Disposition characteristics of mitomycin C-dextran conjugate in normal and tumor-bearing muscles of rabbits.

Disposition characteristics of the macromolecular prodrug of mitomycin C (MMC), mitomycin C-dextran conjugate (MMC-D), in normal and tumor (VX2 carcinoma)-bearing rabbit thigh muscles were studied using the in situ vascular perfusion technique. Three types of cationic MMC-D (MMC-Dcat) and two types of anionic MMC-D (MMC-Dan) with different carrier molecular weights were used. After bolus arterial injection in normal muscles, 83-96% of injected MMC-D was recovered in the venous outflow regardless of the carrier size or charge, whereas less than 60% of MMC was recovered in the same system. By applying statistical moment analysis to the outflow pattern of these drugs, pharmacokinetic parameters representing their disposition characteristics were obtained. Smaller intrinsic clearance (CLint) and distribution volume (V) were noted for MMC-D than for MMC, indicating low extravascular diffusion of MMC-D. In the tumor-bearing muscle, blood contamination from other parts of the body increased and a shortage of flow recovery due to the neovascularization of the tumors occurred. The disposition parameters of MMC-Dcat with a molecular weight of 500,000 (T-500) indicated some tissue distribution and sequestration in the tumor preparation. After constant infusion of [14C]MMC-D (T-500) for 4 h, tissue radioactivity concentrations were determined in various tissues. A higher radioactivity was observed in the viable region of the tumor and the lymph node compared with the normal muscle tissue and the necrotic region of the tumors. 131I-Labeled human serum albumin also gave similar results. In conclusion, higher tumor localization of antitumor agents may be made possible by the application of macromolecular prodrugs.

Disposition characteristics of macromolecules in the perfused tissue-isolated tumor preparation.

Disposition characteristics of model macromolecules with different physicochemical characteristics and macromolecular prodrugs of mitomycin C, namely mitomycin C-dextran conjugates, were studied in tissue-isolated tumor preparations of Walker 256 carcinoma with the use of a single-pass vascular perfusion technique. In constant infusion experiments, all radiolabeled macromolecules accumulated in the tumor tissue, but the degree and pattern of distribution greatly varied, depending on their electric charges. Positively charged macromolecules were markedly accumulated compared with those that were neutral or negatively charged. In addition, their concentrations were significantly higher in viable than in necrotic regions, while neutral and negative compounds were distributed in necrotic rather than in viable regions. Pharmacokinetic analysis of tissue concentration-time courses of positively charged diethylaminoethyl and neutral dextrans showed that their movement occurred by convective fluid flow, and that high tissue accumulation of positively charged macromolecules could be explained by strong binding due to electrostatic interaction. For neutral and anionic macromolecules with negligible affinity to the tissue, it was suggested that the final concentration gradient between the viable and necrotic regions was decided by their tissue fluid content. Thus, the present study revealed the basic disposition characteristics of macromolecules in tumor tissue relative to their physicochemical properties.

Determination of theophylline and its metabolites in biological samples by liquid chromatography-mass spectrometry.

Liquid chromatography-mass spectrometry (LC-MS) is a powerful tool for analysis of drugs and their metabolites. We used a column-switching system in combination with atmospheric pressure chemical ionization LC-MS (LC-APCI-MS) for the determination of theophylline and its metabolites in biological samples. The separation was carried out on a reversed-phase column using methanol-20 mM ammonium acetate as a mobile phase at a flow-rate of 1 ml/min in 30 min. In the mass spectrum, the molecular ions of these drugs and metabolites were clearly observed as base peaks. This method is sufficiently sensitive and accurate for the pharmacokinetic studies of these drugs.

Establishment and functional characterization of an in vitro model of the blood-brain barrier, comprising a co-culture of brain capillary endothelial cells and astrocytes.

