Analysis of microdialysates from cancer patients by capillary electrophoresis

Microdialysis (MD) is an innovative clinical technique for measuring interstitial tissue pharmacokinetics and plasma-to-tissue transfer rates of drugs in humans. However, microdialysis requires the availability of specialized analytical techniques. Capillary electrophoresis (CE), which enables concentration measurements of small volume samples, theoretically constitutes an ideal analytical technique for measuring drug concentrations in microdialysates. In the present experiments, we aimed at assessing the potential utility and limitations of CE for analysis of microdialysates in a clinical situation. Microdialysates were obtained from primary breast cancer patients who received chemotherapy including 5-fluorouracil (5-FU; 600 mg/m2). Subsequently, 5-FU concentrations were measured in tumor - and subcutaneous adipose tissue - microdialysates by CE. By combining MD and CE, complete time versus concentrations profiles could be obtained for 5-FU in the interstitial tumor space and important clinical questions could be addressed. We conclude that the combination of MD and CE leads to important and previously inaccessible information about the drug distribution process in a clinical setting.     

Characterization of 5-fluorouracil loaded liposomes prepared by reverse-phase evaporation or freezing-thawing extrusion methods: study of drug release

Entrapment of the anti-tumoral drug 5-fluorouracil (5-FU) in unilamellar liposomes prepared by freeze-thawing extrusion technique (FATVET) and the reverse-phase evaporation method (REV) from natural (bovine brain) sphingomyelin (SM) and synthetic distearoylphosphatidylcholine (DSPC) phospholipids was studied. Reverse-phase evaporation vesicles obtained from DSPC sized through polycarbonate membranes of 0.2 micron pore size were found to entrap roughly double amounts of drug than did extruded liposomes (0.1 micron pore size); however, s-REV in these preparations were more heterogenous in vesicle size than FATVET. The rate of in vitro drug release from the liposomes was found to be dependent of the bilayer composition and the method used to prepare the vesicles. The permeability coefficient P obtained was approx. 10(-11) m/s. The results suggest that 5-FU release is kinetically controlled by an interfacial process seemingly dependent on the surface activity of the drug. Also, the physical state of the bilayer determines the retention capacity of the vesicles. Thus, liposomes consisting of distearoylphosphatidylcholine whose acyl chains were in a gel state at the working temperature (37 degrees C) retained 70% of encapsulated 5-FU after 1 h, whereas liposomes composed of natural bovine brain sphingomyelin retained only 15% over the same period.     

Cardiac arrhythmias in chronic obstructive pulmonary disease

This study was designed to assess a local drug delivery system of an anticancer agent, doxorubicin (DOX), using fibrin glue (Beriplast P) as a drug carrier. In vitro release of DOX from the fibrin glue was examined by a dialysis method in the presence and absence of sodium alginate. The in vitro mean dissolution times of DOX with solution, fibrin glue, and fibrin glue containing sodium alginate were 3.7 h, 8.7 h, and 81 h, respectively, indicating a sustained release of DOX from fibrin glue, especially in the presence of sodium alginate. Fibrin glue containing 6 mg of DOX and 2.5 mg of sodium alginate was applied on the surface of an AH60C tumor at the back of rats. DOX concentrations in the tumor extracellular fluid were monitored by a microdialysis method. Local application of DOX using fibrin glue containing sodium alginate to the tumor resulted in extremely higher concentrations in the tumor extracellular fluid than those in plasma (AUC ratio > 800), indicating an advantage of the site-specific delivery of DOX using fibrin glue with sodium alginate. The tumor volumes were inversely correlated with tumor extracellular fluid-to-plasma AUC ratios (r = 0.882), suggesting the relevance of tumor size in the drug efflux from tumor to blood. In conclusion, the site-specific delivery of DOX using fibrin glue with sodium alginate to the tumor was demonstrated to be advantageous with regard to the extent and duration of drug concentrations in the tumor extracellular fluid, as assessed by a microdialysis technique.     

