Direct observation of geometric-phase interference in dynamics around a conical intersection

Conical intersections are ubiquitous in chemistry and physics, often governing processes such as light harvesting, vision, photocatalysis and chemical reactivity. They act as funnels between electronic states of molecules, allowing rapid and efficient relaxation during chemical dynamics. In addition, when a reaction path encircles a conical intersection, the molecular wavefunction experiences a geometric phase, which can affect the outcome of the reaction through quantum-mechanical interference. Past experiments have measured indirect signatures of geometric phases in scattering patterns and spectroscopic observables, but there has been no direct observation of the underlying wavepacket interference. Here we experimentally observe geometric-phase interference in the dynamics of a wavepacket travelling around an engineered conical intersection in a programmable trapped-ion quantum simulator. To achieve this, we develop a technique to reconstruct the two-dimensional wavepacket densities of a trapped ion. Experiments agree with the theoretical model, demonstrating the ability of analogue quantum simulators-such as those realized using trapped ions-to accurately describe nuclear quantum effects.

Hypofractionated, 3-week, preoperative radiotherapy for patients with soft tissue sarcomas (HYPORT-STS): a single-centre, open-label, single-arm, phase 2 trial

BACKGROUND

The standard preoperative radiotherapy regimen of 50 Gy delivered in 25 fractions for 5 weeks for soft tissue sarcomas results in excellent local control, with major wound complications occurring in approximately 35% of patients. We aimed to investigate the safety of a moderately hypofractionated, shorter regimen of radiotherapy, which could be more convenient for patients.

METHODS

This single-centre, open-label, single-arm, phase 2 trial (HYPORT-STS) was done at a single tertiary cancer care centre (MD Anderson Cancer Center, Houston, TX, USA). We administered preoperative radiotherapy to a dose of 42·75 Gy in 15 fractions of 2·85 Gy/day for 3 weeks (five fractions per week) to adults (aged ≥18 years) with non-metastatic soft tissue sarcomas of the extremities or superficial trunk and an Eastern Cooperative Oncology Group performance status of 0-3. The primary endpoint was a major wound complication occurring within 120 days of surgery. Major wound complications were defined as those requiring a secondary operation, or operations, under general or regional anaesthesia for wound treatment; readmission to the hospital for wound care; invasive procedures for wound care; deep wound packing to an area of wound measuring at least 2 cm in length; prolonged dressing changes; repeat surgery for revision of a split thickness skin graft; or wet dressings for longer than 4 weeks. We analysed our primary outcome and safety in all patients who enrolled. We monitored safety using a Bayesian, one-arm, time-to-event stopping rule simulator comparing the rate of major wound complications at 120 days post-surgery among study participants with the historical rate of 35%. This trial is registered with ClinicalTrials.gov, NCT03819985, recruitment is complete, and follow-up continues.

FINDINGS

Between Dec 18, 2018, and Jan 6, 2021, we assessed 157 patients for eligibility, of whom 120 were enrolled and received hypofractionated preoperative radiotherapy. At no time did the stopping rule computation indicate that the trial should be stopped early for lack of safety. Median postoperative follow-up was 24 months (IQR 17-30). Of 120 patients, 37 (31%, 95% CI 24-40) developed a major wound complication at a median time of 37 days (IQR 25-59) after surgery. No patient had acute radiation toxicity (during radiotherapy or within 4 weeks of the radiotherapy end date) of grade 3 or worse (Common Terminology Criteria for Adverse Events [CTCAE] version 4.0) or an on-treatment serious adverse event. Four (3%) of 115 patients had late radiation toxicity (≥6 months post-surgery) of at least grade 3 (CTCAE or Radiation Therapy Oncology Group/European Organisation for Research and Treatment of Cancer Late Radiation Morbidity Scoring Scheme): femur fractures (n=2), lymphoedema (n=1), and skin ulceration (n=1). There were no treatment-related deaths.

INTERPRETATION

Moderately hypofractionated preoperative radiotherapy delivered to patients with soft tissue sarcomas was safe and could therefore be a more convenient alternative to conventionally fractionated radiotherapy. Patients can be counselled about these results and potentially offered this regimen, particularly if it facilitates care at a sarcoma specialty centre. Results on long-term oncological, late toxicity, and functional outcomes are awaited.

