Radiation-Associated Lymphopenia in Advanced Prostate Cancer Treated with Contemporary Radiation Techniques

PURPOSE/OBJECTIVE(S)

Lymphocytes play a critical role in the immune system as primary effector cells for cancer control, often depleted by external beam radiation therapy (EBRT). Radiation-associated lymphopenia (RAL) has been shown to be a poor prognostic factor in the management of multiple solid tumors. We hypothesize RAL is similarly observed in advanced prostate cancer (PC) RT with contemporary techniques.

MATERIALS/METHODS

We identified patients with advanced PC (high-risk or clinical/pathologic node-positive) receiving EBRT including lymph node/prostatic lesion boost on a prospective collection protocol for whom 1 baseline and ≥2 subsequent complete blood count (CBC) with differential samples were available, collected at RT end, 3-, 6-, and 12-months post-RT. Clinicopathological characteristics were retrieved from chart review. Common Terminology Criteria for Adverse Events (CTCAE)v5 was used to grade absolute lymphocyte count (ALC); RAL was defined as CTCAEv5 grade ≥2. As these patients received pelvic nodal irradiation, they were pooled with low/intermediate-risk PC cohort treated with high dose-rate (HDR) brachytherapy or prostate alone EBRT with similar CBC timepoints for univariable analysis to understand RT field size effect on RAL.

RESULTS

Between 2019 and 2022, among 17 patients in the low/intermediate-risk PC cohort, 6 patients had grade ≥2 lymphopenia. Among 25 patients in the advanced PC cohort, all received androgen deprivation therapy (ADT), 6 received lymph node boost, and 5 received prostatic lesion boost. At RT end, leukopenia was prominently observed (median nadir count 75.1% of baseline), with ALC as major driver (median nadir count 27.3% of baseline). Grade ≥2 lymphopenia was observed in 76% of patients (n = 19) Of 19 advanced PC patients who reached 6 months post-RT follow-up, median ALC was 53.0% of baseline, and Grade ≥2 lymphopenia remained in 37% (n = 7) of patients. Of 8 advanced PC patients who reached 12 months post-RT follow-up, median ALC was 55.6% of baseline. When evaluating whether RT dose or field size contributed to lower nadir ALC counts, combining the low/intermediate-risk and advanced PC cohorts (n = 42), univariable analysis demonstrated Gleason grade group (p = 0.009), RT field size (p = 0.020), ADT use (p = 0.020), baseline ALC (p = 0.037), and baseline hemoglobin (p = 0.009) were independent predictors of Grade ≥2 lymphopenia. Age, prostatic lesion/lymph node boost, and equivalent dose in 2 Gy/fraction (EQD2) were nonsignificant.

CONCLUSION

Grade ≥2 RAL was observed in patients with advanced PC at end of RT, irrespective of age, RT boost, or EQD2. Lymphocyte recovery from baseline can be prolonged even at 12 months post-RT. Ongoing analyses include expanding data with additional serial CBC, increasing cohort size, and integrating effect of additional systemic therapies. RAL has downstream implications for future chemotherapy/radiopharmaceuticals.

Transition of care of patients with eosinophilic gastrointestinal diseases: Challenges and opportunities

Eosinophilic gastrointestinal disorders (EGID) are a group of allergen-mediated conditions which are characterized by eosinophilic inflammation affecting one or more parts of the gastrointestinal tract. A disproportionately higher number of EGID patients are diagnosed in the pediatric age group. Given the chronic course of EGIDs and lack of curative therapies at this time, majority of the pediatric EGID patients may require continued care well into their adulthood. However, to date, scant data are available regarding the health care transition (HCT), the transition of care (TC), and the effectiveness of transfer of care EGID patients from pediatric-oriented to adult-oriented providers. Herein, we review the lessons learnt from transfer of care of children with other chronic gastrointestinal and allergic conditions, analyze the current knowledge, potential barriers, the role of various stakeholders in successful transfer of care of EGID patients, propose a conceptual framework for HCT and TC of EGID patients, and identify outcome measures to ensure the quality of progression of care.

[Training in reconstructive surgery in sub-Saharan Africa : the « 2nd Chance » model]

Based in Geneva since 2010, 2^nd Chance's mission is the development of reconstructive surgery care in resource-limited countries with a focus on sub-Saharan Africa, through teaching and advocacy activities. We develop the surgical management of patients on the one hand, providing training for African surgical teams. On the other hand, we support surgical procedures for patients, in the areas of reconstructive surgery, giant goiters, obstetric fistulas and anesthesia so that quality care is guaranteed for the long term. Despite the hurdles caused by the COVID crisis, training programs resumed at the end of 2020, with the implementation of the 2021-2025 strategy focusing on patient care and follow-up in the surgical setting through improved peri-operative safety and prevention of complications.

[Femoral hernia in geriatric patient]

When facing an elderly patient with cognitive impairment and unspecific digestive symptoms, the physical examination should include the research of a groin hernia. Additional radiological exam may be required to confirm the diagnosis. Femoral hernia is a diagnostic pitfall, as clinical signs are not always obvious. It occurs late in life and is often found to be already complicated when the patient seeks attention. While the elective surgical treatment is simple, it needs an emergency surgical repair when it is incarcerated that is often associated with intestinal resection and post-operative complications including death.

Hidden sources of joy, fear, and sadness: Explicit versus implicit neural processing of musical emotions

Music is often used to regulate emotions and mood. Typically, music conveys and induces emotions even when one does not attend to them. Studies on the neural substrates of musical emotions have, however, only examined brain activity when subjects have focused on the emotional content of the music. Here we address with functional magnetic resonance imaging (fMRI) the neural processing of happy, sad, and fearful music with a paradigm in which 56 subjects were instructed to either classify the emotions (explicit condition) or pay attention to the number of instruments playing (implicit condition) in 4-s music clips. In the implicit vs. explicit condition, stimuli activated bilaterally the inferior parietal lobule, premotor cortex, caudate, and ventromedial frontal areas. The cortical dorsomedial prefrontal and occipital areas activated during explicit processing were those previously shown to be associated with the cognitive processing of music and emotion recognition and regulation. Moreover, happiness in music was associated with activity in the bilateral auditory cortex, left parahippocampal gyrus, and supplementary motor area, whereas the negative emotions of sadness and fear corresponded with activation of the left anterior cingulate and middle frontal gyrus and down-regulation of the orbitofrontal cortex. Our study demonstrates for the first time in healthy subjects the neural underpinnings of the implicit processing of brief musical emotions, particularly in frontoparietal, dorsolateral prefrontal, and striatal areas of the brain.

Recurrence of Helicobacter pylori infection in Bolivian children and adults after a population-based "screen and treat" strategy

BACKGROUND

Strategies to prevent gastric cancer by decreasing Helicobacter pylori infections in high-prevalence, low-income countries could include a population-based "screen and treat" eradication program.

METHODS

We tested residents of two rural villages for H. pylori infection using urea breath test (UBT), treated infected persons using directly observed therapy (DOT), retested for cure, and retested after 1 year later for H. pylori infection.

