Higher-order neural networks, Polyà polynomials, and Fermi cluster diagrams

The problem of controlling higher-order interactions in neural networks is addressed with techniques commonly applied in the cluster analysis of quantum many-particle systems. For multineuron synaptic weights chosen according to a straightforward extension of the standard Hebbian learning rule, we show that higher-order contributions to the stimulus felt by a given neuron can be readily evaluated via Polyà's combinatoric group-theoretical approach or equivalently by exploiting a precise formal analogy with fermion diagrammatics.

Neural Representation of Probabilistic Information

It has been proposed that populations of neurons process information in terms of probability density functions (PDFs) of analog variables. Such analog variables range, for example, from target luminance and depth on the sensory interface to eye position and joint angles on the motor output side. The requirement that analog variables must be processed leads inevitably to a probabilistic description, while the limited precision and lifetime of the neuronal processing units lead naturally to a population representation of information. We show how a time-dependent probability densityρ(x; t) over variable x, residing in a specified function space of dimension D, may be decoded from the neuronal activities in a population as a linear combination of certain decoding functions φi(x), with coefficients given by the N firing rates ai(t) (generally with D ≪ N). We show how the neuronal encoding process may be described by projecting a set of complementary encoding functions [Formula: see text]i(x) on the probability density ρ(x; t), and passing the result through a rectifying nonlinear activation function. We show how both encoders [Formula: see text]i (x) and decoders φi(x) may be determined by minimizing cost functions that quantify the inaccuracy of the representation. Expressing a given computation in terms of manipulation and transformation of probabilities, we show how this representation leads to a neural circuit that can carry out the required computation within a consistent Bayesian framework, with the synaptic weights being explicitly generated in terms of encoders, decoders, conditional probabilities, and priors.

A human cardiopulmonary system model applied to the analysis of the Valsalva maneuver

Previous models combining the human cardiovascular and pulmonary systems have not addressed their strong dynamic interaction. They are primarily cardiovascular or pulmonary in their orientation and do not permit a full exploration of how the combined cardiopulmonary system responds to large amplitude forcing (e.g., by the Valsalva maneuver). To address this issue, we developed a new model that represents the important components of the cardiopulmonary system and their coupled interaction. Included in the model are descriptions of atrial and ventricular mechanics, hemodynamics of the systemic and pulmonic circulations, baroreflex control of arterial pressure, airway and lung mechanics, and gas transport at the alveolar-capillary membrane. Parameters of this combined model were adjusted to fit nominal data, yielding accurate and realistic pressure, volume, and flow waveforms. With the same set of parameters, the nominal model predicted the hemodynamic responses to the markedly increased intrathoracic (pleural) pressures during the Valsalva maneuver. In summary, this model accurately represents the cardiopulmonary system and can explain how the heart, lung, and autonomic tone interact during the Valsalva maneuver. It is likely that with further refinement it could describe various physiological states and help investigators to better understand the biophysics of cardiopulmonary disease.

Quality of informed consent in cancer clinical trials: a cross-sectional survey

BACKGROUND

Investigators have to obtain informed consent before enrolling participants in clinical trials. We wanted to measure the quality of understanding among participants in clinical trials of cancer therapies, to identify correlates of increased understanding, and to assess providers' beliefs about clinical research. We also sought evidence of therapeutic misconceptions in participants and providers.

METHODS

We sent a standard questionnaire to 287 adult patients with cancer who had recently enrolled in a clinical trial at one of three affiliated institutions, and surveyed the provider who obtained each patient's consent.

FINDINGS

207 of 287 (72%) patients responded. 90% (186) of these respondents were satisfied with the informed consent process and most considered themselves to be well informed. Nevertheless, many did not recognise non-standard treatment (74%), the potential for incremental risk from participation (63%), the unproven nature of the treatment (70%), the uncertainty of benefits to self (29%), or that trials are done mainly to benefit future patients (25%). In multivariate analysis, increased knowledge was associated with college education, speaking only English at home, use of the US National Cancer Institute consent form template, not signing the consent form at initial discussion, presence of a nurse, and careful reading of the consent form. Only 28 of 61 providers (46%) recognised that the main reason for clinical trials is benefit to future patients.

INTERPRETATION

Misconceptions about cancer clinical trials are frequent among trial participants, and physician/investigators might share some of these misconceptions. Efforts to educate providers and participants about the underlying goals of clinical trials are needed.

Phase I clinical trial of 7-cyanoquinocarcinol (DX-52-1) in adult patients with refractory solid malignancies

PURPOSE

A phase I study of the antitumor antibiotic 7-cyanoquinocarcinol, DX-52-1, was conducted in patients with refractory solid malignancies. This study sought to determine the maximum tolerated dose and principal toxicities of this agent and to characterize its pharmacokinetic behavior.