FUNDING

The National Cancer Institute.

Tight junction channels claudin-10b and claudin-15: Functional mapping of pore-lining residues

Although functional and structural models for paracellular channels formed by claudins have been reported, mechanisms regulating charge and size selectivity of these channels are unknown in detail. Here, claudin-15 and claudin-10b cation channels showing high-sequence similarity but differing channel properties were analyzed. Mutants of pore-lining residues were expressed in MDCK-C7 cells. In claudin-15, proposed ion interaction sites (D55 and E64) conserved between both claudins were neutralized. D55N and E64Q substitutions decreased ion permeabilities, and D55N/E64Q had partly additive effects. D55N increased cation dehydration capability and decreased pore diameter. Additionally, residues differing between claudin-15 and -10b close to pore center were analyzed. Claudin-10b-mimicking W63K affected neither assembly nor function of claudin-15 channels. In contrast, in claudin-10b, corresponding (claudin-15b-mimicking) K64W and K64M substitutions disturbed integration into tight junction and slightly altered relative permeabilities for differently sized monovalent cations. Removal of claudin-10b-specific negative charge (D36A substitution) was without effect. The data suggest that a common tetra-aspartate ring (D55/D56) in pore center of claudin-15/-10b channels directly attracts cations, while E64/D65 may be at least partly shielded by W63/K64. Charge at position W63/K64 affects assembly and properties for claudin-10b but not for claudin-15 channels. Our findings add to the mechanistic understanding of the determinants of paracellular cation permeability.

POS0410 BIOMARKERS REFLECTING DISTURBED GUT BARRIER DIFFER IN PATIENTS WITH SPONDYLOARTHRITIS, CROHN’S DISEASE AND ACUTE ANTERIOR UVEITIS

Background:

Spondyloarthritides (SpA) are characterized by frequent extra-musculoskeletal manifestations (EMM) among them acute anterior uveitis (AAU) and Crohn’s disease (CD). Vice versa, about 50% of AAU and 20% of CD patients have concomitant SpA. SpA patients show gut dysbiosis together with frequent subclinical gut inflammation. Biomarkers reflecting disturbed gut barrier (intestinal-fatty acid binding protein (iFABP), lipopolysaccharide binding protein (LBP) and zonulin) were previously found to be elevated in patients with radiographic axial SpA (r-axSpA) (1).

Objectives:

To evaluate whether biomarkers reflecting leaky gut are altered in patients with AAU, CD and SpA compared to healthy controls and whether they differ between patients with EMM with and without concomitant SpA.

Methods:

A total of 100 patients from the German Spondyloarthritis Inception Cohort (GESPIC) were included – among them 20 patients with r-axSpA without EMM, 40 patients with CD and 40 patients with non-infectious AAU – out of which 19 and 20 patients, respectively, had concomitant SpA (11/8 and 20/0 axial/peripheral SpA, respectively). The GESPIC patients were compared to 20 age- and sex-matched healthy donors (HD). The following five serum biomarkers were analyzed with ELISA: calprotectin, iFABP, LBP, soluble CD14 (sCD14) and zonulin.

Results:

Patient characteristics are shown in Table 1. Serum levels of calprotectin, LBP, sCD14 and zonulin differed significantly between patients with r-axSpA, AAU and CD with and without concomitant SpA and HD (Figure 1). When comparing patients with EMM with and without underlying SpA, calprotectin serum levels were significantly elevated in CD patients with SpA (8.6µg/ml (SD 5.5µg/ml)) compared to CD patients without SpA (5.7µg/ml (SD 4.1µg/ml); Mann-Whitney U Test, p=0.031). Serum levels of the analyzed biomarkers did not differ between AAU patients with and without axSpA. Spearman rank correlation revealed a significant association between CRP and calprotectin (correlation coefficient r=0.230; p=0.012), LBP (r=0.596; p<0.0001), sCD14 (r=0.428; p<0.0001) and zonulin (r=0.221; p=0.016), respectively. Furthermore, LBP and zonulin serum levels correlated positively (r=0.208; p=0.023); as well as LBP and sCD14 levels (r=0.418; p<0.0001).

Table 1.

Patient characteristics. Mean values (standard deviation) or absolute numbers are shown.