FINDINGS

We tested 1,065 (92%) of 1153 residents from two villages in rural Bolivia. Baseline H. pylori prevalence was 80% (95% confidence interval [CI]: 78-84). Age-specific cure rates were similar (≥92%) after DOT. Among those cured, 12% (95% CI: 8-15) had recurrent infection. Age-specific annual H. pylori recurrence rates for combined villages were 20% (95% CI: 10-29) in persons <5 years, 20% (95% CI: 10-29) in 5-9 years, 8% (95% CI: 1-15) in 10-14 years, and 8% (95% CI: 4-12) in persons ≥15 years. Compared with the referent population, those ≥15 years, recurrent infections were significantly more likely in children <5 years (odds ratios [OR] 2.7, 95% CI: 1.2-5.8) and 5-9 years (OR 2.7, 95% CI: 1.4-5.1).

INTERPRETATION

Children <10 years had high H. pylori recurrence rates following a population-based screen and treat program; this H. pylori eradication strategy may not be feasible in high-prevalence, low-income settings.

Minor Amputation and Palliative Wound Care as a Strategy to Avoid Major Amputation in Patients With Foot Infections and Severe Peripheral Arterial Disease

Foot infections occurring in patients with severe peripheral arterial disease (PAD) who are not considered candidates for revascularization and limb salvage efforts are generally treated with major amputations. Herein we describe our early experiences in managing foot infections with minor amputations and palliative wound care as a strategy to avoid the functional disability often associated with major amputations. Patients with severe PAD that underwent minor amputations and subsequent palliative wound care for moderate/severe infections were paired with age-matched controls with PAD that underwent primary major amputations for foot infections. Eleven patients who underwent minor amputations and palliative wound care of 13 limbs were compared to an age-matched cohort of 12 patients undergoing 13 major amputations.The median age was 80 years in both groups. Survival at 1 and 2 years did not differ significantly between groups. All patients who were ambulatory and/or independently living remained so following palliative management; in contrast, major amputation changed ambulatory status in 75% of patients and independent living status in 50%. Palliative management did not result in ascending/systemic sepsis or progressive necrosis. The need for reoperations was uncommon in both groups. In summary, minor amputations and operative drainage with subsequent palliative wound care appears to be a safe management option in patients with severe PAD and moderate or severe foot infections that are not candidates for revascularization. Palliative management may result in less functional impairment than major amputation.

Effects of D-cycloserine on the extinction of appetitive operant learning

Four experiments with rat subjects examined whether D-cycloserine (DCS), a partial NMDA agonist, facilitates the extinction of operant lever-pressing reinforced by food. Previous research has demonstrated that DCS facilitates extinction learning with methods that involve Pavlovian extinction. In the current experiments, operant conditioning occurred in Context A, extinction in Context B, and then testing occurred in both the extinction and conditioning contexts. Experiments 1A and 1B tested the effects of three doses of DCS (5, 15, and 30 mg/kg) on the extinction of lever pressing trained as a free operant. Experiment 2 examined their effects when extinction of the free operant was conducted in the presence of nonresponse-contingent deliveries of the reinforcer (that theoretically reduced the role of generalization decrement in suppressing responding). Experiment 3 examined their effects on extinction of a discriminated operant, that is, one that had been reinforced in the presence of a discriminative stimulus, but not in its absence. A strong ABA renewal effect was observed in all four experiments during testing. However, despite the use of DCS doses and a drug administration procedure that facilitates the extinction of Pavlovian learning, there was no evidence in any experiment that DCS facilitated operant extinction learning assessed in either the extinction or the conditioning context. DCS may primarily facilitate learning processes that underlie Pavlovian, rather than purely operant, extinction.

The E. coli monothiol glutaredoxin GrxD forms homodimeric and heterodimeric FeS cluster containing complexes

Monothiol glutaredoxins (mono-Grx) represent a highly evolutionarily conserved class of proteins present in organisms ranging from prokaryotes to humans. Mono-Grxs have been implicated in iron sulfur (FeS) cluster biosynthesis as potential scaffold proteins and in iron homeostasis via an FeS-containing complex with Fra2p (homologue of E. coli BolA) in yeast and are linked to signal transduction in mammalian systems. However, the function of the mono-Grx in prokaryotes and the nature of an interaction with BolA-like proteins have not been established. Recent genome-wide screens for E. coli genetic interactions reported the synthetic lethality (combination of mutations leading to cell death; mutation of only one of these genes does not) of a grxD mutation when combined with strains defective in FeS cluster biosynthesis (isc operon) functions [Butland, G., et al. (2008) Nature Methods 5, 789-795]. These data connected the only E. coli mono-Grx, GrxD to a potential role in FeS cluster biosynthesis. We investigated GrxD to uncover the molecular basis of this synthetic lethality and observed that GrxD can form FeS-bound homodimeric and BolA containing heterodimeric complexes. These complexes display substantially different spectroscopic and functional properties, including the ability to act as scaffold proteins for intact FeS cluster transfer to the model [2Fe-2S] acceptor protein E. coli apo-ferredoxin (Fdx), with the homodimer being significantly more efficient. In this work, we functionally dissect the potential cellular roles of GrxD as a component of both homodimeric and heterodimeric complexes to ultimately uncover if either of these complexes performs functions linked to FeS cluster biosynthesis.

Pharmacological inhibition of poly(ADP-ribose) polymerase (PARP) activity in PARP-1 silenced tumour cells increases chemosensitivity to temozolomide and to a N3-adenine selective methylating agent

We recently demonstrated that poly(ADP-ribose) polymerase (PARP)-1 is involved in angiogenesis and tumour aggressiveness. In this study we have compared the influence of abrogation of PARP-1 expression by stable gene silencing to that of the pharmacological inhibition of cellular PARP activity using PARP-1/-2 inhibitors on the chemosensitivity of tumour cells to the wide spectrum methylating agent temozolomide (TMZ) and to the N3-adenine selective methylating agent {1-methyl-4-[1-methyl-4-(3-methoxysulfonylpropanamido)pyrrole-2-carboxamido]-pyrrole-2-carboxamido}propane (Me-Lex). Silencing of PARP-1 in melanoma or cervical carcinoma lines enhanced in vitro sensitivity to TMZ and Me- Lex, and induced a higher level of cell accumulation at the G2/M phase of cell cycle with respect to controls. GPI 15427, which inhibits both PARP-1 and PARP-2, increased sensitivity to TMZ and Me-Lex both in PARP-1-proficient and - deficient cells. However, it induced different cell cycle modulations depending on PARP-1 expression, provoking a G2/M arrest only in PARP-1 silenced cells. Treatment of PARP-1 silenced cells with TMZ or Me-Lex resulted in a more extensive phosphorylation of Chk-1 and p53 as compared to PARP-1 proficient cells. The combination of the methylating agents with GPI 15427 increased Chk-1 and p53 phosphorylation both in PARP-1 proficient or deficient cells. When mice challenged with PARP-1 silenced melanoma cells were treated with the TMZ and PARP inhibitor combination there was an additional reduction in tumour growth with respect to treatment with TMZ alone. These results suggest the involvement of PARP-2 or other PARPs, in the repair of DNA damage provoked by methylating agents, highlighting the importance of targeting both PARP-1 and PARP-2 for cancer therapy.