METHODS

Patients were required to have adequate bone marrow, renal and hepatic function. DX-52-1 was administered by i.v. continuous infusion over a 6-h period each week for four consecutive weeks followed by a 2-week rest period, which constituted one cycle of treatment.

RESULTS

Initial dose levels were 3, 6, and 10 mg/m2. An intermediate dose level of 8 mg/m2 was added after acceptable toxicity was observed at the 6 mg/m2 dose level, but dose-limiting toxicities, including life-threatening ones, were seen at the 10 mg/m2 dose level in all three patients. The maximum tolerated dose (MTD) was subsequently determined to be 6 mg/m2. Because a clear pattern of toxicities was not initially evident, a larger than usual number of additional patients (16) were enrolled at the MTD to better distinguish toxicities due to the study drug from those secondary to the patients' underlying malignancies. Even at the MTD, the drug was poorly tolerated, with gastrointestinal toxicities (abdominal pain, nausea, vomiting and increased liver function tests) predominating and dose-limiting. Pharmacokinetic studies revealed that the mean maximum plasma concentration of DX-52-1 in patients evaluated at the MTD (138.8 +/- 59.3 ng/ml, n = 19) was considerably lower than the concentrations required for cytostatic or cytotoxic activity against sensitive human tumor cell lines in vitro. Further, the weekly dose intensity of the most efficacious treatment schedule identified during in vivo antitumor efficacy studies was 60 times greater than the 6 mg/m2 weekly dose tolerated by cancer patients. None of the 33 patients participating in this study, including the 22 patients evaluated at the MTD, had any response to treatment.

CONCLUSION

Given the poor tolerability, the inability to achieve drug levels necessary to inhibit in vitro or in vivo tumor growth, and the lack of any responses in our study, DX-52-1, as given by this schedule, does not appear to warrant further investigation in phase II studies.

Pancreatic cancer: cost-effectiveness of imaging technologies for assessing resectability

PURPOSE

To evaluate the cost-effectiveness of imaging strategies for the assessment of resectability in patients with pancreatic cancer.

MATERIALS AND METHODS

A decision model was developed to calculate costs and benefits (survival) accruing to hypothetical cohorts of patients with known or suspected pancreatic cancer. Results are presented as cost per life-year gained under various scenarios and assumptions of diagnostic test characteristics, surgical mortality, disease characteristics, and costs.

RESULTS

With best estimates for all data inputs, the strategy of computed tomography (CT) followed by laparoscopy and laparoscopic ultrasonography (US) had an incremental cost-effectiveness ratio of $87,502 per life-year gained, compared with best supportive care. This strategy was significantly more cost-effective than CT followed by magnetic resonance (MR) imaging and was significantly less expensive than other imaging strategies while providing a statistically and clinically insignificant difference in life-year gains. A strategy involving no imaging (immediate surgery) was more expensive but less effective than all imaging strategies. A hypothetical perfect test with cost equal to that of CT followed by MR had an incremental cost-effectiveness ratio of $64,401 per life-year gained, compared to best supportive care.

CONCLUSION

Most available imaging tests for assessing resectability of pancreatic cancer do not differ in effectiveness, but a strategy of CT, laparoscopy, and laparoscopic US would consistently result in significantly lower costs than other imaging tests under a wide range of scenarios.

Double bond in the side chain of 1alpha,25-dihydroxy-22-ene-vitamin D(3) is reduced during its metabolism: studies in chronic myeloid leukemia (RWLeu-4) cells and rat kidney

