A sterol-PI(4)P exchanger modulates the Tel1/ATM axis of the DNA damage response

Upon DNA damage, cells activate the DNA damage response (DDR) to coordinate proliferation and DNA repair. Dietary, metabolic, and environmental inputs are emerging as modulators of how DNA surveillance and repair take place. Lipids hold potential to convey these cues, although little is known about how. We observed that lipid droplet (LD) number specifically increased in response to DNA breaks. Using Saccharomyces cerevisiae and cultured human cells, we show that the selective storage of sterols into these LD concomitantly stabilizes phosphatidylinositol-4-phosphate (PI(4)P) at the Golgi, where it binds the DDR kinase ATM. In turn, this titration attenuates the initial nuclear ATM-driven response to DNA breaks, thus allowing processive repair. Furthermore, manipulating this loop impacts the kinetics of DNA damage signaling and repair in a predictable manner. Thus, our findings have major implications for tackling genetic instability pathologies through dietary and pharmacological interventions.

On the trapping of neutrons in Fabry–Pérot nano-structures and potential applications for cold neutron lifetime Investigations

Correlated to the neutron total reflection phenomenon is the so-called frustrated total reflection, also known as neutron channeling, observed with both thermal and cold neutrons. Within this contribution, such a phenomenon is validated in various additional distinctive Fabry–Pérot nano-resonating configurations; namely in: (i) dual reflection and transmission neutron Fabry–Pérot nano-resonator (Ni/V/Ni/Si substrate), (ii) isotope-based neutron Fabry–Pérot nano-resonator (58Ni/62Ni/58Ni/Silicon substrate), and (iii) multilayered neutron Fabry–Pérot nano-resonator of 8 superposed (B4C/Ti/B4C) single nano-resonators. While such Fabry–Pérot nano-resonators allow effective neutron trapping, the precision of the trapping time of free neutrons in such nano-resonators is governed by the Heisenberg uncertainty and hence offers, a priori, an additional attractive precise approach for potential lifetime investigations. Depending on the configuration of the Fabry–Pérot nano-resonators and the available cold neutron beam, the trapping time is found to be within the temporal regime of 3 to 19 ps. While the main intention of this contribution is to validate the possibility of trapping cold neutrons in nano-structured Fabry–Pérot resonators with a picosecond precision in various configurations, it is hoped that these preliminary results will attract the interest of the neutron lifetime community specifically and the neutron scattering community in general. The potential integration of such trapping method into the bottle or beam methods would elucidate the origin of the difference in neutron lifetime between the two approaches.

Unscheduled DNA replication in G1 causes genome instability and damage signatures indicative of replication collisions

DNA replicates once per cell cycle. Interfering with the regulation of DNA replication initiation generates genome instability through over-replication and has been linked to early stages of cancer development. Here, we engineer genetic systems in budding yeast to induce unscheduled replication in a G1-like cell cycle state. Unscheduled G1 replication initiates at canonical S-phase origins. We quantifiy the composition of replisomes in G1- and S-phase and identified firing factors, polymerase α, and histone supply as factors that limit replication outside S-phase. G1 replication per se does not trigger cellular checkpoints. Subsequent replication during S-phase, however, results in over-replication and leads to chromosome breaks and chromosome-wide, strand-biased occurrence of RPA-bound single-stranded DNA, indicating head-to-tail replication collisions as a key mechanism generating genome instability upon G1 replication. Low-level, sporadic induction of G1 replication induces an identical response, indicating findings from synthetic systems are applicable to naturally occurring scenarios of unscheduled replication initiation.

Top1p targeting by Fob1p at the ribosomal Replication Fork Barrier does not account for camptothecin sensitivity in Saccharomyces cerevisiae cells

Camptothecin (CPT) is a specific inhibitor of the DNA topoisomerase I (Top1p), currently used in cancer therapy, which induces DNA damage and cell death. Top1p is highly active at the repeated ribosomal DNA locus (rDNA) to relax DNA supercoiling caused by elevated transcription and replication occurring in opposite directions. Fob1p interacts with, and stabilizes, Top1p at the rDNA Replication Fork Barrier (rRFB), where replication and transcription converge. Here, we have investigated if the absence of Fob1p and the consequent loss of Top1p specific targeting to the rRFB impact the sensitivity and the cell cycle progression of wild-type cells to CPT. We have also investigated the consequences of the absence of Fob1p in rad52∆ mutants, which are affected in the repair of CPT-induced DNA damage by homologous recombination. The results show that CPT sensitivity and the global cell cycle progression in cells exposed to CPT is not changed in the absence of Fob1p. Moreover, we have observed in fob1∆ cells treated with CPT that the homologous recombination factor Rad52p still congregates in the shape of foci in the nucleolus, which hosts the rDNA. This suggests that, in the absence of Fob1p, Top1p is still recruited to the rDNA, presumably at sequences other than the rRFB, and its inhibition by CPT leads to recombination events.

