Biomedical subjects
Publications and source records attributed to H M Dodds.
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Various clinical and laboratory parameters have been investigated for their ability to predict toxicity arising from the use of the anticancer drug, irinotecan (CPT-11). In particular, patients deficient in the conjugation of SN-38, a metabolite of CPT-11, are known to be at greater risk. We describe one case of a patient with metastatic colorectal cancer treated with a single dose of CPT-11 at 125 mg/m(2). Although this patient lacked any known predictive factors for toxicity, he experienced severe side-effects several days later. We hypothesized that the toxicity in this patient was due to compromised SN-38 conjugation. Plasma samples were analyzed by reversed-phase high-performance liquid chromatography assay for CPT-11 and its metabolites at 96, 144, 168, 192 and 288 h post-administration. We observed that the concentrations of both the parent drug and its metabolites were markedly raised (11- to 60-fold expected). Additionally the estimated terminal half-lives were 1.5-7 times those expected (29.5, 101, 39.6 and 41.8 h for CPT-11, APC, SN-38G and SN-38, respectively). We conclude that the toxicity in this patient was not caused by deficient SN-38 conjugation, but by decreased drug excretion through both hepatic and renal routes.
PURPOSE: To investigate the clinical relevance of 4-piperidinopiperidine (4PP) in the activity of irinotecan (CPT-11), a high-performance liquid chromatography-turboionspray-tandem mass spectrometry assay for plasma 4PP was developed. METHODS: Plasma samples were prepared for analysis following C18 solid-phase extraction. Chromatography was performed on a Waters Nova-Pak Phenyl column. Selected reaction monitoring with the mass transitions m/z 169.2 --> 84.2 and 139.2 --> 98.1 was used for the detection of 4PP and the internal standard (IS), 1-piperidineproprionitrile, respectively. RESULTS: The assay was linear from 14.8 to 591.0 nM with absolute recoveries of 4PP (59.1 nM) and IS (143.7 nM) of 85.7% (n = 10) and 86.7% (n = 10), respectively. The accuracy and imprecision of the method (total) was > or = 96.8% and < or = 8.5% over the concentration range studied, respectively. 4PP was detectable in plasma following the administration of 125, 350, 500 mg/m2 and 600 mg/m2 CPT-11 to patients, with AUC(4PP) correlated with the dose (r2 = 0.66). Plasma concentrations of 4PP declined slowly with a long terminal half-life (33.4 +/- 17.1 h). CONCLUSIONS: Overall, the concentrations of 4PP in plasma were in the sub-micromolar range (< 206.9 nM) and substantially lower than those capable of inducing apoptosis of cancer cells.
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Irinotecan (CPT-11) is an anticancer drug that occasionally produces acute cholinergic side effects. Preliminary findings suggest that these are mediated through the inhibition of acetylcholinesterase (AChE). In this study, the inhibition of various AChEs by CPT-11 was studied. The lactone form of CPT-11 resulted in apparent noncompetitive inhibition of electric eel and both human recombinant and erythrocyte AChE with K(i) values of 0.065, 0.19, and 0.29 microM, respectively. The carboxylate form of CPT-11 was approximately 10 times less potent. Apparent noncompetitive inhibition of AChE may arise through several mechanisms, and those relevant to CPT-11 were identified from key experimental findings. First, the inhibition by CPT-11 was found to be instantly reversible in dilution studies. Second, incubation of the enzyme with CPT-11 before the introduction of neostigmine protected the enzyme from inactivation. Third, regeneration of the active enzyme after preincubation with neostigmine was totally suppressed by the addition of 2 microM CPT-11, indicating that CPT-11 is a potent inhibitor of decarbamoylation and, by inference, deacylation. Additional experiments with tacrine revealed functional differences between these two inhibitors. Also, preliminary molecular modeling of the interaction between AChE and CPT-11 indicated that the latter does not bind at the same site as tacrine. Displacement studies with the peripheral site-specific ligand, propidium, confirmed that CPT-11 binds at this site. The rapid reversibility of the inhibition of AChE by CPT-11 and the lower activity of the carboxylate form are likely reasons for the transient nature of the cholinergic toxicity observed clinically.
