Comparison of methods for the estimation of carboplatin pharmacokinetics in paediatric cancer patients

The antitumour and toxic effects of platinum drugs, in particular carboplatin, have been related to their plasma concentration and this has led to the concept of a target area under the plasma concentration-time curve (AUC) for carboplatin dosing. A formula based on renal function has been successfully applied to carboplatin dosing in adults and modified versions have also been proposed for paediatric patients. In order to monitor carboplatin AUC with maximum efficiency and minimum patient inconvenience, limited sampling strategies are desirable. A population method with Bayesian estimation is described, based on one or two samples taken following a dose of carboplatin. Population data were obtained from 22 paediatric patients treated with 200-1000 mg/m2 carboplatin as a 60-90 min infusion. Ultrafilterable carboplatin was determined by atomic absorption spectrophotometry. A two compartment model was fitted to each data set using the Maximum Likelihood estimator of the ADAPT programme. These parameter estimates provided the prior means and covariance matrix for the Bayesian estimator using a lognormal distribution. The test data sets consisted of ultrafilterable carboplatin concentrations in 23 patients (aged 1 month-18 years) who received similar treatment. The two compartment model was fitted to data sets containing one or two points, using the Bayesian maximum a posteriori (MAP) estimator and an error model derived from the population error model parameters. Results from the Bayesian analysis and other methods for the estimation of AUC, including relating clearance to surface area or to renal function, were evaluated by comparing the AUC estimate with the AUC determined by model-independent analysis. Overall, the optimal sampling strategy performed better than estimates based on renal function, which had a median bias of 5% and precision of 22%. With one data point at 60 min postinfusion, the median bias and precision were 3 and 6%, respectively. Addition of a second data point at 30 min during the infusion improved the estimate slightly (median bias -2%, precision 3%). Bayesian estimation produced more reliable estimates of AUC compared to values based on renal function, which in turn was slightly better than using surface area. A technique, developed in adult patients, for estimating AUC from a measurement of 24 h total plasma platinum was comparable to estimates based on renal function, but was less reliable. The estimation of carboplatin AUC can be performed using only one or two plasma samples and Bayesian analysis. This approach is less biased and more precise than methods based on surface area, renal function or total platinum at 24 h postdose, but is probably best used in combination with dosing based on renal function.

An anti-murine CD3 monoclonal antibody with a low affinity for Fc gamma receptors suppresses transplantation responses while minimizing acute toxicity and immunogenicity

145-2C11, a hamster mAb directed against the mouse CD3 complex, is a potent immunosuppressive agent. Upon initial treatment, 145-2C11 triggers a systemic release of multiple cytokines that is responsible for the acute toxicity of the mAb. This cellular activation is a consequence of the cross-linking between T lymphocytes and Fc gamma R-bearing cells, mediated by the high affinity of the hamster mAb for murine Fc gamma Rs. Repeated mAb injections result in the onset of a neutralizing humoral response. Therefore, there has been an increased interest in developing nonmitogenic forms of anti-CD3 mAbs, although it is not clear whether these Abs will retain immunosuppressive properties. To determine whether the initial cytokine production is necessary for the immunosuppressive properties and the immunogenicity of anti-CD3 mAbs in vivo, we have generated chimeric (hamster 145-2C11 F(ab')2 region/mouse Fc gamma portion) mAbs using murine isotypes with different affinities for Fc gamma Rs. The 145-2C11 and a chimeric IgG2a isotype, both of which bind murine Fc gamma Rs avidly, had similar activating, immunogenic, and immunosuppressive properties in mice. The administration of a chimeric IgG3 isotype with a very low affinity for murine Fc gamma Rs did not result in cytokine production, a humoral response against the mAb, or TCR desensitization. Nevertheless, prolongation of skin graft survival was similar in the IgG3, IgG2a, and 145-2C11-treated mice, indicating that Fc gamma R nonbinding anti-CD3 mAbs retain potent immunosuppressive properties in vivo while not being immunogenic. This enhanced therapeutic to toxic profile may be beneficial in clinical transplantation.

