Turn-on DNA damage sensors for the direct detection of 8-oxoguanine and photoproducts in native DNA

The integrity of the genetic information in all living organisms is constantly threatened by a variety of endogenous and environmental insults. To counter this risk, the DNA-damage response is employed for repairing lesions and maintaining genomic integrity. However, an aberrant DNA-damage response can potentially lead to genetic instability and mutagenesis, carcinogenesis, or cell death. To directly monitor DNA damage events in the context of native DNA, we have designed two new sensors utilizing genetically fragmented firefly luciferase (split luciferase). The sensors are comprised of a methyl-CpG binding domain (MBD) attached to one fragment of split luciferase for localizing the sensor to DNA (50-80% of the CpG dinucleotide sites in the genome are symmetrically methylated at cytosines), while a damage-recognition domain is attached to the complementary fragment of luciferase to probe adjacent nucleotides for lesions. Specifically, we utilized oxoguanine glycosylase 1 (OGG1) to detect 8-oxoguanine caused by exposure to reactive oxygen species and employed the damaged-DNA binding protein 2 (DDB2) for detection of pyrimidine dimer photoproducts induced by UVC light. These two sensors were optimized and validated using oligonucleotides, plasmids, and mammalian genomic DNA, as well as HeLa cells that were systematically exposed to a variety of environmental insults, demonstrating that this methodology utilizing MBD-directed DNA localization provides a simple, sensitive, and potentially general approach for the rapid profiling of specific chemical modifications associated with DNA damage and repair.

Introduction of human adenomatous polyposis coli gene into Min mice via cationic liposomes

BACKGROUND

The adenomatous polyposis coli (APC) gene is a tumor-suppressor gene involved in familial polyposis coli (FAP), a hereditary disease heralded by the development of hundreds of colorectal adenomas. A mouse model for FAP, the multiple intestinal neoplasia (Min) mouse, develops multiple adenomatous polyps of the large and small intestine similar to their human counterparts. To test the feasibility of introducing normal human APC as a means of either preventing or reversing polyp formation, we describe a method of in vivo transfection of APC into colonic epithelium of the Min mouse.

METHODS

Anesthetized young (4 weeks) Min mice were treated with enemas containing lipofectant and a normal human APC cDNA plasmid every 72 hours for 2 months and then euthanized at 24, 48, and 72 hours after the last treatment. Polymerase chain reaction (PCR) was used to detect the presence of the plasmid DNA.

RESULTS

PCR on the extracted colonic epithelial DNA showed the presence of plasmid DNA up to 72 hours after the last treatment. Expression of the plasmid construct was confirmed by reverse transcriptase-PCR.

CONCLUSIONS

We have demonstrated the repeated introduction and detection of normal human APC in the colonic epithelium of the Min Mouse in vivo during an extended period of time with no toxic side effects by means of our prolonged therapy.

A turn-on split-luciferase sensor for the direct detection of poly(ADP-ribose) as a marker for DNA repair and cell death

Designed sensors comprising split-firefly luciferase conjugated to tandem poly(ADP-ribose) binding domains allow for the direct solution phase detection of picogram quantities of PAR and for monitoring temporal changes in poly(ADP-ribosyl)ation events in mammalian cells.

Cell-mediated immune responses in patients with paracoccidioidomycosis

We tested the hypothesis that symptomatic infection with Paracoccidioides brasiliensis caused impaired host cellular immune responses. In a cross-sectional study in Colombia, the immune responses of thirty-six patients with paracoccidioidomycosis were compared with those of sixty normal individuals. Patients demonstrated increased skin sensitivity to paracoccidioidin (para) and histoplasmin, and reduced reactivity to candidin and dinitrochlorobenzene as compared to controls. The skin test response to tuberculin (PPD) was similar to that of controls. In vitro lymphocyte transformation (LT) and leucocyte migration responses to phytohaemagglutinin and PPD did not differ in patients and controls; these responses to PPD correlated with skin sensitivity in controls, but not in patients. LT and inhibition of leucocyte migration to para were seen in more patients than controls; the latter response correlated with skin sensitivity in controls only. Positive LT to para was associated with absence of antibodies to P. brasiliensis. Analysis of symptomatic patients suggests that the prevalence of para skin test positivity was lowest in patients with the longest duration of disease; this implies decrease in specific cell-mediated immunity with prolonged active infection. Analysis of clinically cured patients suggests that the prevalence of para skin sensitivity and LT to para and PPD increased with time elapsed since diagnosis; this implies development or restoration of immunocompetence upon clinical recovery. Results of a preliminary longitudinal study on the immunological responses of six patients with active paracoccidioidomycosis are compatible with the above observations.