OBJECTIVE: The aim was to establish a flexible, abundantly available, reproducible and functionally characterized in vitro model of the blood-brain barrier (BBB). METHODS: In a first step, bovine brain capillaries and newborn rat astrocytes were isolated. Subsequently, a co-culture of primary brain capillary endothelial cells (BCEC) on semi-permeable filter inserts, with astrocytes on the bottom of the filter was established. The cell material was characterized on the basis of specific cell-type properties and (functional expression of) specific BBB properties. RESULTS: BCEC displayed: (1) characteristic endothelial cell morphology; (2) expression of endothelial cell markers (i.e., CD51, CD62P, CD71 and cadherin 5); (3) marginal F-actin localization; (4) tight junction formation between the cells; (5) expression of gamma-glutamyl-transpeptidase (gamma-GTP); (6) expression of P-glycoprotein (Pgp); (7) functional transendothelial transferrin transport and uptake; (8) restriction of paracellular transport; and (9) high transendothelial electrical resistance (TEER). Astrocytes displayed characteristic astrocyte morphology and expressed glial fibrillary acidic protein (GFAP). Co-culture with astrocytes increased TEER and decreased paracellular transport. In addition, expression of the glucocorticoid receptor (GR) was demonstrated in the endothelial cells of the BBB, while no expression of the mineralocorticoid receptor (MR) was found. CONCLUSIONS: A high quality and mass-production in vitro BBB model was established in which experiments with physiological (e.g., regulation of BBB permeability), pharmacological (e.g., pharmacokinetics and pharmacodynamics) and pathophysiological (e.g., disease influence on BBB permeability) objectives can be reproducibly performed.

Hair-discoloration of Japanese elite swimmers.

To understand hair-discoloration in relation to swimming, we examined sixty-seven elite swimmers of the Japan National Swimming Team and fifty-four, age-matched subjects as controls. The incidence of hair discoloration (61%) in the swimmers' group was significantly higher than that in controls (0%) (p<0.0001). Interestingly, surface damage of the nail plates coexisted in the swimmers with the scalp-hair discoloration. The hairs picked from the eight swimmers and two age-matched individuals as controls were examined by electron microscope (EM) and EM X-ray microanalyzer. The swimmers' discolored, golden hair revealed complete disappearance of hair cuticle both by scanning EM (SEM) and transmission EM (TEM). The quantity of melanosomes in the cortex decreased, and their diameter was smaller than that of controls. In addition, irregularly shaped melanosomes with variable electron density and less electron-dense melanosomes with white haloes were frequently observed in the swimmers' golden hair. The X-ray elemental spectrograph by SEM revealed that the content of sulfur in all the swimmers' discoloured hair was lower than that in the normal controls and that the content of chlorine in the male swimmers' discoloured hair was higher than that in the female swimmers and the normal controls. The X-ray elemental microanalysis by TEM focused on melanosomes in the cortex of the cross section and detected elemental chlorine in all swimmers' golden hairs. It did not detect any element in the control hairs. The 14C-tyrosine uptake test of hairbulbs found no significant difference between the swimmers and the normal controls. These findings suggest that hair discoloration was mainly due to cuticle damage by friction with water. Hypochlorous acid in the swimming pool water can penetrate to the hair cortex through the cuticle. It can oxidize and degenerate melanosomes there.

Identification of the metabolites of irinotecan, a new derivative of camptothecin, in rat bile and its biliary excretion.

1. To investigate the metabolites and biliary excretion of new camptothecin analogue, irinotecan, the drug was administered i.v. to rats (10 mg/kg) and bile, urine and faeces were collected. 2. In rat bile, unchanged irinotecan, the metabolite 7-ethyl-10-hydroxycamptothecin (EHCPT) and unknown metabolite M-1 were found by t.l.c. and h.p.l.c. From beta-glucuronidase hydrolysis, n.m.r. spectrometry and mass spectrometry, M-1 was identified as EHCPT-glucuronide (EHCPT Glu). Other metabolites in the bile were negligible. 3. The cumulative biliary and urinary excretion of radioactivity after dosage of rats with irinotecan were 62.2% and 33.3% dose, respectively, and 9.0% of the radioactivity was excreted in the faeces. 4. Approx. 55% of the biliary radioactivity excreted in 24 h was unchanged irinotecan, 22% was EHCPT Glu, and 9% was EHCPT. 5. Approx. 18% of the biliary radioactivity was reabsorbed from the intestine.

