Faster CL Research Articles

Population pharmacokinetic analysis of free and bound aflibercept in patients with advanced solid tumors

Aflibercept (Zaltrap®) is a novel antiangiogenic agent that binds to vascular endothelial growth factor (VEGF) and inhibits VEGF-dependent tumor growth. We aimed to characterize the population pharmacokinetics (PK) of free and bound aflibercept in patients with solid tumors to examine the influence of covariates on their PK and to evaluate the proposed dosing regimens by simulation. Data from 9 clinical trials with 1,506 cancer patients receiving aflibercept (2-9 mg/kg every 2 or 3 weeks; 1 h IV infusion) as a monotherapy or in combination with various chemotherapies were included. Free and bound aflibercept concentrations were analyzed using a non-linear mixed-effects modeling approach with MONOLIX 4.1.2. An approximation of a target-mediated drug disposition model with irreversible binding of free aflibercept to VEGF adequately described the PK of free and bound aflibercept. The typical estimated clearances for free (CL(f)) and bound aflibercept (CL(b)) were 0.88 and 0.19 L/day, respectively. The volumes of distribution for free (V(p)) and bound (V(b)) aflibercept were similar (~4 L). CL f and V(p) increased with body weight and were lower in women. Patients with low albumin (ALB) or high alkaline phosphatase (ALK) had faster CL(f) compared to a typical patient. Pancreatic cancer may be associated with changes in binding of aflibercept to VEGF. Simulations of different dosing regimens showed that adequate saturation of circulating VEGF was achieved with a dose of 4 mg/kg every 2 weeks. Aflibercept kinetics was most affected by gender, body weight, ALB, ALK and pancreatic cancer. Simulations supported the rationale for the recommended dose of 4 mg/kg every 2 weeks for aflibercept.

Pharmacokinetics of 5‐fluorouracil in rats with diabetes mellitus induced by streptozotocin

The pharmacokinetic parameters of 5-fluorouracil were compared after intravenous administration at a dose of 30 mg/kg to control Sprague-Dawley rats and to rats with diabetes mellitus induced by streptozotocin (DMIS). In DMIS rats, the area under the plasma concentration-time curve from time zero to time infinity (AUC) was significantly smaller (603 versus 909 microg min/ml) due to the significantly faster total body clearance (Cl; 47.8 versus 33.0 ml/min/kg). The faster Cl was due to the significantly faster renal (8.54 versus 4.02 ml/min/kg) and nonrenal (38.5 versus 28.7 ml/min/kg) clearances. In DMIS rats, the total amount of unchanged 5-fluorouracil excreted in 24 h urine was significantly greater (34.1% versus 13.0% of intravenous dose) due to the urine flow rate-dependent renal clearance of 5-fluorouracil in rats (the greater the urine flow rate, the greater the urinary excretion of 5-fluorouracil). Greater urinary excretion and a significantly smaller AUC resulted in a significantly faster Cl(r) in DMIS rats. The faster Cl(nr) in DMIS rats could be due to an increase in the expression and mRNA level of CYP1A1/2 in the rats.

A population pharmacokinetic model for bevacizumab

BV, a recombinant humanized IgG1 monoclonal antibody against vascular endothelial growth factor (VEGF) was demonstrated to improve survival in previously untreated metastatic colorectal cancer when added to standard chemotherapy. Pooled data (total 4629 BV concentration from 491 subjects) from 8 Phase I to Phase III clinical trials were analyzed using NONMEM and a two-compartment structural model. Body weight and gender were the most significant covariates for both CL and Vc. The change in BV CL for extreme body weights (49 and 114 kg) was 30% around the typical value. After adjusting the weight, men had a 26% faster CL than females. In the final model, CL and Vc were 0.207 L/day and 2.66 L, respectively for the typical (female) patient. The inter-patient variability (%CV) in CL and Vc was 26% and 17%, respectively. BV terminal half-life was 19.9 and 19.3 days for a typical male and female patient. Low albumin and high alkaline phosphatase serum concentrations were associated with a faster CL (+19% and 23%, respectively). Concomitant administration of the combination irinotecan/5-fluorouracil in patients with colon cancer did not influence BV CL. The effect of various dosing regimen on bevacizumab exposure will be explored using simulations. Clinical Pharmacology & Therapeutics (2004) 75, P91–P91; doi: 10.1016/j.clpt.2003.11.347

SDS polyacrylamide gel electrophoresis for N-terminal protein sequencing.