An anti-murine CD3 monoclonal antibody with a low affinity for Fc gamma receptors suppresses transplantation responses while minimizing acute toxicity and immunogenicity

145-2C11, a hamster mAb directed against the mouse CD3 complex, is a potent immunosuppressive agent. Upon initial treatment, 145-2C11 triggers a systemic release of multiple cytokines that is responsible for the acute toxicity of the mAb. This cellular activation is a consequence of the cross-linking between T lymphocytes and Fc gamma R-bearing cells, mediated by the high affinity of the hamster mAb for murine Fc gamma Rs. Repeated mAb injections result in the onset of a neutralizing humoral response. Therefore, there has been an increased interest in developing nonmitogenic forms of anti-CD3 mAbs, although it is not clear whether these Abs will retain immunosuppressive properties. To determine whether the initial cytokine production is necessary for the immunosuppressive properties and the immunogenicity of anti-CD3 mAbs in vivo, we have generated chimeric (hamster 145-2C11 F(ab')2 region/mouse Fc gamma portion) mAbs using murine isotypes with different affinities for Fc gamma Rs. The 145-2C11 and a chimeric IgG2a isotype, both of which bind murine Fc gamma Rs avidly, had similar activating, immunogenic, and immunosuppressive properties in mice. The administration of a chimeric IgG3 isotype with a very low affinity for murine Fc gamma Rs did not result in cytokine production, a humoral response against the mAb, or TCR desensitization. Nevertheless, prolongation of skin graft survival was similar in the IgG3, IgG2a, and 145-2C11-treated mice, indicating that Fc gamma R nonbinding anti-CD3 mAbs retain potent immunosuppressive properties in vivo while not being immunogenic. This enhanced therapeutic to toxic profile may be beneficial in clinical transplantation.

Decreased brain reward produced by ethanol withdrawal

Abstinence from chronic administration of various drugs of abuse such as ethanol, opiates, and psychostimulants results in withdrawal syndromes largely unique to each drug class. However, one symptom that appears common to these withdrawal syndromes in humans is a negative affective/motivational state. Prior work in rodents has shown that elevations in intracranial self-stimulation (ICSS) reward thresholds provide a quantitative index that serves as a model for the negative affective state during withdrawal from psychostimulants and opiates. The current study sought to determine whether ICSS threshold elevations also accompany abstinence from chronic ethanol exposure sufficient to induce physical dependence. Rats prepared with stimulating electrodes in the lateral hypothalamus were trained in a discrete-trial current-intensity ICSS threshold procedure; subsequently they were subjected to chronic ethanol administration in ethanol vapor chambers (average blood alcohol level of 197 mg/dl). A time-dependent elevation in ICSS thresholds was observed following removal from the ethanol, but not the control, chambers. Thresholds were significantly elevated for 48 hr after cessation of ethanol exposure, with peak elevations observed at 6-8 hr. Blood alcohol levels were directly correlated with the magnitude of peak threshold elevation. Ratings of traditional overt signs of withdrawal showed a similar time course of expression and resolution. The results suggest that decreased function of reward systems (elevations in reward thresholds) is a common element of withdrawal from chronic administration of several diverse classes of abused drugs.

Exposure of neonatal rats to alcohol by vapor inhalation demonstrates specificity of microcephaly and Purkinje cell loss but not astrogliosis