Metabolism of irinotecan to SN-38 in a tissue-isolated tumor model.

The objective of this study is to investigate the metabolism of the antitumor drug, irinotecan (CPT-11), to its active metabolite, SN-38, in tumor tissue. Using Walker 256 carcinoma, we prepared a tissue-isolated tumor model: tumor preparation was continuously perfused with Krebs-Henseleit bicarbonate buffer containing 4% bovine serum albumin (BSA) and CPT-11 (10 micrograms/ml), and the concentration of SN-38 in the perfusate was monitored using HPLC. The concentration of SN-38 in the perfusate was gradually increased to a level of 9.69 ng/ml 60 min after the start of perfusion. As a control, an aliquot of the perfusate was separately incubated; however, no significant increase in SN-38 levels was observed. At the end of the perfusion, a part of the tumor tissue was homogenized and the level of SN-38 was determined; the levels in tumor tissue were 2.2-4.5 times higher than in the perfusate. From above results, CPT-11 was found to be metabolized to its active metabolite, SN-38, in tumor tissue--a desirable feature of an antitumor prodrug.

Pharmacokinetics of SN-38 [(+)-(4S)-4,11-diethyl-4,9-dihydroxy-1H- pyrano[3',4':6,7]-indolizino[1,2-b]quinoline-3,14(4H,12H)-dione], an active metabolite of irinotecan, after a single intravenous dosing of 14C-SN-38 to rats.

Irinotecan (CPT-11) is a camptothecin derivative used for the treatment of cancer. It is a prodrug that is metabolized to its active form, SN-38 [(+)-(4S)-4,11-diethyl-4,9-dihydroxy-1H-pyrano[3',4':6,7]- indolizino[1,2-b]quinoline-3,14(4H,12H)-dione]. To clarify the pharmacokinetic difference between CPT-11 and SN-38, the plasma levels, tissue distribution and excretion of SN-38 were investigated after dosing rats with 14C-labeled SN-38. The plasma radioactivity showed bi-exponential decay with a terminal half-life of 9.91 h. TLC separation revealed that the plasma radioactivity consisted mainly of SN-38 at 5 min after dosing; however, it was soon replaced with SN-38 glucuronide (SN-38 Glu) and an unknown metabolite (M-2). The half-life of unchanged SN-38 after dosing with SN-38 was about 7 min, which was much shorter than that after dosing with CPT-11 (2.8 h) as reported previously. Its radioactivity was excreted mainly in feces (70.0% within 168 h), and biliary excretion (64.1% within 48 h) could account for the fecal excretion. The major component of urinary and biliary radioactivity was found by TLC to be SN-38. Whole body autoradiograms revealed that the tissue distribution of the radioactivity was low except in the liver and kidney. The radioactivity decreased rapidly and little was found in the body 24 h after dosing. In conclusion, SN-38 was excreted rapidly from bile and showed poor tissue distribution. These characteristics lead to a shorter SN-38 half-life, more so than dosing with CPT-11.

Metabolic activation of CPT-11, 7-ethyl-10-[4-(1-piperidino)-1- piperidino]carbonyloxycamptothecin, a novel antitumor agent, by carboxylesterase.

We measured the plasma concentrations of 7-ethyl-10-[4-(1-piperidino)-1- piperidine]carbonyloxycamptothecin (CPT-11) and the active metabolite 7-ethyl-10-hydroxycamptothecin (SN-38), after treatment with CPT-11 to rats pretreated with bis-p-nitrophenylphosphate (BNPP) which is a specific inhibitor of carboxylesterase, and non-pretreated rats. The plasma level of SN-38 was decreased in the BNPP-pretreated group compared with these of non-pretreated group, indicating that the esterase involved in CPT-11 metabolism is a carboxylesterase. We also characterized the molecular species of carboxylesterase involved in CPT-11 metabolism using enzyme preparations purified from liver microsomes. Thirteen carboxylesterase isozyme activities towards CPT-11 were compared and guinea pig GLP1 was found to have the highest activity, while human HU1 isozyme had relatively lower activity than those of animal species. In studies on the kinetic parameters of the hydrolysis of CPT-11 by the purified carboxylesterase isozymes the highest Vmax value of the isozymes was found in human HU1 and the smallest was seen in rat RL1. The Vmax/Km for RL1 showed the largest value of 21.7 nmol/mg protein/mM.

