BackgroundElucidation of the mechanisms by which gastric cancer cells acquire resistance to 5-fluorouracil (5FU) may provide important clues to the development of effective chemotherapy for 5FU-resistant gastric cancerMethodsFour 5FU-resistant cell lines (MKN45/5FU, MKN74/5FU, NCI-N87/5FU, and KATOIII/5FU) were established by continuous exposure of the cells to progressively increasing concentrations of 5FU for about 1 year. Then, mRNA expression levels of four genes associated with 5FU metabolism, i.e., thymidylate synthase (TS), dihydropyrimidine dehydrogenase, thymidine phosphorylase, and orotate phosphoribosyltransferase, were quantitatively evaluated by real-time reverse transcriptase-polymerase chain reaction. In addition, TS protein expression was measured by Western blot analysis.ResultsAs compared with the parent cell lines, the 5FU-resistant cell lines showed 3.8- to 11.6-fold higher resistance to 5FU, as well as 1.9- to 3.5-fold higher TS mRNA expression and 1.6- to 7.1-fold higher TS protein expression. In contrast, the expressions of other genes did not differ significantly among the cell lines. The cytotoxicity of 5FU was enhanced 2.3- to 2.8 fold by leucovorin (LV) against three of the four 5FU-resistant cell lines.ConclusionsCollectively, LV enhanced the cytotoxicity of 5FU not only against the parent gastric cancer cell lines, but also against the 5FU-resistant cell lines, even those with elevated TS expression levels. These results suggest that clinical studies of a combination of 5FU and LV are warranted in patients who have recurrent gastric cancer after 5FU-based therapy.

Excessive production of sputum is one of the major symptoms in patients with chronic airway diseases. Because endogenous prostaglandins may play a role in the regulation of airway secretions, blockade of cyclooxygenase pathway with indomethacin could decrease respiratory tract fluid and mucus by inhibiting Cl secretion and glandular secretion and by enhancing Na absorption across airway mucosa. To test this hypothesis, we studied the effect of inhaled indomethacin on bronchorrhea in patients with chronic bronchitis, diffuse panbronchiolitis, and bronchiectasis in a double-blind, placebo-controlled fashion. Patients who inhaled 2 ml of indomethacin (1.2 micrograms/ml) three times a day for 14 days showed a decrease in the amount of sputum, from 189 +/- 19 to 95 +/- 21 g/day (p less than 0.001) and an increase in the solid component of sputum without alterations in parameters of systemic inflammatory responses. Although pulmonary function remained unchanged, perceived dyspnea was improved so that Borg's ratio scale was decreased from 7.1 +/- 0.5 to 4.5 +/- 0.4 (p less than 0.01). Adverse effects, including hypotension and bronchoconstriction, were not observed. The reduction of sputum was accompanied by a significant decrease in the concentrations of prostaglandin (PG)E2, PGF2 alpha, thromboxane B2, and 6-oxo-PGF1 alpha in the sputum. Thus, indomethacin inhalation may be of value in reducing bronchorrhea sputum, probably through the inhibition of PG-dependent airway secretions.

Endothelin, an endothelium-derived vasoconstrictor peptide, has recently been reported to exist in airway epithelial cells. To elucidate a possible role of endothelin on epithelial functions, we studied the effects of this peptide on ciliary beat frequency (CBF) and electrical properties of canine cultured tracheal epithelium by a microphoto-oscillation method and Ussing's short-circuited technique, respectively. Endothelin dose-dependently increased CBF, the maximal increase above the baseline value and EC50 being 32.3 +/- 4.0% (P less than 0.001) and 3 nM, respectively. This effect was moderately attenuated by pretreatment of cells with indomethacin and greatly reduced by Ca2(+)-free medium. Addition of endothelin (10(-6) M) to the mucosal bath of Ussing chamber increased short-circuit current from 5.1 +/- 1.2 to 9.4 +/- 1.7 microA/cm2 (P less than 0.05) and potential difference from 2.9 +/- 0.4 to 5.0 +/- 0.9 mV (P less than 0.05), an effect that was inhibited by indomethacin or Ca2(+)-deficiency and was abolished by the Cl transport inhibitor bumetanide or substitution of Cl with iodide in the medium. These results indicate that endothelin stimulates ciliary motility and Cl secretion probably through an increase in cytosolic Ca2+ and partially a prostaglandin synthesis in canine tracheal epithelium, and suggest that this peptide might play a role in modulating airway mucociliary transport functions.

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To study the effect of atrial natriuretic factor (ANF) on airway ciliary motility, we measured ciliary beat frequency by a photoelectric method in response to ANF in cultured tracheal epithelial cells from rabbits. Addition of ANF but not [Tyr8]ANF-(5-27) decreased ciliary beat frequency in a dose-dependent fashion; the maximal decrease from the baseline value was 24.1 +/- 1.5% (+/- SE, P less than 0.001), and a half-maximal inhibitory concentration (IC50) was 3 x 10(-12) M. Inhibition of neutral endopeptidase activity by phosphoramidon (10(-6) M) or thiorphan (10(-6) M) potentiated the effect of ANF so that the dose-response curve for ANF was shifted to lower concentrations by approximately 0.5 log units (P less than 0.05, in each case). The inhibition of ciliary motility induced by ANF was not affected by the blockade of arachidonic acid metabolism with indomethacin, piroxicam, or nordihydroguaiaretic acid, but it was blocked by methylene blue, a soluble guanylate cyclase inhibitor, and was potentiated by M & B 22948, a guanosine 3',5'-cyclic monophosphate (cGMP) phosphodiesterase inhibitor. The intracellular cGMP levels were increased by ANF, an effect that was further potentiated by phosphoramidon or thiorphan. These results suggest that ANF inhibits ciliary motility presumably through a guanylate cyclase-dependent regulatory pathway and that neutral endopeptidase may play a role in modulating the ANF effect on airway mucociliary transport function.