Use of genome-wide scan in women with breast cancer to identify common germline variants that may be associated with recurrence

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Background: Studies of normal DNA variation have identified several common single nucleotide polymorphisms (SNPs) associated with susceptibility to breast cancer. It is not known whether common SNPs are associated with breast cancer outcomes. Methods: Subjects were Ashkenazi Jewish women with familial breast cancer and without BRCA mutations. Subjects were genotyped on an Affymetrix 500K SNP platform in the first phase of a genome-wide association study seeking susceptibility loci (Gold et. al, Proc Natl Acad Sci 2008;105:4340). Clinical variables and outcomes for these women were abstracted from medical records. Using a Cox proportional hazards model, we assessed associations between clinical outcomes and the 111 SNPs that were most significantly associated with susceptibility in the case-control study and heterozygous in the subset of affected patients. Dominant, codominant, and recessive models were explored. A secondary analysis assessed associations with recurrence of 48,562 additional SNPs that were not strongly associated with susceptibility. Results: The 173 subjects were a median of 51 years of age at diagnosis (range 27–74). Median follow-up for surviving subjects was 85.5 months. Most cancers (74.6%) were T1/T2; 62% were N0. Most were ER positive (81.5%), HER2 negative (87.5%). For the entire group, the 5- and 10-year freedom from recurrence was 84% and 72%, respectively. The 5- and 10-year overall survival was 94% and 86%, respectively. Minor alleles at rs6439927 (within CLSTN2,calsyntenin2, a post-synaptic calcium-binding membrane protein, MAF 27%) and rs7943562 ( linked to GALNTL4, an N-acetylgalactosaminyltransferase, MAF 47%) were most strongly associated with disease recurrence (log likelihood ratio chi square P=0.003 and P=0.002, respectively). No additional SNPs from the secondary analysis achieved genome-wide significance. Conclusions: Genome-wide SNP genotyping of women with breast cancer identified two novel loci that may be associated with disease recurrence. Further studies in larger cohorts will be performed to replicate these findings.

No significant financial relationships to disclose.

Mycobacterium tuberculosis expresses methionine sulphoxide reductases A and B that protect from killing by nitrite and hypochlorite

Methionine sulphoxide reductases (Msr) reduce methionine sulphoxide to methionine and protect bacteria against reactive oxygen intermediates (ROI) and reactive nitrogen intermediates (RNI). Many organisms express both MsrA, active against methionine-(S)-sulphoxide, and MsrB, active against methionine-(R)-sulphoxide. Mycobacterium tuberculosis (Mtb) expresses MsrA, which protects DeltamsrA-Escherichia coli from ROI and RNI. However, the function of MsrA in Mtb has not been defined, and it is unknown whether Mtb expresses MsrB. We identified MsrB as the protein encoded by Rv2674 in Mtb and confirmed the distinct stereospecificities of recombinant Mtb MsrA and MsrB. We generated strains of Mtb deficient in MsrA, MsrB or both and complemented the mutants. Lysates of singly deficient strains displayed half as much Msr activity as wild type against N-acetyl methionine sulphoxide. However, in contrast to other bacteria, single mutants were no more vulnerable than wild type to killing by ROI/RNI. Only Mtb lacking both MsrA and MsrB was more readily killed by nitrite or hypochlorite. Thus, MsrA and MsrB contribute to the enzymatic defences of Mtb against ROI and RNI.

Surgical management and long-term outcome of complicated liver hydatid cysts caused by Echinococcus granulosus

BACKGROUND

The aim of this retrospective study was to evaluate clinical presentation and long-term outcome of patients treated surgically for complicated liver hydatid cysts.

PATIENTS AND METHODS

Eighty-four patients with liver hydatid cysts underwent an operation at the Geneva University Hospital between 1980 and 1999. Clinical presentation, postoperative morbidity, mortality, and long-term recurrence rate were evaluated.

RESULTS

Among the 84 patients with liver hydatid disease, 35 patients (41%) presented complicated cysts (ie, cysts that had developed a fistula into adjacent structures or organs). In most patients, the fistula communicated with the biliary tree (n = 25), but we also observed communication with the right lung (n = 3), the right diaphragm (n = 2), liver parenchyma (n = 1), and peritoneal cavity (n = 1). Complete removal of the cystic disease was possible in 24 of 35 patients (70%). In 11 patients, fragments of cysts were not removed because of their location adjacent to main vessels. Postoperatively, 8 patients (23%) developed a severe complication (grade II and III). There were no postoperative deaths, and no recurrences of hydatid disease were observed with a median follow-up of 8.6 years (complete follow-up was obtained in 69% of patients).

CONCLUSIONS

Complicated liver hydatid disease is frequent and was observed in almost half of patients operated for liver hydatid cysts at our center. Using a surgical strategy aimed at complete removal of cystic and pericystic tissue with simultaneous treatment of the fistulous tract, we observed 23% postoperative morbidity, no mortality, and no recurrence of disease with a median follow-up of >8 years.

Role of nucleotide- and base-excision repair in genotoxin-induced neuronal cell death

Base-excision (BER) and nucleotide-excision (NER) repair play pivotal roles in protecting the genomes of dividing cells from damage by endogenous and exogenous agents (i.e. environmental genotoxins). However, their role in protecting the genome of post-mitotic neuronal cells from genotoxin-induced damage is less clear. The present study examines the role of the BER enzyme 3-alkyladenine DNA glycosylase (AAG) and the NER protein xeroderma pigmentosum group A (XPA) in protecting cerebellar neurons and astrocytes from chloroacetaldehyde (CAA) or the alkylating agent 3-methyllexitropsin (Me-Lex), which produce ethenobases or 3-methyladenine (3-MeA), respectively. Neuronal and astrocyte cell cultures prepared from the cerebellum of wild type (C57BL/6) mice or Aag(-/-) or Xpa(-/-) mice were treated with 0.1-50 microM CAA for 24h to 7 days and examined for cell viability, DNA fragmentation (TUNEL labeling), nuclear changes, and glutathione levels. Aag(-/-) neurons were more sensitive to the acute (>20 microM) and long-term (>5 microM) effects of CAA than comparably treated wild type neurons and this sensitivity correlated with the extent of DNA fragmentation and nuclear changes. Aag(-/-) neurons were also sensitive to Me-Lex at comparable concentrations of CAA. In contrast, Xpa(-/-) neurons were more sensitive than either wild type or Aag(-/-) neurons to CAA (>10 microM), but less sensitive than Aag(-/-) neurons to Me-Lex. Astrocytes from the cerebellum of wild type, Aag(-/-) or Xpa(-/-) mice were essentially insensitive to CAA at the concentrations tested. These studies demonstrate that BER and NER are required to protect neurons from genotoxin-induced cell death.

Real-time measurement of in vitro transcription

We have developed a simple method to measure RNA synthesis in real time. In this technique, transcription reactions are performed in the presence of molecular beacons that possess a 2'-O-methylribonucleotide backbone. These probes become fluorescent as they hybridize to nascent RNA during the course of synthesis. We found that molecular beacons synthesized from natural deoxyribonucleotides were not suitable, because they are copied by RNA polymerases, generating complementary product strands that bind to the molecular beacons, causing a conformational change that results in unwanted fluorescence. However, when the molecular beacons are synthesized from 2'-O-methylribonucleotides, they are not copied and fluorescence is strictly dependent upon transcription of the added template. Utilizing these modified molecular beacons, quantitative comparisons were made of the activity of a variety of RNA polymerases and the effect of an inhibitor of transcription was determined.

