Cell Lines Of Human Origin Research Articles

Lack of correlation between ATM protein expression and tumour cell radiosensitivity

Purpose: Cells derived from individuals in which the ataxia telangiectasia (ATM) gene is mutated are hypersensitive to ionizing radiation. Whether differences in ATM protein levels exist among human malignant glioma cell lines and whether such differences are correlated with cellular radiosensitivity were determined. Materials and methods: Polyclonal antibodies were raised to separate regions of the ATM protein. ATM protein expression in human malignant glioma cell lines, SV40 transformed normal human fibroblasts and SV40 transformed AT fibroblasts was analysed by Western blotting. Reverse transcriptase polymerase chain reaction (RT-PCR) was used to assess the presence of ATM transcript. Results: While ATM protein was detected in all cell extracts, significant differences in the level of expression were observed. There was no apparent correlation between cellular radiosensitivity and differences in ATM protein levels in these human glioma cells. Extremely low levels of ATM protein were observed in M059J cells, which provide the only example of DNA-dependent protein kinase (DNA-PKcs) deficiency in a cell line of human origin. Conclusions: Variations in the levels of ATM protein are insufficient to explain the differences in cellular radiosensitivity observed in a panel of human malignant glioma cell lines.

Synthesis, Characterization and Antitumour Activity of Di‐n‐Butyltin Salicyloxamate

The synthesis and characterization of di‐n‐butyltin and dimethyltin salicyloxamate, respectively compounds 1 and 2, are reported. Compound 1 is more active than cisplatin, 5‐fluorouracil and etoposide against seven tumoural cell lines of human origin, but less active than methotrexate and doxorubucin.

Synthesis, Characterization and In Vitro Antitumour Activity ofDi‐n‐Butyl, Tri‐n‐Butyl and Triphenyltin 3,6‐Dioxaheptanoates and3,6,9‐Trioxadecanoates

A series of di- and triorganotin 3,6-dioxaheptanoates and 3,6,9-trioxadecanoates were synthesized and characterized by 1H, 13 and 117Sn NMR, electrospray mass and 119mSn Mössbauer spectroscopy, as well as elemental analysis. Their in vitro antitumour activity against seven tumoural cell lines of human origin, two breast cancers (MCF-7, EVSA-T), a colon carcinoma (WiDr), an ovarian cancer (IGROV), a melanoma (M 19 MEL), a renal cancer (A 498) and a non small cell lung cancer (H 226), is reported. They are characterized by similar inhibition doses ID50 as the analogous di- and triorganotin derivatives of 4-carboxybenzo-15-crown-5 and -18-crown-6 and in some cases by much lower ID50 values than clinically used reference compounds such as doxorubicine and methotrexate.

Wed-P41 - Active 3H-dopamine uptake occurs in platelets and in artificial neuronal cell lines of human origin but not in lymphocytes

Wed-P41 - Active 3H-dopamine uptake occurs in platelets and in artificial neuronal cell lines of human origin but not in lymphocytes

Synthesis, Characterization and Antitumour Activities of Di‐n‐Butyl‐ and Dimethyltin D‐(+)‐Camphorates

The synthesis and characterization di‐n‐butyl‐ and dimethyltin D‐(+)‐camphorates, respectively compounds 1 and 2, are reported. Compound 1 displays antitumoural activity in vitro, and is more active than cisplatin, 5‐fluorouracil and etoposide against seven tumoural cell lines of human origin, but less active than methotrexate and doxorubucin.

Long-term gene delivery into the livers of immunocompetent mice with E1/E4-defective adenoviruses.

