thiourea and Leukemia--Promyelocytic--Acute

Human promyelocytic leukemia cells, HL-60, were treated with cisplatin [cis-diamminedichloroplatinum (II)] (2 mM, 1 h). DNA-cisplatin-protein complexes were isolated and exposed to thiourea (1 M), NaCN (100 mM), diethyldithio-carbamate (500 mM), or N-methyl-D-glucamine dithiocarbamate (500 mM) for 12 h. The release of platinum was measured by atomic absorption spectroscopy. Sodium cyanide was the most effective agent, releasing about 90% of the DNA-bound platinum. Thiourea was the least effective agent, while dithiocarbamates exhibited an intermediate. The ability of the same group of agents to split the proteins off from the protein-cisplatin-DNA complex was also evaluated and similarly dithiocarbamate were also the most effective.

Topics: Chelating Agents; Cisplatin; Ditiocarb; DNA; DNA Adducts; DNA, Neoplasm; Humans; Indicators and Reagents; Leukemia, Promyelocytic, Acute; Mercaptoethanol; Neoplasm Proteins; Sodium Cyanide; Sorbitol; Spin Labels; Thiocarbamates; Thiourea; Tumor Cells, Cultured

Histamine H1 receptors mediate activation of phospholipase C, with subsequent increases in cytosolic Ca2+ concentration ([Ca2+]i), and H2 receptors mediate accumulation of cAMP. HL-60 promyelocytes possess H2 receptors, but it is not known whether these cells also possess H1 receptors. We studied the effects of histamine on [Ca2+]i and the functional importance of histamine receptors in HL-60 promyelocytes. In these cells, histamine and dimaprit increased [Ca2+]i with EC50 values of 15 microM and 30 microM, respectively. Diphenhydramine inhibited the effect of histamine (100 microM) on [Ca2+]i up to 40%, with an IC50 of 100 nM. Famotidine and cimetidine diminished the effect of histamine (100 microM) up to 75%, with IC50 values of 85 nM and 300 nM, respectively. Diphenhydramine plus famotidine abolished histamine-induced rises in [Ca2+]i. Impromidine, with an IC50 of 100 nM, abolished the effect of histamine (100 microM) on [Ca2+]i. Diphenhydramine, famotidine, cimetidine, and impromidine showed marked noncompetitive antagonism with histamine. Histamine-induced increases in [Ca2+]i were largely due to influx of Ca2+ from the extracellular space. Ca2+ influx was inhibited by 1-(beta-[3-(4-methoxyphenyl)propoxyl]-4-methoxyphenethyl)-1H-imida zole hydrochloride (SK&F 96365). Histamine activated phospholipase C. Histamine induced expression of formyl peptide receptors, which effect was abolished by famotidine. In U-937 promonocytes and in the human erythroleukemia cell lines HEL and K-562, histamine did not induce rises in [Ca2+]i. Our data suggest the following. (i) In HL-60 promyelocytes, histamine increases [Ca2+]i predominantly via H2 receptors and to a lesser extent via H1 receptors. (ii) The agonist/antagonist profile of the H2 receptor-mediated increases in [Ca2+]i differs markedly from that for cAMP accumulation, suggesting the involvement of different H2 receptor subtypes. (iii) In HL-60 promyelocytes, histamine activates nonselective cation channels and induces functional differentiation via H2 receptors.

Topics: Adenosine Triphosphate; Calcium; Cations; Cell Differentiation; Cyclic AMP; Cytosol; Dimaprit; Famotidine; Guanidines; Histamine; Histamine Antagonists; Histamine H1 Antagonists; Histamine H2 Antagonists; Humans; Imidazoles; Impromidine; Ion Channels; Leukemia, Experimental; Leukemia, Promyelocytic, Acute; Phosphatidylinositols; Receptors, Histamine H2; Stimulation, Chemical; Thiourea; Tumor Cells, Cultured