The artificial rearing model (AR) of fetal alcohol syndrome (FAS) has been shown to induce several major pathologies in the early postnatal rat brain development: microcephaly, selective neuronal cell loss, and activation of astroglia in the neocortex. The purpose of this study was to determine whether these pathologies were specific to the action of alcohol or, in contrast, could result from confounds attributed to this model of FAS. For this purpose, the pathological effects of AR were compared with those of a vapor inhalation (VI) model of FAS. Our studies showed that the microcephaly that developed after exposure to periodic blood alcohol levels (BALs) of 300-350 mg% during postnatal days 4-9 could be achieved by both AR and IV models of FAS, and thus is independent of the method of alcohol administration. In contrast, the gliosis measured by glial fibrillary acidic protein (GFAP) mRNA levels in cortex, as well as by immunohistochemical staining for GFAP, was found only in the AR-FAS model, but not in the VI model. However, the lack of gliosis in VI was apparently not due to a less intrusive intervention of alcohol, because VI exposure resulted in a reduction in Purkinje cell number comparable with that found after AR or intragastric intubation of alcohol. Based on these observations, we conclude that the activation of gliosis observed after AR is not a specific effect of alcohol, but rather is caused by an interaction of alcohol with as yet unidentified factors present in AR.

Urinary creatinine adjusted reference ranges for homovanillic and vanillylmandelic acid in children and adults

The relationship between urinary homovanillic acid (HVA), vanillylmandelic acid (VMA) and creatinine is investigated and reference ranges are constructed for HVA and VMA. A total of 769 urine samples were obtained from children and adults. The ratios HVA/creatinine and VMA/creatinine were highly correlated with creatinine concentration; hence, reference to creatinine was found to be an inappropriate adjustment for urinary dilution. An alternative method based upon linear regression is proposed. After allowing for differing levels of creatinine, HVA and VMA were found to be significantly correlated with age, height and weight for individuals aged less than 20 years. In those aged over 20 years, HVA was significantly correlated with weight and VMA with age. Differences between sexes were found in the levels of HVA and VMA, the exception being VMA in the over 20 age group. Reference ranges were constructed for HVA and VMA which are variously dependent upon creatinine, age, sex and weight.

Primary angiitis and angiopathy of the central nervous system and their relationship to systemic giant cell arteritis

Three cases of primary angiitis of the central nervous system were compared with previously published cases. Most cases occurred in older adults, were diagnosed histologically, and had a male-female ratio of 2:1. Angiographically identified cases, demonstrating angiopathy but not necessarily vasculitis as might be seen in histologically identified cases, were found in younger adults and showed a male-female ratio of 1:2. The autopsy cases had some similarities to systemic giant cell arteritis, including many cases with vasculitis in large branches of the circle of Willis and foci of systemic vasculitis. Vasculitides in arteries of different sizes may result from different responses to a variety of antigens or immune complexes rather than represent different disease processes. If causative immune mechanisms can be identified, primary angiitis of the central nervous system may become classified immunologically rather than histopathologically.

Screening for Wilms' tumour in patients with aniridia, Beckwith syndrome, or hemihypertrophy

The role of screening for early detection of Wilms' tumour (WT) in patients with aniridia (A), Beckwith-Weidemann syndrome (BWS) and hemihypertrophy (HH) has been explored. Of the 1,622 Wilms' tumour patients registered with the National Childhood Cancer Registry from 1971 to 1991, 41 were recorded as having A, BWS or HH. Twenty-eight of these had their anomaly diagnosed before the WT and 13 had screening procedures carried out, mainly abdominal ultrasound. In 8 patients the screening procedure detected the WT. There was no significant difference in stage distribution or outcome for any of the three subgroups who were not screened, screen-positive or screen-negative. We conclude that regular screening with abdominal ultrasound is not of proven value. Parents should be taught abdominal palpation and advised to seek appropriate advice for untoward symptoms.

Cyclophosphamide metabolism in children

The alkylating agent cyclophosphamide is a prodrug which is metabolized in vivo to produce both therapeutic and toxic effects. Cyclophosphamide metabolism was investigated in 36 children with various malignancies. Concentrations of cyclophosphamide and its principal metabolites were measured in plasma and urine using a quantitative high-performance TLC method. The results indicated a high degree of inter-patient variation in metabolism. In contrast to previous adult studies on urinary metabolites, plasma carboxyphosphamide concentrations did not support the existence of polymorphic metabolism. Plasma concentrations of dechlorethylcyclophosphamide and carboxyphosphamide were correlated in individual patients, suggesting that the activity of both aldehyde dehydrogenase and cytochrome P450 enzyme(s) determine carboxyphosphamide production in vivo. The presence of ketocyclophosphamide in plasma was strongly associated with dexamethasone pretreatment and was also accompanied by a high clearance of the parent drug. Interpatient differences in metabolism reflect individual levels of enzyme expression and may contribute to variation in clinical effect.