We have compared the in vitro and in vivo behaviors of a set of isogenic E1- and E1/E4-defective adenoviruses expressing the lacZ gene of Escherichia coli from the Rous sarcoma virus long terminal repeat. Infection of tumor-derived established cell lines of human origin with the doubly defective adenoviruses resulted in (i) a lower replication of the viral backbone that correlated with reduced levels of E2A-specific RNA and protein, (ii) a significant shutoff of late gene and protein expression, and (iii) no apparent virus-induced cytotoxicity. Independently of the extent of the deletion, the additional inactivation of E4 from the viral backbone therefore drastically disabled the virus in vitro, with no apparent effect on transgene expression. A lacZ-transgenic model was used to compare the different recombinant adenoviruses in the livers of C57BL/6 mice. The immune response to the virally encoded beta-galactosidase was minimal in this model, as infusion of the E1-defective adenovirus resulted in a time course of transgene expression that mimicked that in immunodeficient (nu/nu) mice, with very little inflammation and necrosis in the liver. Administration of a doubly defective adenovirus to the transgenic animals led to long-term extrachromosomal persistence of viral DNA in the liver, with no detectable methylation of CpG dinucleotides. However, transient transgene expression was observed independently of the extent of the E4 deletion, suggesting that the choice of the promoter may be critical to maintain transgene expression from these attenuated adenovirus vectors.

Characterization of FR173657, a novel nonpeptide B2antagonist: in vitro and in vivo studies

Bradykinin (BK) is involved in different pathophysiological conditions, including allergic and (or) inflammatory reactions. Thus, BK antagonists are considered as a potential drug in allergic and (or) inflammatory diseases. Orally active BK antagonist would be desirable for this purpose. Here, we describe the pharmacological characterization of FR173657 ((E)-3-(6-acetamido-3-pyridyl)-N-[N-[2,4-dichloro-3-[(2-methyl-8- quinolinyl)oxymethyl]phenyl]-N-methylaminocarbonylmethyl]acr ylamide) obtained from our screening for nonpeptide, orally active B2 antagonists. (i) FR173657 antagonized [3H]BK binding with IC50 values of 4.6 x 10(-10) and 8.6 x 10(-9) M in membrane preparations of guinea pig ileum and lung, respectively. FR173657 inhibited [3H]BK binding to A431, W138, and IMR90 cell lines of human origin with IC50 values of 2.0 x 10(-9), 2.3 x 10(-9), and 1.7 x 10(-9) M, respectively. FR173657 did not affect [3H]des-Arg10-kallidin (B1 ligand) binding onto IMR90 cells. (ii) FR173657 inhibited guinea pig ileum contractions by BK (6 x 10(-8) M) with an IC50 value of 6.1 x 10(-9) M. Acetylcholine- and histamine-induced contraction of guinea pig ileum was unaffected by FR173657. (iii) Oral administration of FR173657 dose-dependently inhibited BK (5 micrograms/kg) and dextran sulfate (activator of kinin-kallikrein cascade) induced bronchoconstriction with ED50 values of 0.075 and 0.057 mg/kg, respectively. In conclusion, FR173657 is a selective potent, orally active B2 receptor antagonist that can be used to investigate the role of BK in allergic and inflammatory diseases.

Selective induction of cyclo-oxygenase-2 activity in the permanent human endothelial cell line HUV-EC-C: biochemical and pharmacological characterization.

