Dose escalation of cyclophosphamide in patients with breast cancer: consequences for pharmacokinetics and metabolism

PURPOSE: The alkylating anticancer agent cyclophosphamide (CP) is a prodrug that undergoes a complex metabolism in humans producing both active and inactive metabolites. In parallel, unchanged CP is excreted via the kidneys. The aim of this study was to investigate the influence of dose escalation on CP pharmacokinetics and relative contribution of activating and inactivating elimination pathways. PATIENTS AND METHODS: Pharmacokinetics of CP were assessed in 12 patients with high-risk primary breast cancer who received an adjuvant chemotherapy regimen that included four courses of conventional-dose CP (500 mg/m2 over 1 hour every 3 weeks) followed by one final course of high-dose CP (100 mg/kg over 1 hour). Plasma concentrations of CP were analyzed by high-performance liquid chromatography (HPLC), 24-hour urinary concentrations of CP, and its inactive metabolites (carboxyphosphamide, dechloroethylcyclophosphamide [dechlorethylCP], ketocyclophosphamide [ketoCP]) were determined by 31-phosphorus-nuclear magnetic resonance (31P-NMR)-spectroscopy. RESULTS: There was no difference in dose-corrected area under the concentration-time curve (AUC) (216 v 223 [mumol.h/[mL.g]), elimination half-life (4.8 v 4.8 hours), systemic clearance (79 v 77 mL/min) and volume of distribution (0.49 v 0.45 L/kg) of CP between conventional- and high-dose therapy, respectively. However, during high-dose chemotherapy, we observed a significant increase in the renal clearance of CP (15 v 23 mL/min; P < .01) and in the formation clearance of carboxyphosphamide (7 v 12 mL/min; P < .05) and dechloroethylCP (3.2 v 4.2 mL/min; P < .05), whereas metabolic clearance to ketoCP remained unchanged (1.3 v 1.2 mL/min). Consequently, metabolic clearance to the remaining (reactive) metabolites decreased from 52 to 38 mL/min (P < .001). The relative contribution of the different elimination pathways to overall clearance of CP demonstrated wide interindividual variability. CONCLUSION: Overall pharmacokinetics of CP are apparently not affected during eightfold dose escalation. However, there is a shift in the relative contribution of different clearances to systemic CP clearance in favor of inactivating elimination pathways, thereby indicating saturation of bioactivating enzymes during dose escalation. Besides individual enzyme capacity, hydration and concomitant medication with dexamethasone modulated CP disposition.     

The mechanisms of cracks formation of silver-based contact materials under arc and making pressure

The arc erosion experiments on five kinds of silver-based contact materials,AgZnO (10), AgSnO2 (8.5) In2O3 (4), AgCdO (12), AgNi(10), AgWC(12)C(3) were carried out according to different breaking times, breaking currents, and making pressures. Then based on the theoretical analysis and the photographs taken by scanning electronic microscope with EDAX analyzer, the crack morphology was studied scientifically. Three types of cracks, which are cavity cracks, grain boundaries (or phase boundaries) slipping cracks, and thermal stress cracks, were put forward under arc and making pressure through establishing their physical models and discussing their formation mechanisms.     

Melatonin hype hard to swallow

Melatonin is being touted as the latest cure-all. But in their eagerness to explain to the public the possible health benefits of this natural hormone, the mass media as well as some scientists have misrepresented the scientific data.     

Efficient expression of the gene for spinach phosphoribulokinase in Pichia pastoris and utilization of the recombinant enzyme to explore the role of regulatory cysteinyl residues by site-directed mutagenesis

Phosphoribulokinase (PRK), unique to photosynthetic organisms, is regulated in higher plants by thioredoxin-mediated thiol-disulfide exchange in a light-dependent manner. Prior attempts to overexpress the higher plant PRK gene in Escherichia coli for structure-function studies have been hampered by sensitivity of the recombinant protein to proteolysis as well as toxic effects of the protein on the host. To overcome these impediments, we have spliced the spinach PRK coding sequence immediately downstream from the AOX1 (alcohol oxidase) promoter of Pichia pastoris, displacing the chromosomal AOX1 gene. The PRK gene is now expressed, in response to methanol, at 4-6% of total soluble protein, without significant in vivo degradation of the recombinant enzyme. This recombinant spinach PRK is purified to homogeneity by successive anion-exchange and dye-affinity chromatography and is shown to be electrophoretically and kinetically indistinguishable from the authentic spinach counterpart. Site-specific replacement of all of PRK's cysteinyl residues (both individually and in combination) demonstrates a modest catalytically facilitative role for Cys-55 (one of the regulatory residues) and the lack of any catalytic role for Cys-16 (the other regulatory residue), Cys-244, or Cys-250. Mutants with seryl substitutions at position 55 display non-hyperbolic kinetics relative to the concentration of ribulose 5-phosphate. Sulfate restores hyperbolic kinetics and enhances kinase activity, presumably reflecting conformational differences between the position 55 mutants and wild-type enzyme. Catalytic competence of the C16S-C55S double mutant proves that mere loss of free sulfhydryl groups by oxidative regulation cannot account entirely for the accompanying total inactivation.     