The kinetics of the auto-induction of ifosfamide metabolism during continuous infusion

It has often been reported that the oxazaphosphorines ifosfamide and cyclophosphamide induce their own metabolism. This phenomenon was studied in 21 paediatric patients over 35 courses of therapy. All patients received 9 gm-2 of ifosfamide as a continuous infusion over 72 h. Plasma concentrations of parent drug and of the major metabolite in plasma, 3-dechloroethylifosfamide (3DC) were determined, using a quantitative thin-layer chromatography (TLC) technique. A one-compartment model was fitted simultaneously to both ifosfamide and 3DC data. The model included a time-dependent clearance term, increasing asymptotically from an initial value to a final induced clearance and characterised by a first-order rate constant. A time lag, before induction of clearance began, was determined empirically. Metabolite kinetics were characterised by an elimination rate constant for the metabolite and a composite parameter comprising a formation clearance, proportional to the time-dependent clearance of parent drug, divided by the volume of distribution of the metabolite. Thus, the parameters to estimate were the volume of distribution of parent drug (V), initial clearance (Cli), final clearance (Cls), the rate constant for changing clearance (Kc), the elimination rate constant for the metabolite (Km) and Vm/fm, the metabolite volume of distribution divided by the fractional clearance to 3DC. The model of drug and metabolite kinetics produced a good fit to the data in 22 of 31 courses. In a further 4 courses an auto-inductive model for parent drug alone could be used. In the remaining courses, auto-induction could be demonstrated, but there were insufficient data to fit the model. For some patients this was due to a long time lag (up to 54 h) relative to the infusion time. The time lag varied from 6 to 54 (median, 12)h and values for the other parameters were Cli, 3.27 +/- 2.52 lh-1 m-2, Cls, 7.50 +/- 3.03 lh-1 m-2, V, 22.0 +/- 11.0 1 m-2, Kc, 0.086 +/- 0.074 h-1; Km, 0.159 +/- 0.077 h-1 and Vm/fm, 104 +/- 82 1m-2. The values of Kc correspond to a half-life of change in clearance ranging from 2 to 157 h, although for the majority of the patients the half-life was less than 7 h and a new steady-state level was achieved during the 72 h infusion period. This model provides insight into the time course of enzyme induction during ifosfamide administration, which may continue for up to 10 days in some protocols.(ABSTRACT TRUNCATED AT 400 WORDS)

Alcohol selectively attenuates stress-induced c-fos expression in rat hippocampus

The ability of ethyl alcohol to modify responses to stress has been well documented (cf. Pohorecky, 1990). However, the structural substrate mediating these effects of alcohol remains undefined. Using immediate early gene (IEG) expression in the brain as a marker of altered neuronal response, we investigated the effect of acute alcohol exposure on the activity of brain regions of rats exposed to 15 min of restraint stress. Immunocytochemical localization c-Fos protein demonstrated that restraint stress led to an induction of c-Fos expression in several brain structures including cingulate and piriform cortex, cortico-amygdaloid and hippocampo-amygdaloid transition zones, hippocampus, hypothalamus, supramammillary nucleus, and centromedial nucleus of thalamus. An intraperitoneal injection of 2 g/kg alcohol prior to stress decreased c-Fos expression in several but not all of these structures. In particular, alcohol strongly attenuated the stress-induced expression of c-Fos in hippocampus and cingulate cortex. Using slot-blot hybridization, significant induction of c-fos mRNA after restraint stress was demonstrated both in hippocampus and cortex, but prior alcohol exposure specifically attenuated c-fos induction only in the hippocampus. The response of c-fos mRNA expression to stress and alcohol differed from the effects on jun-B, c-jun and jun-D mRNA levels. Perhaps surprisingly, acute exposure to alcohol in otherwise unstressed rats did not induce significant changes in expression of IEGs in comparison to control (saline-injected) animals even with doses sufficient to elevate plasma corticosterone. In summary, these studies demonstrate a selective sensitivity of stress-induced activity of neurons of hippocampus and cingulate cortex to acute alcohol exposure.