1alpha,25-Dihydroxyvitamin D(3) [1alpha,25(OH)(2)D(3)] is mainly metabolized via the C-24 oxidation pathway and undergoes several side chain modifications which include C-24 hydroxylation, C-24 ketonization, C-23 hydroxylation and side chain cleavage between C-23 and C-24 to form the final product, calcitroic acid. In a recent study we reported that 1alpha,25-dihydroxyvitamin D(2) [1alpha,25(OH)(2)D(2)] like 1alpha,25(OH)(2)D(3), is also converted into the same final product, calcitroic acid. This finding indicated that 1alpha,25(OH)(2)D(2) also undergoes side chain cleavage between C-23 and C-24. As the side chain of 1alpha,25(OH)(2)D(2) when compared to the side chain of 1alpha,25(OH)(2)D(3), has a double bond between C-22 and C-23 and an extra methyl group at C-24 position, it opens the possibility for both (a) double bond reduction and (b) demethylation to occur during the metabolism of 1alpha,25(OH)(2)D(2). We undertook the present study to establish firmly the possibility of double bond reduction in the metabolism of vitamin D(2) related compounds. We compared the metabolism of 1alpha,25-dihydroxy-22-ene-vitamin D(3) [1alpha,25(OH)(2)-22-ene-D(3)], a synthetic vitamin D analog whose side chain differs from that of 1alpha,25(OH)(2)D(3) only through a single modification namely the presence of a double bond between C-22 and C-23. Metabolism studies were performed in the chronic myeloid leukemic cell line (RWLeu-4) and in the isolated perfused rat kidney. Our results indicate that both 1alpha,25(OH)(2)-22-ene-D(3) and 1alpha,25(OH)(2)D(3) are converted into common metabolites namely, 1alpha,24(R),25-trihydroxyvitamin D(3) [1alpha,24(R),25(OH)(3)D(3)], 1alpha,25-dihydroxy-24-oxovitamin D(3) [1alpha,25(OH)(2)-24-oxo-D(3)], 1alpha,23(S),25-trihydroxy-24-oxovitamin D(3) and 1alpha,23-dihydroxy-24,25,26,27-tetranorvitamin D(3). This finding indicates that the double bond in the side chain of 1alpha,25(OH)(2)-22-ene-D(3) is reduced during its metabolism. Along with the aforementioned metabolites, 1alpha,25(OH)(2)-22-ene-D(3) is also converted into two additional metabolites namely, 1alpha,24,25(OH)(3)-22-ene-D(3) and 1alpha,25(OH)(2)-24-oxo-22-ene-D(3). Furthermore, we did not observe direct conversion of 1alpha,25(OH)(2)-22-ene-D(3) into 1alpha,25(OH)(2)D(3). These findings indicate that 1alpha,25(OH)(2)-22-ene-D(3) is first converted into 1alpha,24,25(OH)(3)-22-ene-D(3) and 1alpha,25(OH)(2)-24-oxo-22-ene-D(3). Then the double bonds in the side chains of 1alpha,24,25(OH)(3)-22-ene-D(3) and 1alpha,25(OH)(2)-24-oxo-22-ene-D(3) undergo reduction to form 1alpha,24(R),25(OH)(3)D(3) and 1alpha,25(OH)(2)-24-oxo-D(3), respectively. Thus, our study indicates that the double bond in 1alpha,25(OH)(2)-22-ene-D(3) is reduced during its metabolism. Furthermore, it appears that the double bond reduction occurs only during the second or the third step of 1alpha,25(OH)(2)-22-ene-D(3) metabolism indicating that prior C-24 hydroxylation of 1alpha,25(OH)(2)-22-ene-D(3) is required for the double bond reduction to occur.

Superfluid phase transitions in dense neutron matter

The phase transitions in a realistic system with triplet pairing, dense neutron matter, have been investigated. The spectrum of phases of the 3P2-3F2 model, which adequately describes pairing in this system, is analytically constructed with the aid of a separation method for solving BCS gap equations in states of arbitrary angular momentum. In addition to solutions involving a single value of the magnetic quantum number (and its negative), there exist ten real multicomponent solutions. Five of the corresponding angle-dependent order parameters have nodes, and five do not. In contrast to the case of superfluid 3He, transitions occur between phases with nodeless order parameters.

A few minor suggestions

We agree with almost all of the analysis in this excellent presentation of the molecular view of avoidance behavior. A few suggestions are made as follows: Referring to response-generated stimuli as ''readily observable" seems not quite right for the kinesthetic components of such stimuli, although their scientific legitimacy is not questioned. Interpreting response-generated stimuli as a form of positive reinforcement is contested, and an alternative interpretation is offered. A possibly simpler interpretation of the Sidman (1962) two-lever experiment is suggested. We question Dinsmoor's (2001) explanation for warning stimuli not being avoided, except for the reference to the weakness of third-order conditioning effects. A final question is raised regarding the nature of the variables that are responsible for the momentary evocation of the avoidance response.

A phase I clinical and pharmacokinetic study of the dolastatin analogue cemadotin administered as a 5-day continuous intravenous infusion

PURPOSE

The dolastatins are a class of naturally occurring cytotoxic peptides which function by inhibiting microtubule assembly and tubulin polymerization. Cemadotin is a synthetic analogue of dolastatin 15 with potent antiproliferative and preclinical antitumor activity. This report describes a phase I study to evaluate the administration of cemadotin to adult cancer patients by a 5-day continuous intravenous (CIV) infusion.