A method for the detection of the photodegradation products of irinotecan (CPT-11, Campto, Camptosar) was developed using high-performance liquid chromatography (HPLC) with fluorescence detection and HPLC/atmospheric pressure chemical ionisation/mass spectrometry (HPLC/APCI/MS). Remnants of infusion solution as well as samples of urine and plasma collected at the end of the infusion of CPT-11 to cancer patients were screened for the five principal known photodegradation products (PDPs) of CPT-11. The concurrent use of standards of the PDPs with ion-extract HPLC/APCI/MS chromatograms enabled the identification of trace quantities of two PDPs in most samples analysed. However, similar analyses of fresh clinical drug solutions revealed that the PDPs were not generated significantly by exposure to light during the infusion period, but were already present in the drug ampoules. Furthermore, this appears to be the source of traces of PDPs detectable in urine and plasma of patients rather than metabolism, per se.
The authors report the use of high-performance liquid chromatography-electrospray-tandem mass spectrometry (HPLC-ESI-MS/MS) for the quantification of indomethacin (IND) in plasma with microscale sample preparation. Plasma samples (100 microL) and mefanamic acid (internal standard [IS]), buffered to pH 3.5, were prepared using solid phase extraction and chromatographed using a C8 column. The mobile phase composition was 80% methanol to 20% ammonium acetate buffer (40 mM, pH 5.1). A flow rate of 300 microL per minute was used with a 1-to-12 postcolumn split into the mass spectrometer. Selected reaction monitoring with mass transitions m/z 357.9-->139.0 and m/z 242-->209.0 were used for IND and IS, respectively. The chromatographic analysis time was 4 minutes. The assay was linear from 5 microg/L to 2000 microg/L with interday imprecision (n=5) over the analytic range (5%). At four concentrations (10 microg/L, 25 microg/L, 250 microg/L, 1500 microg/L), assay imprecision was 9% (total coefficient of variation [CV]) and accuracy ranged between 96.5% and 102.8% (n=16). The absolute recovery of IND and IS was 74% (n=8) and 95% (n=24), respectively. This method was developed and validated in less than 10 working days, had a lower limit of quantification than reported HPLC-ultraviolet (UV) methods, and uses small sample volumes. These factors illustrate the power of HPLC-ESI-MS/MS for drug analysis. Furthermore, the ability of this method to measure IND over a wide concentration range makes it suitable for therapeutic drug monitoring and pharmacokinetic studies.
Irinotecan, or CPT-11 (7-ethyl-10-[4-(1-piperidino)-1-piperidino]carbonyloxycamptothecine++ +), is a water-soluble derivative of camptothecine with promising activity against several types of malignancies. In addition to 7-ethyl-10-hydroxycamptothecine (SN-38), its active metabolite, we were able to identify several metabolites in the plasma of patients treated with this drug, especially an oxidative metabolite, 7-ethyl-10[4-N-(5-aminopentanoic acid)-1-piperidino] carbonyloxy-camptothecine. During our study of the biosynthesis of 7-ethyl-10[4-N-(5-aminopentanoic acid)-1-piperidino] carbonyloxy-camptothecine from CPT-11 by human liver microsomes, we were able to detect another quantitatively important polar metabolite, which was also present in the plasma and urine of patients treated with CPT-11. On the basis of preliminary experiments, the structure of this compound was postulated to be 7-ethyl-10-(4-amino-1-piperidino)carbonyloxycamptothecine, and this structure was synthesized by Rhône-Poulenc Rorer. Urine samples and human liver microsomal extracts were studied by high-performance liquid chromatography/atmospheric pressure chemical ionization/tandem mass spectrometry to identify its structure formally. The identification of the metabolite was supported by identical retention time, mass-to-charge ratio and tandem mass spectrometry fragmentation as a synthetic standard. Like irinotecan, 7-ethyl-10-(4-amino-1-piperidino) carbonyloxycamptothecine was a weak inhibitor of cell growth of P388 cells in culture (IC50 = 3.4 micrograms/ml vs. 2.8 micrograms/ml for irinotecan and 0.001 microgram/ml for SN-38). It was also a poor inducer of topoisomerase I-DNA cleavable complexes (100-fold less potent than SN-38). However, unlike 7-ethyl-10[4-N-(5-aminopentanoic acid)-1-piperidino] carbonyloxy-camptothecine, this new metabolite could be hydrolyzed to SN-38 by human liver microsomes and purified human liver carboxylesterase, though to a lesser extent than irinotecan. This compound can therefore contribute to the activity and toxicity profile of irinotecan in vivo.