Expression of mu class glutathione S-transferase correlates with event-free survival in childhood acute lymphoblastic leukemia

Expression of the main classes (pi, mu, and alpha) of glutathione S-transferase (GST) was assessed in the blasts of children presenting with acute lymphoblastic leukemia using an immunohistochemical technique. Bone marrow trephine biopsies obtained at presentation from 71 cases were studied (42 boys, 29 girls; age range, 6 months-14 years; median age, 4 years) and expression was correlated with event-free survival. The period of follow-up was 12-108 months, during which time 21 patients (30%) relapsed. All the samples examined were negative for alpha class GST. Samples from 8 patients, all of whom remained in remission at the time of analysis, were found to be negative for pi class GST at presentation. Samples from 44 (patients were negative for mu class GST (62%); of these, 36 patients (82%) remained in remission. In comparison, of the 27 patients who were positive for mu class GST, only 14 (52%) remained in remission. Analysis of event-free survival demonstrated that expression of mu class GST predicts a 3-fold increased risk of relapse (95% confidence interval, 1.25-7.26). This risk factor appears to be independent of other recognized prognostic factors.

Loss of red blood cell viability associated with limited thermal inactivation of extracellular HIV-1

The effects of incubation at mildly elevated temperatures on HIV-1 inactivation and in vitro red blood cell properties were investigated. Red cells (55% Hct) were leukodepleted (3 log10) by filtration, maintained at 45 or 47 degrees C for 4 or 8 h, and then stored at 4 degrees C. Hemolysis was twice that of controls after 42-day storage for samples treated for 4 h at 45 degrees C, and five times larger for samples heated at 47 degrees C. There was also a significant increase in the rate of potassium loss, an early decrease in ATP levels, and an initial drop in pH for samples treated at either temperature. Larger differences were observed for samples exposed to these elevated temperatures for 8 h. Osmotic deformability curves obtained by ektacytometry showed dramatic decreases in red cell deformability at both temperatures and for both time periods. HIV-1 inactivation in red cells treated at 45 degrees C (approximately 0.25 log10/h) was considerably less than that obtained in tissue culture medium (1-2 log10/h). Since the decrease in red cell deformability is likely to indicate reduced red cell function and survival, and the rate of HIV-1 inactivation is low, mild heat treatment is not an adequate process for viral inactivation of red cell products.

Intraventricular cerebral neuroblastoma. Analysis of subtypes and comparison with hemispheric neuroblastoma

Two cases of intraventricular neuroblastomas were compared with cases of intraventricular and hemispheric neuroblastomas that have been reported in the published literature. The following order of tumor subtypes was found in patients with increasing age: hemispheric neuroblastoma, intraventricular undifferentiated neuroblastoma, intraventricular differentiated neuroblastoma, and intraventricular neurocytoma; for patients with intraventricular neuroblastomas, this was also the order of increasing cellular maturation and survival. Neuronal morphologic or epitope differentiation was associated with a longer survival time than lack of differentiation by Kaplan-Meier product-limit estimates and with a better survival rate (chi 2) for intraventricular tumors but not for hemispheric tumors. Pathologic distinction of a neurocytoma was confirmed with immunostaining or ultrastructural studies that suggested that a neurocytoma is a matured neuroblastoma of a granule-cell (interneuron) phenotype. Differences among neuroblastoma groups bolster previous suggestions that intraventricular tumors arise differently than do cases of hemispheric tumors and follow a more benign course when neuronal differentiation is present.