Proton beam therapy and localised prostate cancer: current status and controversies.

Proton therapy is a promising, but costly, treatment for prostate cancer. Theoretical physical advantages exist; yet to date, it has been shown only to be comparably safe and effective when compared with the alternatives and not necessarily superior. If clinically meaningful benefits do exist for patients, more rigorous study will be needed to detect them and society will require this to justify the investment of time and money. New technical advances in proton beam delivery coupled with shortened overall treatment times and declining device costs have the potential to make this a more cost-effective therapy in the years ahead.

Pathological effects of cortical architecture on working memory in schizophrenia.

Neural connectivity of the prefrontal cortex is essential to working memory. Reduction of prefrontal connectivity and abnormal prefrontal dopamine modulation are common characteristics associated with schizophrenia. Two experiments separately modeled the effects of exaggerated pruning and of synaptic depression to imitate schizophrenic performance in a prefrontal neural network. In the first model, effects of cortical pruning were simulated with a set of scale-free networks of neurons and compared with empirical results from the Sternberg working memory task. The second set of simulations were based on the synaptic theory of working memory. Simulations of this model measured memory duration in relation to synaptic facilitation and depression constants and in relation to the level of neural connectivity. In the first set of simulations, modulating levels of cortical pruning resulted in a gain or loss in accuracy and speed of memory recollection. In the second set of simulations, increased facilitation time constants and decreased inhibitory time constants resulting in longer memory durations, and overly connected networks resulted in very low memory durations. In the first model, the decline in memory performance can be attributed to the emergence of pathological memory behavior brought about by the warping of the basins of attraction. Collectively, the simulations demonstrate that a reduction of prefrontal cortical hubs can lead to schizophrenia like performance in neural networks, and may account for pathological working memory in the disorder.

Heat shock factor 1 represses estrogen-dependent transcription through association with MTA1.

Heat shock factor 1 (HSF1), the transcriptional activator of the heat shock genes, is increasingly implicated in cancer. We have shown that HSF1 binds to the corepressor metastasis-associated protein 1 (MTA1) in vitro and in human breast carcinoma samples. HSF1-MTA1 complex formation was strongly induced by the transforming ligand heregulin and complexes incorporated a number of additional proteins including histone deacetylases (HDAC1 and 2) and Mi2alpha, all components of the NuRD corepressor complex. These complexes were induced to assemble on the chromatin of MCF7 breast carcinoma cells and associated with the promoters of estrogen-responsive genes. Such HSF1 complexes participate in repression of estrogen-dependent transcription in breast carcinoma cells treated with heregulin and this effect was inhibited by MTA1 knockdown. Repression of estrogen-dependent transcription may contribute to the role of HSF1 in cancer.

Mitochondrial and nuclear DNA damage induced by sulphur mustard in keratinocytes.

The extent and role of mitochondrial DNA damage in the mechanism of action of sulphur mustard (SM) is poorly understood. In this study, a combination of quantitative polymerase chain reaction and Southern hybridization was used to determine the levels of both total DNA adducts and DNA interstrand crosslinks in genomic and mitochondrial DNA isolated from normal human epidermal keratinocytes exposed to SM. The formation of both types of lesions occurred simultaneously in nuclear and mitochondrial DNA, however, SM produced significantly higher levels of both total adducts and crosslinks in genomic DNA than mitochondrial DNA. The total lesion frequency was 0.45 lesions/kb per 100 microM SM in the DHFR gene and 0.12 lesions/kb per 100 microM SM in the mitochondrial segment. Interstrand crosslinks occurred at a frequency of 0.28 crosslinks/10 kb per 100 microM SM in the DHFR gene and 0.05 crosslinks/10 kb per 100 microM SM in the mitochondrial segment. DNA interstrand crosslinks are thought to be the critical lesion produced by similar bi-functional alkylating agents. However, the levels of DNA cross-linking revealed in this study show that even at vesicating doses of SM mitochondrial DNA is still largely free of cross-links and the predominant form of DNA damage contributing to cell death occurs in the nucleus.

Nuclear and mitochondrial distribution of organoamidoplatinum(II) lesions in cisplatin-sensitive and -resistant adenocarcinoma cells.

