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21.
Hoitink MA Beijnen JH Bult A Damen JM van der Houwen OA Kruijtzer JA Tibben MM Wiese G Underberg WJ 《Journal of pharmaceutical sciences》2000,89(1):108-114
Three model tripeptides, N-acetyl-Tyr-Pro-azaGly-NH(2) (NYPaG), Tyr-Pro-azaGly-NH(2) (YPaG), and Tyr-Pro-Gly-NH(2)(YPG), were subjected to a systematic degradation study to get information about the degradation of the azaglycinamido residue. The degradation products were characterized with LC-MS. Main degradation products of NYPaG possess partially or totally eliminated azaglycinamido residues, while YPaG and YPG are exhibit cyclo(Tyr-Pro) formation, a diketopiperazine. The influence of the pH on the degradation rate constant k(obs) was investigated for NYPaG and YPaG in the pH range 0.4-11. An U-shaped profile with an inflexion around pH 9 was found for NYPaG while the degradation rate of YPaG was independent of the pH. NYPaG apparently was subject to proton-, solvent-, and hydroxyl-catalyzed degradation reactions whereas YPaG only underwent solvent-catalyzed reactions. Some influence of acetate and phosphate ions on k(obs) was found for YPaG. Arrhenius plots of NYPaG and YPaG were found to be linear. 相似文献
22.
Use of maximum intensity projections (MIP) for target volume generation in 4DCT scans for lung cancer 总被引:4,自引:0,他引:4
Underberg RW Lagerwaard FJ Slotman BJ Cuijpers JP Senan S 《International journal of radiation oncology, biology, physics》2005,63(1):253-260
PURPOSE: Single four-dimensional CT (4DCT) scans reliably capture intrafractional tumor mobility for radiotherapy planning, but generating internal target volumes (ITVs) requires the contouring of gross tumor volumes (GTVs) in up to 10 phases of a 4DCT scan, as is routinely performed in our department. We investigated the use of maximum intensity projection (MIP) protocols for rapid generation of ITVs. METHODS AND MATERIALS: 4DCT data from a mobile phantom and from 12 patients with Stage I lung cancer were analyzed. A single clinician contoured GTVs in all respiratory phases of a 4DCT, as well as in three consecutive phases selected for respiratory gating. MIP images were generated from both phantom and patient data, and ITVs were derived from encompassing volumes of the respective GTVs. RESULTS: In the phantom study, the ratio between ITVs generated from all 10 phases and those from MIP scans was 1.04. The corresponding center of mass of both ITVs differed by less than 1 mm. In scans from patients, good agreement was observed between ITVs derived from 10 and 3 (gating) phases and corresponding MIPs, with ratios of 1.07 +/- 0.05 and 0.98 +/- 0.05, respectively. In addition, the center of mass of the respective ITVs differed by only 0.4 and 0.5 mm. CONCLUSION: MIPs are a reliable clinical tool for generating ITVs from 4DCT data sets, thereby permitting rapid assessment of mobility for both gated and nongated 4D radiotherapy in lung cancer. 相似文献
23.
Boone CM Waterval JC Lingeman H Ensing K Underberg WJ 《Journal of pharmaceutical and biomedical analysis》1999,20(6):2327-863
This review article presents an overview of current research on the use of capillary electrophoretic techniques for the analysis of drugs in biological matrices. The principles of capillary electrophoresis and its various separation and detection modes are briefly discussed. Sample pretreatment methods which have been used for clean-up and concentration are discussed. Finally, an extensive overview of bioanalytical applications is presented. The bioanalyses of more than 200 drugs have been summarised, including the applied sample pretreatment methods and the achieved detection limits. 相似文献
24.
Reubsaet JL Beijnen JH Belshof EH Bouyakhrichan M Bult A Hop E Kellekule Y van Maanen RJ Teeuwsen J Underberg WJ 《Journal of pharmaceutical and biomedical analysis》1999,19(3-4):277-284
The tripeptides Arg-Trp-Phe, Arg-Trp-Phe-NH2, Phe-Trp-Arg and Phe-Trp-Arg-NH2 were subjected to a degradation study to get a more detailed insight into the degradation processes of the antitumor hexapeptide antagonist [Arg(6), D-Trp(7,9), MePhe(8)] substance P?6-11? which was investigated in earlier research. Degradation kinetics as well as identities of degradation products of the tripeptides emerging in alkaline and acidic media were studied. The amidated forms (Arg-Trp-Phe-NH2, Phe-Trp-Arg-NH2) appear to be less stable than the carboxylic forms (Arg-Trp-Phe, Phe-Trp-Arg). Deamidation of the amide C-terminus, racemization of the Phe and Arg residues, ornithine formation, hydrolysis of the peptide backbone and diketopiperazine formation with elimination of the N-terminal fragments were the major degradative processes. Comparing these reactions with the reactions of antagonist [Arg(6), D-Trp(7,9), MePhe(8)] substance P?6-11? it appeared that racemization of Phe and Arg, hydrolysis of the peptide backbone and diketopiperazine formation did not occur in detectable amounts in the hexapeptide. probably due to lower reaction rates of these reactions compared to the overall degradation rate of antagonist [Arg(6), D-Trp(7,9) MePhe(8)] substance P?6-11?. 相似文献
25.