1. Cyclo-oxygenase (COX), the enzyme responsible for the conversion of arachidonic acid (AA) to prostaglandin H2 (PGH2), exists in two forms, termed COX-1 and COX-2 which are encoded by different genes. COX-1 is expressed constitutively and is known to be the site of action of aspirin and other nonsteroidal anti-inflammatory drugs. COX-2 may be induced by a series of pro-inflammatory stimuli and its role in the development of inflammation has been claimed. 2. Endothelial cells are an important physiological source of prostanoids and the selective induction of COX-2 activity has been described for finite cultures of endothelial cells, but not for permanent endothelial cell lines. 3. The HUV-EC-C line is a permanent endothelial cell line of human origin. We have determined the COX activity of these cells under basal conditions and after its exposure to two different stimuli, phorbol 12-myristate 13-acetate (PMA) and interleukin-1 beta (IL-1 beta). 4. Both PMA and IL-1 beta produced dose- and time-dependent increases of the synthesis of the COX-derived eicosanoids. These increases were maximal after the treatment with 10 nM PMA for 6 to 9 h. Under these conditions, the main eicosanoid produced by the cells was PGE2. 5. The increase of COX activity by PMA or IL-1 beta correlated with an increase of the enzyme's apparent Vmax, whilst the affinity for the substrate, measured as apparent Km, remained unaffected. 6. Treatment of the cells with PMA induced a time-dependent increase in the expression of both COX-1 and COX-2 mRNAs. Nevertheless, this increase was reflected only as an increase of the COX-2 isoenzyme at the protein level. 7. The enzymatic activity of the PMA-induced COX was measured in the presence of a panel of enzyme inhibitors, and the IC50 values obtained were compared with those obtained for the inhibition of human platelet COX activity, a COX-1 selective assay. Classical non-steroidal anti-inflammatory drugs (NSAIDs) inhibited both enzymes with varying potencies but only the three compounds previously shown to be selective COX-2 inhibitors (SC-58125, NS-398 and nimesulide) showed higher potency towards the COX of PMA-treated HUV-EC-C. 8. Overall, it appears that the stimulation of the HUV-EC-C line with PMA selectively induces the COX-2 isoenzyme. This appears to be a suitable model for the study of the physiology and pharmacology of this important isoenzyme, with a permanent endothelial cell line of human origin.

PRODUCTION OF ARACHIDONIC ACID LIPOXYGENASE METABOLITES BY THE INTESTINAL EPITHELIAL CELL LINE HT29 CL. 19A AND THEIR EFFECT ON CHLORIDE SECRETION.

Arachidonic acid (AA) lipoxygenase products may be important in the pathogenesis of diarrhoea associated with intestinal inflammation, because they may stimulate electrogenic chloride secretion in the epithelium. However, the role of the epithelial cells as producers or as targets for lipoxygenase products remains controversial. To clarify this role, we measured the following on the same clone of a chloride-secreting intestinal cell line of human origin (HT29 cl. 19A): 1) the expression of the mRNAs of 5-lipoxygenase, platelet and leukocyte type 12-lipoxygenase, 15-lipoxygenase, LTA4 hydrolase, Five-Lipoxygenase-Activating-Protein (FLAP), prostaglandin H (PGH) synthase-1 and PGH synthase-2 after total RNA extraction, reverse transcription and cDNA amplification by PCR, using specific primers; 2) the formation of AA metabolites by high pressure liquid chromatography (HPLC) and 3) the effect of such metabolites on the stimulation of short-circuit current (Isc). an index of chloride secretion, in filter-grown HT29 cl. 19A cells mounted in Ussing chambers. Results: The mRNAs of 5-lipoxygenase, 15-lipoxygenase, LTA4 hydrolase, PGH synthase-1 and PGH synthase-2 were equally expressed in HT29 cl. 19A cells at different stages of culture, but FLAP, platelet and leukocyte type 12-lipoxygenase mRNAs were not expressed. When dispersed HT29 cl. 19A cells were incubated with [1-14C] arachidonic acid, calcium ionophore A23187, Mg2+ and Ca2+, they produced 5-hydroxyeicosatetraenoic acid (5-HETE), 15-hydroxyeicosatetraenoic acid (15-HETE), and a peak containing leukotriene B4 (LTB4) unresolved from its 6-trans-stereoisomers, and 5(S)-12(S)-di-HETEs. No peptidoleukotriene were detected. Unlabelled AA metabolites, analyzed by HPLC and enzyme immunoassay, were mainly 6-trans-stereoisomers of LTB4 and unidentified di-HETEs, but only a small amount of LTB4 was detected. In addition to prostaglandin E2 (PGE2), which was the most potent compound, several hydroperoxyeicosatetraenoic acids (HPETEs) produced by autoxidation of AA (5-, 9-, 11-, 12- and 15-HPETEs) induced bumetanide-sensitive chloride secretion by HT29 cl. 19A cells (Δ Isc: 3.2 ± 0.4 to 12.1 ± 3.7 μA cm-2). The 9-, 12- and 15-HETEs obtained by triphenylphosphine reduction of the corresponding HPETEs, displayed the same activity as the parent compound, but the 5- and 11-HETEs lose their potencies. LTB4 had no effect on chloride secretion. The present results suggest that the enterocyte may participate in the production of AA metabolites through the lipoxygenase and prostaglandin synthase pathways. In addition, the enterocytes are a target for the lipoxygenase pathway metabolites they and other cells produce.