Prolonged release of tegafur from S/O/W multiple emulsion

To develop a prolonged and sustained release preparation, we prepared an albumin microsphere-in-oil-in-water emulsion (S/O/W) and examined sustained release from it in comparison with other control preparations such as water-in-oil (W/O) emulsions and microspheres in vitro and in vivo, respectively. Tegafur was used as a model drug. A microsphere-in-oil emulsion was prepared by adding albumin microspheres to soybean oil containing 20% Span 80. To prepare an S/O/W emulsion, the microsphere-in-oil emulsion was added into an aqueous solution of hydroxypropyl methylcellulose containing Pluronic F68. The mean particle size of the albumin microspheres was 3 microns, and the ratio of entrapment of tegafur into albumin microspheres was about 25%. In an in vitro release test, the t75 of the S/O/W emulsion was fourfold greater and in an in vivo release test the mean residence time of tegafur from the S/O/W emulsion was more than twofold that from a W/O emulsion or microsphere system. The mean residence time of 5-fluorouracil (5-FU) from an S/O/W emulsion was also greater than with other dosage forms. These results suggest the possible usefulness of an S/O/W emulsion for the sustained and prolonged release of tegafur.     

Magnolol decreases body temperature by reducing 5-hydroxytryptamine release in the rat hypothalamus

1. The effects of magnolol, isolated and purified from the cortex of Magnolia officinalis Rehd. et Wils, on thermoregulation and hypothalamic release of 5-hydroxytryptamine (5-HT) by in vivo microdialysis were assessed in normothermic rats and in febrile rats treated with interleukin-1 beta. 2. Intraperitoneal administration of magnolol (25-100 mg/kg) produced a decrease in colon temperature, an increase in foot skin temperature, a decrease in metabolic rate and a decrease in the endogenous release of 5-HT in the rat hypothalamus. 3. Depletion of rat brain 5-HT, produced by intracerebroventricular pretreatment with 5,7-dihydroxytryptamine, attenuated the magnolol-induced hypothermia, cutaneous vasodilation and decreased metabolism. 4. Intracerebroventricular administration of (+/-)-2,5-dimethoxy-4-iodoamphetamine (a 5-HT2 receptor agonist; 5-10 micrograms/5 microL) increased basal colon temperature and reversed the magnolol-induced hypothermia. 5. The increases in both colon temperature and hypothalamic 5-HT release produced by interleukin-1 beta injection were attenuated by treatment with magnolol. 6. The data suggest that magnolol decreases body temperature (due to increased heat loss and decreased heat production) by reducing 5-HT release in rat hypothalamus.     

Release of 5-fluorouracil from poly(acrylamide-co-monopropyl itaconate) hydrogels

The aim of this work was to test the application of copolymeric poly(acrylamide-co-monopropyl itaconate) (A-MPI) hydrogels on the release of 5-fluorouracil (5-FU). The equilibrium degree of swelling in saline solution was 83 +/- 2%. 5-FU, as the sodium salt, was trapped in gels by placing it in the polymerization feed mixture. The diffusion coefficients for both swelling of the gels and the release of 5-FU were determined, in addition to the activation energies for both processes. To determine the applicability of these copolymers, A-MPI (75:25) gel was subcutaneously implanted in rats and the drug plasma concentration was determined by HPLC.     

Intratumoral conversion of 5-fluorocytosine to 5-fluorouracil by monoclonal antibody-cytosine deaminase conjugates: noninvasive detection of prodrug activation by magnetic resonance spectroscopy and spectroscopic imaging

The monitoring of antibody-directed enzyme-prodrug therapies requires evaluation of drug activation within the tissues of interest. We have demonstrated the feasibility of noninvasive magnetic resonance spectroscopy and spectroscopic imaging (chemical shift imaging) to detect activation of the prodrug 5-fluorocytosine (5-FCyt) to the cytotoxic species 5-fluorouracil (5-FU) by monoclonal antibody-cytosine deaminase (CD) conjugates. In vitro, L6-CD but not 1F5-CD selectively metabolized 5-FCyt to 5-FU on H2981 human lung adenocarcinoma cells because of the presence and absence of cell surface L6 and CD20 antigens, respectively. After pretreatment of H2981 tumor-bearing mice with L6-CD, in vivo metabolism of 5-FCyt to 5-FU within the tumors was detected by 19F magnetic resonance spectroscopy; the chemical shift separation between 5-FCyt and 5-FU resonances was approximately 1.2 ppm. 5-FU levels were 50-100% of 5-FCyt levels in tumors 10-60 min after 5-FCyt administration. Whole body 19F chemical shift imaging (6 x 6 mm in-plane resolution) of tumor-bearing mice demonstrated the highest signal intensity of 5-FU within the tumor region. This study supports further development of noninvasive magnetic resonance methods for preclinical and clinical monitoring of CD enzyme-prodrug therapies.     