CD + SpACDr-axSpAAAU + axSpAAAUHDN192120202020Age39.1 (11.3)38.7 (14.4)38.4 (10.3)39.6 (12.0)39.2 (12.5)38.6 (12.9)Male (%)9 (47%)9 (43%)9 (45%)9 (45%)9 (45%)9 (45%)HLA-B27 positive (%)5 (26%)3 (14%)17 (85%)17 (85%)13 (65%)2 (10%)CRP in mg/l14.3 (25.6)18.0 (41.8)9.1 (11.3)6.7 (9.9)2.3 (3.4)0.6 (0.7)ASDAS2.8 (1.1)3.2 (0.6)2.2 (1.0)BASDAI4.1 (2.2)5.4 (1.2)3.2 (2.4)Figure 1.

Biomarkers reflecting disturbed gut barrier show distinct signatures in patients with acute anterior uveitis, Crohn’s disease and axial Spondyloarthritis. Kruskal Wallis Test; p values shown. Dunn-Bonferroni Post-Hoc analyses, significant pairwise differences are marked; * p<0.05; **p<0.01; ***p<0.0001Conclusion:

We found substantial differences in biomarkers reflecting disturbed gut barrier between with SpA, CD, AAU and healthy controls. The presence of SpA was associated with higher calprotectin serum levels in CD as compared to CD without SpA.

References:

[1]Ciccia F, et al. Dysbiosis and zonulin upregulation alter gut epithelial and vascular barriers in patients with ankylosing spondylitis. 2017.

Acknowledgements:

Dr. Judith Rademacher is participant in the BIH-Charité Clinician Scientist Program funded by the Charité –Universitätsmedizin Berlin and the Berlin Institute of Health.

Disclosure of Interests:

None declared

Claudin-15 forms a water channel through the tight junction with distinct function compared to claudin-2

AIM

Claudin-15 is mainly expressed in the small intestine and indirectly involved in glucose absorption. Similar to claudin-2 and -10b, claudin-15 is known to form a paracellular channel for small cations. Claudin-2, but not claudin-10b, also forms water channels. Here we experimentally tested whether claudin-15 also mediates water transport and if yes, whether water transport is Na⁺ -coupled, as seen for claudin-2.

METHODS

MDCK C7 cells were stably transfected with claudin-15. Ion and water permeability were investigated in confluent monolayers of control and claudin-15-expressing cells. Water flux was induced by an osmotic or ionic gradient.

RESULTS

Expression of claudin-15 in MDCK cells strongly increased cation permeability. The permeability ratios for monovalent cations indicated a passage of partially hydrated ions through the claudin-15 pore. Accordingly, its pore diameter was determined to be larger than that of claudin-2 and claudin-10b. Mannitol-induced water flux was elevated in claudin-15-expressing cells compared to control cells. In contrast to the Na⁺ -coupled water flux of claudin-2 channels, claudin-15-mediated water flux was inhibited by Na⁺ flux. Consequently, water flux was increased in Na⁺ -free solution. Likewise, Na⁺ flux was decreased after induction of water flux through claudin-15.

CONCLUSION

Claudin-15, similar to claudin-2, forms a paracellular cation and water channel. In functional contrast to claudin-2, water and Na⁺ fluxes through claudin-15 inhibit each other. Claudin-15 allows Na⁺ to retain part of its hydration shell within the pore. This then reduces the simultaneous passage of additional water through the pore.

4314Cardiac involvement of Wilsons disease

Background

Wilson's disease (WD) is an inherited autosomal recessive disorder resulting from abnormal copper metabolism. Relatively little is known about the effects of copper accumulation on the heart.

Objective

We aimed to determine if patients with Wilson's disease show signs of cardiac involvement and structural heart disease.

Methods

In this prospective trial, we studied 61 patients with Wilson's disease and compared them to 61 age- and gender-matched healthy controls.

Results

While left ventricular function assessed by global longitudinal and global radial strain did not differ significantly between the groups, Wilson's disease patients had significantly reduced global radial strain (table 1).

Wilson's disease patients demonstrated significantly more late gadolinium enhancement than the control patients (4.9±1.4 vs. 1.1±0.2% p<0.001).

The severity of Wilson's disease, based on the Unified Wilson's Disease Rating Scale, was significantly correlated with the extent of late gadolinium enhancement (r=0.53, P=0.001), cardiac troponin (r=0.56, P=0.001), the number of premature ventricular contraction (r=0.66, P=0.001).