Paclitaxel as a radiosensitiser: A proposed schedule of administration based on in vitro data and pharmacokinetic calculations

Paclitaxel is efficacious against many human cancers. Because it blocks cells at the radiosensitive G2-M interface, paclitaxel has been investigated as a radiosensitiser. The results have been equivocal and somewhat contradictory. It is impossible to obtain proper pharmacokinetic calculations, aimed at obtaining maximum cytotoxicity and/or radiosensitisation, without knowing (i) how long the drug must be in contact with the cells, (ii) how long the effect lasts after the drug is removed from the cellular environment, (iii) whether the drug acts as a radiosensitiser even when, like cis-platinum, it is added after the radiation and (iv) what the minimum quantity of drug in the cellular environment is required for both chemotoxicity and radiosensitisation. The present work addresses the above questions. Two radioresistant cell lines of human origin were used, A375 melanoma and S549 lung carcinoma, in a clonogenic assay where only colonies with 50 or more cells were counted. For the irradiation, 6 MV X-rays were used. Any G2-M block was quantified by cell cycle kinetics analysis. From the results, a simulation of pharmacokinetics was conducted to calculate the schedule of administration of paclitaxel most likely to achieve and maintain significant chemotoxocity and radiosensitisation. The minimum concentration of paclitaxel for measurable cytotoxicity was 3 nM for both cell lines, but the drug was more toxic to the A549 cells. The minimum concentration for measurable radiosensitisation was 3 nM for A375 and approximately 0.1 nM for A549, but whereas above 3 nM the radiosensitivity increased in A375, it decreased above 1 nM for A549. A minimum of 18 h incubation with the drug was necessary for measurable effects and the radiosensitising effects were lost soon after its removal. There was no radiosensitisation if paclitaxel was added after the radiation, and, at the minimum effective concentrations, it caused only a minor and transient G2-M block. The pharmacokinetic calculations predict that 15 mg/m 2 paclitaxel given as a 1 h infusion 5 days/week for 3 weeks during the radiotherapy should achieve both cytotoxicity and radiosensitisation. The mechanism of radiosensitisation by paclitaxel at the concentrations suggested by our results does not appear to be via a G2-M block and is probably concentration dependent. The results imply that low-dose, daily infusions of paclitaxel for as long as possible during a course of radiotherapy are more likely to result in radiosensitisation and prolonged cytotoxicity than high-dose infusions given once a week.

Paclitaxel as a Radiosensitiser: A Proposed Schedule of Administration Based on In Vitro Data and Pharmacokinetic Calculations