Biliary excretion of mitomycin C dextran conjugates in relation to physicochemical characteristics of carrier dextran.

Biliary excretion characteristics of polymeric prodrugs of mitomycin C (MMC), mitomycin C-dextran conjugates with cationic or anionic charge (MMC-Dcat, MMC-Dan) and with different molecular weights of dextran (10,000, 70,000, and 500,000) were studied in rat. Following intravenous injection, bile was periodically collected and concentrations of free and dextran-conjugated MMC in it were determined by bioassay. MMC administered as a free form was excreted rapidly into bile and 1.8% of the dose was recovered within 2 h. A small amount of MMC was gradually excreted into bile after administration of all MMC-Ds and total recovery at 8 h was less than 1% of dose. In this case, a major part of excreted MMC was recovered as a conjugated form. MMC-Dcat gave a larger total excretion of MMC than MMC-Dan and excretion was also affected by the molecular weight of carrier dextran. The biliary recovery of MMC-Dcat labeled with 14C at a spacer moiety was significantly higher than that of conjugated MMC determined by bioassay suggesting release and/or inactivation of MMC in MMC-D during the circulation in the body. These results were compared with biliary excretion of model macromolecules with the same molecular weight but different electric charge in order to clarify the effect of electric charge on the biliary excretion of macromolecules. Cationic macromolecules exhibited higher biliary excretion in relation to greater hepatic uptake.

Urinary metabolites of DX-8951, a novel camptothecin analog, in rats and humans.

Urinary metabolites of DX-8951 ((1S,9S)-1-amino-9-ethyl-5-fluoro- 1,2,3,9,12,15-hexahydro-9-hydroxy-4-methyl-10H,13H- benzo[de]pyrano[3',4':6,7]indolizino[1,2-b]quinoline-10,13-dione, CAS 171335-80-1, exatecan) in rats and humans were identified. Rats were dosed with the drug, and two major metabolites (UM-1 and UM-2) in the urine were isolated and purified by using ion-exchange column and HPLC. From NMR and mass spectra, they are suggested to be 4-hydroxymethyl metabolite (UM-1) and 3-hydroxy metabolite (UM-2) of the drug. Their chemical structures were confirmed by comparing their NMR spectra with those of chemically synthesized metabolites. Two major metabolites were found in human urine obtained in phase I trial. They were also confirmed to be UM-1 and UM-2 by LC/MS/MS by comparing their mass fragment patterns with those of synthetic metabolites.

Pharmaceutical and biological properties of doxorubicin encapsulated in liposomes (L-ADM): the effect of repeated administration on the systemic phagocytic activity and pharmacokinetics.

We investigated the biodistribution and antitumour activity of doxorubicin (ADM) encapsulated in liposomes (L-ADM) after two administrations in tumour bearing mice. The effect of the first administration on phagocytic activity was also examined. The biodistribution of L-ADM after the second dosing at an interval of 4d was remarkably different from that after the first. The concentration of ADM in plasma and tumour after the second injection was higher, but that in the liver was lower than after the first administration. This decrease in distribution to the liver is thought to have contributed to the difference in the biodistribution characteristics of L-ADM. With regard to antitumour effect, the activity was similar between L-ADM and a solution of ADM (F-ADM). To investigate the effect of the first administration of L-ADM on biodistribution, systemic phagocytic activity was measured after the injection of F-ADM, L-ADM, or 'empty' liposomes not containing ADM. F-ADM and L-ADM (7.5 mg ADM/kg body weight) reduced phagocytic activity to approximately 50% and 30% of control, respectively. This finding suggests that entrapment of ADM in liposomes enhances both the distribution of the drug to the reticuloendothelial system (RES) and its suppressive effect on RES activity. These results indicate that the decrease in RES activity by L-ADM must be considered in estimation of the pharmacokinetics, antitumour activity, and toxicity of L-ADM in clinical use when given by repeat administration or used in combination with other antitumour agents.