Allergen-induced histamine release in intact human skin in vivo assessed by skin microdialysis technique: characterization of factors influencing histamine releasability

BACKGROUND: The purposes of the study were to characterize allergen-induced histamine release in intact human skin in vivo by using a novel microdialysis technique and to study covariates influencing histamine releasability. METHODS: Hollow microdialysis fibers were inserted into the upper dermis in 15 timothy-sensitivity subjects. Up to 12 fibers were inserted in each subject. Each fiber was perfused with Krebs-Ringer's solution at a rate of 3.0 microliters/min. Three to four serial dilutions of allergen were applied to the skin by intracutaneous injections or skin prick test above individual fibers. Samples were collected in two 2-minute fractions before skin challenge and in 10 consecutive samples for 20 minutes after skin challenge. Histamine was assayed spectrofluorometrically. RESULTS: A significant dose-response relationship for histamine release was demonstrated with intracutaneous tests and skin prick tests. The time to reach peak histamine release after an intracutaneous test was 4 to 8 minutes, compared with 12 to 14 minutes for a skin prick test. Histamine release correlated significantly with wheal size. Intrasubject coefficient of variation on histamine release was about 20%. A substantial intersubject variation in histamine releasability was observed. Seventy to seventy-five percent of the variation could be accounted for by a combination of gender, total and allergen-specific IgE, and an in vitro basophil histamine release test. CONCLUSIONS: Using a skin microdialysis technique, we have described in detail histamine release in intact human skin by allergen. The microdialysis method proved to be a reproducible technique for monitoring histamine release in allergic skin reactions and for studying histamine releasability of skin mast cells in vivo.     

The in vitro and in vivo indomethacin release from self-setting bioactive glass bone cement

The in vivo and in vitro drug release profiles from a self-setting bioactive CaO-SiO2-P2O5 glass bone cement containing indomethacin as a model drug were investigated. The cement containing 2% and 5% indomethacin (IMC) powder hardened within 5 min after mixing with ammonium phosphate buffer. After setting, in vitro drug release from drug-loaded cement pellets in a simulated body fluid (SBF) at pH 7.25 and 37 degrees C continued for two weeks. The hardened cement gradually formed low-crystallinity hydroxyapatite during the drug release test in SBF. An IMC-loaded cement device (2% and 5% drug) was implanted in the subcutaneous tissue on the back of rats. The in vivo IMC release from the cement increased and attained maximum levels (Cmax of 2% and 5% drug-loaded cements was 0.27 and 3.37 micrograms/ml, respectively) at Tmax, 3 and 0.5 d, respectively, upon subcutaneous (s.c.) administration in rats. This suggested that the s.c. administration of the cement provided IMC release for a much longer period than s.c. administration of the solution, and the plasma IMC concentration was dependent on the drug concentration in the cement. The plasma IMC concentration and the area under the curve from 2% and 5% IMC-loaded cements in rats were dependent on the concentration of IMC in the cements. The in vivo IMC concentration in plasma obtained by the deconvolution method was much lower than that delivered in SBF in vitro. Scanning electron microscopy and photomicrographs of cross sections showed that the bioactive bone cement had excellent biocompatibility with the surrounding soft tissues.     

Lethal drug interactions of sorivudine, a new antiviral drug, with oral 5-fluorouracil prodrugs

Rats were orally co-administered sorivudine (SRV: 1-beta-D-arabinofuranosyl-(E)-5-(2-bromovinyl)uracil), a new oral antiviral drug for herpes zoster, with the oral anticancer drug tegafur (FT: 1-(2-tetrahydrofuryl)-5-fluorouracil) as a prodrug of 5-flourouracil (5-FU) once daily to investigate a toxicokinetic mechanism of 15 Japanese patients' deaths recently caused within a brief period by the drug interaction of these drugs. All the rats showed extremely elevated levels of 5-FU in plasma and tissues, including bone marrow and small intestine, and died within 10 days, whereas the animals given the same dose of SRV or FT alone were still alive over 20 days without any appreciable toxic symptom. Before their death, there was marked damage of bone marrow, marked atrophy of intestinal membrane mucosa, marked decreases in white blood cells and platelets, diarrhea with bloody flux, and severe anorexia as reported with the Japanese patients. Data obtained by in vivo and in vitro studies strongly suggested that (E)-5-(2-bromovinyl)uracil generated from SRV by gut flora was reduced in the presense of NADPH to a reactive form by hepatic dihydropyrimidine dehydrogenase (DPD), a key enzyme determining the tissue 5-FU levels, bound covalently to DPD as a suicide inhibitor, and markedly retarded the catabolism of 5-FU.     