A high-performance liquid chromatography-atmospheric pressure chemical ionization-tandem mass spectrometry (HPLC-APCI-MS/MS) reference method for the quantitation of aldosterone in serum and plasma has been developed. Samples were extracted with dichloromethane/diethyl ether, containing flumethasone as internal standard (IS). Chromatography was performed on a phenyl column using 50 mm ammonium formate (pH 7.1)/methanol (50/50, v/v) as mobile phase. Analysis was in negative-ionization mode by selected reaction monitoring (aldosterone m/z 359.2 --> 331.2; IS m/z 455.0 --> 379.0). The assay was linear over the range 15-500 pg/mL, with limits of detection and quantitation of 10 and 15 pg/mL, respectively. Imprecisions of the assay at 15, 20, 150, and 450 pg/mL were 18.5, 8. 8, 10.6, and 9.5%, respectively. The accuracy of the method ranged from 93.1 to 98.9% with absolute recoveries between 84.0 and 91.3% (aldosterone) and 88.0 and 92.3% (IS). We present a case study of a patient admitted, with suspected primary hyperaldosteronism, on the basis of a high radioimmunoassay (RIA) aldosterone concentration. The results suggest that RIA was unreliable, causing unnecessary patient discomfort and a costly 6-day hospital stay. The specific HPLC-API-MS/MS assay described offers the sensitivity and accuracy required to assess abnormal aldosterone production in hypertensive patients.
A reversed-phase high-performance liquid chromatography-electrospray-tandem mass spectrometry assay (HPLC-ESI-MS/MS) was developed to quantitate cortisol, cortisone, 20 alpha- and beta-dihydrocortisol, 20 alpha- and beta-dihydrocortisone, tetrahydrocortisol, and tetrahydrocortisone. The technique was used to analyze perfusate from the isolated human placental lobule for cortisol and its metabolites. Analytes were prepared from the perfusion medium using C18 solid-phase extraction cartridges. The internal standard for the analyses was 6 alpha-methylprednisolone. Chromatography was performed on a Novapak C18 column at ambient temperature using 53% methanol and 47% 10 mM ammonium formate buffer (pH 4.0) as mobile phase, at a flow rate of 80 microL/min. A PE-SCIEX API III triple quadrupole instrument was used for mass spectrometric detection. An ionspray (pneumatically assisted electrospray) interface was used in negative and positive ionization mode. The assay was linear over the range 100-2000 micrograms/L for each analyte. The instrumental limit of detection was 50 pg. Assay imprecision at 400 and 800 micrograms/L was < or = 10% (total coefficient of variation). Accuracy ranged between 83.2% for 20 beta-dihydrocortisone to 102.6% for cortisone. Recovery of 1000 micrograms/L analyte ranged from 91.3% for cortisone to 109.7% for tetrahydrocortisol.
We have previously reported the placental metabolism of prednisolone to prednisone, 20alpha- and beta-dihydroprednisone and 20beta-dihydroprednisolone. In this study, the disposition of cortisol was investigated in vitro in the dual perfused, isolated human placental lobule after the addition of cortisol (1.2 micromol, n = 3 and 12 micromol, n = 4) to the maternal compartment. Analysis of 5 h maternal and fetal perfusate samples by high performance liquid chromatography-electrospray-tandem mass spectrometry (HPLC-ESI-MS/MS) revealed that cortisol was mainly metabolized to cortisone, but a significant production of 20alpha-dihydrocortisone, 20beta-dihydrocortisone, 20alpha-dihydrocortisol and 20beta-dihydrocortisol was also detected. Saturability of metabolism but not transfer was demonstrated. Metabolism was eliminated by co-perfusion with the potent 11beta-hydroxysteroid dehydrogenase (11beta-HSD) enzyme inhibitor 18beta-glycyrrhetinic acid (GA). The disposition of GA was analysed using HPLC-atmospheric pressure chemical ionisation-MS/MS (HPLC-APCI-MS/MS). GA was found to transfer from the maternal to the fetal circulations without detectable metabolism during 6 h of perfusion.