Differential expression of iron-, carbon-, and oxygen-responsive mycobacterial genes in the lungs of chronically infected mice and tuberculosis patients

Pathogenetic processes that facilitate the entry, replication, and persistence of Mycobacterium tuberculosis (MTB) in the mammalian host likely include the regulated expression of specific sets of genes at different stages of infection. Identification of genes that are differentially expressed in vivo would provide insights into host-pathogen interactions in tuberculosis (TB); this approach might be particularly valuable for the study of human TB, where experimental opportunities are limited. In this study, the levels of selected MTB mRNAs were quantified in vitro in axenic culture, in vivo in the lungs of mice, and in lung specimens obtained from TB patients with active disease. We report the differential expression of MTB mRNAs associated with iron limitation, alternative carbon metabolism, and cellular hypoxia, conditions that are thought to exist within the granulomatous lesions of TB, in the lungs of wild-type C57BL/6 mice as compared with bacteria grown in vitro. Analysis of the same set of mRNAs in lung specimens obtained from TB patients revealed differences in MTB gene expression in humans as compared with mice.

The interference of medical radionuclides with occupational in vivo gamma spectrometry

Radiation workers undergo routine monitoring for the evaluation of external and internal radiation exposures. The monitoring of internal exposures involves gamma spectrometry of the whole body (whole body counting) and measurements of excreta samples. Medical procedures involving internal administration of radioactive radionuclides are widely and commonly used. Medical radionuclides are typically short-lived, but high activities are generally administered, whereas occupational radionuclides are mostly long-lived and, if present, are found generally in relatively smaller quantities. The aim of the present work was to study the interference of some common medical radionuclides (201Tl, 9mTc, 57Co, and 131I) with the detection of internal occupational exposures to natural uranium and to 137Cs. Workers having undergone a medical procedure with one of the radionuclides mentioned above were asked to give frequent urine samples and to undergo whole body and thyroid counting with phoswich detectors operated at the Nuclear Research Center Negev. Urine and whole body counting monitoring were continued as long as radioactivity was detectable by gamma spectrometry. The results indicate that the activity of medical radionuclides may interfere with interpretation of occupational intakes for months after administration.

Long term results after complete or incomplete surgical resection of liver hydatid disease

BACKGROUND

The liver is the organ most frequently infected by hydatid disease and medical therapy alone is ineffective in eliminating the parasite. Surgical options vary from complete resection (e.g. total pericystectomy or hepatectomy) to limited procedures (e.g. percutaneous aspiration or unroofing of cysts). The aim of this study was to determine the long-term outcome after complete or partial resection of liver hydatid cysts.

PATIENTS AND RESULTS

Between 1980 and 1996, 78 patients were operated upon at our institution for liver hydatid cysts. In Group 1, complete resection was achieved in 57 patients (73 %), whereas in Group 2, incomplete resection was performed in 21 patients (27 %), due to multiplicity, bilaterality of cysts or close contact between a cyst and portal or hepatic veins. The post-operative morbidity in Groups 1 and 2, was 31 % and 47 % (N.S.), respectively. Mean duration of hospital stay was 17 and 26 days (p=0.004), respectively. Recurrence rate of hydatid disease after a mean follow-up of 6.6 years was 0 % and 12% (N.S.), respectively. There was no mortality in either group.

CONCLUSIONS

Complete surgical resection of hepatic hydatid disease should be attempted whenever possible. Our results, with a mean follow-up of 6.6 years, indicate limited post-operative debilitating complications, low recurrence rate and no mortality.

Long term results after complete or incomplete surgical resection of liver hydatid disease

BACKGROUND

The liver is the organ most frequently infected by hydatid disease and medical therapy alone is ineffective in eliminating the parasite. Surgical options vary from complete resection (e.g. total pericystectomy or hepatectomy) to limited procedures (e.g. percutaneous aspiration or unroofing of cysts). The aim of this study was to determine the long-term outcome after complete or partial resection of liver hydatid cysts.

PATIENTS AND RESULTS

Between 1980 and 1996, 78 patients were operated upon at our institution for liver hydatid cysts. In Group 1, complete resection was achieved in 57 patients (73 %), whereas in Group 2, incomplete resection was performed in 21 patients (27 %), due to multiplicity, bilaterality of cysts or close contact between a cyst and portal or hepatic veins. The post-operative morbidity in Groups 1 and 2, was 31 % and 47 % (N.S.), respectively. Mean duration of hospital stay was 17 and 26 days (p=0.004), respectively. Recurrence rate of hydatid disease after a mean follow-up of 6.6 years was 0 % and 12% (N.S.), respectively. There was no mortality in either group.

CONCLUSIONS

Complete surgical resection of hepatic hydatid disease should be attempted whenever possible. Our results, with a mean follow-up of 6.6 years, indicate limited post-operative debilitating complications, low recurrence rate and no mortality.

ideR, An essential gene in mycobacterium tuberculosis: role of IdeR in iron-dependent gene expression, iron metabolism, and oxidative stress response

The mycobacterial IdeR protein is a metal-dependent regulator of the DtxR (diphtheria toxin repressor) family. In the presence of iron, it binds to a specific DNA sequence in the promoter regions of the genes that it regulates, thus controlling their transcription. In this study, we provide evidence that ideR is an essential gene in Mycobacterium tuberculosis. ideR cannot normally be disrupted in this mycobacterium in the absence of a second functional copy of the gene. However, a rare ideR mutant was obtained in which the lethal effects of ideR inactivation were alleviated by a second-site suppressor mutation and which exhibited restricted iron assimilation capacity. Studies of this strain and a derivative in which IdeR expression was restored allowed us to identify phenotypic effects resulting from ideR inactivation. Using DNA microarrays, the iron-dependent transcriptional profiles of the wild-type, ideR mutant, and ideR-complemented mutant strains were analyzed, and the genes regulated by iron and IdeR were identified. These genes encode a variety of proteins, including putative transporters, proteins involved in siderophore synthesis and iron storage, members of the PE/PPE family, a membrane protein involved in virulence, transcriptional regulators, and enzymes involved in lipid metabolism.

The use of an oral fluid immunoglobulin G ELISA for the detection of Helicobacter pylori infection in children

BACKGROUND

Enzyme linked immunosorbent assay (ELISA) evaluation of oral fluid immunoglobulin G (IgG) antibodies to Helicobacter pylori is a unique approach for both epidemiological studies and the diagnosis of infection, especially in children. The use of oral fluid sampling to evaluate specific H. pylori IgG antibodies has advantages over serum, including reduced biohazard risk and noninvasive collection. Oral fluid sampling is fast and involves minimal patient discomfort. Since children facilitate transmission of H. pylori infection, a simple, accurate, noninvasive diagnostic test is necessary for large epidemiologic studies. The aim of our study was to evaluate a new oral fluid ELISA for detection of IgG antibodies to H. pylori in children.

