A nonpromoting phorbol from the Samoan medicinal plant Homalanthus nutans inhibits cell killing by HIV-1

Abstract

Extracts of Homalanthus nutans, a plant used in Samoan herbal medicine, exhibited potent activity in an in vitro, tetrazolium-based assay which detects the inhibition of the cytopathic effects of human immunodeficiency virus (HIV-1). The active constituent was identified as prostratin, a relatively polar 12-deoxyphorbol ester. Noncytotoxic concentrations of prostratin from greater than or equal to 0.1 to greater than 25 microM protected T-lymphoblastoid CEM-SS and C-8166 cells from the killing effects of HIV-1. Cytoprotective concentrations of prostratin greater than or equal to 1 microM essentially stopped virus reproduction in these cell lines, as well as in the human monocytic cell line U937 and in freshly isolated human monocyte/macrophage cultures. Prostratin bound to and activated protein kinase C in vitro in CEM-SS cells and elicited other biochemical effects typical of phorbol esters in C3H10T1/2 cells; however, the compound does not appear to be a tumor promoter. In skin of CD-1 mice, high doses of prostratin induced ornithine decarboxylase only to 25-30% of the levels induced by typical phorbol esters at doses 1/30 or less than that used for prostratin, produced kinetics of edema formation characteristic of the nonpromoting 12-deoxyphorbol 13-phenylacetate, and failed to induce the acute or chronic hyperplasias typically caused by tumor-promoting phorbols at doses of 1/100 or less than that used for prostratin.

Michellamine B, a novel plant alkaloid, inhibits human immunodeficiency virus-induced cell killing by at least two distinct mechanisms

“…X-Gal (5-bromo-4-chloro-3-indolyl-␤-D-galactopyranoside) was also purchased from Sigma. Polymerase assays utilized the reagents poly(rAdT) [12][13][14][15][16][17][18] , poly(rC-dG) [12][13][14][15][16][17][18] , and poly(dT-dA) [12][13][14][15][16][17][18] (Pharmacia LKB, Piscataway, N.J.) and 16S-23S rRNA (Boehringer Mannheim, Indianapolis, Ind.) and random nonamer primers (Synthetic Genetics, San Diego, Calif.).…”

“…The preparation, enzymatic activities, and drug sensitivities of these two variant RTs have been previously described (5, 6). The three template-primer systems used to evaluate the inhibition of the various RT preparations by michellamine B consisted of poly(rA-dT) [12][13][14][15][16][17][18] , poly(rC-dG) [12][13][14][15][16][17][18] , and rRNA-primer. Recombinantderived DNA polymerases ␣ and ␤ were the kind gift of Sam Wilson (University of Texas Medical Branch, Center for Molecular Sciences).…”

Analysis by Fluorescence Resonance Energy Transfer of the Interaction between Ligands and Protein Kinase Cδ in the Intact Cell

“…Indeed, a number of compounds targeting protein kinase C are currently at different stages of drug development. Examples include LY333531, being evaluated for diabetic retinopathy and anti-angiogenesis (1, 2), prostratin and dPP, being evaluated for AIDS chemotherapy (3,4), and bryostatin 1 and ingenol 3-angelate, being evaluated as cancer chemotherapeutic agents (5)(6)(7).…”

Ensuring Equitable Benefits: The Falealupo Covenant and the Isolation of Anti-Viral Drug Prostratin from a Samoan Medicinal Plant

“…Because prostratin was structurally very close to a known tumor promoter, NCI considered stopping the research, but I argued that the contemporary ethnobotanical profile and the long history of use by the Samoan people indicated that it was not acutely toxic as were other phorbol esters. Based on these arguments, the NIH team continued in vivo studies with mice, and discovered that while prostratin activates protein kinase C, it does not promote tumors (Gustafson et al, 1992). Further field studies with Andrew Sorensen of the University of California, San Francisco medical school showed the disease "fiva samasama" (which I originally translated as "yellow fever" in my collection notes) was in fact hepatitis, raising the possibility that prostratin may serve to protect healthy cells from a range of viral pathogens.…”