Table 1. Myocardial strain and CMR characteristics of patients and controls Parameter Patients (n=61) Controls (n=61) p value Left ventricular parameters   GLS, % −22.8 (4.8) −21.8 (5.1) 0.124   GRS, % 43.2 (13.2) 51.6 (13.8) 0.002   GCS, % −29.2 (5.2) −28.6 (4.7) 0.534 Late gadolinium enhancement   LGE, %* 4.9 (1.4) 1.1 (0.2) 0.003   LGE at RVIP, n (%) 58 (95) 3 (5) <0.001   Midwall LGE, n (%) 11 (18) 0 <0.001 Right ventricular parameters   GLS, % −23.6 (4.9) −26.1 (5) 0.01 Data are presented as mean (SD), median (IQR)*, or n (%) unless otherwise stated. GLS, global longitudinal strain; GRS, global radial strain; GCS, global circular strain; LGE: late gadolinium enhancement; RIVP, right ventricular insertion point.

Conclusion

Our data demonstrate that cardiac involvement in Wilson's disease is possible and those patients who are severely affected by the disease carry a higher risk of developing structural heart disease.

Direct Observation of Dynamical Quantum Phase Transitions in an Interacting Many-Body System

The theory of phase transitions represents a central concept for the characterization of equilibrium matter. In this work we study experimentally an extension of this theory to the nonequilibrium dynamical regime termed dynamical quantum phase transitions (DQPTs). We investigate and measure DQPTs in a string of ions simulating interacting transverse-field Ising models. During the nonequilibrium dynamics induced by a quantum quench we show for strings of up to 10 ions the direct detection of DQPTs by revealing nonanalytic behavior in time. Moreover, we provide a link between DQPTs and the dynamics of other quantities such as the magnetization, and we establish a connection between DQPTs and entanglement production.

Swelling behavior of bisensitive interpenetrating polymer networks for microfluidic applications

Bisensitive interpenetrating polymer network (IPN) hydrogels of temperature sensitive net-poly(N-isopropylacrylamide) and pH sensitive net-poly(acrylic acid-co-acrylamide) for microfluidic applications were prepared via a sequential synthesis using free radical polymerization. The IPN indicated a suitable reversible alteration of swelling in response to the change in pH and temperature. The adequate change of the hydrogel volume is a basic requirement for microfluidic applications. Using the introduced correction factor f, it is possible to determine the cooperative diffusion coefficient (Dcoop) of cylindrical samples at any aspect ratio. The determined cooperative diffusion coefficient allowed the evaluation of varying swelling processes of different network structures. The presence of the second sub-network of the IPN improved the swelling behaviour of the first sub-network compared to the individual networks.

Spectroscopy of Interacting Quasiparticles in Trapped Ions

The static and dynamic properties of many-body quantum systems are often well described by collective excitations, known as quasiparticles. Engineered quantum systems offer the opportunity to study such emergent phenomena in a precisely controlled and otherwise inaccessible way. We present a spectroscopic technique to study artificial quantum matter and use it for characterizing quasiparticles in a many-body system of trapped atomic ions. Our approach is to excite combinations of the system's fundamental quasiparticle eigenmodes, given by delocalized spin waves. By observing the dynamical response to superpositions of such eigenmodes, we extract the system dispersion relation, magnetic order, and even detect signatures of quasiparticle interactions. Our technique is not limited to trapped ions, and it is suitable for verifying quantum simulators by tuning them into regimes where the collective excitations have a simple form.

Nitric oxide production by polymorphonuclear leucocytes in infected cystic fibrosis sputum consumes oxygen