Homologous recombination and Mus81 promote replication completion in response to replication fork blockage

Impediments to DNA replication threaten genome stability. The homologous recombination (HR) pathway has been involved in the restart of blocked replication forks. Here, we used a method to increase yeast cell permeability in order to study at the molecular level the fate of replication forks blocked by DNA topoisomerase I poisoning by camptothecin (CPT). Our results indicate that Rad52 and Rad51 HR factors are required to complete DNA replication in response to CPT. Recombination events occurring during S phase do not generally lead to the restart of DNA synthesis but rather protect blocked forks until they merge with convergent forks. This fusion generates structures requiring their resolution by the Mus81 endonuclease in G2 /M. At the global genome level, the multiplicity of replication origins in eukaryotic genomes and the fork protection mechanism provided by HR appear therefore to be essential to complete DNA replication in response to fork blockage.

Mec1 Is Activated at the Onset of Normal S Phase by Low-dNTP Pools Impeding DNA Replication

The Mec1 and Rad53 kinases play a central role during acute replication stress in budding yeast. They are also essential for viability in normal growth conditions, but the signal that activates the Mec1-Rad53 pathway in the absence of exogenous insults is currently unknown. Here, we show that this pathway is active at the onset of normal S phase because deoxyribonucleotide triphosphate (dNTP) levels present in G₁ phase may not be sufficient to support processive DNA synthesis and impede DNA replication. This activation can be suppressed experimentally by increasing dNTP levels in G₁ phase. Moreover, we show that unchallenged cells entering S phase in the absence of Rad53 undergo irreversible fork collapse and mitotic catastrophe. Together, these data indicate that cells use suboptimal dNTP pools to detect the onset of DNA replication and activate the Mec1-Rad53 pathway, which in turn maintains functional forks and triggers dNTP synthesis, allowing the completion of DNA replication.

Assessment of neurocognitive decline in cancer patients, except brain cancer, under long-term treatment with bevacizumab

PURPOSE

We performed a cross-sectional study of neurocognitive function in non-brain cancer patients treated with long-term bevacizumab.

METHODS/PATIENTS

From 2015 to 2017, we included patients with different types of cancer treated with bevacizumab with or without chemotherapy (BEV; N = 20) or only chemotherapy (ChT; N = 19) for at least 34 weeks, patients who received non-brain radiotherapy (RxT; N = 19), and healthy controls (HC; N = 19) were assessed once at week 34 of treatment (BEV and ChT) or at completion of radiotherapy. Neurocognition was evaluated with the Hopkins Verbal Learning Test-Revised (HVLT-R) total and delayed recall, the Trail Making Test A and B, and the Controlled Oral Word Association Test in the four groups. Non-parametric tests were used to assess differences between groups.

RESULTS

The BEV, ChT, and RxT groups scored significantly lower than the HC group on all tests and especially on the HVLT-R total recall. In no case were the mean scores of the BEV group significantly lower than those of the ChT or RxT groups.

CONCLUSIONS

Neurocognitive impairment was seen even in patients treated with local non-brain radiotherapy. Treatment with bevacizumab for a long period of time does not seem to worsen neurocognitive function to a greater extent than chemotherapy.

qDSB-Seq is a general method for genome-wide quantification of DNA double-strand breaks using sequencing

DNA double-strand breaks (DSBs) are among the most lethal types of DNA damage and frequently cause genome instability. Sequencing-based methods for mapping DSBs have been developed but they allow measurement only of relative frequencies of DSBs between loci, which limits our understanding of the physiological relevance of detected DSBs. Here we propose quantitative DSB sequencing (qDSB-Seq), a method providing both DSB frequencies per cell and their precise genomic coordinates. We induce spike-in DSBs by a site-specific endonuclease and use them to quantify detected DSBs (labeled, e.g., using i-BLESS). Utilizing qDSB-Seq, we determine numbers of DSBs induced by a radiomimetic drug and replication stress, and reveal two orders of magnitude differences in DSB frequencies. We also measure absolute frequencies of Top1-dependent DSBs at natural replication fork barriers. qDSB-Seq is compatible with various DSB labeling methods in different organisms and allows accurate comparisons of absolute DSB frequencies across samples.

Mrc1 and Rad9 cooperate to regulate initiation and elongation of DNA replication in response to DNA damage

The S-phase checkpoint maintains the integrity of the genome in response to DNA replication stress. In budding yeast, this pathway is initiated by Mec1 and is amplified through the activation of Rad53 by two checkpoint mediators: Mrc1 promotes Rad53 activation at stalled forks, and Rad9 is a general mediator of the DNA damage response. Here, we have investigated the interplay between Mrc1 and Rad9 in response to DNA damage and found that they control DNA replication through two distinct but complementary mechanisms. Mrc1 rapidly activates Rad53 at stalled forks and represses late-firing origins but is unable to maintain this repression over time. Rad9 takes over Mrc1 to maintain a continuous checkpoint signaling. Importantly, the Rad9-mediated activation of Rad53 slows down fork progression, supporting the view that the S-phase checkpoint controls both the initiation and the elongation of DNA replication in response to DNA damage. Together, these data indicate that Mrc1 and Rad9 play distinct functions that are important to ensure an optimal completion of S phase under replication stress conditions.