Recurrent nasopharyngeal carcinoma masquerading as acoustic neuroma

This is the first report of recurrent nasopharyngeal carcinoma (NPC) presenting as a cerebellopontine angle mass. The clinical presentation, investigation and management of this case, as well as the confusion and dilemma caused, are discussed. We hope to increase awareness on the multifaceted ways in which recurrent NPC could present and to share the lessons learnt from our management of this unusual and unfortunate case.

Swallowing problems in post irradiated NPC patients

We present three patients with Nasopharyngeal Carcinoma (NPC) developing swallowing problems after radiotherapy as the primary modality of treatment. All patients had advanced stage NPC presenting with enlarged neck nodes and underwent radical external beam radiotherapy. All three patients had both CN X and CN XII palsies and had difficulty in both the oral and pharyngeal phases of swallowing. None of them has any clinical or radiological evidence of local recurrence in the post nasal space and neck or metastasis to the skull base. One patient underwent cricopharyngeal myotomy with epiglottopexy and hyoid suspension which failed and subsequently underwent laryngectomy. Another patient had medialisation thyroplasty and the third underwent a percutaneous endoscopic gastrostomy (PEG).

Squamous cell carcinoma of the temporal bone: diagnosis, treatment and prognosis

Squamous cell carcinoma of the external ear canal is an uncommon condition that is associated with a poor outcome. The development of an accepted staging system has not been forthcoming and this has inhibited the formation of an evidence-based therapeutic protocol. We report the findings in 14 patients with squamous cell carcinoma of the external ear canal treated in our institutions. The most common presenting symptoms were otorrhoea and otalgia. Four patients had a history of chronic ear discharge and one had previous radiotherapy for nasopharyngeal carcinoma. Five patients had facial palsy which was a poor prognostic sign. Only one patient had clinical neck disease. Pre-operative imaging with CT or MRI scans was accurate in determining the extent of tumour involvement. The initial T-staging relied heavily on these findings. With combination treatment involving surgery, radiotherapy and chemotherapy, disease free survival achieved was 69% (9 of 13) over a mean follow-up period of 24.7 months. One patient absconded treatment. Patients with early stage tumours faired better than patients with advanced tumours (100% vs 33%). There was low incidence of involvement of the parotid gland (1 of 7 patients). Patients with facial nerve involvement had a significantly poorer outcome (p = 0.035).

A quality assurance survey to improve communication between ENT specialists and general practitioners

INTRODUCTION

Communication between medical specialists and primary care providers in the community plays a pertinent role in patient care and doctor education. Referral and reply letters are the most common means by which doctors exchange information. Much of clinician time is spent writing letters, but the information or the format in which the letter is written may not meet the needs of the recipient. This study aimed to determine the type of reply letter preferred by general practitioners (GPs) and as such, attempts to improve communication between doctors as part of a quality assurance survey.

METHODS

Questionnaires were mailed out to 1,700 GPs in Singapore. Each questionnaire was accompanied by two sample reply letters from the Department of Otorhinolaryngology-Head and Neck Surgery. The sample letters were written in different formats. Letter 1 was written in a non-structured, free text format and Letter 2 included a structured summary at the beginning. Both letters contained the same amount of information and the same number of words.

RESULTS

A total of 535 replies (response rate 32 percent) were received. Letter 2 was preferred in 97 percent of the responses. 96 percent of the doctors found Letter 2 to be easier to read, while 86 percent felt it contained more information and 64 percent felt that Letter 1 took a longer time to read.

CONCLUSION

Our study shows that there is a preference for diagnosis and treatment plan to be presented in a summary style report rather than as free text. A structured format for reply letters, including the use of headings, allows readers to easily identify the information desired and thus improves the quality of correspondence between specialists and GPs.