Paclitaxel is efficacious against many human cancers. Because it blocks cells at the radiosensitive G2-M interface, paclitaxel has been investigated as a radiosensitiser. The results have been equivocal and somewhat contradictory. It is impossible to obtain proper pharmacokinetic calculations, aimed at obtaining maximum cytotoxicity and/or radiosensitisation, without knowing (i) how long the drug must be in contact with the cells, (ii) how long the effect lasts after the drug is removed from the cellular environment, (iii) whether the drug acts as a radiosensitiser even when, like cis-platinum, it is added after the radiation and (iv) what the minimum quantity of drug in the cellular environment is required for both chemotoxicity and radiosensitisation. The present work addresses the above questions. Two radioresistant cell lines of human origin were used, A375 melanoma and S549 lung carcinoma, in a clonogenic assay where only colonies with 50 or more cells were counted. For the irradiation, 6 MV X-rays were used. Any G2-M block was quantified by cell cycle kinetics analysis. From the results, a simulation of pharmacokinetics was conducted to calculate the schedule of administration of paclitaxel most likely to achieve and maintain significant chemotoxocity and radiosensitisation. The minimum concentration of paclitaxel for measurable cytotoxicity was 3 nM for both cell lines, but the drug was more toxic to the A549 cells. The minimum concentration for measurable radiosensitisation was 3 nM for A375 and approximately 0.1 nM for A549, but whereas above 3 nM the radiosensitivity increased in A375, it decreased above 1 nM for A549. A minimum of 18 h incubation with the drug was necessary for measurable effects and the radiosensitising effects were lost soon after its removal. There was no radiosensitisation if paclitaxel was added after the radiation, and, at the minimum effective concentrations, it caused only a minor and transient G2-M block. The pharmacokinetic calculations predict that 15 mg/m2 paclitaxel given as a 1 h infusion 5 days/week for 3 weeks during the radiotherapy should achieve both cytotoxicity and radiosensitisation. The mechanism of radiosensitisation by paclitaxel at the concentrations suggested by our results does not appear to be via a G2-M block and is probably concentration dependent. The results imply that low-dose, daily infusions of paclitaxel for as long as possible during a course of radiotherapy are more likely to result in radiosensitisation and prolonged cytotoxicity than high-dose infusions given once a week.

Hepatitis C virus (HCV) specific sequences are demonstrable in the DNA fraction of peripheral blood mononuclear cells from healthy, anti-HCV antibody-negative individuals and cell lines of human origin.

No convincing support has been provided so far for the existence of extrahepatic hepatitis C virus particles that should correspond to the sometimes extremely high concentration of 'HCV-RNA' in serum or plasma. If a naturally occurring HCV-specific DNA were to be found, a concept for at least some phenomena in terms of the pathophysiology of HCV should become conceivable. DNA was extracted from peripheral blood mononuclear cells of eleven healthy, anti-HCV-negative individuals, including five long term blood donors, and cells from different cell lines. DNA was subjected to nested polymerase chain reaction omitting a reverse transcriptase step with primers of the 5'NC as well as part of the core region of HCV. Direct polymerase chain reaction, i.e. without a reverse transcriptase step, revealed HCV-specific sequences in the DNA fraction of peripheral blood mononuclear cells of different origin: healthy anti-HCV negative individuals, furthermore in HeLa and MT2 cells. The fragments found were of expected length as well as of shorter and of longer than expected length with respect to the sequence of the HCV genome framed by the primers applied. The results derived from additional hybridization, restriction endonuclase analysis, and sequencing demonstrated HCV-specific sequences in the expected fragments with both a high degree of homology and deletions, respectively, substitutions, as compared to a prototype strain. However, the longer than expected fragments also contained sequences not specific for HCV.

Synchronization of cancer cell lines with methotrexate in vitro

Detailed procedure are described for inducing synchrony in cancer cell lines of human origin (Jurkat, K562, U937, SW626) and L1210 cell line of murine origin by using very low non-toxic concentrations (0.04–0.08 μM for 13–24 hours) of methotrexate under standard culture conditions. This protocol offers a method for synchronization of cells at the G1/S boundary and through the S-G2-M phases of the cell cycle. Kinetic behavior and biological properties of the synchronized cells are considered for characterisation of the system. Comparisons are made with MTX synchronization and that induced by aphidicolin alone or by a combination of serum deprivation and aphidicolin. Methotrexate appears to be the best choice for obtaining highly synchronous human cancer cell population without cytotoxicity or detectable physiological perturbations.

