole polyamides

In recent years, many diseases including cancer and hereditary and viral diseases have been understood at the DNA sequence level. Direct control of the expression level of a specific gene would provide a promising approach for knowledge-based therapy. N-Methylpyrrole (Py) and N-methylimidazole (Im) polyamides are a new type of small compound that precisely bind to the minor groove of the DNA duplex in a sequence-specific fashion and recruit alkylating agents to the target sequence. We designed and synthesized a series of sequence-specific alkylating Py-Im polyamide conjugates that selectively alkylate predetermined DNA sequences. We have demonstrated that sequence-specific alkylating agents possess gene-silencing activities and a promising potency against human cancer cell lines as well as against xenografts of human cancer cell lines. In this Account, we focus on recent progress in alkylating Py-Im polyamides with regard to sequence specificity and biological activities and the future direction of rational molecular design of genetic switches in the postgenome era is described.

Influence of netropsin's charges on the minor groove width of d(CGCGAATTCGCG)2

The exact understanding of the interaction of minor groove binding drugs with DNA is of interest due to their importance as transcription controlling drugs. In this study we performed four molecular dynamics simulations, one of the uncomplexed d(CGCGAATTCGCG)(2) dodecamer and three simulations of the DNA complexed with the minor groove binder netropsin. The charged guanidinium and amidinium ends of the small ligand were in one simulation formally uncharged, in the second one normally charged, and in the third simulation we doubled the charges of the two ends. So we are able to filter out the influence the charges exert on the DNA structure. The positive charges reduce the width of the minor groove showing that charges are able to modify the groove width by charge neutralization of the negative phosphate groups. The quality of the used force field was successfully tested by comparing the results of the uncomplexed dodecamer with already reported NMR and x-ray studies. Thus our simulations should be able to describe the minor groove width of DNA in a correct manner underlying the validity of the results.

Conjugates of antisense oligonucleotides with the Tat and antennapedia cell-penetrating peptides: effects on cellular uptake, binding to target sequences, and biologic actions

PURPOSE

The attainment of effective intracellular delivery remains an important issue for pharmacologic applications of antisense oligonucleotides. Here, we describe the synthesis, binding properties, and biologic properties of peptide-oligonucleotide conjugates comprised of the Tat and Ant cell-penetrating peptides with 2'-O-methyl phosphorothioate oligonucleotides.

METHODS

The biologic assay used in this study measures the ability of the antisense molecule to correct splicing of an aberrant intron inserted into the Luciferase gene; thus, this assay clearly demonstrates the delivery of functional antisense molecules to the splicing machinery within the nucleus. The binding affinities of the conjugates to their target sequences were measured by surface plasmon resonance (BIAcor) techniques.

RESULTS

The peptide-oligonucleotide conjugates progressively entered cells over a period of hours and were detected in cytoplasmic vesicles and in the nucleus. Peptide-oligonucleotide conjugates targeted to the aberrant splice site, but not mismatched controls, caused an increase in Luciferase activity in a dose-responsive manner. The kinetics of Luciferase appearance were consistent with the course of the uptake process for the conjugates. The effects of peptide conjugation on the hybridization characteristics of the oligonucleotides were also examined using surface plasmon resonance. The peptide-oligonucleotide conjugates displayed binding affinities and selectivities similar to those of unconjugated oligonucleotides.

CONCLUSIONS

Conjugation with cell-penetrating peptides enhances oligonucleotide delivery to the nucleus without interfering with the base-pairing function of antisense oligonucleotides.

Significance of ligand tails for interaction with the minor groove of B-DNA

Minor groove binding ligands are of great interest due to their extraordinary importance as transcription controlling drugs. We performed three molecular dynamics simulations of the unbound d(CGCGAATTCGCG)(2) dodecamer and its complexes with Hoechst33258 and Netropsin. The structural behavior of the piperazine tail of Hoechst33258, which has already been shown to be a contributor in sequence-specific recognition, was analyzed. The simulations also reveal that the tails of the ligands are able to influence the width of the minor groove. The groove width is even sensitive for conformational transitions of these tails, indicating a high adaptability of the minor groove. Furthermore, the ligands also exert an influence on the B(I)/B(II) backbone conformational substate behavior. All together these results are important for the understanding of the binding process of sequence-specific ligands.