J. D. de Vries J. Winkelhorst W. J. M. Underberg R. E. C. Henrar J. H. Beijnen 《International journal of pharmaceutics》1993,100(1-3):181-188
The chemical stability of the new anticancer drug EO9 in aqueous solution has been investigated utilizing a stability-indicating reversed-phase high-performance liquid Chromatographie assay with ultraviolet detection and ultraviolet spectrophotornetry. The degradation kinetics of EO9 have been studied as a function of pH, buffer composition, ionic strength and temperature. A pH-rate profile, using rate constants extrapolated to zero buffer concentration, was constructed demonstrating that EO9 is most stable in the pH region 8–9. The degradation mechanism of EO9 in aqueous solution is discussed. 相似文献
26.
O. Bekers J. H. Beijnen M. Otagiri A. Bult W. J. M. Underberg 《Journal of pharmaceutical and biomedical analysis》1990,8(8-12):671-674
The interaction of -, β- and γ-cyclodextrins with the anthracycline antibiotics doxorubicin and daunorubicin was investigated by LC, circular dichroism (CD) and absorption spectroscopy. All studies were performed in aqueous media at different temperatures and pH values. The anthracyclines complex only with γ-cyclodextrin. Lineweaver—Burk and Scott's plots were used to calculate the stability constants of the anthracycline-γ-cyclodextrin inclusion complexes. 相似文献
27.
E A A M Vernooij J J Kettenes-van den Bosch W J M Underberg D J A Crommelin 《Journal of controlled release》2002,79(1-3):299-303
In this study the hydrolysis kinetics of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine (DOPE) and 1,2-dioleoyltrimethylammoniumpropane (DOTAP) in net neutral DPPC-DOPE (3:1, mol/mol) and cationic DOTAP-DOPE (1:1, mol/mol) liposomes are described. The log k(obs)-pH profile for DOTAP-DOPE liposomes differs markedly from earlier observed hydrolysis profiles: the slope approaches zero in the acidic region and +1 in the alkaline region. The concept of amine-influenced hydrolysis is introduced to explain the lack of pH dependency in the acidic region of the log k(obs)-pH profiles. 相似文献
28.
O Bekers J H Beijnen M J Tank A Bult W J Underberg 《Journal of pharmaceutical and biomedical analysis》1991,9(10-12):1055-1060
The effects of cyclodextrins on the chemical stability of several mitomycin antibiotics in an alkaline medium have been investigated. A stability-indicating high-performance liquid chromatographic method was used to determine the overall degradation rate constants. The influence of various parameters such as structural variations of the cyclodextrins and mitomycins, temperature and pH was studied. It appears that complexation is most favourable with gamma-cyclodextrin. All mitomycin-gamma-cyclodextrin complexes degrade at lower rates than those of the free drugs. Moreover, it was shown that gamma-cyclodextrin influences the equilibrium between mitomycin C and its zwitterion mesomer. 相似文献
29.
W J Underberg 《Journal of pharmaceutical sciences》1978,67(8):1133-1138
The kinetics of the thermal degradation of promethazine in an acidic medium under various conditions were investigated. The degradation of promethazine and the formation of some degradation products were studied under aerobic and anaerobic conditions. The influence of pH, metal ions such as copper(II) and iron (III), and antioxidants was investigated. In an oxygen-saturated medium, promethazine generally followed first-order kinetics. Increasing the pH increased the degradation rate to a limiting value at pH 5. Addition copper (II) increased the degradation rate over the whole process, while iron (III) caused an increase for only a short time. Ascorbic acid sometimes increased the degradation rate, while higher concentrations of hydroquinone also accelerated the degradation. Pyrosulfite did not have any influence. Under anaerobic conditions, promethazine degraded only in the presence of copper (II) and iorn (III) ions. As a result of the studies on the qualitative and quantitative aspects of the oxidation process, a mechanism for the oxidative degradation of promethazine is suggested. Promethazine 5-oxide and a number of degradation products without intact side chains are formed via a semiquinone free radical. The influence of several factors on the degradation process is discussed. 相似文献
30.
Stroink T Wiese G Teeuwsen J Lingeman H Waterval JC Bult A de Jong GJ Underberg WJ 《Journal of pharmaceutical and biomedical analysis》2002,30(4):1393-1401
On-line coupled analytical techniques can be advantageous in the assay of smaller peptides in complex biological matrices such as plasma, cerebro-spinal fluid (CSF) and tissues. The present study shows the feasibility of the recently reported on-line coupled size exclusion chromatography (SEC) and reversed phase liquid chromatography (RP-LC) separation system for the quantitation of structural related peptides in biological matrices, as demonstrated for a number of enkephalins in CSF. The degradation of the peptides, caused by endogenous peptidases in the matrix, could sufficiently be inhibited with imipramine HCL to allow an assay with satisfactory linearity and intraday (0.70-4.9%) precision. The sensitivity of the method, with a concentration limit of quantitation (LOQ) of 2 microgram/ml is comparable with other kinds of assays for peptides and sufficient for the quantitation of peptide drugs with higher therapeutic ranges in biological matrices. However, for the assay of low concentrations of peptides, such as endogenous components of a biological matrix, the sensitivity may need improvement. The LOQ cannot be improved by increasing the sample amount, because of interference of other endogenous components of the CSF. This indicates that a larger selectivity is desired. The LOQ may be improved by using more sensitive and selective detection methods such as mass spectrometry or fluorescence after post-column derivatization. Miniaturization of the system, combined with on-line trapping may also contribute to a better sensitivity. 相似文献