The DNA binding pattern of the organoamidoplatinum(II) compound 1a is of considerable interest because of its known activity against cisplatin-resistant cells. The activity of 1a appears to be due at least in part to a greater cellular uptake than cisplatin into cisplatin-resistant cells, but little is known of the DNA reactions of the organoamidoplatinum(II) compounds. In this study the level of DNA cross-linking and total DNA lesions formed by 1 a were measured by gene-specific Southern hybridization cross-linking assays and by quantitative PCR in cisplatin-sensitive (2008) and in cisplatin-resistant 2008/R human adenocarcinoma cell lines. The surprising result was that the major difference between cisplatin and 1a was that the number of interstrand cross-links induced by 1a were approximately 5-fold greater than that induced by cisplatin in the nuclear (but not mitochondrial) DNA of resistant cells, even though the total number of lesions were essentially the same in both sensitive and resistant cells. This result suggests that the extent of interstrand cross-linking is a critical determinant of the cellular response to 1a and that the enhanced uptake of 1a into resistant cells results in this elevated level of cross-linking, leading to good activity of 1a against cisplatin-resistant cells. It remains unclear as to why 1a exhibits such selective damage to nuclear DNA, and insight into the molecular aspects of this selectivity will provide new opportunities for the further development of new platinum-based agents with activity against cisplatin-resistant cells.

DNA damage by nitrogen mustard in a gene containing multiple Sp1-binding sites.

The human cytochrome c(1) gene TATA-less promoter contains 10 Sp1-binding elements that regulate the activation of transcription of this gene. Quantitative PCR was used to show that nitrogen mustard induces DNA lesions within this Sp1-binding region following exposure of HeLa cells to clinical levels of the drug. Alkylation of the cytochrome c(1) gene in HeLa cells increased with reaction time up to 4 h following exposure to nitrogen mustard, with 50% of the lesions (approximately 0.8/kb) forming within 1 h. An Sp1 competition assay showed that nitrogen mustard inhibited the binding of Sp1 to the promoter region of the cytochrome c(1) gene in HeLa cells. These results show that nitrogen mustard-induced damage to Sp1-binding sites may contribute to the toxicity of this compound by interfering with the activation of specific genes.

Differential sensitivity of transcription factors to mustard-damaged DNA.

Nitrogen mustard (bis(2-chloroethyl) methylamine, HN2) inhibited the binding of upstream factors Sp1 and AP2 to their consensus sequences. At concentrations where 50% of the consensus sequence DNA contained at least one lesion, HN2 inhibited formation of the Sp1 complex by 37% (40 microM HN2) and the AP2 complex by 40% (50 microM HN2). The binding of the TATA binding protein (TBP) to the TATA element was also inhibited by HN2, whereas sulphur mustard and the monofunctional sulphur mustard 2-chloroethyl ethyl sulphide (CEES) resulted in a disproportional extent of inhibition with respect to the level of alkylation. The level of alkylation of the TBP oligonucleotide varied significantly at 100 microM drug, with 80, 42 and 15% of HN2, sulphur mustard and CEES, respectively. However, this level of alkylation inhibited formation of the TBP-DNA complex by 70, 70 and 45%, respectively. This differential sensitivity of transcription factors to mustard-induced DNA damage therefore appears to reside dominantly in the stereochemical differences between the specific mustard lesions.

Intravitreal cilia in phakic penetrating eye injury.

BACKGROUND: Intraocular cilia present clinical perplexity due to their radiolucency, the extremely variable ocular response to such cilia, and the inadvisability of using MRI in cases of suspected metallic intraocular foreign bodies (IOFB). METHODS: Two cases of intravitreal cilia associated with phakic penetrating eye injury are described where preoperative CT scan revealed no retained IOFB. RESULTS: B-scan ultrasonography detected intravitreal cilia in one patient and raised this suspicion in the other. One patient presented with endophthalmitis unresponsive to intravitreal antibiotics, the other with culture-negative anterior uveitis. Both underwent vitrectomy and removal of cilia. CONCLUSIONS: Intravitreal cilia should be considered in penetrating eye injuries even in phakic eyes with no radiological evidence of IOFB, especially if associated with endophthalmitis. B-scan ultrasonography may aid detection of intravitreal cilia and thus alter clinical management.

Effect of sulphur mustard on the initiation and elongation of transcription.

Sulphur mustard is a potent alkylating agent that causes severe vesication as well as systemic and genotoxic effects. Despite its long history as a chemical warfare agent, the mechanism of its toxicity remains unknown and no successful pharmacological intervention has yet been found. In this study we have examined the effects of mustard alkylation of DNA on transcriptional processes. Gel mobility shift analysis shows that mustard alkylation of the lac UV5 promoter increases the stability of the promoter-RNA polymerase binary complex. Following formation of the initiation complex and addition of elongation nucleotides, approximately 45% of the RNA polymerase in the initiated complex remained associated with the alkylated promoter, compared to only 7% remaining associated with the unalkylated promoter. For the RNA polymerase able to escape the initiation complex, mustard alkylation of the DNA template resulted in the production of truncated transcripts. Analysis of these truncated transcripts revealed that sulphur mustard alkylates DNA preferentially at 5'-AA, 5'-GG and 5'-GNC sequences on the DNA template strand and this is significantly different from the alkylation sites observed with nitrogen mustard. This study represents the first report at the molecular level of sulphur mustard-induced effects on transcriptional processes.