METHODS

All patients had histologically confirmed refractory solid tumors. The dose was escalated from an initial level of 2.5 mg/m2 (0.5 mg/m2 daily) according to a modified Fibonacci algorithm. A minimum of three patients was evaluated at each dose level until the maximum tolerated dose (MTD) was established. Treatment was repeated every 21 days until patients were removed from the study due to toxicity or disease progression. Drug-related toxicities were evaluated and graded by the U.S. National Cancer Institute's Common Toxicity Criteria. A radioimmunoassay (RIA) that detected both the parent drug and its metabolites with an intact N-terminal region of the molecule was used for pharmacokinetic studies.

RESULTS

Twenty heavily pretreated patients received a total of 40 courses of cemadotin over five dose levels ranging from 2.5 to 17.5 mg/m2. Reversible dose-related neutropenia was the principal dose-limiting toxicity and 12.5 mg/m2 was established as the MTD. Nonhematologic toxicities attributed to the drug were moderate, and there was no evidence of the cardiovascular toxicity noted in the prior phase I studies of cemadotin given IV as a 5-min injection or 24-h infusion. There were no objective antitumor responses. Time courses of the cemadotin RIA equivalent concentration in whole blood were defined in 14 patients during the first cycle of therapy. The RIA-detectable species exhibited apparent first-order pharmacokinetics across the entire range of doses. The mean +/- SD of the observed steady-state blood concentration at the 12.5 mg/m2 MTD was 282 +/- 7 nM (n = 3). Blood levels decayed monoexponentially following the end of the infusion, with a mean half-life of 13.2 +/- 4.3 h (n = 14) in all patients. Mean values (n = 14) of the total blood clearance and apparent volume of distribution at steady state were 0.52 +/- 0.09 lh/m2 and 9.9 +/- 3.3 l/m2, respectively.

CONCLUSIONS

The cardiotoxic effects of cemadotin were completely avoided by administering it as a 120-h CIV infusion. Thus. cardiovascular toxicity appears to be associated with the magnitude of the peak blood levels of the parent drug or its metabolites, whereas myelotoxicity is related to the duration of time that blood levels exceed a threshold concentration. Nevertheless, the data acquired during the extensive clinical experience with cemadotin requires careful examination to assess whether advancing this compound into disease-oriented efficacy studies is merited.

Coevolution between a cockroach and its bacterial endosymbiont: a biogeographical perspective

Cryptocercus are subsocial, xylophagous cockroaches that live in temperate forests. Like other cockroaches, Cryptocercus harbour endosymbiotic bacteria in their fat bodies. Two species of Cryptocercus occur in the palaearctic, one each in eastern Russia and south-central China. In the USA, there are five species: one in the north-west and four in the south-east. Little is known about the relationship between the Eurasian and North American Cryptocercus or the causes of the disjunct distribution. Here, a molecular phylogeny for six out of the seven Cryptocercus species and their endosymbionts is inferred in an attempt to understand the evolution and biogeography of the genus. Our analysis showed that the North American Cryptocercus are monophyletic, suggesting that a single colonization event was followed by vicariance. There was complete concordance between the host and endosymbiont phylogenetic trees. Divergence estimates based on endosymbiont DNA sequences suggested that the palaearctic and nearctic Cryptocercus diverged 70-115 million years (Myr) ago and the eastern- and western-USA species diverged 53-88 Myr ago. These divergence estimates were correlated with biogeographical events, and a hypothesis is presented to explain the current distribution of Cryptocercus. Our findings suggest that Cryptocercus has had a long evolutionary history, dating back to the Jurassic.

Phase I and pharmacokinetic study of ecteinascidin 743 administered as a 72-hour continuous intravenous infusion in patients with solid malignancies