3-Cyano-2,6-dihydroxypyridine (CNDP), a new potent inhibitor of dihydrouracil dehydrogenase

3-Cyano-2,6-dihydroxypyridine (CNDP) was identified as a potent inhibitor (IC50 value, 4.4 nM) of dihydrouracil dehydrogenase (DHUDase) [EC 1.3.1.2], a rate-limiting enzyme in 5-fluorouracil (5-FU) degradation. The inhibitory activity of CNDP was about 2,000 times that of uracil under our assay conditions. Kinetic analyses with partially purified enzyme from rat liver revealed that the mechanism of inhibition of DHUDase by CNDP was of mixed type with an inhibition constant (Ki) of 1.51 nM. CNDP had less effect on 5-FU phosphorylation than on 5-FU degradation. The inhibitory effect of CNDP on ribosylation of 5-FU was 600 to 1,000 times less than that on DHUDase. Moreover, CNDP did not inhibit uridine kinase, thymidine kinase, or pyrimidine phosphoribosyltransferase. Coadministration of CNDP with 1-ethoxymethyl-5-fluorouracil (EM-FU) to rats with Yoshida sarcoma elevated the level of 5-FU in both the blood and the tumor and enhanced the antitumor effect of EM-FU. These findings indicated that CNDP would be a useful chemical modulator in chemotherapy with 5-FU or its prodrugs.     

The relationships between p53-dependent apoptosis, inhibition of proliferation, and 5-fluorouracil-induced histopathology in murine intestinal epithelia

The relationship between acute (<36 h) induction of apoptosis and longer-term (>72 h) intestinal histopathology was systematically investigated in vivo using p53 wild-type (+/+) and null (-/-) mice. Administration of the enterotoxin 5-fluorouracil (5-FU) at either 40 or 400 mg/kg to BDF1 mice induced an acute p53-dependent apoptosis in the crypts of both small intestine and midcolon. Although the amount of apoptosis was of the same order of magnitude at its peak (24 h) at both doses, only 400 mg/kg 5-FU brought about histopathological changes to the gut after 96 h, quantified as losses of crypt and villus cellularity. Only after the administration of 400 mg/kg 5-FU were mitotic index and DNA synthesis significantly suppressed in both small intestinal and midcolonic crypts at 24 h. This correlated with a prolonged, p53-dependent expression of p21waf-1/cip1. In p53 null (-/-) mice, significant reductions in both 5-FU-induced apoptosis and inhibition of cell cycle progression allowed retention of crypt integrity 96 h after 5-FU. These results show that quantitative measures of acute apoptosis in vivo may not accurately predict subsequent pathological changes in the gut. Rather, p53-dependent inhibition of cell cycle progression, together with cell loss by apoptosis, caused a loss of crypt integrity. Importantly, the tissue toxicity of 5-FU was genetically determined at a locus (p53) separate from that directly associated with drug action.     

Invention of a tumor-selective 5-fluorouracil derivative named S-1 by biochemical modulation of 5-fluorouracil