AbstractPolyacrylamide gel electrophoresis in the presence of sodium dodecylsulfate (SDS-PAGE) is a very common technique used for analysis of complex mixtures of polypeptides. It has great resolving powers, is rapid, and is suitable for proteins of either acidic or basic pI. The last is because the protein is reacted with SDS, which binds to the protein in the approximate ratio 1∶4∶1 (SDS:protein, w/w) and imparts a negative charge to the SDS-protein complex. The charged complexes move toward the anode when placed in an electric field, and are separated on the basis of differences in charge and size. SDS-PAGE is commonly used to estimate proteins’ molecular weights, but estimates are approximate (being termed “apparent molecular weights”) and sometimes prone to marked error. For instance, disproportionally large increases in apparent molecular weight may occur upon covalent phosphorylation of a protein (1), or artificial entrapment of phosphoric acid (2). Most designs of SDS-PAGE employ a “stacking gel.” Such a system enables concentration of samples from comparatively large volumes to very small zones within the gel, thus giving narrow bands of the different proteins, which are then better resolved. The principle involved in this protein concentration (or “stacking”) is that of isotachophoresis. It is set up by making a stacking gel on top of the “separating gel,” which is of a different pH. The sample is applied at the stacking gel and when the electric field is applied, the negatively charged complexes and smaller ions move toward the anode. At the pH prevailing in the stacking gel, protein-SDS complexes have mobilities intermediate between the faster Cl- ions (present throughout the electrophoresis system) and the slower glycinate ions (present in the cathode reservoir buffer). The protein-SDS complexes concentrate in the narrow zone between Cl- and glycinate ions. When the moving zones reach the separating gel with its different pH, their respective mobilities change and glycinate overtakes the protein-SDS complexes, which then move at rates governed by then size and charge in a uniformly buffered electric field. Isotachophoresis is described in more detail in the literature (3).KeywordsApparent Molecular WeightAmmonium PersulfateAnalar GradeAcrylamide MonomerReservoir BufferThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Hyperthermal CI Atom Beam Produced by Laser Vaporization of Cryogenic ICI Films

ABSTRACTA source of energetic, neutral Cl atoms is produced by laser vaporization of cryogenic ICI films using either the 532 nm or 266 nm output of a pulsed Nd:YAG laser. The pulsed Cl mean kinetic energy can be tuned from 0.4 eV to 3.4 eV by varying the laser repetition rate or the rate of deposition of the ICl film. Also present in the beam are ICI, I, I2, and Cl2 The heavier species all have lower velocities than the Cl atoms, and this difference in velocities can be accentuated by vaporizing thinner films. Using a mechanical velocity chopper, the fastest part of the beam can be selected, which consists of > 90% Cl atoms. Results suggest that the vaporization process involves a directed mass flow in which the heavier molecules are propelled to higher velocities by the faster Cl atom flux. The atom source may be used for selective etching studies.

GABA-induced potentiation of neuronal excitability occurs during contiguous pairings with intracellular calcium elevation

The temporal convergence of neuronal signals is commonly considered as a likely prerequisite for enhanced neuronal excitability underlying the induction of associative memories. Here we report that transmitter application on presynaptic terminals of the Hermissenda Type B photoreceptors, when paired with depolarization, results in a potentiation of the excitability of the B-cell which derives from an increase in input resistance across the B-cell soma membrane. Pressure microapplication of gamma-aminobutyric acid (GABA) (12.5 microM) on the terminal branches of the Hermissenda Type B photoreceptors results in the fast (less than 1 s) activation of an inward Cl- conductance, characterized by a decrease in neuronal membrane resistance and an accompanying hyperpolarization (3-6 mV) of the B-cell. A slower effect of GABA, characterized by a slight depolarization (2-4 mV) and increase in resistance was observed approximately 2 min after GABA application. Following bath application of the Cl- channel blocker picrotoxin (100 microM), this increase in resistance was observed within 20 s of GABA application, suggesting that it was normally masked by the faster Cl- conductance. The magnitude of the resistance increase in response to GABA was enhanced when the B-cell was held at depolarized membrane potentials (-40 to -20 mV), but was eliminated if Ca2+ was removed from the extracellular bath, or if the non-specific protein kinase inhibitor H7 (100 microM) was added to the extracellular bath. In a final experiment, GABA application was paired with a transient (10 s) depolarization of the B-cell (to -20 mV).(ABSTRACT TRUNCATED AT 250 WORDS)