Phase I and pharmacokinetic study of TZT-1027, a novel synthetic dolastatin 10 derivative, administered as a 1-hour intravenous infusion every 3 weeks in patients with advanced refractory cancer.

BACKGROUND: TZT-1027 is a synthetic dolastatin 10 analog with antineoplastic properties in various cell lines and tumor xenografts. The purpose of this phase I study was to evaluate the safety and toxicity, maximum tolerated dose, pharmacokinetics and pharmacodynamics, clinical and metabolic antitumor activity of TZT-1027 when given as a 1-h intravenous infusion every 3 weeks in patients with refractory solid tumors. PATIENTS AND METHODS: Patients had a histologically verified refractory tumor with measurable disease, were > or = 18 years old, had an Eastern Cooperative Oncology Group performance status <2 and adequate bone marrow, liver, renal and cardiac function. Dose-limiting toxicity was defined as platelets <25 x 10(9)/l, neutrophils <0.5 x 10(9)/l for >5 days, febrile neutropenia > or = 38.5 degrees C with grade 4 (National Cancer Institute-common toxicity criteria) neutropenia, or grade 3/4 non-hematological toxicity excluding nausea and vomiting. The last dose was the dose where > or = 2 out of six patients experienced dose-limiting toxicity in cycle one. The maximum tolerated dose was one dose level below with less than two of six patients with dose-limiting events. RESULTS: Twenty-one non-selected, fully evaluable patients were enrolled. The majority were male (19) and the median age was 55 years (range 39-67). Dose levels of TZT-1027 ranged from 1.35 to 3.0 mg/m(2). The median number of cycles was two (range 1-4). Dose-limiting toxicities were observed in three patients at the 3.0 mg/m(2) dose level, including neutropenia, fatigue and a short lasting, reversible peripheral neurotoxic syndrome. The most common toxicities per patient were fatigue, anorexia, alopecia, nausea, constipation, leukopenia and neutropenia. Based on RECIST criteria, the best response was stable disease in seven patients. The pharmacokinetic evaluation revealed a T(1/2) of approximately 7 h and linear kinetics. CONCLUSIONS: The recommended dose of TZT-1027 for the 3-weekly administration is 2.7 mg/m(2). Neutropenia, fatigue and a reversible peripheral neurotoxic syndrome are dose-limiting with this schedule. TZT-1027 may be associated with neurological side-effects in patients previously exposed to neurotoxic compounds such as oxaliplatin.

A phase I clinical and pharmacokinetic study of the angiogenesis inhibitor, tecogalan sodium.

BACKGROUND: Tecogalan sodium is an angiogenesis inhibitor isolated from a sulfated polysaccharide produced by the bacterium Arthrobacter. The antiangiogenic effect of tecogalan sodium is thought to be mediated by the inhibition of binding of basic fibroblast growth factor to cellular receptors. PATIENTS AND METHODS: A phase I study was conducted in thirty-three patients with refractory malignancies, including AIDS-associated Kaposi's sarcoma. Patients received a single i.v. infusion every three weeks with the infusion duration ranging from one to twenty-four hours. Seven different dosage levels were studied (125, 185, 240, 300, 390, 445, and 500 mg/m2). RESULTS: The primary dose-limiting toxicity was prolongation of the activated partial thromboplastin time with peak times being between 1.0-4.0 times the upper limit of normal. This toxicity was ameliorated at a given dose level by prolonging the infusion time. Other common toxicities included fever (40%) and rigors (31%) which were well controlled with acetominophen and meperidine. The serum half-life of tecogalan sodium was between 1-1.5 hours and < 25% of unchanged drug was excreted in the urine. CONCLUSIONS: The recommended phase II dose of tecogalan sodium on this schedule is 390 mg/m2 over 24 hours. Other schedules including continuous administration should be investigated to maximize the efficacy of this novel angiogenesis inhibitor.