h-89 and azidopine

The inotropic actions of xanthine derivatives with long alkyl chains were investigated in guinea pig ventricular papillary muscle. A potent and nonselective phosphodiesterase (PDE) inhibitor, 3-isobutyl-1-methylxanthine, elicited a positive inotropy and inhibited the negative inotropic effects of calcium channel inhibitors, as did a selective PDE III inhibitor, amrinone, and these effects were canceled by a protein kinase inhibitor, N-[2-(p-bromocinnamylamino)ethyl]-5-isoquinolinesulfonamide (H-89). However, 1,3-di-n-butyl-7-(2'oxopropyl)xanthine (denbufylline) and 1-n-butyl-3-n-propylxanthine (XT-044), which have potent and selective PDE IV-inhibitory activities, showed negative inotropic actions that became more potent in the presence of H-89. Denbufylline abolished the late restoration phase induced by ryanodine. This xanthine derivative attenuated the effects of both the calcium channel acting agents Bay K 8644 and verapamil, without interaction with caffeine and dihydropyridine calcium channel inhibitors, and denbufylline had little direct influence on the specific binding of [(3)H]azidopine and [(3)H]desmethoxyverapamil to cardiac membranes. A nonxanthine PDE IV inhibitor, Ro 20-1724, did not affect the inotropic actions of calcium channel inhibitors. The attenuation by denbufylline or XT-044 of the negative inotropic action of verapamil was not influenced by treatment with H-89. These results suggest that in the ventricular papillary muscle, these xanthine derivatives elicit negative inotropy by acting on a verapamil-sensitive site of the calcium channel without involving their PDE-inhibitory activity.

Topics: 3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester; Animals; Azides; Caffeine; Calcium Channels; Depression, Chemical; Dihydropyridines; Guinea Pigs; In Vitro Techniques; Isoquinolines; Male; Myocardial Contraction; Papillary Muscles; Phosphodiesterase Inhibitors; Ryanodine; Sulfonamides; Xanthines

The effects of an isoquinolinesulfonamide compound, H-87, on naturally acquired multidrug-resistance (MDR) in rat hepatoma AH66 cells were examined. AH66 cells were highly resistant to vinblastine, SN-38, an active camptothecin analog, adriamycin, and etoposide, compared with the sensitive variant AH66F cells. Although H-87 hardly affected the sensitivities to antitumor agents of AH66F cells, this compound completely inhibited the resistance to vinblastine, moderately inhibited the resistance to SN-38 and adriamycin and had little effect on etoposide, mitomycin C, cisplatin, and 5-fluorouracil. H-87 significantly decreased the efflux of vinblastine from the resistant cells and increased the drug accumulation. SN-38 and adriamycin also exhibited a weak but significant increase in vinblastine accumulation in AH66 cells. H-87 inhibited [3H]azidopine-photolabeling to 160 kDa P-glycoprotein in the plasma membrane of AH66 cells, as reported in acquired MDR leukemic cells. Consequently, the MDR-overcoming effect of H-87 seems to be due to its direct inhibition of the binding of antitumor agents on P-glycoprotein in the plasma membrane.

Topics: Affinity Labels; Animals; Antineoplastic Agents; ATP Binding Cassette Transporter, Subfamily B, Member 1; Azides; Camptothecin; Dihydropyridines; Doxorubicin; Drug Resistance, Multiple; Drug Resistance, Neoplasm; Etoposide; Female; Irinotecan; Isoquinolines; Protein Binding; Protein Kinase Inhibitors; Rats; Sulfonamides; Tritium; Tumor Cells, Cultured; Vinblastine