Chronic Pseudomonas aeruginosa lung infection in cystic fibrosis (CF) patients is characterized by persisting mucoid biofilms in hypoxic endobronchial mucus. These biofilms are surrounded by numerous polymorphonuclear leucocytes (PMNs), which consume a major part of present molecular oxygen (O(2)) due to production of superoxide (O(2)(-)). In this study, we show that the PMNs also consume O(2) for production of nitric oxide (NO) by the nitric oxide synthases (NOS) in the infected endobronchial mucus. Fresh expectorated sputum samples (n = 28) from chronically infected CF patients (n = 22) were analysed by quantifying and visualizing the NO production. NO production was detected by optode measurements combined with fluorescence microscopy, flow cytometry and spectrophotometry. Inhibition of nitric oxide synthases (NOS) with N(G) -monomethyl-L-arginine (L-NMMA) resulted in reduced O(2) consumption (P < 0·0008, n = 8) and a lower fraction of cells with fluorescence from the NO-indicator 4-amino-5-methylamino-2',7'-difluorofluorescein diacetate (DAF-FM) (P < 0·002, n = 8). PMNs stained with DAF-FM and the superoxide indicator hydroethidine (HE) and host cells with inducible NOS (iNOS) were identified in the sputum. In addition, the production of the stable end-products of NO in CF sputum was correlated with the concentration of PMNs; NO(3)(-) (P < 0·04, r = 0·66, n = 10) and NO(2)(-) (P< 0·006, r = 0·78, n = 11). The present study suggests that besides consumption of O(2) for production of reactive oxygen species, the PMNs in CF sputum also consume O(2) for production of NO.

Experimental violation of multipartite Bell inequalities with trapped ions

We report on the experimental violation of multipartite Bell inequalities by entangled states of trapped ions. First, we consider resource states for measurement-based quantum computation of between 3 and 7 ions and show that all strongly violate a Bell-type inequality for graph states, where the criterion for violation is a sufficiently high fidelity. Second, we analyze Greenberger-Horne-Zeilinger states of up to 14 ions generated in a previous experiment using stronger Mermin-Klyshko inequalities, and show that in this case the violation of local realism increases exponentially with system size. These experiments represent a violation of multipartite Bell-type inequalities of deterministically prepared entangled states. In addition, the detection loophole is closed.

Measurement-based quantum computation with trapped ions

Measurement-based quantum computation represents a powerful and flexible framework for quantum information processing, based on the notion of entangled quantum states as computational resources. The most prominent application is the one-way quantum computer, with the cluster state as its universal resource. Here we demonstrate the principles of measurement-based quantum computation using deterministically generated cluster states, in a system of trapped calcium ions. First we implement a universal set of operations for quantum computing. Second we demonstrate a family of measurement-based quantum error correction codes and show their improved performance as the code length is increased. The methods presented can be directly scaled up to generate graph states of several tens of qubits.

Experimental generation of quantum discord via noisy processes

Quantum systems in mixed states can be unentangled and yet still nonclassically correlated. These correlations can be quantified by the quantum discord and might provide a resource for quantum information processing tasks. By precisely controlling the interaction of two ionic qubits with their environment, we investigate the capability of noise to generate discord. Firstly, we show that noise acting on only one quantum system can generate discord between two. States generated in this way are restricted in terms of the rank of their correlation matrix. Secondly, we show that classically correlated noise processes are capable of generating a much broader range of discordant states with correlation matrices of any rank. Our results show that noise processes prevalent in many physical systems can automatically generate nonclassical correlations and highlight fundamental differences between discord and entanglement.

Positive allosteric modulation by ivermectin of human but not murine P2X7 receptors

BACKGROUND AND PURPOSE

In mammalian cells, the anti-parasitic drug ivermectin is known as a positive allosteric modulator of the ATP-activated ion channel P2X4 and is used to discriminate between P2X4- and P2X7-mediated cellular responses. In this paper we provide evidence that the reported isoform selectivity of ivermectin is a species-specific phenomenon.

EXPERIMENTAL APPROACH

Complementary electrophysiological and fluorometric methods were applied to evaluate the effect of ivermectin on recombinantly expressed and on native P2X7 receptors. A biophysical characterization of ionic currents and of the pore dilation properties is provided.

KEY RESULTS

Unexpectedly, ivermectin potentiated currents in human monocyte-derived macrophages that endogenously express hP2X7 receptors. Likewise, currents and [Ca(2+) ](i) influx through recombinant human (hP2X7) receptors were potently enhanced by ivermectin at submaximal or saturating ATP concentrations. Since intracellular ivermectin did not mimic or prevent its activity when applied to the bath solution, the binding site of ivermectin on hP2X7 receptors appears to be accessible from the extracellular side. In contrast to currents through P2X4 receptors, ivermectin did not cause a delay in hP2X7 current decay upon ATP removal. Interestingly, NMDG(+) permeability and Yo-Pro-1 uptake were not affected by ivermectin. On rat or mouse P2X7 receptors, ivermectin was only poorly effective, suggesting a species-specific mode of action.

