ABSTRACT
Arglabin [1(R),10(S)-epoxy-5(S),5(S),7(S)-guaia-3(4),11(13)-dien-6, 12-olide], a sesquiterpene gamma-lactone is isolated from Artemisia glabella, a species of wormwood endemic to the Karaganda region of Kazakstan. The compound has been modified to render it water-soluble through addition of a dimethylaminohydrochloride group to the C(13) carbohydride moiety to yield Arglabin-DMA. Arglabin-DMA is a registered antitumor substance in the Republic of Kazakstan. Previously, we have shown that this compound prevents protein farnesylation without altering geranylgeranylation. We now report that Arglabin-DMA inhibits the incorporation of [(3)H]farnesylpyrophosphate into human H-ras protein by FTase with an IC(50) of no greater than 25 microM. Kinetic studies show that the phosphorylated form of this compound competitively inhibits the binding of farnesyl diphosphate to FTase. This mechanism of action is different from other reported peptidomimetic FTIs which lower the affinity of ras protein to FTase. Our in vitro studies confirm that Arglabin-DMA inhibits post-translational modification of ras protein in cells. Arglabin-DMA inhibits anchorage-dependent proliferation of NB cells (IC50=10 microg/ml) and inhibits anchorage-independent growth of NB and KNRK cells with about the same IC(50). Soft-agar colony formation assay of H-ras and K-ras transformed cells show IC(50)s to be 2 and 5 microg/ml, respectively. In primary cultures of human tumor cells, Arglabin-DMA inhibits cell proliferation of a variety of tumor types with IC(90)s in the range of 0.85 to 5.0 microg/ml. Because of these pharmacologic properties, we propose that Arglabin-DMA is suitable for the treatment of ras related malignancies.
Subject(s)
Alkyl and Aryl Transferases/antagonists & inhibitors , Antineoplastic Agents, Phytogenic/pharmacology , Artemisia/chemistry , Enzyme Inhibitors/pharmacology , Neoplasm Proteins/antagonists & inhibitors , Plants, Medicinal , Protein Processing, Post-Translational/drug effects , Proto-Oncogene Proteins p21(ras)/metabolism , Sesquiterpenes/pharmacology , 3T3 Cells/drug effects , Animals , Antineoplastic Agents, Phytogenic/chemistry , Binding, Competitive , Cell Division/drug effects , Cell Line, Transformed/drug effects , Cell Transformation, Neoplastic , Enzyme Inhibitors/chemistry , Farnesyltranstransferase , Mice , Molecular Structure , Neoplasm Proteins/metabolism , Neoplasms/pathology , Neuroblastoma/pathology , Polyisoprenyl Phosphates/metabolism , Protein Prenylation/drug effects , Sesquiterpenes, Guaiane , Solubility , Tumor Cells, Cultured/drug effects , Tumor Stem Cell AssayABSTRACT
It was shown that cytosol of primary sheep vesicular gland cells inhibits peroxidase activity of prostaglandin H synthase (PGHS). The degree of the enzyme inactivation depends on cytosol concentration. It was established that cytosol contains glycoprotein haptoglobin that is one of the cytosol basic components responsible for its property to inhibit PGHS. Haptoglobin is supposed to participate in endogenous regulation of PGHS activity in sheep vesicular glands.
