Screening for anticancer agents from Sonoran Desert plants: A chemical ecology approach

This study evaluates the potential benefits of using ecology-based theories of plant chemical defense when screening plants for pharmaceutical activity. Extracts from 63 Sonoran Desert plant species representing 26 families were screened in microtiter/optical density-based assays against a cervix epithelial carcinoma cell line (HeLa) and mouse fibroblast cells (3T3). In HeLa cytotoxicity assays, 34 of 63 species (54%) showed significant inhibitory effects. Nine of these active extracts were significantly less toxic to a noncancerous mouse fibroblast cell line (3T3) and, thus, showed potentially cancer specific activity. Using the plant apparency/predictability hypothesis as a theoretical basis, this study used plant growth habit (e.g., annual, herbaceous perennial, woody perennial, evergreen) as an indicator of plant predictability, and hence likelihood of having well-established chemical defenses. This approach led to predictions that may be useful in locating plant species that produce biologically active secondary metabolites. As predicted, extracts from evergreen species exhibited the highest activity with 41.7% of extracts showing inhibition, followed by woody perennials (37.3%), herbaceous perennials (35.7%), and annuals (23.3%). Average percent inhibition was significantly higher in the evergreen and woody perennial groups as compared to other growth forms. These results support predictions made by the plant predictability hypothesis and illustrate the potential value of incorporating ecological theories of plant chemical defenses in plant screening efforts.