CONCLUSIONS AND IMPLICATIONS

The data indicate a previously unrecognized species-specific modulation of human P2X7 receptors by ivermectin that should be considered when using this cell-biological tool in human cells and tissues.

Quantum simulation of the Klein paradox with trapped ions

We report on quantum simulations of relativistic scattering dynamics using trapped ions. The simulated state of a scattering particle is encoded in both the electronic and vibrational state of an ion, representing the discrete and continuous components of relativistic wave functions. Multiple laser fields and an auxiliary ion simulate the dynamics generated by the Dirac equation in the presence of a scattering potential. Measurement and reconstruction of the particle wave packet enables a frame-by-frame visualization of the scattering processes. By precisely engineering a range of external potentials we are able to simulate text book relativistic scattering experiments and study Klein tunneling in an analogue quantum simulator. We describe extensions to solve problems that are beyond current classical computing capabilities.

Ion imaging in a high-gradient magnetic guide

We study a photoionization method to detect and image a narrow beam of cold atoms traveling along a high-gradient two-wire magnetic guide that is continuously on. Ions are accelerated in a compact acceleration region, directed through a drift region several centimeters in length, and detected using a position-sensitive ion detector. The potentials of several electrodes can be varied to adjust the imaging properties. Using ion trajectory simulations as well as experiments, we study the passage of the ions through the detection system, the magnification of the detection system, and the time-of-flight characteristics.

Image-guided surgery of the anterior skull base

Minimally invasive surgical procedures have revolutionized surgery of the paranasal sinuses. The endonasal procedure has become standard practice due to a better understanding of pathological physiology. However, malformations, previous operations and bleeding can interfere greatly with intraoperative orientation. Together with microscopy and endoscopy, image-guided surgery has the potential to be of significant assistance to the surgeon. We evaluated the electromagnetic navigation system InstaTrak 2000 (Visualization Technologies Inc., Lawrence, MA) in 168 patients with various disorders of the paranasal sinuses who underwent endonasal surgery. The system consists of a headset attached to an electronic transmitter which is fitted on the dorsum of the nose and in the external auditory canal. With the aid of low-frequency magnetic fields the position of the instrument equipped with an electromagnetic receiver is calculated on the basis of the reaction of ferromagnetic components in the magnetic field; the location is displayed in orthogonal sections on a high resolution screen. The intraoperative accuracy of the system was estimated to be 1.2-2.8 mm. The preparation time amounted to < 10 min. No system failures were observed. The InstaTrak 2000 navigation system is only suitable for endonasal surgery. The placement of the electromagnetic transmitter and receiver allows flexible head positioning through the use of a headset. This system is a valuable aid for the surgeon under anatomically complex conditions. The technology also lends itself well to training purposes, as visualization in different sectional planes augments the understanding of anatomy and pathological anatomy.

Seasonal use of savanna landscapes by the Gouldian finch, Erythrura gouldiae, in the Yinberrie Hills area, Northern Territory

The diet, attributes of feeding sites and patterns of seasonal movements of a population of the Gouldian finch, Erythrura gouldiae, were studied in the Yinberrie Hills area north of Katherine in the Northern Territory. In the dry season (April–November) Gouldian finches foraged mostly on burnt ground and fed on exposed seed of annual grasses, especially seed of spear-grass, Sorghum spp. In the wet season (December–March) Gouldian finches fed on seed of a sequence of perennial grass species, including Themeda triandra, Alloteropsis semialata, Chrysopogon fallax and Heteropogon triticeus. Gouldian finches undertake regular seasonal shifts in habitat, from breeding areas in hill woodland in the dry season to adjacent lowlands throughout much of the wet season, in response to seasonal changes in food availability. There is an annual pulse in abundance of fallen seed in the early dry season that is depleted to near zero levels by germination of annual grasses early in the wet season. Thereafter, finches depend on seed from other sources, principally ripe and ripening seed of perennial grasses. Observations over three successive wet seasons suggest that Gouldian finches track seed resources provided by seeding perennial grasses over an extensive area of lowland grassy woodland adjacent to the breeding area, favouring small patches of grassy woodland for brief periods until seed fall. There were subtle differences between years in the types of resources used. Management of Gouldian finch populations will entail protection and management of the full range of grassland habitats used throughout the annual cycle, and will require predictive knowledge of the causes of patterning of seed resources and probably an ability to exert control over the timing and extent of fires in fire-prone seasonal savanna landscapes.