Biotransformation of the MPTP Analogtrans-1-Methyl-4-[4-dimethylaminophenylethenyl]-1,2,3,6-tetrahydropyridine to a Fluorescent Pyridinium Metabolite by Intact Neuroblastoma Cells

The possibility of imaging monoamine oxidase (MAO) containing neurons through the MAO-mediated conversion of the nonfluorescent tetrahydropyridine compoundtrans-1-methyl-4-[4-dimethylaminophenylethenyl]-1,2,3,6-tetrahydropyridine (t-THP) to the corresponding fluorescenttrans-1-methyl-4-[4-dimethylaminophenylethenyl]pyridinium species (t-P+) was examined with the aid of human neuroblastoma cells (SH-SY5Y). Fluorescence microscopy and fluorescence measurements established the intracellular formation of a fluorescent species with maximal excitation/emission wavelengths of 485/620 and 530/620 nm corresponding to the fluorescence characteristics of synthetict-P+. An independent assay confirmed the presence of both MAO-A and MAO-B in these cells. As expected, the development of the fluorescence was inhibited by both clorgyline (an MAO-A inhibitor) and deprenyl (an MAO-B inhibitor). Cytotoxic effects, as determined by trypan blue dye exclusion for viability and by the MTT [3-(4,5-dimethylthiazole-2-yl)-2,5-diphenyltetrazolium bromide] assay for mitochondrial integrity, were not observed in cells incubated with concentrations oft-THP as high as 10−3Mfor 4 hr. The results from these studies with a neuronal cell line of human origin suggest: (1) that SH-SY5Y cells metabolize and, therefore, can be used for study of tetrahydropyridine compoundsin vitro,and (2) thatt-THP may be a useful agent to monitor neurodegenerative processes in MAO-rich neurons, including the dopaminergic nigrostriatal neurons that are damaged by the parkinsonian-inducing tetrahydropyrridine MPTP. The potential advantage of usingt-THP over related imaging techniques is the possibility of assessing neuronal function by anin vivoprocessing of the reporter molecule rather than by postmortem immunofluorescent or formaldehyde-based procedures.

Impact of different fluorouracil biochemical modulators on cellular dihydropyrimidine dehydrogenase.

In attempts to increase fluorouracil (FU) activity by pharmacomodulation, most attention has been paid to FU activation pathways without consideration of the presence and possible role of FU catabolism in the target tumoral cell itself. The first step in the catabolism of FU is hydrogenation by the enzyme dihydropyrimidine dehydrogenase (DPD). The purpose of the present study was to test the DPD-inhibitory effects of several agents whose use as FU biomodulators has been clinically established: cisplatin, hydroxyurea, dipyridamole, and allopurino. Five cancer cell lines of human origin were used. Dipyridamole and hydroxyurea were the only modulators for which an augmentation in FU cell-growth inhibition (MTT test) was clearly evident for the whole panel of cell lines investigated (P<1.10(-4) and P=0.005, respectively). With dipyridamole the efficacy of FU was multiplied by a factor of around 5. Allopurinol and cisplatin had no obvious effect on cellular DPD activity (biochemical method). For dipyridomole and hydroxyurea, DPD activity showed a more or less marked concentration-related inhibition according to the cell line tested. Only dipyridamole produced reductions in FU IC50 values (50% growth-inhibitory concentrations), i.e., potentiation of FU cytotoxicity, that were significantly related to inhibition of cellular DPD activity. This DPD-mediated interaction between dipyridamole and FU is a new finding that could be important for a better understanding of FU-dipyridamole combination chemotherapy.

Development of human IL-6 receptor antagonists.

We have shown that through mutagenesis of IL-6 it is possible to separate receptor binding from signal transduction of the cytokine. Mutations in residues important for signal transduction via gp130 result in IL-6 variants that can competitively inhibit wtIL-6 activity in vitro. The differential effects of these signaling deficient mutants on various cell lines of human origin suggest that receptor composition and/or signal transduction pathways may vary between cells of different origin. The observations that three sites have been identified which are important for gp130 interaction raises the question what the role of each region is in the stepwise formation of the active IL-6 receptor complex. The overall tertiary conformation of the beta-site mutants is intact, as judged from their binding characteristics to conformation specific mAbs and IL-6R alpha. As can be deduced from Figure 1, beta-site mutations may therefore affect a direct interaction with gp130, dimerization of IL-6, or maybe a conformational change in IL-6R alpha, important for gp130 interaction. A future challenge will therefore be to determine the function of each of the beta-sites in IL-6 receptor interaction.