Ecteinascidin 743 (ET-743) is a cytotoxic tetrahydroisoquinoline alkaloid that covalently binds to DNA in the minor groove. The in vitro chemosensitivity of cancer cells to ET-743 is markedly enhanced by prolonging the duration of exposure to the drug. A Phase I study of ET-743 given as a 72-h continuous i.v. infusion every 21 days was performed. Characteristics of the 21 adult patients with refractory solid tumors enrolled in the study were as follows: (a) 12 men; (b) 9 women; (c) median age, 59 years; (d) Eastern Cooperative Oncology Group performance status < or = 1, 20 patients; and (e) two prior regimens of chemotherapy, 7 patients. Dose limiting toxicity (DLT) was defined by typical criteria, except that grade 3 transaminitis did not constitute a DLT. There were no DLTs in the six patients evaluated at the first two dose levels of 600 and 900 microg/m2. Reversible grade 4 transaminitis occurred in two of nine patients after treatment with the first cycle of therapy at the third dose level of 1200 microg/m2. Another patient experienced grade 4 rhabdomyolysis, renal failure requiring hemodialysis, grade 4 neutropenia, and grade 3 thrombocytopenia during the second cycle of therapy with this dose. The maximum tolerated dose was 1200 microg/m2, and an additional six patients were enrolled at an intermediate dose level of 1050 microg/m2. This well-tolerated dose was established as the recommended Phase II dose. The disposition of ET-743 was distinctly biexponential, and a departure from linear pharmacokinetic behavior was evident at the 1200-microg/m2 dose level. Pharmacokinetic parameters determined at 1050 microg/m2 were (mean +/- SD): maximum plasma concentration, 318 +/- 147 pg/ml; initial disposition phase half-life, 9.0 +/- 10.3 min; terminal phase half-life, 69.0 +/- 56.7 h; and total plasma clearance, 28.4 +/- 22.5 liters/h/m2. Prolonged systemic exposure to concentrations of the agent that are cytotoxic in vitro were achieved. Toxicity of the drug is clearly schedule-dependent, because increasing the duration of infusion from 3 or 24 h to 72 h results in decreased myelosuppression and comparable hepatotoxicity. Although there were no objective responses to therapy, clear evidence of antitumor activity was observed in a patient with epithelioid mesothelioma, as confirmed by positron emission tomography studies. A Phase II trial to assess the efficacy of ET-743 against this highly refractory neoplasm has been initiated on the basis of this observation. The therapeutically optimal administration schedule remains to be established, inasmuch as there have been indications of activity against a variety of tumors during Phase I studies when the drug was infused over times ranging from 1 to 72 h. Characterizing the pharmacokinetics of ET-743 during the course of Phase II trials and Phase I combination studies is recommended to assure that this promising new anticancer drug can be used with an acceptable margin of safety.

Quality of informed consent: a new measure of understanding among research subjects

BACKGROUND

The informed consent of participants is ethically and legally required for most research involving human subjects. However, standardized methods for assessing the adequacy of informed consent to research are lacking.

METHODS AND RESULTS

We designed a brief questionnaire, the Quality of Informed Consent (QuIC), to measure subjects' actual (objective) and perceived (subjective) understanding of cancer clinical trials. The QuIC incorporates the basic elements of informed consent specified in federal regulations, assesses the therapeutic misconception (the belief that all aspects of a clinical trial are designed to directly benefit the subject), and employs the language and structure of the new National Cancer Institute template for informed consent documents. We modified the QuIC after receiving feedback from pilot tests with cancer research subjects, as well as validation from two independent expert panels. We then sent the QuIC to 287 adult cancer patients enrolled on phase I, II, or III clinical trials. Two hundred seven subjects (72%) completed the QuIC. To assess test-retest reliability, a random sample of 32 respondents was selected, of whom 17 (53%) completed the questionnaire a second time. The test-retest reliability was good with intraclass correlation coefficients of.66 for tests of objective understanding and.77 for tests of subjective understanding. The current version of the QuIC, which consists of 20 questions for objective understanding and 14 questions for subjective understanding, was tested for time and ease of administration in a sample of nine adult cancer patients. The QuIC required an average of 7.2 minutes to complete.

CONCLUSIONS

The QuIC is a brief, reliable, and valid questionnaire that holds promise as a standardized way to assess the outcome of the informed consent process in cancer clinical trials.

A model of the L-type Ca2+ channel in rat ventricular myocytes: ion selectivity and inactivation mechanisms

1. We have developed a mathematical model of the L-type Ca2+ current, which is based on data from whole-cell voltage clamp experiments on rat ventricular myocytes. Ion substitution methods were employed to investigate the ionic selectivity of the channel. Experiments were configured with Na+, Ca2+ or Ba2+ as the majority current carrier. 2. The amplitude of current through the channel is attenuated in the presence of extracellular Ca2+ or Ba2+. Our model accounts for channel selectivity by using a modified Goldman-Hodgkin-Katz (GHK) configuration that employs voltage-dependent channel binding functions for external divalent ions. Stronger binding functions were used for Ca2+ than for Ba2+. 3. Decay of the ionic current during maintained depolarization was characterized by means of voltage- and Ca2+-dependent inactivation pathways embedded in a five-state dynamic channel model. Particularly, Ca2+ first binds to calmodulin and the Ca2+-calmodulin complex is the mediator of Ca2+ inactivation. Ba2+-dependent inactivation was characterized using the ttau same scheme, but with a decreased binding to calmodulin. 4. A reduced amount of steady-state inactivation, as evidenced by a U-shaped curve at higher depolarization levels (>40 mV) in the presence of [Ca2+]o, was observed in double-pulse protocols used to study channel inactivation. To characterize this phenomenon, a mechanism was incorporated into the model whereby Ca2+ or Ba2+ also inhibits the voltage-dependent inactivation pathway. 5. The five-state dynamic channel model was also used to simulate single channel activity. Calculations of the open probability of the channel model are generally consistent with experimental data. A sixth state can be used to simulate modal activity by way of introducing long silent intervals. 6. Our model has been tested extensively using experimental data from a wide variety of voltage clamp protocols and bathing solution manipulations. It provides: (a) biophysically based explanations of putative mechanisms underlying Ca2+- and voltage-dependent channel inactivation, and (b) close fits to voltage clamp data. We conclude that the model can serve as a predictive tool in generating testable hypotheses for further investigation of this complex ion channel.