A new oral type of 5-fluorouracil (5-FU) derivative possessed of both potent antitumor activity and less gastrointestinal (GI) toxicity was investigated and developed in the form of a combination of tegafur (FT), a masked form of 5-FU, and its two peculiar biochemical modulators. One is 5-chloro-2,4-dihydroxypyridine (CDHP), a new potent inhibitor of 5-FU degradation in vivo, and another is potassium oxonate (Oxo), a characteristic inhibitor of 5-FU phosphorylation, which distributes much higher in GI tract after p.o. administration. 5-FU levels in blood of rats following administration of FT, were markedly elevated and persisted for a long-time by co-oral CDHP corresponding to over 0.4 molar ratio to FT, like the case in continuous infusion of 5-FU, which resulted in an augmentation of antitumor efficacy in Yoshida sarcoma-bearing rats, although severe GI toxicity simultaneously occurred. To reduce 5-FU-induced toxicities such as diarrhea and body weight loss and to maintain the augmented antitumor activity, 0.5 to 2 molar Oxo was orally given to rats with one molar FT plus 0.4 molar CDHP. As a result, both severe GI injury and body weight loss were markedly inhibited by coadministration of 0.5 to 1.0 molar Oxo while high antitumor efficacy (about 90% inhibition of tumor growth) was maintained. However, such almost complete antitumor effect was reduced to about 50% inhibition of tumor growth by over 2 molar Oxo combined with one molar FT plus 0.4 molar CDHP. Based on these results, a novel 5-FU derivative, named S-1, was composed of one molar FT, 0.4 molar CDHP and one molar Oxo. S-1 showed an antitumor activity over 3-fold stronger than UFT (one molar FT plus 4 molar uracil) against Yoshida sarcoma and Sato lung carcinoma in rats and human colon carcinoma (KM12C) xenografted in nude rats when its minimum toxic dose was administered. Co-oral Oxo also significantly reduced the incidence of diarrhea and stomatitis induced by administration of FT-CDHP in beagle dogs. These results suggest that high antitumor activity and less GI toxicity of S-1 was brought about by the elevation in blood and tumor tissues and by selective decrease of 5-fluoronucleotides, an active metabolite of 5-FU, in GI tract.     

Kinetic correlates of methotrexate transport and therapeutic responsiveness in murine tumors

Net accumulation of methotrexate by carrier-mediated transport in different murine tumor cells in vitro exhibits a positive correlation with the relative drug pharmacokinetics and therapeutic responsiveness in these tumors in vivo. The transport of methotrexate by Sarcoma 180, Ehrlich carcinoma, P388, P288, and L1210 leukemia cells is qualitatively similar. Influx of drug exhibits saturation kinetics and is highly temperature dependent (Q10, 6.1 to 9.4). Efflux of exchangeable methotrexate from all of the different tumor cells exhibited first-order kinetics and the same high temperature dependence seen for influx (Q10, 6.1 to 8.0). The major kinetic determinant of responsiveness is the Km for influx. Values vary from 3.1 to 11.2 X 10(-6) M and are highest in cells from a nonresponsive Sarcoma 180 tumor, somewhat lower in the poorly responsive Ehrlich tumor, lower in moderately responsive P388 and P288 leukemias, and lowest in the highly responsive L1210 leukemia. Values for the influx Vmax differ to some extent, but in a manner not correlatable with responsiveness. The level of responsiveness of the P388 leukemia in vivo can also be partially attributed to an efflux rate that is lower than that measured for the other tumor cells. Steady-state levels of drug accumulation in vitro reflected influx and efflux rates and were consistently correlatable with therapeutic responsiveness. There was no significant difference in the extent to which folate and reduced 5-substituted folate derivatives compete with methotrexate for uptake in cells from all five tumors. The average value for Ki measured with folate for each tumor cell type was 50- and 80-fold higher than for 5-formyltetrahydrofolate and 5-methyltetrahydrofolate.     

Role of p53 in hematopoietic recovery after cytotoxic treatment

Prompt reconstitution of hematopoiesis after cytoreductive therapy is essential for patient recovery and may have a positive impact on long-term prognosis. We examined the role of the p53 tumor suppressor gene in hematopoietic recovery in vivo after treatment with the cytotoxic drug 5-fluorouracil (5-FU). We used p53 knock-out (p53-/-) and wild-type (p53+/+) mice injected with 5-FU as the experimental model. Analysis of the repopulation ability and clonogenic activity of hematopoietic stem cells (HSCs) and their lineage-committed descendants showed a greater number of HSCs responsible for reconstitution of lethally irradiated recipients in p53-/- bone marrow cells (BMCs) recovering after 5-FU treatment than in the corresponding p53+/+ BMCs. In post-5-FU recovering BMCs, the percentage of HSC-enriched Lin- Sca-1(+) c-Kit+ cells was about threefold higher in p53-/- than in p53+/+ cells. Although the percentage of the most primitive HSCs (Lin- Sca-1(+) c-Kit+ CD34(low/-)) did not depend on p53, the percentage of multipotential HSCs and committed progenitors (Lin- Sca-1(+) c-Kit+ CD34(high/+)) was almost fourfold higher in post-5-FU recovering p53-/- BMCs than in their p53+/+ counterparts. The pool of HSCs from 5-FU-treated p53-/- BMCs was exhausted more slowly than that from the p53+/+ population as shown in vivo using pre-spleen colony-forming unit (CFU-S) assay and in vitro using long-term culture-initiating cells (LTC-ICs) and methylcellulose replating assays. Clonogenic activity of various lineage-specific descendants was significantly higher in post-5-FU regenerating p53-/- BMCs than in p53+/+ BMCs, probably because of their increased sensitivity to growth factors. Despite all these changes and the dramatic difference in sensitivity of p53-/- and p53+/+ BMCs to 5-FU-induced apoptosis, lineage commitment and differentiation of hematopoietic progenitors appeared to be independent of p53 status. These studies suggest that suppression of p53 function facilitates hematopoietic reconstitution after cytoreductive therapy by: (1) delaying the exhaustion of the most primitive HSC pool, (2) stimulating the production of multipotential HSCs, (3) increasing the sensitivity of hematopoietic cells to growth factors, and (4) decreasing the sensitivity to apoptosis.     