Inhibition of cell growth by macrophage membrane lipid molecule.

Macrophage hybridoma clone 5 suppressed B-cell proliferation induced by lipopolysaccharide (LPS). Since paraformaldehyde-fixed macrophages exerted the effect, macrophage-derived mediators were excluded from the inhibition. The inhibitory property of macrophages was present in the membrane fraction and was recovered in the organic phase after extraction using a chloroform/methanol/water system followed by hexane extraction. Therefore, the inhibitory activity found in macrophage clone 5 was concluded to arise from a lipid component. The inhibitory substance was further purified to a homogeneity by LH20 column fractionation using methanol/chloroform as the mobile phase. The purified lipid did not have any effect on the LPS-mediated induction of MHC class II molecules on the B-cell surface. Moreover, the inhibitory property was shown to affect growth of a wide variety of tumor cell lines of human origin. These results suggest that a lipid molecule found on the cell membrane of cloned macrophage hybridoma may participate in the regulation of cell growth through cell contact.

Molecular Cloning of the Human Placental Folate Transporter

We have isolated a cDNA clone from a human placental library which codes for a functional folate transporter (hFOLT). An RT-PCR product obtained from mouse intestinal mRNA using primers specific for the mouse folate transporter cDNA was used to screen the cDNA library. The hFOLT cDNA predicts a protein of 590 amino acids with twelve potential transmembrane domains. The amino acid sequence has 65% identity to the mouse and hamster folate transporters. When transfected into COS-1 and HeLa cells, the hFOLT cDNA causes a significant increase in the uptake of 5-methyltetrahydrofolate. The mRNA transcripts hybridizing to the hFOLT cDNA are detectable in the placenta and liver and also in several cell lines of human origin. The size of the principal transcript is 2.7 kb. This constitutes the first report on the cloning of a vitamin transporter from a human tissue.

Synthesis, Characterization and In vitro Antitumour Activityof Novel Organotin Derivatives of 1,2‐ and1,7‐Dicarba‐Closo‐dodecaboranes

Several organotin derivatives of 1,2- and 1,7-dicarba-closo-dodecaboranes were synthesized and characterized by 119Sn Mössbauer, 1H, 13C and 119Sn NMR spectroscopy. Their antitumour activities in vitro against cancerous cell lines of human origin are reported.

Antiepileptic drugs—calcium current interaction in cultured human neuroblastoma cells

The voltage-dependent calcium channel current (ICa) in the neuroblastoma cell line of human origin (NB-I) was studied by the whole-cell clamp recording. Three types of ICa were identified in NB-I cells. Our electrophysiological and pharmacological findings have suggested that these three types of ICa are consistent with the T-, N- and L-type ICa, respectively. Phenytoin (PHT) inhibited T-type ICa by 13.0% at a concentration of 5 microM, and L-type ICa by 6.3% at a concentration of 100 microM. At a concentration of 100 microM, carbamazepine (CBZ) inhibited T- and L-type ICa by 6.0% and 5.9%, respectively. At a concentration of 50 microM, sodium valproate (VPA) blocked T- and L-type ICa by 6.1% and 47.5%, respectively. At a concentration of 50 microM, zomisamide (ZNS) inhibited T- and L-type ICa by 38.3% and 41.9%, respectively. Na+ channel blockade has been reported to be responsible for the clinical efficacy of PHT or CBZ. Inhibition of T-type ICa by PHT may enhance the efficacy of its anticonvulsant action. CBZ had little effect on ICa. The anticonvulsant activity may be related to the blockade of T-type ICa in the case of VPA and ZNS.