i-BLESS is an ultra-sensitive method for detection of DNA double-strand breaks

Maintenance of genome stability is a key issue for cell fate that could be compromised by chromosome deletions and translocations caused by DNA double-strand breaks (DSBs). Thus development of precise and sensitive tools for DSBs labeling is of great importance for understanding mechanisms of DSB formation, their sensing and repair. Until now there has been no high resolution and specific DSB detection technique that would be applicable to any cells regardless of their size. Here, we present i-BLESS, a universal method for direct genome-wide DNA double-strand break labeling in cells immobilized in agarose beads. i-BLESS has three key advantages: it is the only unbiased method applicable to yeast, achieves a sensitivity of one break at a given position in 100,000 cells, and eliminates background noise while still allowing for fixation of samples. The method allows detection of ultra-rare breaks such as those forming spontaneously at G-quadruplexes.

Anna Biernacka, Yingjie Zhu et al. present i-BLESS, a universal method for detecting genome-wide DNA double strand breaks, optimized here for yeast. By immobilizing cells on agarose beads, the authors are able to achieve efficient diffusion of reagents and labeling of double strand breaks, including ultra-rare breaks such as those at G-quadruplexes.

Signaling pathways of replication stress in yeast

Eukaryotic cells activate the S-phase checkpoint in response to a variety of events affecting the progression of replication forks, collectively referred to as replication stress. This signaling pathway is divided in two branches: the DNA damage checkpoint (DDC) and the DNA replication checkpoint (DRC). Both pathways are activated by the sensor kinase Mec1 and converge on the effector kinase Rad53. However, the DDC operates throughout the cell cycle and depends on the checkpoint mediator Rad9 to activate Rad53, whereas the DRC is specific to S phase and is mediated by Mrc1 and other fork components to signal replication impediments. In this review, we summarize current knowledge on these two pathways, with a focus on the budding yeast Saccharomyces cerevisiae, in which many important aspects of the replication stress response were discovered. We also discuss the differences and similarities between DDC and DRC and speculate on how these pathways cooperate to ensure the complete and faithful duplication of the yeast genome under various replication stress conditions.

A new role for Rrm3 in repair of replication-born DNA breakage by sister chromatid recombination

Replication forks stall at different DNA obstacles such as those originated by transcription. Fork stalling can lead to DNA double-strand breaks (DSBs) that will be preferentially repaired by homologous recombination when the sister chromatid is available. The Rrm3 helicase is a replisome component that promotes replication upon fork stalling, accumulates at highly transcribed regions and prevents not only transcription-induced replication fork stalling but also transcription-associated hyper-recombination. This led us to explore the possible role of Rrm3 in the repair of DSBs when originating at the passage of the replication fork. Using a mini-HO system that induces mainly single-stranded DNA breaks, we show that rrm3Δ cells are defective in DSB repair. The defect is clearly seen in sister chromatid recombination, the major repair pathway of replication-born DSBs. Our results indicate that Rrm3 recruitment to replication-born DSBs is crucial for viability, uncovering a new role for Rrm3 in the repair of broken replication forks.

DNA replication needs to be precise to ensure cell survival and to avoid genetic instability. Different DNA obstacles, such as those originated by transcription, frequently hamper replication fork progression leading to fork stalling or even fork breakage. This requires the homologous recombination machinery to repair the damage. Here, we uncovered a role for yeast Rrm3, a replisome component known to promote replication upon fork stalling, in the repair of replication-born double strand breaks. In particular, rrm3Δ cells show a defect in the recombination with the sister chromatid, the preferred template for the maintenance of genome integrity. Our results support the possibility that the known accumulation of Rrm3 at sites of active transcription reflects an active role of Rrm3 in the repair of broken forks.

The regulation of neuronal mitochondrial metabolism by calcium

Calcium signalling is fundamental to the function of the nervous system, in association with changes in ionic gradients across the membrane. Although restoring ionic gradients is energetically costly, a rise in intracellular Ca(2+) acts through multiple pathways to increase ATP synthesis, matching energy supply to demand. Increasing cytosolic Ca(2+) stimulates metabolite transfer across the inner mitochondrial membrane through activation of Ca(2+) -regulated mitochondrial carriers, whereas an increase in matrix Ca(2+) stimulates the citric acid cycle and ATP synthase. The aspartate-glutamate exchanger Aralar/AGC1 (Slc25a12), a component of the malate-aspartate shuttle (MAS), is stimulated by modest increases in cytosolic Ca(2+) and upregulates respiration in cortical neurons by enhancing pyruvate supply into mitochondria. Failure to increase respiration in response to small (carbachol) and moderate (K(+) -depolarization) workloads and blunted stimulation of respiration in response to high workloads (veratridine) in Aralar/AGC1 knockout neurons reflect impaired MAS activity and limited mitochondrial pyruvate supply. In response to large workloads (veratridine), acute stimulation of respiration occurs in the absence of MAS through Ca(2+) influx through the mitochondrial calcium uniporter (MCU) and a rise in matrix [Ca(2+) ]. Although the physiological importance of the MCU complex in work-induced stimulation of respiration of CNS neurons is not yet clarified, abnormal mitochondrial Ca(2+) signalling causes pathology. Indeed, loss of function mutations in MICU1, a regulator of MCU complex, are associated with neuromuscular disease. In patient-derived MICU1 deficient fibroblasts, resting matrix Ca(2+) is increased and mitochondria fragmented. Thus, the fine tuning of Ca(2+) signals plays a key role in shaping mitochondrial bioenergetics.

