The antitumor effect of CGP41251 (4′-N-benzoyl staurosporine), a selective protein kinase C (PKC) inhibitor, was examined on two kinds of human non-small cell lung cancer (NSCLC) cell lines ...(adenocarcinoma: A549 and squamous cell carcinoma: NCI-H520). CGP41251 at 0.5 or 1.0 μM inhibited the proliferation of these tumor cell lines significantly; However, at 0.1 μM, it did not show any significant inhibition. Cell cycle analysis indicated that CGP41251 at 0.5 or 1.0 μM arrested the cell cycle progression at the G2/M phase up to 24 hr but 0.1 μM did not. It seems that the antiproliferative action of CGP41251 against human NSCLC is related to G2/M accumulation. In NCI-H520, CGP41251 caused DNA re-replication without mitosis. In a nude mice xenograft, CGP41251 at a dose of 200mg/kg showed antitumor activity against these cell lines. Histopathologically, expansion of central necrosis was observed, although no destruction of tumor nests was seen by CGP41251 administration. In both tumor tissues, the PKC activity of the particulate fraction was significantly decreased by CGP41251 treatment. From these results, it is thought that the antitumor activity of CGP41251 against human NSCLS is accompanied by the decrease of PKC activity in the particulate fraction. Moreover, the G2/M arrest of the cell cycle induced by CGP41251 might be important for the growth inhibitory action of this compound.
Mobilization of Ca++ was estimated in single rabbit blood platelets with digital imaging microscopy. Concanavalin A (Con A) caused a rapid initial increase in intracellular concentration of Ca++ ...(Ca++i) with a latent time of about 20 sec, followed by a sustained increase in Ca++i. This effect of Con A was antagonized by α-methyl-D-mannose, which already was shown to antagonize the inhibitory effect of Con A on 5-HT transport, indicating that this effect of Con A was also derived from its binding to cell surface glycoproteins. The presence of EGTA in the medium did not affect the initial rise, but inhibited the latter phase of sustained rise. Thus, Con A induced elevation of Ca++i was suggested to consist of two different processes: mobilization of Ca++ from the intracellular storage sites and successive Ca++ influx through Ca++ channels. The effect of Con A on the 5-HT transport was tested in the presence of EGTA, a condition where no Ca++ influx occurs. The results indicate that Con A induced inhibition of 5-HT transport was not influenced by EGTA in the medium. It is suggested that the effect of Con A on 5-HT transport might be exerted through the Ca++ mobilization from its intracellular storage sites.
Intracellular concentration of Ca^++ (Ca^++ _i ) was monitored continuously in single rabbit blood platelets by digital imaging microscopy in cooperation with specific Ca^++ -indicative dye fura-2. ...One μM serotonin (5-HT), in the presence of 1 mM CaCl_2 , increased Ca^++ _i with oscillation, which had been undetectable in cell populations because they were not synchronous. This effect of 5-HT was diminished when CaCl_2 was omitted in the medium, and antagonized by 1 μM ketanserin, a specific 5-HT_2 receptor antagonist. Both 1 μM ionomycin and AlF_4 ^- (10 mM NaF + 3 μM AlCl_3 ) also increased Ca^++ _i in the platelet, but the oscillation of Ca^++ _i was not observed. Existence of receptor (5-HT_2 ) mediated Ca^++ oscillation through activation of a specific effector system (phospholipase C) was suggested in rabbit blood platelets.
Cytoplasmic free Ca2+ concentration, Ca2+i, was estimated in single rabbit blood platelets by digital imaging microscopy with the use of the specific Ca(2+)-indicator dye Fura-2. Uneven distribution ...and low level of Ca2+i was found in the resting platelet even in the presence of extracellular 1 mM Ca2+. Thrombin at 1 unit/ml immediately caused a transient increase in Ca2+i, which was followed by a secondary and sustained increase in Ca2+i. The distribution of increased levels of Ca2+i was also shown to be uneven within the cell. The presence of 1 mM EGTA in the medium only slightly decreased the initial rise in Ca2+i, but completely inhibited the latter phase, a sustained rise in Ca2+i. This result shows that the initial rise of Ca2+i might not be caused by Ca2+ influx, but might be induced by mobilization of Ca2+ from intracellular Ca2+ storage sites. This speculation is further supported by the fact that the elevated Ca2+i induced by thrombin immediately decreased to the base line value when 3 mM EGTA was applied. Thus, thrombin induced elevation of Ca2+i is suggested to consist of two different processes, namely the mobilization of Ca2+ from the intracellular storage sites and the successive Ca2+ influx through the receptor activated Ca2+ channels. Stimulation with ADP also caused a rapid elevation of platelet Ca2+i, but this effect of ADP was different form that of thrombin. Thus, the ADP induced rise in Ca2+i was accompanied by oscillation and was inhibited by extracellular EGTA. Our present experiment is the first report that clearly and directly reveals the differences between the effects of thrombin and ADP on Ca2+i of platelets.