Application of thermosensitive polymers as a new embolic material for intravascular neurosurgery

Application of thermosensitive polymers as an embolic material for intravascular neurosurgery was investigated. We intended to use thermosensitive polymers to occlude vessels by precipitation in response to body temperature. Copolymers of N-isopropylacrylamide (NIPAM) and N-n-propylacrylamide (NPAM) were selected as thermosensitive polymers. To determine the optimal lower critical soluble temperature (LCST) for the embolic material, we developed an in vitro flow model. In this study the copolymers with an LCST of 24-26 degrees C showed appropriate precipitation. To prove the occlusion of vessels in vivo, we injected the copolymers into a rabbit kidney through a microcatheter. The extent of embolization was judged by angiography and histological examination. An acute toxicity test of the copolymer of NIPAM and NPAM was performed in comparison with that of the NIPAM monomer. The copolymer used in this paper showed no acute toxicity in mice. Water solubility, non-adhesiveness, and non-toxicity are the advantages of the use of thermosensitive polymers as an embolic material. By changing the LCST, various embolic materials can be designed. Based on our results, we believe that the application of thermosensitive polymers as a new embolic material is very promising.     

Phase I and pharmacologic study of intermittent twice-daily oral therapy with capecitabine in patients with advanced and/or metastatic cancer

PURPOSE: Capecitabine is an orally administered fluoropyrimidine carbamate selectively activated to fluorouracil (5-FU) in tumors. It passes through the intestinal mucosal membrane intact and is subsequently activated by a cascade of three enzymes that results in the preferential release of 5-FU at the tumor site. PATIENTS AND METHODS: In this phase I study, capecitabine was administered twice daily as outpatient therapy, each cycle administered for 2 weeks followed by 1 week of rest. Thirty-four patients with solid tumors, all of whom except three patients were pretreated, were treated at dose levels from 502 to 3,514 mg/m2 daily. RESULTS: The median treatment duration was four cycles (85 days; range, 14 to 833+ days). Two patients continue on treatment at 686 and 833+ days. Capecitabine 3,000 mg/m2 daily was not tolerable, with dose-limiting toxicities of diarrhea with hypotension, abdominal pain, and leukopenia. Palmar-plantar erythrodysesthesia (PPE) became evident at higher dose levels after prolonged treatment. Evidence of objective tumor response was reported in four patients at 2,510 mg/m2 daily and greater (one complete response [CR] and three partial responses [PRs]) with subjective minor tumor responses in a further seven patients. Pharmacokinetic studies showed rapid gastrointestinal absorption of capecitabine, followed by extensive conversion into 5'-deoxy-5-fluorouridine (5'-DFUR), with only low systemic 5-FU levels. CONCLUSION: Capecitabine is a tolerable oral outpatient therapy that shows promising clinical activity in a variety of cancers. The recommended phase II dose is 2,510 mg/m2 daily administered by this intermittent schedule.     