An ionic current model for medullary respiratory neurons

Neurons of the mammalian medullary respiratory center have complex patterns of electrophysiological behavior. Three typical phenomena associated with these patterns are spike frequency adaptation (SFA), delayed excitation (DE), and postinhibitory rebound (PIR). Although several nuclei are associated with the medullary-pontine respiratory center, we focused on neurons from two nuclei: (1) the ventral subnucleus of the nucleus tractus solitarius (vNTS) of the dorsal respiratory group and (2) the nucleus ambiguus (NA) of the ventral respiratory group. We developed a Hodgkin-Huxley (HH) type model of the typical medullary neuron that is capable of mimicking the discharge pattern of real neurons to a very high degree. Closer examination of typical data revealed, however, that there was not one type of medullary respiratory neuron, but at least three (types A, B1, and B2). We classified these neurons based on the electrophysiologic phenomena that they exhibited (type A exhibits DE but not PIR; types B1 and B2 exhibit PIR but not DE; all types are adapting). Our objective was to relate each of these well-known phenomena to specific ionic current mechanisms. In the model, three currents directly affect the phenomena investigated: the Ca2+-activated K+ current, I(K,Ca), controls peak and steady-state firing rates and the time constant of adaptation; the transient outward K+ current, I(A), is responsible for all aspects of DE, including the dependence of delay on the magnitude and duration of conditioning hyperpolarization; and the hyperpolarization-activated current, Ih, elicits PIR and dictates its dependencies. We consider that our HH model represents a unifying structure, whereby different electrophysiological phenomena or discharge patterns can be emulated using different strengths of the component ionic membrane currents (particularly I(K,Ca), I(A), and Ih). Moreover, its predictions suggest that the electrophysiological characteristics of medullary respiratory neurons, from different areas of the brainstem and even from different species, can be modeled using the same structural framework, wherein the specific properties of individual neurons are emulated by adjusting the strengths of key ionic membrane currents in the model.

Current perspectives on locally advanced pancreatic cancer

This year, approximately 40% of the 28,300 patients diagnosed with pancreatic carcinoma in the United States will present with locally advanced disease. Radiotherapeutic approaches are often employed, as these patients have unresectable tumors by virtue of local invasion into the retroperitoneal vessels in the absence of clinically detectable metastases. These treatments include external-beam irradiation with and without fluorouracil (5-FU)-based chemotherapy, intraoperative irradiation, and more recently, external-beam irradiation with new systemic agents, such as gemcitabine (Gemzar).

A closed-loop model of the canine cardiovascular system that includes ventricular interaction

A closed-loop model of cardiopulmonary circulation has been developed for the study of right-left ventricular interaction under physiologically normal and altered conditions. The core model provides insight into the effects of ventricular interaction and pericardial mechanics on hemodynamics. The complete model contains realistic descriptions of (a) the interacting ventricular free walls and septum, (b) the atria, (c) the pericardium, and (d) the systemic and pulmonary vascular loads. The current analysis extends previous work on ventricular interaction and pericardial influence under isolated heart conditions to loading conditions imposed by a closed-loop model of the circulation. A nonlinear least-squares parameter identification method (Levenberg-Marquardt algorithm) is used, together with parameter sensitivity analysis, to estimate the values of key parameters associated with the ventricular and circulation models. Pressure measurements taken at several anatomical locations in the circulation during open-chest experiments on dogs are used as data in the identification process. The complete circulatory model, including septal and pericardial coupling, serves as a virtual testbed for assessing the global affects of localized mechanical or hemodynamic alterations. Studies of both direct and series ventricular interaction, as well as the effect of the pericardium on cardiac performance, are accomplished with this model. Alterations in model parameter values are used to predict the impact of disease and/or clinical interventions on steady-state hemodynamic performance. Additionally, a software package titled CardioPV has been developed to integrate the complete model with data acquisition tools and a sophisticated graphical user interface. The complete software package enables users to collect experimental data, use the data to estimate model parameters, and view the model outputs in an online setting.