Serotonin (5-HT) caused immediate elevation of intracellular Ca2+ concentration (Ca2+i) in blood platelets, and it was completely inhibited by 1 mM EGTA. In Ca2+ replenished platelets, however, 2 mM ...EGTA did not affect the 5-HT induced elevation of Ca2+i when EGTA was applied just before or during the stimulation by 5-HT. At the same concentration 5-HT was also found to enhance Ca2+ influx through the activation of 5-HT2 receptor, but with rather longer latent time. From these results it is suggested that 5-HT induced elevation of Ca2+i is caused by mobilization of Ca2+ from intracellular Ca2+ storage sites, but not by direct stimulation of Ca2+ influx. Depletion of such Ca2+ stores might impair the effect of 5-HT on Ca2+i. Thus, 5-HT induced augmentation of Ca2+ influx might be secondary to replenishment of the depleted Ca2+ stores which was caused by 5-HT induced internal release of Ca2+. It is concluded that the effects of 5-HT on Ca2+i and Ca2+ influx in platelets are manifested sequentially or independently.
The therapeutic effect of the new nonsteroidal aromatase inhibitor fadrozole hydrochloride (4-(5,6,7,8-tetrahydro-imidazo1,5apyridin-5-yl)benzonitrile monohydrochloride, fadrozole, CAS 102676-31-3, ...CGS16949A) was assessed using a surgically induced endometriosis model in rats. In nontreated rats, the endometrial transplants on the abdominal wall developed large cysts with fluid. In the fadrozole treated group, the cystic volume of the transplants decreased in a dose-dependent manner. The weights of the hemi-uteri were markedly reduced by fadrozole treatment. Fadrozole produced a dose-dependent increase in percentage of vaginal diestrous days. In ovariectomized group, the growth of the transplants was also suppressed, and the weights of the hemi-uteri decreased markedly. Histologically, the signs of growth suppression and/or atrophic changes such as minimization of luminal size, cuboidal piknotic epithelium and/or contraction of stroma were observed in ovariectomized or fadrozole treated groups. The right uterine horns also showed marked atrophic changes as with the transplants. The present study strongly indicates that the new selective aromatase inhibitor fadrozole should be useful for the treatment of endometriosis.
CGP 41251 (4'-N-benzoyl staurosporine, CAS 120685-11-2) exerts increased selectivity for Ca(2+)- and phospholipid-dependent protein kinase C inhibition. In this study, the effects of CGP 41251 on ...cell cycle distribution and growth inhibition were examined in SBC3 human small cell lung cancer (SCLC) cell line. CGP 41251 caused the inhibition of cell proliferation and at 1.0 mumol/l showed almost complete effect. In early S phase synchronized SBC3 cells, CGP 41251 at 1.0 mumol/l did not inhibit an initial progression from early S to G2 phase, but it blocked a process from G2/M to G1 phase completely. After removal of nocodazole block, CGP 41251 at 1.0 mumol/l caused DNA re-replication and induction of polyploidy. In nude mice xenograft, CGP 41251 at a dose of 200 mg/kg showed statistically significant inhibition against this tumor with a T/C value of 21.4%. Histopathologically, expansion of central necrosis was observed by the administration of CGP 41251. These results in SBC3 cells indicated that CGP 41251 showed antitumor activity through the inhibition of cell cycle progression from G2/M to G1 phase, and through induction of cells with higher DNA content.
1. The saponin-permeabilized platelet was used to examine the effect of mezerein, a moderate activator of protein kinase C (C-kinase), on the sequestration of Ca2+ to its intracellular storage sites. ...2. We found that the activation of C-kinase by mezerein causes the potentiation of the Ca2+ sequestration. 3. It was suggested that C-kinase in platelets might function as a negative feedback regulator for the agonist-induced Ca2+ mobilization and might be involved in its oscillation.
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