Complex chromosomal rearrangements mediated by break-induced replication involve structure-selective endonucleases

DNA double-strand break (DSB) repair occurring in repeated DNA sequences often leads to the generation of chromosomal rearrangements. Homologous recombination normally ensures a faithful repair of DSBs through a mechanism that transfers the genetic information of an intact donor template to the broken molecule. When only one DSB end shares homology to the donor template, conventional gene conversion fails to occur and repair can be channeled to a recombination-dependent replication pathway termed break-induced replication (BIR), which is prone to produce chromosome non-reciprocal translocations (NRTs), a classical feature of numerous human cancers. Using a newly designed substrate for the analysis of DSB-induced chromosomal translocations, we show that Mus81 and Yen1 structure-selective endonucleases (SSEs) promote BIR, thus causing NRTs. We propose that Mus81 and Yen1 are recruited at the strand invasion intermediate to allow the establishment of a replication fork, which is required to complete BIR. Replication template switching during BIR, a feature of this pathway, engenders complex chromosomal rearrangements when using repeated DNA sequences dispersed over the genome. We demonstrate here that Mus81 and Yen1, together with Slx4, also promote template switching during BIR. Altogether, our study provides evidence for a role of SSEs at multiple steps during BIR, thus participating in the destabilization of the genome by generating complex chromosomal rearrangements.

One year oral Toxicity of D-004, a lipid extract from Roystonea regia fruits, in Sprague Dawley rats

D-004, a lipid extract of royal palm (Roystonea regia) fruits that contains a reproducible mixture of fatty acids, has been shown to prevent testosterone and phenylephrine-induced prostate hyperplasia in rodents. This study investigated the long-term oral toxicity of D-004 in rats. Rats from both sexes were randomized into four groups (20 rats sex/group): a control and three treated with D-004 (800, 1500 or 2000 mg/kg/day, respectively). At study completion, rats were sacrificed under anaesthesia. Determinations of blood biochemical and haematological parameters and organ weight were done. Also, necropsy and histopathological studies were performed. Four of 160 rats died before study completion. No clinical signs of toxicity were observed throughout the study. Food and water consumption, bodyweight, blood biochemical and haematological parameters, organ weight ratios and histopathological findings were similar in control and treated groups. The histological lesions found in treated animals are commonly present in this specie and strain according to literature and our historical data. In conclusion, long-term (12 months) oral treatment of rats with D-004 (800-2000 mg/kg/day) did not show evidences of D-004-related toxicity under our conditions. The highest dose tested (2000 mg/kg) was a no-observed adverse effect level in this study.

Photoinduced phase transitions by time-resolved far-infrared spectroscopy in V2O3

Using time-resolved far-infrared spectroscopy, we observe multiple routes for photoinduced phase transitions in V(2)O(3). This includes (i) a photothermal antiferromagnetic to paramagnetic transition and (ii) an incipient strain-generated paramagnetic metal to paramagnetic insulator transition, which manifests as coherent oscillations in the far-infrared conductivity. The ∼100 ps conductivity oscillation results from coherent acoustic phonon modulation of the bandwidth W. Our results indicate that poor metals are particularly amenable to coherent strain control of their electronic properties.

ATM gene analysis in neuroblastoma: A report from the COG

10058

Background: Neuroblastoma (NB) is the most common malignant disease of infancy and accounts for approximately 8% of all childhood cancers. The clinical hallmark of this tumor is the marked variability in prognosis depending of the age, stage, and biological characteristics. There is evidence to suggest that the long arm of chromosome 11 (11q) plays a role in NB biology. The ATM gene is located at 11q22–23 and hereditary mutations of this gene cause ataxia-telangiectasia, a recessive disorder associated with a high incidence of neoplasia. The aim of this project was to determine the prevalence of ATM gene mutation and ATM methylation status in 50 NB samples. Methods: Following DNA extraction, PCR products of the 65 exons of the ATM gene and its promoter were screened by DHPLC. This screening was also performed on DNA from 60 blood donors. Alterations detected were analyzed by direct sequencing. Direct and indirect criteria were used to classify the observed nucleotide alterations as mutation (if pathogenic), rare variant (if the allelic frequency in controls was < or = 1%), variant (1.1–2.4%) or polymorphism (> or = 2.5%). The ATM methylation status was analyzed by MS-MLPA (Methylation-Specific Multiplex Ligation-dependent Probe Amplification). Results: Except polymorphisms, 17 different sequence alterations were found in 17 NB samples (34%). Ten of these 17 alterations, found in 11 NB (22%), were rare variants (RV). In 5 NB (10%), RV were found homozygous. At the same time, we found 20 different sequence alterations in 19 controls (32%). Sixteen of these 20 alterations were RV and one was a heterozygous pathogenic mutation. These 17 alterations concern 15 controls (25%). No homozygous RV was found in controls. We found no evidence of ATM promoter hypermethylation in the 48 NB samples analyzed. Conclusions: We found no difference in ATMvariant and RV frequency between NB and control samples. However, as ATM deletion is a frequent event in NB, we found a high frequency of homozygous RV (10%). At present, we are completing this study by screening ATMlarge genomic deletion/duplication using MLPA. Finally, our observations indicate that epigenetic ATM silencing by methylation is uncommon in neuroblastoma.