Rearrangement of the Fermi Surface of Dense Neutron Matter and the Direct Urca Cooling of Neutron Stars

It is proposed that a rearrangement of single-particle degrees of freedom may occur in a portion of the quantum-fluid interior of a neutron star. Such a rearrangement is associated with the pronounced softening of the spin-isospin collective mode which, under increasing density, leads to pion condensation. Arguments and estimates based on fundamental relations of many-body theory show that one realization of this phenomenon could produce very rapid cooling of the star via a direct nucleon Urca process displaying a T5 dependence on temperature.

Activity of multitargeted antifolate (pemetrexed disodium, LY231514) in patients with advanced colorectal carcinoma: results from a phase II study

BACKGROUND

The aim of this study was to confirm the activity and assess the safety profile of multitargeted antifolate (MTA) for patients with metastatic colorectal adenocarcinoma.

METHODS

Forty-six patients were enrolled in the study, 35 with colon and 11 with rectal carcinoma. Adjuvant therapy was allowed if completed 1 year previously. Patients received MTA 600 mg/m(2) as a 10-minute intravenous infusion once every 21 days. Blood samples were taken every cycle for pharmacokinetic and vitamin metabolite assays.

RESULTS

Among 39 patients eligible for efficacy analysis, 1 complete response and 5 partial responses were identified, for an overall response rate of 15.4% (95% confidence interval [CI], 4.1-26. 7%) for all patients. Fifteen patients had stable disease, with 9 living longer than 1 year. The median survival was 16.2 months (95% CI, 10.5-17.0%); 65% of patients were alive at 1 year, and the median time to progression was 4.4 months (range, 3.2-5.7 months). The main toxicities were hematologic, with common toxicity criteria (CTC) Grades 3 or 4 noted as follows: thrombocytopenia (18%), neutropenia (55%), and anemia (18%). Nonhematologic toxicities included Grade 2 or 3 skin reaction (53%), ameliorated by dexamethasone, and Grade 3 transaminases (23%). Dose omissions were not required and 21% of doses were reduced.

CONCLUSIONS

MTA has clear activity in patients with colorectal carcinoma, and encouraging survival times were noted. MTA was well tolerated in this patient group, but myelosuppression was frequent. Toxicity may be increased with folate deficiency.

A phase I study of gemcitabine and docetaxel in patients with metastatic solid tumors

BACKGROUND

A Phase I study was initiated to determine the maximum tolerated dose of weekly gemcitabine combined with monthly, fixed-dose docetaxel.

METHODS

Patients with metastatic solid tumors were treated with docetaxel, 60 mg/m(2), on Day 1 every 28 days. Gemcitabine was administered on Days 1, 8, and 15 and underwent dose adjustment in cohorts of 3-6 patients. At the maximum tolerated dose, 11 additional patients were enrolled.

RESULTS

Twenty-six patients received 85 cycles of therapy. At the first dose level, the planned gemcitabine dose on Days 1, 8, and 15 was 800 mg/m(2). Two of the 6 patients treated at this dose level experienced dose-limiting toxicities (DLTs) requiring the reduction of gemcitabine to 600 mg/m(2) per dose and the administration of ciprofloxacin, 500 mg orally twice daily, on Days 8-18. At the second dose level the first 3 patients experienced no DLTs and the dose of gemcitabine was increased to 700 mg/m(2). Two of the 6 patients treated at the 700 mg/m(2) dose level experienced DLTs. Eleven additional patients were enrolled at the recommended Phase II dose of gemcitabine (600 mg/m(2)). At this dose level, Grade 3/4 (according the National Cancer Institute's common toxicity criteria) neutropenia and thrombocytopenia occurred in 12.5% and 2.1% of cycles, respectively. Grade 3 and 4 nonhematologic toxicities were uncommon. Three of seven evaluable patients with pancreatic carcinoma had evidence of significant antineoplastic activity (three partial responses). In addition, two complete responses (one patient with gastric carcinoma and one patient with ovarian carcinoma) and one partial response (patient with hepatocellular carcinoma) were noted in patients with other solid tumors.

CONCLUSIONS

The regimen comprised of docetaxel, 60 mg/m(2), on Day 1 and gemcitabine, 600 mg/m(2), on Days 1, 8, and 15 with ciprofloxacin on Days 8-18 every 28 days is safe, well tolerated, and active.