MATERIALS AND METHODS

We compared this new oral fluid ELISA with the HM-CAPTM serum ELISA and gastric biopsy histology using 779 oral fluid samples from children collected at 11 clinical sites across the United States. This cohort included 315 children symptomatic for abdominal pain and 464 asymptomatic. All samples were evaluated in a double blind manner. The oral fluid ELISA demonstrated a sensitivity of 76.2% and a specificity of 94.0% in children 2 months old to 201/2 years, as compared with the HM-CAPTM serologic assay. The assay's sensitivity improved to 81.3% in children aged 5 or greater and the specificity remained at 94.0%. When compared with gastric biopsy histology in the same age group, the oral fluid ELISA demonstrated a sensitivity of 71.7% and a specificity of 90.4%.

RESULTS

This new oral fluid ELISA is moderately sensitive and offers a very specific method for detecting H. pylori infection in older children, but it is of little value in children under the age of 5 years.

CONCLUSIONS

Overall, we conclude that this oral fluid ELISA does not appear to be a helpful clinical tool for the diagnosis of H. pylori infection in children.

Robot printing of reverse dot blot arrays for human mutation detection

We report on a generally useful, partially automated, human mutation detection method based upon printing moderate density oligonucleotide arrays using a biorobot on activated nylon membranes. The Beckman Biomek 2000 was adapted to this task through fabrication of aluminum membrane filter holders and the development of an addressable Tool Command Language (Tcl) program, which can be invoked through BioScript. During program execution, a robot arm is moved along the x, y, and z axes to expel liquid, without dripping, from disposable barrier pipette tips and then to touch the drops on preactivated membranes. Printed arrays consist of alternating rows of oligonucleotides containing normal and mutant sequences. Hybridization of biotin labeled polymerase chain reaction products derived from human patient genomic DNA samples are visualized using chemiluminescent or chromogenic indicators. This technique allows unequivocal genotyping of 32 mutations at the beta-thalassemia locus (11p15.5) and of 34 mutations and one polymorphism at the cystic fibrosis transconductance membrane regulator locus (7p35).

The Mycobacterium tuberculosis IdeR is a dual functional regulator that controls transcription of genes involved in iron acquisition, iron storage and survival in macrophages

In this work, we characterize genes in Mycobacterium tuberculosis that are regulated by IdeR (iron-dependent regulator), an iron-responsive DNA-binding protein of the DtxR family that has been shown to regulate iron acquisition in Mycobacterium smegmatis. To identify some of the genes that constitute the IdeR regulon, we searched the M. tuberculosis genome for promoter regions containing the consensus IdeR/DxR binding sequence. Genes preceded by IdeR boxes included a set encoding proteins necessary for iron acquisition, such as the biosynthesis of siderophores (mbtA, mbtB, mbtI), aromatic amino acids (pheA, hisE, hisB-like) and others annotated to be involved in the synthesis of iron-storage proteins (bfrA, bfrB). Some putative IdeR-regulated genes identified in this search encoded proteins predicted to be engaged in the biosynthesis of lipopolysaccharide (LPS)-like molecules (rv3402c), lipids (acpP) and peptidoglycan (murB). We analysed four promoter regions containing putative IdeR boxes, mbtA-mbtB, mbI, rv3402c and bfrA-bfd, for interaction with IdeR and for iron-dependent expression. Gel retardation experiments and DNase footprinting analyses with purified IdeR showed that IdeR binds to these IdeR boxes in vitro. Analysis of the promoters by primer extension indicated that the IdeR boxes are located near the -10 position of each promoter, suggesting that IdeR acts as a transcriptional repressor by blocking RNA polymerase binding. Using quantitative reverse transcriptase-polymerase chain reaction (RT-PCR) coupled to molecular beacons, we showed that mRNA levels of mbtA, mbtB, mbtI, rv3402c and bfd are induced 14- to 49-fold in cultures of M. tuberculosis starved for iron, whereas mRNA levels of bfrA decreased about threefold. We present evidence that IdeR not only acts as a transcriptional repressor but also functions as an activator of bfrA. Three of the IdeR- and iron-repressed genes, mbtB, mbtI and rv3402c, were induced during M. tuberculosis infection of human THP-1 macrophages.

Identification and sequencing of the Syrian Golden hamster (Mesocricetus auratus) p16(INK4a) and p15(INK4b) cDNAs and their homozygous gene deletion in cheek pouch and pancreatic tumor cells

Previous studies have shown that the p16(INK4a) tumor suppressor gene is inactivated in up to 98% of human pancreatic cancer specimens and 83% of oral squamous cell carcinomas. Inactivation of the related p15(INK4b) gene has also been identified in a number of tumors and cell lines, however, its role as an independent tumor suppressor remains to be elucidated. Chemically-induced tumors in the Syrian Golden hamster (Mesocricetus auratus) have been shown to be excellent representative models for the comparative development and progression of a number of human malignancies. The purpose of this study was to determine the importance of the p16(INK4a) and p15(INK4b) genes in two experimental hamster models for human pancreatic and oral carcinogenesis. First, hamster p16(INK4a) and p15(INK4b) cDNAs were cloned and sequenced. The hamster p16(INK4a) cDNA open reading frame (ORF) shares 78%, 80%, and 81% identity with the human, mouse, and rat p16(INK4a) sequences, respectively. Similarly, the hamster p15(INK4b) cDNA ORF shares 82% and 89% sequence identity with human and mouse p15(INK4b), respectively. Second, a deletion analysis of hamster p16(INK4a) and p15(INK4b) genes was performed for several tumorigenic and non-tumorigenic hamster cell lines and revealed that both p16(INK4a) and p15(INK4b) were homozygously deleted in a cheek pouch carcinoma cell line (HCPC) and two pancreatic adenocarcinoma cell lines (KL5B, H2T), but not in tissue matched, non-tumorigenic cheek pouch (POT2) or pancreatic (KL5N) cell lines. These data strongly suggest that homozygous deletion of the p16(INK4a) and p15(INK4b) genes plays a prominent role in hamster pancreatic and oral tumorigenesis, as has been well established in correlative studies in comparable human tumors. Furthermore, this study supports the comparative importance of the hamster pancreatic and cheek pouch models of carcinogenesis in subsequent mechanistic-, therapeutic-, and preventive-based studies aimed at providing important translational data applicable to pancreatic adenocarcinoma and oral squamous cell carcinoma in humans.

Incorporation of a cationic aminopropyl chain in DNA hairpins: thermodynamics and hydration

We report on the physicochemical effects resulting from incorporating a 5-(3-aminopropyl) side chain onto a 2'-deoxyuridine (dU) residue in a short DNA hairpin. A combination of spectroscopy, calorimetry, density and ultrasound techniques were used to investigate both the helix-coil transition of a set of hairpins with the following sequence: d(GCGACTTTTTGNCGC) [N = dU, deoxythymidine (dT) or 5-(3-aminopropyl)-2'-deoxyuridine (dU*)], and the interaction of each hairpin with Mg(2+). All three molecules undergo two-state transitions with melting temperatures (T(M)) independent of strand concentration that indicates their intramolecular hairpin formation. The unfolding of each hairpin takes place with similar T(M) values of 64-66 degrees C and similar thermodynamic profiles. The unfavorable unfolding free energies of 6.4-6.9 kcal/mol result from the typical compensation of unfavorable enthalpies, 36-39 kcal/mol, and favorable entropies of approximately 110 cal/mol. Furthermore, the stability of each hairpin increases as the salt concentration increases, the T(M)-dependence on salt yielded slopes of 2.3-2.9 degrees C, which correspond to counterion releases of 0.53 (dU and dT) and 0.44 (dU*) moles of Na(+) per mole of hairpin. Absolute volumetric and compressibility measurements reveal that all three hairpins have similar hydration levels. The electrostatic interaction of Mg(2+) with each hairpin yielded binding affinities in the order: dU > dT > dU*, and a similar release of 2-4 electrostricted water molecules. The main result is that the incorporation of the cationic 3-aminopropyl side chain in the major groove of the hairpin stem neutralizes some local negative charges yielding a hairpin molecule with lower charge density.