Effects of exogenous recombinant ovine interferon tau on circulating concentrations of progesterone, cortisol, luteinizing hormone, and antiviral activity; interestrous interval; rectal temperature; and uterine response to oxytocin in cyclic ewes

Interferon tau (IFN tau) is the conceptus-produced antiluteolytic signal in ruminants. Three experiments examined the effects of s.c. administration of recombinant ovine (ro)IFN tau on interestrous interval (IEI), oxytocin (OT)-induced uterine prostaglandin F2alpha metabolite (PGFM) production, rectal temperature (RT), respiration rate (RR), and plasma concentrations of progesterone, cortisol, LH, and antiviral activity (AVA) in plasma and uterine flushings. In experiment I, 20 ewes were treated s.c. with either 0, 1, 2, or 4 mg/day roIFN tau (0.7 x 10(8) U/mg; 5 ewes/dosage) from Days 11 to 15 of the estrous cycle (estrus = Day 0) and were challenged with OT (30 IU) on Day 15. Jugular blood samples were collected at -10, 0, 10, 20, 30, 40, 50, and 60 min relative to the OT challenge and assayed for PGFM. Recombinant oIFN tau increased IEI (16.7, 18.7, and 22.6 +/- 0.6 days for 0, 2, and 4 mg roIFN tau, respectively, p < 0.01). Recombinant oIFN tau did not affect peak PGFM response to OT (2309 +/- 172 pg/ml; p > 0.1). However, the 4 mg/day dosage delayed the time to peak PGFM (32.4 vs. 47.5 +/- 3.4 min; p < 0.01, 0 vs. 4 mg) and resulted in approximately 200% higher concentrations of PGFM at 60 min post-OT (0 vs. 4 mg/day, p < 0.07). Experiment II was similar to experiment I, except that only the 0- and 4-mg/day dosages of roIFN tau were administered. Ewes were hysterectomized on Day 16, and assay of uterine flushes detected no AVA from ewes treated with either 0 or 4 mg/day roIFN tau. In experiment III, 20 ewes were treated s.c. with either 0, 2, 4, or 6 mg roIFN tau on Day 12. Blood samples, RT, and RR were obtained at frequent intervals for 24 h, and plasma was assayed for progesterone, cortisol, LH, and AVA. Plasma AVA, which increased in a dose-dependent manner, was detectable within 60 min and remained elevated at 24 h compared to control values. RT (elevated 0.5-1.0 degrees C), RR, and cortisol increased in response to all dosages of roIFN tau, with peak values occurring 150-180 min postinjection. For all dosages of roIFN tau, plasma progesterone declined from 120 to 360 min posttreatment and then returned to pretreatment values by 24 h (p < 0.01) as compared to controls. Overall, exogenous roIFN tau altered uterine PGFM response to OT from a pulse to a gradual and sustained elevation and extended IEI with only a transient decline in progesterone and mild hyperthermia, effects that are not expected to compromise pregnancy.     

Subcutaneous nodules as a manifestation of onchocerciasis. A rare condition in the United States

Although infection with tissue nematodes is a significant health problem in many parts of the world, such cases are unusual in the continental United States. This report describes a case of Onchocerca volvulus infection, acquired by a 38-year-old female missionary in northern Brazil, that manifested as subcutaneous nodules in the groin and flank two years after the patient's return to the United States. A year previously, a wrong diagnosis of Wuchereria bancrofti was made at biopsy. At that time, treatment with diethylcarbamazine citrate had to be discontinued because of intense pruritus. Examination of a wet saline impression smear of a new biopsy specimen showed the adult worms to have regularly arranged outer annular ridges, which, together with the pruritus after treatment with diethylcarbamazine (a positive Mazzotti test), led to the diagnosis of onchocerciasis. Retreatment with diethylcarbamazine again caused pruritus, but this was tolerated as were subsequent treatments.     

Gene expression in a subpopulation of luteinizing hormone-releasing hormone (LHRH) neurons prior to the preovulatory gonadotropin surge

Gene expression in luteinizing hormone-releasing hormone (LHRH) neurons was analyzed during the periovulatory period to (1) characterize temporal patterns of LHRH gene expression and their relationship(s) to gonadotropin surges, and (2) determine if any such changes are uniform or dissimilar at different rostrocaudal levels of the basal forebrain. The number of neurons expressing mRNA for the decapeptide, and the relative degree of expression per cell were analyzed using in situ hybridization and quantitative image analysis. Rats were killed at 1800 hr on metestrus (Met), 0800 hr, 1200 hr, 1800 hr, and 2200 hr on proestrus (Pro), or 0200 hr, 0800 hr, and 1800 hr on estrus (E; n = 5-6 rats/group). All sections were processed for LHRH mRNA in a single in situ hybridization assay. Sections were atlas matched and divided into four rostrocaudal groups for analysis: vertical limb of the diagonal band of Broca (DBB), rostral preoptic area/organum vasculosum of the lamina terminalis (rPOA/OVLT), medial preoptic area (mPOA), and suprachiasmatic/anterior hypothalamic area (SCN/AHA). Plasma LH and FSH levels from all animals were analyzed by RIA. The labeling intensity per cell was similar among all time points at all four rostrocaudal levels. The number of cells expressing LHRH mRNA, however, varied as a function of time of death during the estrous cycle, and this temporal pattern varied among the four anatomical regions. At the level of the mPOA, the number of cells was highest at 1200 hr on Pro, and then declined and remained low throughout the morning of E. At the level of the rPOA/OVLT, the greatest number of LHRH neurons was noted later in Pro, at 1800 hr, dropping rapidly to lowest numbers at 2200 hr. No significant changes in LHRH cell number occurred at the DBB or SCN/AHA levels. At all anatomical levels, the secondary surge of FSH was unaccompanied by any change in the number of neurons expressing LHRH mRNA. These data demonstrate that (1) the number of detectable LHRH mRNA-expressing cells fluctuates during the periovulatory period and (2) peak numbers of LHRH-expressing cells are attained in the mPOA before the onset of the LH surge and before peak LHRH cell numbers are seen at more rostral levels. A model is proposed in which gene expression in this subpopulation of LHRH neurons may be activated by preovulatory estrogen secretion and acutely reduced following the proestrous surge of progesterone.