Complex of B-DNA with polyamides freezes DNA backbone flexibility

The development of sequence-specific minor groove binding ligands is a modern and rapidly growing field of research because of their extraordinary importance as transcription-controlling drugs. We performed three molecular dynamics simulations in order to clarify the influence of minor groove binding of two ImHpPyPy-beta-Dp polyamides to the d(CCAGTACTGG)(2) decamer in the B-form. This decamer contains the recognition sequence for the trp repressor (5'-GTACT-3'), and it was investigated recently by X-ray crystallography. On one hand we are able to reproduce X-ray-determined DNA--drug contacts, and on the other hand we provide new contact information which is important for the development of potential ligands. The new insights show how the beta-tail of the polyamide ligands contributes to binding. Our simulations also indicate that complexation freezes the DNA backbone in a specific B(I) or B(II) substate conformation and thus optimizes nonbonded contacts. The existence of this distinct B(I)/B(II) substate pattern also allows the formation of water-mediated contacts. Thus, we suggest the B(I) <==> B(II) substate behavior to be an important part of the indirect readout of DNA.

An approach to gene-specific transcription inhibition using oligonucleotides complementary to the template strand of the open complex

The single-stranded region of DNA within the open complex of transcriptionally active genes provides a unique target for the design of gene-specific transcription inhibitors. Using the Escherichia coli lac UV5 and trp EDCBA promoters as in vitro models of open complex formation, we have identified the sites inside these transcription bubbles that are accessible for hybridization by short, nuclease-resistant, non-extendable oligoribonucleotides (ORNs). Binding of ORNs inside the open complex was determined by linking the chemical nuclease bis(1,10-phenanthroline) cuprous chelate [(OP)(2)Cu(+)] to the ORN and demonstrating template-specific DNA scission. In addition, these experiments were supported by in vitro transcription inhibition. We find that the most effective inhibitors are 5 nt long and have sequences that are complementary to the DNA template strand in the region near the transcription start site. The ORNs bind to the DNA template strand, forming an antiparallel heteroduplex inside the open complex. In this system, RNA polymerase is essential not only to melt the duplex DNA but also to facilitate hybridization of the incoming ORN. This paradigm for gene-specific inactivation relies on the base complementarity of the ORN and the catalytic activity and sequence specificity of RNA polymerase for the site- and sequence-specific recognition and inhibition of transcriptionally active DNA.

An approach to gene-specific transcription inhibition using oligonucleotides complementary to the template strand of the open complex

The single-stranded region of DNA within the open complex of transcriptionally active genes provides a unique target for the design of gene-specific transcription inhibitors. Using the Escherichia coli lac UV5 and trp EDCBA promoters as in vitro models of open complex formation, we have identified the sites inside these transcription bubbles that are accessible for hybridization by short, nuclease-resistant, non-extendable oligoribonucleotides (ORNs). Binding of ORNs inside the open complex was determined by linking the chemical nuclease bis(1,10-phenanthroline) cuprous chelate [(OP)(2)Cu(+)] to the ORN and demonstrating template-specific DNA scission. In addition, these experiments were supported by in vitro transcription inhibition. We find that the most effective inhibitors are 5 nt long and have sequences that are complementary to the DNA template strand in the region near the transcription start site. The ORNs bind to the DNA template strand, forming an antiparallel heteroduplex inside the open complex. In this system, RNA polymerase is essential not only to melt the duplex DNA but also to facilitate hybridization of the incoming ORN. This paradigm for gene-specific inactivation relies on the base complementarity of the ORN and the catalytic activity and sequence specificity of RNA polymerase for the site- and sequence-specific recognition and inhibition of transcriptionally active DNA.

Antisense pharmacodynamics: critical issues in the transport and delivery of antisense oligonucleotides

This review critically examines current understanding of the kinetics and biodistribution of antisense oligonucleotides, both at the cellular level and at the level of the intact organism. The pharmacodynamic relationships between biodistribution and the ultimate biological effects of antisense agents are considered. The problems and advantages inherent in the use of delivery systems are discussed in the light of further enhancing in vivo pharmacological actions of oligonucleotides.