Poly (ADP-ribose) polymerase inhibitor increases apoptosis and reduces necrosis induced by a DNA minor groove binding methyl sulfonate ester

The poly(ADP-ribose) polymerase (PARP) is involved in cell recovery from DNA damage, such as methylation of N3-adenine, that activates the base excision repair process. In the present study we demonstrated that MeOSO(2)(CH(2))(2)-lexitropsin (Me-Lex), a methylating agent that almost exclusively produces N3-methyladenine, induced different modalities of cell death in human leukemic cell lines, depending on the presence of PARP inhibitor. Growth inhibition, provoked by the combination of Me-Lex and PARP inhibitor, was associated with a marked down-regulation of c-myc, increased generation of single strand breaks and apoptosis. When used as single agent, at concentrations that saturated cell repair ability, Me-Lex induced mainly cell death by necrosis. Surprisingly, addition of a PARP inhibitor enhanced apoptosis and reduced the early appearance of necrosis. Telomerase activity was completely suppressed in cells exposed to Me-Lex alone, by 24 h after treatment, whereas it did not change when Me-Lex was combined with PARP inhibitor. Thereafter, inhibition of telomerase was observed with both treatments. The results suggest new insights on different modalities of cell death induced by high levels of N3-methyladenine per se, or by the methylated base in the presence of PARP inhibitor.

p53 mutants can often transactivate promoters containing a p21 but not Bax or PIG3 responsive elements

The human p53 protein acts mainly as a stress inducible transcription factor transactivating several genes involved in cell cycle arrest (e.g. p21) or apoptosis (e.g. Bax, PIG3). Roughly half of all human tumours contains p53 missense mutations. Virtually all tumour-derived p53 mutants are unable to activate Bax transcription but some retain the ability to activate p21 transcription. Identification of these mutants may have valuable clinical implications. We have determined the transactivation ability of 77 p53 mutants using reporter yeast strains containing a p53-regulated ADE2 gene whose promoter is regulated by p53 responsive elements derived from the regulatory region of the p21, Bax and PIG3 genes. We also assessed the influence of temperature on transactivation. Our results indicate that a significant proportion of mutants [16/77 (21%); 10/64 (16%) considering only tumour-derived mutants] are transcriptionally active, especially with the p21 promoter. Discriminant mutants preferentially affect less conserved (P<0.04, Fisher's exact test), more rarely mutated (P<0.006, Fisher's exact test) amino acids. Temperature sensitivity is frequently observed, but is more common among discriminant than non-discriminant mutants (P<0.003, Fisher's exact test). Finally, we extended the analysis to a group of mutants isolated in BRCA-associated tumours that surprisingly were indistinguishable from wild type in standard transcription, growth suppression and apoptosis assays in human cells, but showed gain of function in transformation assays. The incidence of transcriptionally active mutations among this group was significantly higher than in the panel of mutants studied previously (P<0.001, Fisher's exact test). Since it is not possible to predict the behaviour of a mutant from first principles, we propose that the yeast assay be used to compile a functional p53 database and fill the gap between the biophysical, pharmacological and clinical fields.

Two rare confounding polymorphisms proximal to the factor V Leiden mutation

BACKGROUND

Comprehensive assessment of thrombophilia risk includes characterization of the R506Q (Leiden) mutation in factor V in many patients. Although activated protein C resistance is often assessed by means of a coagulation test, molecular interrogation of the G1691A mutation provides confirmation and interpretive utility in patients undergoing anticoagulation. Many molecular methods are available to provide genotyping at this locus. Among these, PCR-restriction fragment length polymorphism (RFLP) is widely used. Unfortunately, because this common mutation is 11 bp from the 3' end of exon 10, one PCR primer often anneals within intron 10. As a consequence, polymorphism can confound test results.

METHOD AND RESULTS

In the course of a clinical diagnostic test of 15,301 patients, two samples repeatedly showed two different unusual electrophoretic mobilities after PCR and restriction enzyme digestion. After stripping patient identifiers and entering a research protocol, the amplicons from these DNAs were sequenced in parallel with normal and heterozygous G1691A control genomic DNA samples. This sequencing showed two novel polymorphisms, each mapping to intron 10.

CONCLUSION

PCR-RFLP-based methods rely on sequence conservation in the interrogated region. Amplification of mutated loci adjacent to introns present a special risk for confounding restriction patterns. Sequencing amplicons with reproducibly unusual restriction patterns resolved the paradoxical restriction pattern in this case.

Evidence in Escherichia coli that N3-methyladenine lesions induced by a minor groove binding methyl sulfonate ester can be processed by both base and nucleotide excision repair

It has been previously reported that a neutral DNA equilibrium binding agent based on an N-methylpyrrolecarboxamide dipeptide (lex) and modified with an O-methyl sulfonate ester functionality (MeOSO(2)-lex) selectively affords N3-methyladenine lesions. To study the interaction of the neutral lex dipeptide with calf thymus DNA, we have prepared stable, nonmethylating sulfone analogues of MeOSO(2)-lex that are neutral and cationic. Thermodynamic studies show that both the neutral and monocationic sulfone compounds bind to DNA with K(b)'s of 10(5) in primarily entropy-driven reactions. To determine how the cytotoxic N3-methyladenine adduct generated from MeOSO(2)-lex is repaired in E. coli, MeOSO(2)-lex was tested for toxicity in wild-type E. coli and in mutant strains defective in base excision repair (tag and/or alkA glycosylases or apn endonuclease), nucleotide excision repair (uvrA), and both base and nucleotide excision repair (tag/alkA/uvrA). The results clearly demonstrate the cellular toxicity of the N3-methyladenine lesion, and the protective role of base excision glycosylase proteins. A novel finding is that in the absence of functional base excision glycosylases, nucleotide excision repair can also protect cells from this cytotoxic minor groove lesion. Interaction between base and nucleotide excision repair systems is also seen in the protection of cells treated with cis-diamminedichloroplatinum(II) but not with anti-(+/-)-r-7,t-8-dihydroxy-t-9,10-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene.

Diagnosis of Fragile X syndrome by Southern blot hybridization using a chemiluminescent probe: a laboratory protocol

BACKGROUND

Unequivocal molecular characterization of the FMR-1 triplet expansion region requires the combined use of PCR to amplify normal- and premutation-length alleles and Southern analysis to detect fully expanded alleles and assess methylation. We provide a detailed laboratory protocol, which can be generalized, for the preparation and use of a digoxigenin (DIG)-labeled probe for Southern analysis of genomic DNA digested with EcoR I and Eag I.

