DNA crosslinking and biological activity of a hairpin polyamide–chlorambucil conjugate

A prototype of a novel class of DNA alkylating agents, which combines the DNA crosslinking moiety chlorambucil (Chl) with a sequence-selective hairpin pyrrole-imidazole polyamide ImPy-beta-ImPy-gamma-ImPy-beta-Dp (polyamide 1), was evaluated for its ability to damage DNA and induce biological responses. Polyamide 1-Chl conjugate (1-Chl) alkylates and interstrand crosslinks DNA in cell-free systems. The alkylation occurs predominantly at 5'-AGCTGCA-3' sequence, which represents the polyamide binding site. Conjugate-induced lesions were first detected on DNA treated for 1 h with 0.1 muM 1-Chl, indicating that the conjugate is at least 100-fold more potent than Chl. Prolonged incubation allowed for DNA damage detection even at 0.01 muM concentration. Treatment with 1-Chl decreased DNA template activity in simian virus 40 (SV40) in vitro replication assays. 1-Chl inhibited mammalian cell growth, genomic DNA replication and cell cycle progression, and arrested cells in the G(2)/M phase. Moreover, cellular effects were observed at 1-Chl concentrations similar to those needed for DNA damage in cell-free systems. Neither of the parent compounds, unconjugated Chl or polyamide 1, demonstrated any cellular activity in the same concentration range. The conjugate molecule 1-Chl possesses the sequence-selectivity of a polyamide and the enhanced DNA reactivity of Chl

Fmoc solid phase synthesis of polyamides containing pyrrole and imidazole amino acids

Polyamides containing N-methylimidazole (Im) and N-methylpyrrole (Py) amino acids are synthetic ligands that have an affinity and specificity for DNA comparable to those of many naturally occurring DNA binding proteins. A machine-assisted Fmoc solid phase synthesis of polyamides has been optimized to afford high stepwise coupling yields (>99%). Two monomer building blocks, Fmoc-Py acid and Fmoc-Im acid, were prepared in multigram scale. Cleavage by aminolysis followed by HPLC purification affords up to 200 mg quantities of polyamide with purities and yields greater than or equal to those reported using Boc chemistry. A broader set of reaction conditions will increase the number and complexity of minor groove binding polyamides which may be prepared and help ensure compatibility with many commercially available peptide synthesizers

Improved nuclear localization of DNA-binding polyamides

Regulation of endogenous genes by DNA-binding polyamides requires effective nuclear localization. Previous work employing confocal microscopy to study uptake of fluorophore-labeled polyamides has demonstrated the difficulty of predicting a priori the nuclear uptake of a given polyamide. The data suggest that dye identity influences uptake sufficiently such that a dye-conjugate cannot be used as a proxy for unlabeled analogs. Polyamides capable of nuclear localization unaided by fluorescent dyes are desirable due to size and other limitations of fluorophores. Recently, a polyamide-fluorescein conjugate targeted to the hypoxia response element (HRE) was found to inhibit vascular endothelial growth factor (VEGF) expression in cultured HeLa cells. The current study uses inhibition of VEGF expression as a biological read-out for effective nuclear localization of HRE-targeted polyamides. We synthesized a focused library of non-fluorescent, HRE-targeted polyamides in which the C-terminus ‘tail’ has been systematically varied. Members of this library bind the HRE with affinities comparable or superior to that of the fluorescein-labeled analog. Although most library members demonstrate modest or no biological activity, two non-fluorescent polyamides are reported with activity rivaling that of the previously reported fluorescein-labeled polyamide. We also show evidence that promoter occupancy by HIF-1, the transcription factor that binds the HRE, is inhibited by HRE-targeted polyamides

Fmoc solid phase synthesis of polyamides containing pyrrole and imidazole amino acids

Polyamides containing N-methylimidazole (Im) and N-methylpyrrole (Py) amino acids are synthetic ligands that have an affinity and specificity for DNA comparable to those of many naturally occurring DNA binding proteins. A machine-assisted Fmoc solid phase synthesis of polyamides has been optimized to afford high stepwise coupling yields (>99%). Two monomer building blocks, Fmoc-Py acid and Fmoc-Im acid, were prepared in multigram scale. Cleavage by aminolysis followed by HPLC purification affords up to 200 mg quantities of polyamide with purities and yields greater than or equal to those reported using Boc chemistry. A broader set of reaction conditions will increase the number and complexity of minor groove binding polyamides which may be prepared and help ensure compatibility with many commercially available peptide synthesizers

Student nurses' experiences of infection prevention and control during clinical placements