Retinal detachment complicating scleral-sutured posterior chamber intraocular lens surgery.

Although retinal detachment has been reported in association with sutured posterior chamber intraocular lenses (PCIOL), detailed analysis of the pathogenesis, clinical features and risk factors is lacking. Thirty-nine patients who had undergone surgery for scleral-sutured PCIOL were therefore reviewed, revealing 8 patients with associated retinal tears or detachments. Retinal breaks resulted from vitreous incarceration by the intraocular suture (6), post-operative vitreous detachment (1), preretinal manipulation of the dislocated PCIOL (1), surgical entry-sites (1) and surgical induction of posterior vitreous detachment (1). An axial length > 25 mm was associated with the development of retinal tears (p < 0.05, Fisher's exact test). All patients had attached retina with median visual acuity of 6/12 (range 6/6 to CF) at last follow-up (median 15 months, range 1-41 months). In patients requiring a pars plana approach, careful attention to the posterior hyaloid face, basal gel, surgical entry-sites and suture tract is recommended to reduce the risk of retinal detachment associated with scleral-sutured PCIOL procedures.

The prevalence of eye disease in elderly Bengalis in Tower Hamlets.

The prevalence of eye disease and uncorrected refractive errors in a group of 167 elderly members of the Bangladeshi community which resides in the London Borough of Tower Hamlets was studied. Of the subjects screened 24.6% were found to have a significant and potentially treatable cause of visual loss and a further 32.3% were visually handicapped through the presence of uncorrected refractive errors. A high prevalence (53.3%) of cataract was found in the elderly Bengalis. The high prevalence of eye disease in this ethnic minority group, has important implications for health service planning.

Sulphur mustards inhibit binding of transcription factor AP2 in vitro.

The bifunctional sulphur mustard (bis-(2-chloroethyl)sulphide, HD) and its monofunctional analogue (2-chloroethyl ethyl sulphide, CEES) are both vesicants. In this study, both mustards were shown to rapidly alkylate the AP2 consensus binding sequence incorporated in a 26mer oligonucleotide. The reaction was essentially complete within 10 min under the conditions employed in this study and -95% of the oligonucleotides were alkylated at least once using 500 microM HD and 1 mM CEES. Progressive alkylation of the consensus sequence was parallelled by a decrease in transcription factor binding. Under reaction conditions which alkylated approximately 95% of the oligonucleotides at least once, the binding of cloned human AP2 was reduced by 93 and 76% by HD and CEES, respectively, compared with control values. The interference with binding is a result of alkylation of the DNA and not damage to the transcription factor by mustard or its hydrolysis products. Interference with transcription factor binding would be expected to have a profound influence on the ability of the cell to function normally and to respond to DNA damage and may contribute significantly to the skin damage produced by these compounds.

Nitrogen mustard inhibits transcription and translation in a cell free system.

Nitrogen mustard and its derivatives such as cyclophosphamide, chlorambucil and melphalan are widely used anti-cancer agents, despite their non-specific reaction mechanism. In this study, the effect of alkylation by nitrogen mustard of DNA and RNA (coding for a single protein) was investigated using both a translation system and a coupled transcription/translation system. When alkylated DNA was used as the template for coupled transcription and translation, a single translation product corresponding to the 62 kDa luciferase protein was synthesised. Production of the translated product encoded by this template was inhibited by mustard concentrations as low as 10 nM, and 50% inhibition occurred with 30 nM mustard. A primer extension assay employed to verify alkylation sites on the DNA revealed that all guanine residues on the DNA template are susceptible to alkylation by nitrogen mustard. Similarly, when alkylated RNA was used as the template for protein synthesis, the amount of the 62 kDa luciferase protein decreased with increasing mustard concentration and a range of truncated polypeptides was synthesised. Under these conditions 50% inhibition of translation occurred with approximately 300 nM mustard (i.e. approximately 10 times that required for similar inhibition using an alkylated DNA template). Furthermore, a gel mobility shift assay revealed that mustard alkylation of the RNA template results in the formation of a more stable retarded RNA complex. The functional activity of the luciferase protein decreased with alkylation of both the DNA and RNA templates, with a half-life of loss of activity of 1.1 h for DNA exposed to 50 nM mustard, and 0.5 h for RNA exposed to 50 microM mustard. The data presented support the notion that DNA is a critical molecule in the mode of action of mustards.