METHODS AND RESULTS

The StB12.3 probe cloned in a recombinant plasmid is labeled by PCR amplification using M13 primers, in the presence of DIG-11-dUTP. Hybridization signal is visualized on x-ray film using an alkaline phosphatase anti-DIG-Fab conjugate in the presence of chemiluminescent substrate CDP-Star (Tropix, Bedford, MA). We provide details of probe labeling and quantitation, preparation, and hybridization of the alkaline Southern blot and an analysis of data.

CONCLUSION

Several publications describe PCR-based methods that claim to preclude the requirement of Southern analysis for the diagnosis of Fragile X syndrome. However, none of these is as robust as the method described here. Currently, rapid Southern analysis is an important part of molecular detection of all possible normal and abnormal FMR-1 alleles. This nonradioactive approach is a convenient and rapid alternative to using a radioactive probe.

Cytotoxic and clastogenic effects of a DNA minor groove binding methyl sulfonate ester in mismatch repair deficient leukemic cells

Mismatch repair deficiency contributes to tumor cell resistance to O6-guanine methylating compounds and to other antineoplastic agents. Here we demonstrate that MeOSO2(CH2)2-lexitropsin (Me-Lex), a DNA minor groove alkylating compound which generates mainly N3-methyladenine, has cytotoxic and clastogenic effects in mismatch repair-deficient leukemic cells. Moreover, MT-1 cells, which express p53 upon drug treatment and possess low levels of 3-methylpurine DNA glycosylase activity, are more susceptible to cytotoxicity induced by Me-Lex, with respect to p53-null and 3-methylpurine DNA glycosylase-proficient Jurkat cells. In both cell lines, the poly(ADP-ribose) polymerase inhibitor 3-aminobenzamide, which inhibits base excision repair capable of removing N-methylpurines, increases cytotoxicity and clastogenicity induced by Me-Lex or by temozolomide, which generates low levels of N3-methyl adducts. The enhancing effect is more evident at low Me-Lex concentrations, which induce a level of DNA damage that presumably does not saturate the repair ability of the cells. Nuclear fragmentation induced by Me-Lex + 3-aminobenzamide occurs earlier than in cells treated with the single agent. Treatment with Me-Lex and 3-aminobenzamide results in augmented expression of p53 protein and of the X-ray repair cross-complementing 1 transcript (a component of base excision repair). These results indicate that N3-methyladenine inducing agents, alone or combined with poly(ADP-ribose) polymerase inhibitors, could open up novel chemotherapeutic strategies to overcome drug resistance in mismatch repair-deficient leukemic cells.

Testing environment for single-gene disorders in U.S. reference laboratories

Molecular diagnosis is the detection of pathogenic mutations in DNA and RNA samples prepared from at-risk patients. Principles underlying DNA-based diagnosis originate from localization and identification of genes responsible for human disease and the characterization of pathogenic mutations; new diagnostic tests are in constant development. Indications for testing include diagnosis, carrier risk revision, prenatal diagnosis, presymptomatic diagnosis, and population screening. The majority of DNA diagnoses are performed in a reference laboratory in which the referring physician, rather that the patient, is the client of the laboratory. Thus, the role of the genetic counselor in a reference laboratory is quite different from traditional clinical practice. As with all clinical laboratory tests, molecular diagnostics are interpreted within the context of the patient's overall clinical presentation and are overlaid with regulatory programs of quality assurance, quality improvement, and quality control. The greatest challenges facing the clinical laboratory are genetic heterogeneity, cost control, regulatory and patent compliance, technology transfer, and the genetic education of the referring physician.

The yeast p53 functional assay: a new tool for molecular epidemiology. Hopes and facts

The assumption of molecular epidemiology that carcinogens leave fingerprints has suggested that analysis of the frequency, type, and site of mutations in genes frequently altered in carcinogenesis may provide clues to the identification of the factors contributing to carcinogenesis. In this mini-review, we revise the development, and validation of the yeast-based p53 functional assay as a new tool for molecular epidemiology. We show that this assay has some very interesting virtues but also has some drawbacks. The yeast functional assay can be used to determine highly specific mutation fingerprints in the human p53 cDNA sequence. Discrimination is possible when comparing mutation spectra induced by sufficiently different mutagens. However, we also reported that the same carcinogen may induce distinguishable mutation spectra due to known influencing factors.

Identification and characterization of two divergently transcribed iron regulated genes in Mycobacterium tuberculosis

SETTING

Low iron availability in the host induces the expression of iron acquisition systems and virulence genes in many pathogens. IdeR is a mycobacterial iron dependent regulator that controls the iron starvation and oxidative stress responses in Mycobacterium smegmatis. It is important to determine the role of IdeR and its regulon in M. tuberculosis, as identification of iron regulated genes can aid in the design of new drugs and generation of attenuated strains.

OBJECTIVE

A potential IdeR binding site was found in the M. tuberculosis genome flanked by two divergently oriented open reading frames, irg1 and irg2. The aim of this study was to determine whether irg1 and irg2 were iron and IdeR regulated genes.

DESIGN

Interaction of IdeR with the putative binding sequence was examined by gel shift and footprinting assays. Transcriptional fusions of irg1 and irg2 to IacZ were used to study the effect of iron levels on the expression of these genes.

RESULTS

IdeR binds to the predicted binding site, which overlaps with the irg1 promoter. irg1 and irg2 expression was decreased by iron in M. tuberculosis and in wild type M. smegmatis, but not in a M. smegmatis ideR mutant.

CONCLUSION

Two M. tuberculosis iron/IdeR regulated genes were identified. irg1 is predicted to be the M. tuberculosis hisE gene, which is involved in histidine biosynthesis. It is directly upstream of the M. tuberculosis hisG. irg2 encodes a putative membrane protein that is a member of the PPE family.

Extra and intracellular expression of Mycobacterium tuberculosis genes

To understand how Mycobacterium tuberculosis survives and grows in an infected host, we are studying the mycobacterial transcriptional machinery and its response to stresses encountered in vitro and in vivo. Much has been learned about sigma factors and other transcriptional regulators concerning their roles in controlling mycobacterial gene expression. It has recently been shown that sigma A is the essential housekeeping sigma factor and the alternative sigma factor sigma B, not essential for growth in a laboratory setting, is required for a robust protective response to various environmental stresses. We are also studying the mechanism by which the R522H mutation in sigma A prevents the transcription of certain genes, including some that are believed necessary for virulence. Also under investigation is the mycobacterial iron acquisition apparatus and its regulation, as metabolism of this essential element plays a key role in microbial pathogenesis. We have identified and characterized the major mycobacterial iron regulator IdeR that blocks the synthesis of the iron uptake machinery and have identified target genes in M. smegmatis and M. tuberculosis that are directly repressed by IdeR. Recent studies have examined the control of M. tuberculosis gene expression in vivo. Among these new approaches are an in vivo expression technology system to identify M. tuberculosis genes that are induced in macrophages and mice and a novel RT-PCR method that allows an accurate comparison between the levels of specific mRNAs in M. tuberculosis grown in vitro with those found in bacteria growing in human macrophages.