The role of gemcitabine alone and in combination in the treatment of pancreatic cancer

Pancreatic cancer, one of the most frequently reported gastrointestinal tumors, has a 5-year survival of less than 5%. Despite representing only 2-3% of the total cancer incidence, it is the fifth leading cause of cancer death. This is because it is commonly only diagnosed at an advanced stage. Until recently the traditional therapy for patients with advanced disease was palliative 5-fluorouracil (5-FU)-based chemotherapy. However, the novel antinucleoside gemcitabine (Gemzar) has demonstrated a survival benefit over 5-FU, and an improvement in disease-related symptoms and quality of life in patients with advanced disease. This review presents an overview of the clinical studies of gemcitabine, either alone or in combination, with other chemotherapeutic agents and/or radiation therapy, in the treatment of these patients. A comparison of these studies is made with those using alternative treatment regimens. The data suggest that gemcitabine in combination with biomodulated 5-FU should be considered the standard palliative treatment to which other new drug combinations or combined modality chemoradiation regimens should be compared.

Plasmid stability of recombinant Pseudomonas sp. B13 FR1 pFRC20P in continuous culture

Plasmid stability of recombinant Pseudomonas sp. B13 FR1 pFRC20P, a strain capable of mineralizing 3- and 4-chlorobenzoate and 4-methylbenzoate, was investigated in continuous culture. The hybrid cosmid pFRC20P enables the strain to mineralize 4-methylbenzoate. Rapid plasmid loss was observed under nonselective conditions using 3-chlorobenzoate as the substrate. Plasmid stability decreased with increasing dilution rate. Despite the growth advantage of the generated plasmid free cells a total depletion of plasmid bearing cells was not observed. After approximately 50 generations the fraction of plasmid bearing cells reached a constant level of 10%, which was stably maintained during the next 25 generations. Cells from this stage were used to inoculate a new culture that resulted in a stable level of 50% plasmid bearing cells. By a temporary substrate change to selective conditions (4-methylbenzoate), this level could be further increased to 70%. Literature models on plasmid stability could not be applied to describe the experimental data. Therefore, a new but unstructured model was developed to describe the experimental results. The model is based on the existence of three subpopulations: a plasmid free one, an original plasmid bearing one with a growth disadvantage compared to plasmid free cells, and a second plasmid bearing subpopulation with increased stability that is generated from the original one and has a growth rate comparable to the plasmid free cells.

Prognostic factors in children with Ewing's sarcoma

Patient characteristics of 272 patients entered in a clinical trial conducted by the Pediatric Intergroup Ewing's Sarcoma Committee between June 1972 and November 1978 were examined for their relationship to prognosis. Prognosis was defined as disease-free survival time (time to local recurrence and/or metastatic disease) and overall survival time; all times were measured from the start of treatment. In a multivariate regression model, primary site of disease was the major variable that influenced prognosis, and patients with pelvic sites had the least favorable prognoses, followed by those with proximal and rib sites. The most favorable sites were distal and other. The median disease-free and survival times in weeks by primary site were, respectively: pelvis (69, 112), proximal (102, 141), rib (105, 109+), distal (226+, 240), and other (96+, 199+). Females had better prognoses than males; the median survival times were 197 and 147 weeks, respectively. An abnormal liver function as indicated by an abnormal serum glutamic-oxaloacetic transaminase value (greater than 45 IU) was a bad prognostic sign, although only 8 patients had this finding; their median survival time was 94 weeks. Patients who had resections had a slight advantage in survival compared with those having biopsies, though the difference favoring resection patients was not consistent for both sexes in any primary site. Individual characteristics of the patients that were of prognostic significance were: blood lymphocyte counts (high counts favorable), polymorphonuclear leukocyte counts (high counts unfavorable), and time from symptoms to diagnosis (times less than 1 mol favorable). Patients who received treatment 2 had significantly poorer prognoses than those given treatments 1 or 3. The median disease-free and survival times by treatment were (in wk): 1 (134, 198+), 2 (81, 120), and 3 (123, 182).