The search for bioactive compounds from higher plants

Jon Eric Anderson, Purdue University

Abstract

Simple bench-top bioassays involving brine shrimp lethality, Lemna frond proliferation, and inhibition of crown gall tumors on potato discs, and the human tumor cell lines A-549 (lung carcinoma), MCF-7 (breast carcinoma), and HT-29 (colon adenocarcinoma) were compared for accuracy to detect known in vivo 3PS (murine leukemia) active antitumor agents. The potato disc assay showed excellent correlation to in vivo activity (p = 0.008). The brine shrimp assay (p = 0.033) was at least as equally accurate as the in vitro human tumor cell lines (0.033-0.334). The Lemna assay (p = 0.708) showed the poorest correlation to antitumor activity; however from this screening, usnic acid displayed potent phytotoxicity and hippuric acid displayed plant growth stimulating activity to Lemna minor L. Brine shrimp lethality-directed fractionation of Allamanda schottii Pohl (Apocynaceae) led to the isolation of six known compounds; pinoresinol (LC$\sb{50}$ 377 ppm), scopoletin (LC$\sb{50}$ 55 ppm), and scoparone (LC$\sb{50}$ 349 ppm)--new to Allamanda, and isoplumericin (LC$\sb{50}$ 1.7 ppm), plumericin (LC$\sb{50}$ 1.7 ppm), and allamandin (LC$\sb{50}$ 21.3 ppm)--widespread in Allamanda. The iridoids displayed significant activity in the potato disc assay (44-51% inhibition) and in the human tumor panel (ED$\sb{50}$ 1.99 $\times$ 10$\sp{-2}$-9.45 $\times$ 10$\sp{-2}$ $\mu$g/ml). The iridoid, allamcin, was inactive in the brine shrimp and potato disc assays, suggesting that the $\alpha$, $\beta$ unsaturated spirolactone is not the active moiety of cytotoxic iridoidspirolactones. Two new carbazole alkaloids from Clausena harmandiana Pierre (Rutaceae), 2-hydroxy-3-formyl-7-methoxycarbazole and 7-methoxyheptaphylline, showed moderate activity (38.9-40.8% inhibition) in the potato disc assay and marginal cytotoxicity (1.36-5.70 $\mu$g/ml) in the human tumor panel. 2-Hydroxy-3-formyl-7-methoxycarbazole was toxic to brine shrimp (LC$\sb{50}$ 35 ppm) while 7-methoxy-heptaphylline was inactive. Brine shrimp lethality-directed fractionation of Lindera benzoin (L.) Blume (Lauraceae) berries led to the isolation of ten bioactive compounds including the known insect antifeedant and juvenile hormone minic Z(+)-nerolidol (LC$\sb{50}$ 5.75 ppm), the known Z,Z-6,9-pentadecadien-2-one (LC$\sb{50}$ 2.9 ppm) and novel Z,Z,Z-6,9,12-pentadecatrien-2-one (LC$\sb{50}$ 3.0 ppm) (analogs are putative insect pheromones), and three novel and four known C$\sb{17}$-C$\sb{21}$ alkane-alkene $\gamma$-lactones of the obtusilactone series. The new C$\sb{21}$ alkane-alkene $\gamma$-lactones were isolinderanolide (LC$\sb{50}$ 0.96 ppm), linderanolide (LC$\sb{50}$ 5.23 ppm), and isolinderenolide (LC$\sb{50}$ 0.52 ppm), the known C$\sb{19}$ $\gamma$-lactones were obtusilactone A (LC$\sb{50}$ 0.89 ppm) and isoobtusilactone A (LC$\sb{50}$ 0.72 ppm), and the extremely toxic C$\sb{17}$ $\gamma$-lactones were determined to be obtusilactone (LC$\sb{50}$ 0.035 ppm) and isoobtusilactone (LC$\sb{50}$ 0.065 ppm). Isolinderanolide and isolinderenolide displayed moderate (44.9 and 41.4%) and obtusilactone excellent (64.2%) potato disc array tumor inhibition; however, the series displayed weak cytotoxicity in the human solid tumor panel. The brine shrimp and potato disc assays continue to serve as convenient in-house alternatives or prescreens to existing cytotoxicity or antitumor assays.

Degree

Ph.D.

Advisors

McLaughlin, Purdue University.

Subject Area

Pharmacology|Pharmaceuticals|Botany

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