Increase in dopamine release from the nucleus accumbens in response to feeding: a model to study interactions between drugs and naturally activated dopaminergic neurons in the rat brain

The aim of the present study was to investigate the interactions between the in vivo release of dopamine and certain drugs, during conditions of increased dopaminergic activity. Dopaminergic neurons in the nucleus accumbens were activated by feeding hungry rats. 48-96 h after implantation of a microdialysis probe 30 min food ingestion by hungry rats induced an immediate eating response that was accompanied with a reproducible and long-lasting increase in extracellular dopamine and 3,4-dihydroxyphenylacetic acid (DOPAC). The effect of various drugs (infused into the nucleus accumbens via the microdialysis probe), on the extracellular levels of dopamine and DOPAC were recorded, and the effect of eating was determined. Infusion of 5 mumol/l nomifensine and 3.4 mmol/l calcium increased dopamine release respectively 5.4 and 2-fold but did not modify the eating related increase in dopamine and DOPAC release. Infusion (1 mumol/l) as well as intraperitoneal administration (20 mg/kg) of sulpiride induced an increase in basal dopamine release to 220 and 195% of controls, respectively. Both routes of sulpiride pretreatment enhanced the eating related increase in extracellular dopamine and DOPAC. The results of the sulpiride experiments indicate that a behaviorally induced stimulation of dopamine release is modified by autoinhibition.     

Anticancer activity and toxicity of S-1, an oral combination of tegafur and two biochemical modulators, compared with continuous i.v. infusion of 5-fluorouracil

S-1 is an oral combined form of 1 M tegafur [a prodrug of 5-fluorouracil (5-FU)], 0.4 M 5-chloro-2,4-dihydroxypyridine (a reversible inhibitor of dihydropyrimidine dehydrogenase) and 1 M potassium oxonate (an inhibitor of orotate phosphoribosyltransferase). S-1 has been shown to exert a potent antitumor effect with low gastrointestinal toxicity in experimental tumor models. We have therefore compared the antitumor effect of oral S-1 with that of continuous infusion of 5-FU in rats bearing transplants of human and murine tumors. Almost complete inhibition of the tumor growth was obtained on 7 day schedules in Yoshida sarcoma-bearing rats by consecutive administration of 30 mg/kg/day of oral S-1 and 40 mg/kg/day infusion of 5-FU. However, a significant difference between the incidence of toxicities of S-1 and 5-FU, including body weight loss and diarrhea, was noted. The rats given the 5-FU infusion had marked weight loss and severe diarrhea, while those given oral S-1 had neither. Although about 50% inhibition of the tumor growth was attained with 15 mg/kg/day of oral S-1 and 30 mg/kg/day infusion of 5-FU in nude rats with xenografted human colon cancer (KM12C), the rate of body weight loss in the 5-FU-treated group was distinctly higher than in the S-1-treated group. The ratio of the 5-fluoronucleotide concentrations in gastrointestinal tissue to that in the tumor was lower in the S-1-treated rats than in the 5-FU-treated rats. In conclusion, the results suggest that oral S-1 might be more effective in the treatment of cancer patients than continuous infusion of 5-FU, from the standpoint of antitumor potency and toxicity.     

MDMA induced dopamine release in vivo: role of endogenous serotonin

Acting as a substrate at the serotonin (5-HT) transporter, (+)-MDMA (3,4-methylenedioxymethamphetamine), is a potent releaser of 5-HT and causes toxicity to 5-HT neurons after repeated exposure. (+)-MDMA also releases dopamine (DA), although with less potency. Since we have shown previously that the intrastriatal application of 5-HT facilities DA release, it was hypothesized that increased release of striatal 5-HT after MDMA may influence extracellular levels of DA. Using microdialysis in vivo, we found that (+)-MDMA (4.7 mumol/kg, i.v.) administration increased extracellular striatal DA levels to 501% of control (p < 0.01, n = 12). However, in the presence of fluoxetine (14.4 mumol/kg, s.c.), which prevents (+)-MDMA effects on 5-HT release, the (+)-MDMA-induced increase in DA was significantly less (to 375% of control, p < 0.05, vs. no fluoxetine, n = 8). In vitro studies with striatal slices, to test drug selectivity, showed that (+)-MDMA (0.3-3 microM) increased extracellular levels of both DA and 5-HT in a dose-dependent manner. Fluoxetine (3 microM) completely blocked the effects of (+)-MDMA on 5-HT release, but did not alter (+)-MDMA-induced DA release in vitro. The selective DA transport inhibitor GBR-12909 (1 microM), blocked (+)-MDMA's effect on DA release. It is concluded that 5-HT release after (+)-MDMA treatment partially contributes to (+)-MDMA's effect on DA release in vivo.