The photodegradation of irinotecan (CPT-11), the semi-synthetic derivative of the antitumor alkaloid 20(S)-camptothecin, has been investigated. The drug was exposed to laboratory light for up to 5 days in 0.9% saline solution (pH 8.5). Five significant photodegradation products were observed and a high-performance liquid chromatography (HPLC) assay was employed to isolate them from CPT-11 using gradient conditions. The structures were elucidated by nuclear magnetic resonance spectroscopy and tandem mass spectrometry and shown to be the result of extensive modifications of the lactone ring of CPT-11. Three of the compounds were found to belong to the mappicine group of alkaloids. In addition, the effect of light on the stability of CPT-11 in aqueous solutions and biological fluids was also assessed. Potassium phosphate buffers (0.05 M, pH 5.0-8.2) and saline, plasma, urine, and bile solutions containing 20 microM CPT-11 were equilibrated in the dark for 24 h before being exposed to laboratory light for up to 171 h at ambient temperature. Four of the five identified photodegradation products were observed and quantitated by isocratic HPLC, using a different detection mode (fluorescence) than the one used for gradient elution. In general, CPT-11 was found to be unstable under neutral and alkaline conditions for all solutions investigated, with the exception of bile. We conclude that CPT-11 is photolabile and that care should be taken to protect samples, particularly those intended for the isolation and identification of novel metabolites of CPT-11.
Delivering emulsions of anthracycline drugs in Lipiodol, an iodinated poppy-seed oil, via the hepatic artery for the treatment of hepatocellular carcinoma (HCC) has become increasingly popular. However, investigations to determine the extent to which the Lipiodol sequesters the anthracycline in the liver have been limited. Concern has been expressed that such emulsions are not stable and that the anthracycline is, therefore, released rapidly into the circulation. We studied the pharmacokinetics of epirubicin (50 mg m-2) in five patients with nonresectable primary hepatocellular carcinoma after infusion of an epirubicin/Lipiodol emulsion via the hepatic artery. We used a reliable and specific high-performance liquid chromatography assay that allows quantitation of plasma concentrations of epirubicin, epirubicinol, epirubicin glucuronide, and epirubicin aglycone. Although a large interpatient variability in pharmacokinetics was observed, our results were similar to historical data after epirubicin intravenous therapy. Only the results from one patient provided evidence of significant retention of the drug in the liver. It would appear that more stable formulations of epirubicin/Lipiodol are required to increase the efficacy of this form of treatment. We suggest that pharmacokinetic studies should accompany clinical evaluation of emulsions of epirubicin/Lipiodol for the treatment of HCC.
Three automated immunoassays for digoxin in serum were evaluated--Abbott TDxII, Baxter Stratus, and Behring OPUS. The accuracy and precision of the assays were assessed by weighed-in controls and an external quality control program. Coefficients of variation of all methods in serum were < or = 10% at weighed-in concentrations of digoxin of 1 and 2.5 micrograms/L. Accuracy relative to weighed-in concentrations of 1 and 2.5 micrograms/L ranged from 98 to 126% for all methods. Comparative results from patient samples showed little difference between the TDxII and Stratus and a greater difference observed between the TDxII and OPUS assays. The detection of digoxin-free samples containing digoxin-like immunoreactive substances (DLIS) in neonatal cord blood, pregnant patients, and liver and renal recipients by each assay was then assessed. The TDxII exhibited the highest incidence of DLIS. This is evident in neonatal cord blood in which 40.4% of samples tested positive. In comparison, the extent of DLIS detected by Stratus was less and OPUS exhibited no DLIS in any of the groups studied. A case study of a patient treated with anti-digoxin Fab fragments (Digibind) also was included for analysis by each method. Fourteen hours after Digibind administration, the TDxII registered a digoxin concentration of 49.5 micrograms/L compared with 3.73, 1.80, and 2.49 micrograms/L for Stratus, OPUS, and ultrafiltered TDxII methods, respectively. The results indicate that to determine the concentration of digoxin after the administration of Digiband, the OPUS or fluorescence polarization immunoassay (FPIA)-ultrafiltered samples by TDxII are the assays of choice.
A case of leiomyoma arising in the nipple of a 55-year-old male is presented. The patient had undergone two minor surgical procedures on the nipple and areola in prior years. It is not known whether biopsies were taken during these procedures.
Toxic silo gases are a potential danger to livestock housed in close proximity to silos. On the fourth day of ensiling, five fattening pigs were found dead in a pen adjoining a grass silo. Post mortem examination revealed extensive lung damage and methaemoglobinaemia. A dense reddish-brown gas was concentrated at floor level to a height of 1 m in the pen and had diffused into adjoining pens, where dry and suckling sows and litters were showing signs of respiratory distress and weakness. The gas was identified as a mixture of nitrogen dioxide and dinitrogen tetroxide. These gases may be produced in the early stages of silage making. In this case, they had accumulated in a slurry channel below the silo and leaked through an adjoining wall into the piggery. The production and toxicological effects of silo gases are discussed.
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