No significant financial relationships to disclose.

DNA repair in mammalian cells: DNA double-strand break repair: how to fix a broken relationship

DNA double-strand breaks (DSBs) arise in cells from endogenous and exogenous attacks on the DNA backbone, but also as a direct consequence of replication failures. Proper repair of all these DSBs is essential for genome stability. Repair of broken chromosomes is a challenge for dividing cells that need to distribute equal genetic information to daughter cells. Consequently, eukaryotic organisms have evolved multi-potent and efficient mechanisms to repair DSBs that are primarily divided into two types of pathways: nonhomologous end joining (NHEJ) and homologous recombination (HR). Here we briefly describe how eukaryotic cells sense DSBs and trigger cell cycle arrest to allow repair, and we review the mechanisms of both NHEJ and HR pathways and the choice between them. (Part of a Multi-author Review).

Enteric glial cells express full-length TrkB and depend on TrkB expression for normal development

The embryonic development of the enteric nervous system (ENS) from neural crest precursor cells requires neurotrophic signaling. Neurotrophins (NTs) are a family of growth factors that bind Trk receptors to signal diverse functions, including development and maintenance of different cell populations in the peripheral nervous system. In this study we investigated the expression and cell localization of TrkB, the high affinity receptor for brain-derived neurotrophic factor and NT-4, in the murine ENS using Western blot and immunohistochemistry. The results demonstrate that enteric glial cells within the ENS express full-length TrkB at all stages tested. The ENS of TrkB deficient mice have reduced expression of glial cell markers, and a disarrangement of glial cells and the plexular neuropil. These results strongly suggest TrkB has essential roles in the normal development and maintenance of glial cells in the ENS.

Multiple pathways inhibit NHEJ at telomeres

The nonhomologous end-joining (NHEJ) repair pathway is inhibited at telomeres, preventing chromosome fusion. In budding yeast Saccharomyces cerevisiae, the Rap1 protein directly binds the telomere sequences and is required for NHEJ inhibition. Here we show that the Rap1 C-terminal domain establishes two parallel inhibitory pathways through the proteins Rif2 and Sir4. In addition, the central domain of Rap1 inhibits NHEJ independently of Rif2 and Sir4. Thus, Rap1 establishes several independent pathways to prevent telomere fusions. We discuss a possible mechanism that would explain Rif2 multifunctionality at telomeres and the recent evolutionary origin of Rif2 from an origin recognition complex (ORC) subunit.

Phase I combination study of plitidepsin and carboplatin in advanced solid tumours

2558

Background: Plitidepsin is a cyclic depsipeptyde isolated from the marine tunicate Aplidium albicans, nowadays manufactured by synthesis. It is a rapid and potent inductor of apoptosis. In phase I trials, muscle (myalgia and CPK increase) and liver toxicities were dose-limiting and preliminary activity was observed in malignant melanoma, renal, head and neck, lung, neuroendocrine, colorectal and hematological malignancies. Preclinical synergism with carboplatin (CBCDA) against solid tumors and acute leukaemia suggest plitidepsin can reverse platinum chemoresistance in vivo through reduction of glutathione levels. This phase I trial was initiated in order to evaluate the safety, pharmacokinetics (PK) and antitumour activity of the combination of CBCDA and weekly administration of plitidepsin (Recommended dose (RD) in monotherapy: 3.2 mg/m2). Methods: Patients (pts) with advanced solid tumours and good performance status (WHO PS = 2) were enrolled. Plitidepsin was given over 1 hr infusion on days 1 , 8 and 15 every 4 weeks followed by CBDCA (AUC 5) as a 1 hr infusion on day 1. Dose levels planned for plitidepsin were 1.8, 2.4 and 3.0 mg/m2 in cohorts of 3 pts. PK sampling was performed during the first cycle (cy) of treatment. Results: 18 pts have been treated to date (8M/10F). Median age (range): 59 (39–73) yrs. WHO PS>0: 3pts. Tumour types included colorectal (5), malignant melanoma (4), ovary (2), other gastrointestinal tumors (7). No DLT was observed at plitidepsin 1.8 and 2.4 mg/m2 (3 pts treated in each cohort). Two out of 5 pts exhibited DLT at pltidepsin 3.0 mg/m2, consisting of delay of second cy >2 weeks (grade 3 transaminitis and grade 3 thrombocytopenia) and omission of second infusion in first cy (grade 3 ALT increase). Plitidepsin at 2.4 mg/m2 was expanded to 8 pts. There were 4 pts with stable disease (cholangio, liver, colorectal, gatro-esophageal junction and esophagus carcinomas). Conclusions: The RD for the combination is plitidepsin 2.4 mg/m2 (0.8 mg/m2 lower than in monotherapy) days 1, 8 and 15 every 4 weeks followed by CBDCA (AUC 5). DLTs of the combination at the highest dose were different vs single plitidepsin (liver and haematological vs muscular). PK analyses from the three cohorts to detect interactions and updated safety data for the RD cohort are in progress.