Relationship between DNA methylation and mutational patterns induced by a sequence selective minor groove methylating agent

Me-lex, a methyl sulfonate ester appended to a neutral N-methylpyrrolecarboxamide-based dipeptide, was synthesized to preferentially generate N3-methyladenine (3-MeA) adducts which are expected to be cytotoxic rather than mutagenic DNA lesions. In the present study, the sequence specificity for DNA alkylation by Me-lex was determined in the p53 cDNA through the conversion of the adducted sites into single strand breaks and sequencing gel analysis. In order to establish the mutagenic and lethal properties of Me-lex lesions, a yeast expression vector harboring the human wild-type p53 cDNA was treated in vitro with Me-lex, and transfected into a yeast strain containing the ADE2 gene regulated by a p53-responsive promoter. The results showed that: 1) more than 99% of the lesions induced by Me-lex are 3-MeA; 2) the co-addition of distamycin quantitatively inhibited methylation at all minor groove sites; 3) Me-lex selectively methylated A's that are in, or immediately adjacent to, the lex equilibrium binding sites; 4) all but 6 of the 33 independent mutations were base pair substitutions, the majority of which (17/33; 52%) were AT-targeted; 5) AT --> TA transversions were the predominant mutations observed (13/33; 39%); 6) 13 out of 33 (39%) independent mutations involved a single lex-binding site encompassing positions A600-602 and 9 occurred at position 602 which is a real Me-lex mutation hotspot (n = 9, p < 10(-6), Poisson's normal distribution). A hypothetical model for the interpretation of mutational events at this site is proposed. The present work is the first report on mutational properties of Me-lex. Our results suggest that 3-MeA is not only a cytotoxic but also a premutagenic lesion which exerts this unexpected property in a strict sequence-dependent manner.

Transcriptional control of the iron-responsive fxbA gene by the mycobacterial regulator IdeR

Exochelin is the primary extracellular siderophore of Mycobacterium smegmatis, and the iron-regulated fxbA gene encodes a putative formyltransferase, an essential enzyme in the exochelin biosynthetic pathway (E. H. Fiss, Y. Yu, and W. R. Jacobs, Jr., Mol. Microbiol. 14:557-569, 1994). We investigated the regulation of fxbA by the mycobacterial IdeR, a homolog of the Corynebacterium diphtheriae iron regulator DtxR (M. P. Schmitt, M. Predich, L. Doukhan, I. Smith, and R. K. Holmes, Infect. Immun. 63:4284-4289, 1995). Gel mobility shift experiments showed that IdeR binds to the fxbA regulatory region in the presence of divalent metals. DNase I footprinting assays indicated that IdeR binding protects a 28-bp region containing a palindromic sequence of the fxbA promoter that was identified in primer extension assays. fxbA regulation was measured in M. smegmatis wild-type and ideR mutant strains containing fxbA promoter-lacZ fusions. These experiments confirmed that fxbA expression is negatively regulated by iron and showed that inactivation of ideR results in iron-independent expression of fxbA. However, the levels of its expression in the ideR mutant were approximately 50% lower than those in the wild-type strain under iron limitation, indicating an undefined positive role of IdeR in the regulation of fxbA.

N-(2-chloroethyl)-N-nitrosourea tethered to lexitropsin induces minor groove lesions at the p53 cDNA that are more cytotoxic than mutagenic

Many different N-chloroethyl-N-nitrosourea (CENU) derivatives have been synthesized in an attempt to minimize carcinogenic activity while favoring antineoplastic activity. CENU derivatives linked to the dipeptide lexitropsin (lex) showed significant changes in groove- and sequence-selective DNA alkylation inducing thermolabile N3-alkyladenines (N3-Alkyl-As) at lex equilibrium binding sites. CENU-lex sequence specificity for DNA alkylation was determined using 32P-end-labeled restriction fragments of the p53 cDNA. The adducted sites were converted into single-strand breaks by sequential heating at neutral pH and exposure to piperidine. To establish the mutagenic and lethal properties of CENU-lex-specific lesions, a yeast expression vector harboring a human wild-type p53 cDNA was treated in vitro with CENU-lex and transfected into a yeast strain containing the ADE2 gene regulated by a p53-responsive promoter. p53 mutants were isolated from independent ade- transformants. The results revealed that: (a) CENU-lex preferentially induces N3-Alkyl-A at specific lex equilibrium binding sites, the formations of which are strongly inhibited by distamycin; (b) reactivity toward Gs is still present, albeit to a lesser extent when compared to N-(2-chloroethyl)-N-cyclohexyl-N-nitrosourea and to CENU; (c) 91% of the 49 CENU-lex p53 mutations (45 of 49) were bp substitutions, 29 of which were GC-->AT transitions, mainly at 5' purine G sites; (d) all AT-targeted mutations but one were AT-->TA transversions; (e) the distribution of the CENU-lex mutations along the p53 cDNA was not random, with position 273 (codon 91), where only GC-->AT transitions were observed, being a real (n = 3, P < 0.0002) CENU-lex mutation hot spot; and (f) a shift in DNA alkylation sites between lesion spectra induced by CENU-lex and N-(2-chloroethyl-N-cyclohexyl-N-nitrosourea was associated with an increased lethality and a decreased mutagenicity, whereas no dramatic change in mutational specificity was observed. Hence, it is tempting to conclude that, in this experimental system, N3-Alkyl-A is more lethal than mutagenic, whereas O6-alkylguanine is a common premutational lesion formed at non-lex binding sites. These results suggest that CENU derivatives with virtually absolute specificity for A residues would make targeting of lethal, nonmutagenic lesions at A+T-rich regions possible, and this may represent a new strategy for the development of new chemotherapeutic agents with a higher therapeutic index.

Quantitative and qualitative analysis of DNA methylation at N3-adenine by N-methyl-N-nitrosourea

The sequence-specific alkylation of DNA by N-methyl-N-nitrosourea (MNU) has been demonstrated for the minor groove N3-methyladenine (N3-MeAde) adduct using neutral thermal hydrolysis and polyacrylamide sequencing gels. The ratio of relative yields of N7- and N3-MeAde and N7-methylguanine (N7-MeGua) is approximately 0.03:0. 15:1.00, respectively, on the basis of the gel data, and these values are comparable to relative yields determined by bulk digestion of MNU-methylated DNA when HPLC was used to analyze the individual adducts. In contrast to the methylation at N7-guanine (N7-Gua) by MNU, alkylation at Ade shows minimal sequence selectivity. Similar to the methylation at N7-Gua, formation of N3-MeAde by MNU is inhibited by 50-200 mM concentrations of NaCl and DNA binding cations, including distamycin and spermine. However, N3-MeAde formation at Ade residues within methidiumpropyl-EDTA-Fe(II) footprinted distamycin DNA affinity binding regions is selectively inhibited at low concentrations of distamycin relative to Ade sites outside of ligand binding regions, and N7-Gua within or outside the distamycin binding regions. HPLC analysis shows that distamycin also quantitatively inhibits the production of N3-methylguanine when calf thymus DNA is treated with MNU or methyl methanesulfonate. The specific inhibitory effect of distamycin, which binds in the minor groove at Ade/Thy-rich sequences, provides additional evidence that the predominant DNA lesion detected at Ade by sequencing gel analysis involves minor groove N3-MeAde modifications.