Computational model of the serotonergic modulation of sensory neurons in Aplysia

Serotonergic modulation of the sensory neurons that mediate the gill- and tail-withdrawal reflexes of Aplysia is a useful model system for studies of neuronal plasticity that contributes to learning and memory. The effects of serotonin (5-HT) are mediated, in part, via two protein kinases (protein kinase A, PKA, and protein kinase C, PKC), which in turn, modulate at least four membrane currents, including a S ("serotonin-sensitive") K(+) current (I(K, S)), a steeply voltage-dependent K(+) current (I(K-V)), a slow component of the Ca(2+)-activated K(+) current (I(K,Ca-S)), and a L-type Ca(2+) current (I(Ca-L)). The present study investigated how the modulation of these currents altered the spike duration and excitability of sensory neurons and examined the relative contributions of PKA- and PKC-mediated effects to the actions of 5-HT. A Hodgkin-Huxley type model was developed that described the ionic conductances in the somata of sensory neurons. The descriptions of these currents and their modulation were based largely on voltage-clamp data from sensory neurons. Simulations were preformed with the program SNNAP (Simulator for Neural Networks and Action Potentials). The model was sufficient to replicate empirical data that describes the membrane currents, action potential waveform and excitability as well as their modulation by application of 5-HT, increased levels of adenosine cyclic monophosphate or application of active phorbol esters. In the model, modulation of I(K-V) by PKC played a dominate role in 5-HT-induced spike broadening, whereas the concurrent modulation of I(K,S) and I(K,Ca-S) by PKA primarily accounted for 5-HT-induced increases in excitability. Finally, simulations indicated that a PKC-induced increase in excitability resulted from decreases of I(K,S) and I(K,Ca-S), which was likely the indirect result of cross-talk between the PKC and PKA systems. The results provide several predictions that warrant additional experimental investigation and illustrate the importance of considering indirect as well as direct effects of modulatory agents on the modulation of membrane currents.

The potential role for prolactin-inducible protein (PIP) as a marker of human breast cancer micrometastasis

The prolactin-inducible protein (PIP/GCPD15) is believed to originate from a limited set of tissues, including breast and salivary glands, and has been applied as a clinical marker for the diagnosis of metastatic tumours of unknown origin. We have investigated the potential role of PIP mRNA as a marker of human breast cancer metastasis. Using reverse transcription polymerase chain reaction and Southern or dot blot analysis, PIP mRNA was detected in 4/6 breast cell lines, independent of oestrogen receptor (ER) status. In breast primary tumours (n = 97), analysed from histologically characterized sections, PIP mRNA was detected in most cases. Higher PIP mRNA levels correlated with ER+ (P = 0.0004), progesterone receptor positive (PR+) (P = 0.0167), low-grade (P = 0.0195) tumours, and also PIP protein levels assessed by immunohistochemistry (n = 19, P = 0.0319). PIP mRNA expression was also detectable in 11/16 (69%) of axillary node metastases. PIP mRNA expression, however, was also detected in normal breast duct epithelium, skin, salivary gland and peripheral blood leucocyte samples from normal individuals. We conclude that PIP mRNA is frequently expressed in both primary human breast tumours and nodal metastases. However, the presence of PIP expression in skin creates a potential source of contamination in venepuncture samples that should be considered in its application as a marker for breast tumour micrometastases.

Calcium dynamics underlying pacemaker-like and burst firing oscillations in midbrain dopaminergic neurons: a computational study

A mathematical model of midbrain dopamine neurons has been developed to understand the mechanisms underlying two types of calcium-dependent firing patterns that these cells exhibit in vitro. The first is the regular, pacemaker-like firing exhibited in a slice preparation, and the second is a burst firing pattern sometimes exhibited in the presence of apamin. Because both types of oscillations are blocked by nifedipine, we have focused on the slow calcium dynamics underlying these firing modes. The underlying oscillations in membrane potential are best observed when action potentials are blocked by the application of TTX. This converts the regular single-spike firing mode to a slow oscillatory potential (SOP) and apamin-induced bursting to a slow square-wave oscillation. We hypothesize that the SOP results from the interplay between the L-type calcium current (I(Ca,L)) and the apamin-sensitive calcium-activated potassium current (I(K,Ca,SK)). We further hypothesize that the square-wave oscillation results from the alternating voltage activation and calcium inactivation of I(Ca,L). Our model consists of two components: a Hodgkin-Huxley-type membrane model and a fluid compartment model. A material balance on Ca(2+) is provided in the cytosolic fluid compartment, whereas calcium concentration is considered constant in the extracellular compartment. Model parameters were determined using both voltage-clamp and calcium-imaging data from the literature. In addition to modeling the SOP and square-wave oscillations in dopaminergic neurons, the model provides reasonable mimicry of the experimentally observed response of SOPs to TEA application and elongation of the plateau duration of the square-wave oscillations in response to calcium chelation.