[Table: see text]

Phase I clinical and pharmacological trial of trabectedin (T) in 3 hour infusion every 3 weeks (3h/q3w) in patients with advanced cancer and hepatic function disorder

2080

Background: Trabectedin (ET-743) is a marine-derived DNA and transcription interacting agent with activity in pretreated soft tissue sarcoma, breast, prostate and ovarian cancer. T is associated with 2 types of liver function alterations: a frequent acute and reversible elevation of ALT and AST and a less frequent cholestasis, usually reflected by low grade increases in alkaline phosphatase (AP) and bilirubin (B). The main predictors of dose limiting toxicity (DLT) or T-related serious adverse events appear to include elevated baseline or intercycle peaks of AP, B and ALT > 5 × ULN (Gomez J, ASCO 2000). The objectives of this trial are to determine the maximum tolerated dose (MTD) and pharmacokinetics (PK) of T 3h/q3w in patients (pts) with advanced cancer and baseline liver dysfunction. Methods: All pts are stratified according to basal liver function as follows: STRATUM (S) I: ULN < AP ≤ 1.5 × ULN S II: 1.5 × ULN < AP ≤ 2.5 × ULN S III: AP > 2.5 × ULN All pts had to have AST and ALT ≤ 2.5 × ULN, albumin > 2.5 g/dl and B < 2.5 mg/dl. T concentrations in plasma are determined using a validated LC-MS/MS method. PK parameters were calculated by non-compartmental methods. Results: 32 pts were recruited.Median age: 54 years (26–76); PS≤1:28 pts; prior chemotherapy (CT): 31 pts (97%); median number of prior CT: 2 (1–6); B > ULN: 0 pts. In S I, T was administered at 1.1 mg/m2 (3 pts) and 1.3 mg/m2 (13 pts). Two DLTs were reported at 1.3 mg/m2: neutropenia G4 > 5 days with febrile neutropenia and G3 ALT not recovered by day +28. In S II no DLT occurred in 4 pts at T 0.9 mg/m2 nor 3 pts at T 1.1 mg/m2, 1 out of 4 pts at 1.3 mg/m2 suffered DLT: G3 AST not recovered by day +24. In S III one out of 2 pts at 0.9 mg/m2 had DLT: AP increase. Initial PK evaluation from S I and II (8 from each) showed a long half life (geometric mean (GM) S I: 124.6 h, S II: 118.8 h) and wide distribution (GM Vss S I: 2366 l/m2, S II: 3830 l/m2). GM clearance: 18.3 l/(hr*m2) in S I; 26.3 l/(hr*m2) in S II. Clearance is somewhat lower than in normal liver function population (GM under equal dexamethasone treatment 33.8 l/hr*m2) in study ET-B-010. Conclusions: The recommended dose (RD) of T for pts with mild AP elevations (< 1.5 ULN) and B levels < ULN is 1.3 mg/m2 3h/q3w. The study is ongoing to define the RD for S II and III

[Table: see text]

Mismatch tolerance by DNA polymerase Pol4 in the course of nonhomologous end joining in Saccharomyces cerevisiae

In yeast, the nonhomologous end joining pathway (NHEJ) mobilizes the DNA polymerase Pol4 to repair DNA double-strand breaks when gap filling is required prior to ligation. Using telomere-telomere fusions caused by loss of the telomeric protein Rap1 and double-strand break repair on transformed DNA as assays for NHEJ between fully uncohesive ends, we show that Pol4 is able to extend a 3'-end whose last bases are mismatched, i.e., mispaired or unpaired, to the template strand.

Rap1 prevents telomere fusions by nonhomologous end joining

Telomeres protect chromosomes from end-to-end fusions. In yeast Saccharomyces cerevisiae, the protein Rap1 directly binds telomeric DNA. Here, we use a new conditional allele of RAP1 and show that Rap1 loss results in frequent fusions between telomeres. Analysis of the fusion point with restriction enzymes indicates that fusions occur between telomeres of near wild-type length. Telomere fusions are not observed in cells lacking factors required for nonhomologous end joining (NHEJ), including Lig4 (ligase IV), KU and the Mre11 complex. SAE2 and TEL1 do not affect the frequency of fusions. Together, these results show that Rap1 is essential to block NHEJ between telomeres. Since the presence of Rap1 at telomeres has been conserved through evolution, the establishment of NHEJ suppression by Rap1 could be universal.