Background: Little is known about nursing students' experiences of infection control in the clinical setting despite its importance protecting patients and reducing risks of occupational exposure. Methods: We conducted an online survey involving a fixed choice Likert-type scale with 19 items and an open question to solicit more detailed information with a national sample of student nurses in the United Kingdom. Results: Four hundred eighty-eight student nurses completed questionnaires. All participants reported lack of compliance for every item on the Likert scale, most frequently from community settings and long-term care facilities for older people. Incidents most commonly witnessed were failure to comply with hand hygiene protocols, failure to comply with isolation precautions, poor standards of cleaning in the patient environment, not changing personal protective clothing between patients, and poor management of sharp instruments. Qualified nurses did not provide good role models. Medical staff were the occupational group most heavily criticized for poor compliance. Conclusion: Students demonstrated sound understanding of infection control and were able to identify lack of compliance on the basis of preclinical classroom instruction. The study findings indicate that ensuring safe infection control practice remains a challenge in the United Kingdom despite its high priority

Accessibility of nuclear chromatin by DNA binding polyamides

Pyrrole-imidazole polyamides bind DNA with affinities comparable to those of transcriptional regulatory proteins and inhibit the DNA binding activities of components of the transcription apparatus. If polyamides are to be useful for the regulation of gene expression in cell culture experiments, one pivotal issue is accessibility of specific sites in nuclear chromatin. We first determined the kinetics of uptake and subcellular distribution of polyamides in lymphoid and myeloid cells using fluorescent polyamide-bodipy conjugates and deconvolution microscopy. Then cells were incubated with a polyamide-chlorambucil conjugate, and the sites of specific DNA cleavage in the nuclear chromatin were assayed by ligation-mediated PCR. In addition, DNA microarray analysis revealed that two different polyamides generated distinct transcription profiles. Remarkably, the polyamides affected only a limited number of genes

Sequence Specific Alkylation of DNA by Polyamide-Chlorambucil Conjugates

Small molecules that bind selectively to a DNA sequence in the human genome are potentially useful tools for molecular biology and human medicine. Polyamides containing N-methylimidazole (Im) and N-methylpyrrole (Py) are small molecules that bind DNA according to a set of "pairing rules" with affinities and specificities similar to many naturally occurring DNA binding proteins. Two alternate routes of synthesis of polyamides are presented that allowed improved synthesis of commonly used motifs as well as access to polyamides with truncated tails which increase the number of DNA sequences targetable by polyamides with high affinity. Py-Im polyamides may offer a general approach to chemical regulation of gene expression provided inhibition of DNA binding for a variety of transcription factor families can be achieved. Two successful strategies are shown for the inhibition of DNA binding by two such proteins, GCN4 and NF-κB. An alternate method of gene regulation would be inhibition of transcription during the elongation phase by site-specific alkylation in the coding region of genes. A new class of compounds is created by the attachment of a bis (dichloroethylamino)-benzene nonspecific DNA alkylator to polyamides, which alkylate DNA with high yield and specificity. The biological activity and cell permeability of one of these compounds in several systems is studied.</p

Sequence specific alkylation of DNA by hairpin pyrrole-imidazole polyamide conjugates

Background: Pyrrole–imidazole polyamides are synthetic ligands that recognize predetermined sequences in the minor groove of DNA with affinities and specificities comparable to those of DNA-binding proteins. As a result of their DNA-binding properties, polyamides could deliver reactive moieties for covalent reaction at specific DNA sequences and thereby inhibit DNA–protein interactions. Site-specific alkylation of DNA could be a useful tool for regulating gene expression. As a minimal first step, we set out to design and synthesize a class of hairpin polyamides equipped with DNA alkylating agents and characterize the specificity and yield of covalent modification. Results: Bis(dichloroethylamino)benzene derivatives of the well-characterized chlorambucil (CHL) were attached to the γ turn of an eight-ring hairpin polyamide targeted to the HIV-1 promoter. We found that a hairpin polyamide–CHL conjugate binds and selectively alkylates predetermined sites in the HIV promoter at subnanomolar concentrations. Cleavage sites were determined on both strands of a restriction fragment containing the HIV-1 promoter, revealing good specificity and a high yield of alkylation. Conclusions: The ability of polyamide–CHL conjugates to sequence specifically alkylate double-stranded DNA in high yield and at low concentrations sets the stage for testing their use as regulators of gene expression in cell culture and ultimately in complex organisms

Inhibition of DNA Binding by NF-κB with Pyrrole-Imidazole Polyamides

Synthetic ligands that bind to predetermined DNA sequences will offer a chemical approach to gene regulation if inhibition of a broad range of transcription factors can be achieved. NF-κB is a transcription factor that regulates a multitude of genes, including those involved in immune, inflammatory, and anti-apoptotic responses. NF-κB binds as heterodimer predominantly in the major groove. We report the design of polyamides that bind in the minor groove and target overlapping portions of an NF-κB binding site (5‘-GGGACTTTCC-3‘). We find that compounds that target the 5‘-GGGACT-3‘ portion of the site can inhibit DNA binding by NF-κB while those that target the 5‘-ACTTTCC-3‘ portion do not. Addition of NF-κB to the list of protein−DNA complexes that can be disrupted by minor groove binding ligands potentially increases the utility of polyamides as regulators of gene expression