Randomized phase II trial of carboplatin versus paclitaxel and carboplatin in platinum-sensitive recurrent advanced ovarian carcinoma: a GEICO (Grupo Espanol de Investigacion en Cancer de Ovario) study

BACKGROUND

The aim of this study was to determine whether the response rate for the paclitaxel-carboplatin combination is superior to carboplatin alone in the treatment of patients with platinum-sensitive recurrent ovarian carcinoma.

PATIENTS AND METHODS

Patients with recurrent ovarian carcinoma, 6 months after treatment with a platinum-based regimen and with no more than two previous chemotherapy lines, were randomized to receive carboplatin area under the curve (AUC) 5 (arm A) or paclitaxel 175 mg/m(2) + carboplatin AUC 5 (arm B). The primary end point was objective response, following a 'pick up the winner' design. Secondary end points included time to progression (TTP), overall survival, tolerability and quality of life (QoL).

RESULTS

Eighty-one patients were randomized and included in the intention-to-treat analysis. The response rate in arm B was 75.6% [26.8% complete response (CR) + 48.8% partial response (PR)] [95% confidence interval (CI) 59.7% to 87.6%] and 50% in arm A (20% CR + 30% PR) (95% CI 33.8% to 66.2%). No significant differences were observed in grade 3-4 hematological toxicity. Conversely, mucositis, myalgia/arthralgia and peripheral neurophaty were more frequent in arm B. Median TTP was 49.1 weeks in arm B (95% CI 36.9-61.3) and 33.7 weeks in arm A (95% CI 25.8-41.5). No significant differences were found in the QoL analysis.

CONCLUSIONS

Paclitaxel-carboplatin combination is a tolerable regimen with a higher response rate than carboplatin monotherapy in platinum-sensitive recurrent ovarian carcinoma.

[Changes in dietary habits and selected cardiovascular risk factors of the Warsaw population over the 5-year observation period (1993-97/98)]

The aim of the study was to characterise changes in dietary habits and cardiovascular risk factors of the Warsaw cohort population over a 5-year observation period. Two Warsaw population samples (249 men and 259 women), aged 35-64, were surveyed in 1993 and resurveyed in years 1997/98. Over a five-year observation period, daily dietary cholesterol decreased from 363 mg to 319 mg in men and from 263 mg to 232 mg in women, the percentage of energy from fat decreased from 38.8% to 34.7% in men and from 37.1% to 31.2% in women, the percentage of energy from saturated fatty acids from 13.6% to 11.7% and from 12.9% to 10.5% respectively. These changes resulted in a significant reduction in atherogenicity of the average diet as expressed by Keys score. Intakes of vitamins B1 and B2, calcium, magnesium and iron was consistently below Recommended Dietary Allowances (RDA) for the Polish population. Participants of both genders consumed significantly greater amounts of total bread (35%), milk (50%) and butcher meat products (22%). In the same time increase of HDL-cholesterol level (average of 2.0 mg/dl in men and 3.1 mg/dl in women) and decrease of LDL-cholesterol by 5 mg/dl in men was noted.

Parametric and resonant transition radiation in periodic stratified structures

We consider the problem of electromagnetic emission when an electrically charged particle crosses a periodically stratified structure following an arbitrary linear trajectory. A theory generalizing a recently developed method [Phys. Rev. E 63, 016613 (2001)] is presented in the framework of the classical theory of electromagnetism in continuous media. It allows one to account for both the so-called parametric radiation and the resonant transition radiation. We implement our model to interpret the experiments performed by Kaplin et al. [Appl. Phys. Lett. 76, 3647 (2000)] in the x-ray domain with a stack of 300 W/B(4)C bilayers irradiated by 500 MeV electrons.

Citrin and aralar1 are Ca(2+)-stimulated aspartate/glutamate transporters in mitochondria

The mitochondrial aspartate/glutamate carrier catalyzes an important step in both the urea cycle and the aspartate/malate NADH shuttle. Citrin and aralar1 are homologous proteins belonging to the mitochondrial carrier family with EF-hand Ca(2+)-binding motifs in their N-terminal domains. Both proteins and their C-terminal domains were overexpressed in Escherichia coli, reconstituted into liposomes and shown to catalyze the electrogenic exchange of aspartate for glutamate and a H(+). Overexpression of the carriers in transfected human cells increased the activity of the malate/aspartate NADH shuttle. These results demonstrate that citrin and aralar1 are isoforms of the hitherto unidentified aspartate/glutamate carrier and explain why mutations in citrin cause type II citrullinemia in humans. The activity of citrin and aralar1 as aspartate/glutamate exchangers was stimulated by Ca(2+) on the external side of the inner mitochondrial membrane, where the Ca(2+)-binding domains of these proteins are localized. These results show that the aspartate/glutamate carrier is regulated by Ca(2+) through a mechanism independent of Ca(2+) entry into mitochondria, and suggest a novel mechanism of Ca(2+) regulation of the aspartate/malate shuttle.

Fungal infections in patients with solid tumors treated with high-dose chemotherapy and autologous peripheral blood stem cell transplantation

The incidence and risk factors for fungal infection were assessed in 291 patients who had solid tumors and were undergoing autologous peripheral blood stem cell transplantation. The first 162 patients received prophylactic itraconazole, and 129 patients received nystatin. Empiric amphotericin B was given at day 7 of febrile neutropenia. Fungal infections developed in 52 patients: 47 (16%) were superficial and 6 (2%) were systemic. Itraconazole prophylaxis and only a few days of febrile neutropenia were independently associated with a decrease in the incidence of superficial infections. Only two patients required empiric amphotericin B. Systemic antifungal prophylaxis does not seem to be justified for patients with solid tumors and autologous peripheral blood stem cell transplantation. Empiric amphotericin B may be safely started at day 7 of febrile neutropenia.

A matricial theory of soft x-ray resonant transition radiation in periodic multilayer structures

When a charged particle crosses an interface between two different materials, electromagnetic radiation called Transition Radiation is emitted. The spectrum of this radiation extends up to x-ray domain. The Resonant Transition Radiation (R.T.R.) can be observed with a periodic arrangement of interfaces. The R.T.R. in the soft x-ray range has been recently measured by K. Yamada and coll. with a Nickel-Carbon multilayer structure [1]. In this paper, a rigorous electromagnetic theory of the R.T.R in finite and infinite multilayer structures is developed using the matricial formalism and compared with the experimental quoted data [1].

Classical theory of resonant transition radiation in multilayer structures

A rigorous classical electromagnetic theory of the transition radiation in finite and infinite multilayer structures is presented. It makes the standard results of thin-film optics, such as the matrix formalism, accountable; it allows thus an exact treatment of the propagation of the waves induced by the electron. This method is applied to the particular case of the periodic structures to treat the resonant transition radiation (RTR). It is noted that the present theory gives, in the hard x-ray domain, results previously published. The reason for this approach is to make the numerical calculations rigorous and easy. The numerical results of our theory are compared to experimental RTR data obtained recently by Yamada et al. [Phys. Rev. A 59, 3673 (1999)] with a nickel-carbon multilayer structure.

Weight gain and its correlates in Poland between 1983 and 1993

BACKGROUND

Weight gain and its unfavorable consequences on coronary heart disease (CHD) risk have been observed worldwide. Determinants of weight gain were studied in a Polish cohort of 1042 men and women age 35-64 at baseline. Participants were randomly selected from an urban population in Warsaw and a rural population in Tarnobrzeg Province surveyed by investigators in Krakow. The surveys, part of the Pol-MONICA project, were conducted in 1983-1984, 1987-1988, and 1992-1993. The purpose of this report is to gain insight into the dynamics of weight gain in this population that could be helpful in identifying high-risk groups for intervention, and to determine if economic changes that took place shortly after the second survey had any impact on weight gain.

METHODS

Weight, height and demographic characteristics were measured at each visit according to Pol-MONICA standard protocol. Body mass index (BMI) was calculated as kg/m2. Years of schooling, 7-day alcohol history and smoking history were self-reported.

RESULTS

Sixty percent of the cohort gained some weight, averaging 0.3-0.7kg/y. Weight gain was highest in younger rural women, in urban men and in rural women with low education. In multiple linear regression, low education was related to a 1.29 kg greater weight gain (P<0.01), ex-smoking status was related to a 2.54 kg greater weight gain (P<0.001), and younger age was related to a 1.14 kg greater weight gain (P<0.001).

CONCLUSION

Our results indicate a need to target intervention programs at young low SES adults. Developing effective means of reaching these vulnerable groups is a critical research goal.

Differentiation of rat striatal embryonic stem cells in vitro: monolayer culture vs. three-dimensional coculture with differentiated brain cells

Several groups have demonstrated the existence of self-renewing stem cells in embryonic and adult mouse brain. In vitro, these cells proliferate in response to epidermal growth factor, forming clusters of nestin-positive cells that may be dissociated and subcultured repetitively. Here we show that, in stem cell clusters derived from rat embryonic striatum, cell proliferation decreased with increasing number of passages and in response to elevated concentrations of potassium (30 mM KCl). In monolayer culture, the appearance of microtubule-associated protein type-5-immunoreactive (MAP-5(+)) cells (presumptive neurons) in response to basic fibroblast growth factor (bFGF) was reduced at low cell density and with increasing number of passages. In the presence of bFGF, elevated potassium caused a more differentiated neuronal phenotype, characterized by an increased proportion of MAP-5(+) cells, extensive neuritic branching, and higher specific activity of glutamic acid decarboxylase. Dissociated stem cells were able to invade cultured brain cell aggregates containing different proportions of neurons and glial cells, whereas they required the presence of a considerable proportion of glial cells in the host cultures to become neurofilament H-positive. The latter observation supports the view that astrocyte-derived factors influence early differentiation of the neuronal cell lineage.