Evaluation of essential oils from 22 Guatemalan medicinal plants for in vitro activity against cancer and established cell lines

Plant species which produce essential oils are important in the healthcare of rural Guatemalans. Steam distilled essential oils from 22 medicinal plant species were analyzed for activity against tongue, skin, and stomach cancer cell lines using a neutral red assay, Vero C1008 cells to assess cytotoxicity, and [3H]-thymidine incorporation assay to assess inhibition of cancer cell proliferation. IC50, CC50, and therapeutic indices were determined. IC50 values indicated that all oils showed inhibitory activity against one or more cancer cell lines. Highly inhibitory IC50 values (0.10 μL/mL or less) indicated that Citrus aurantiifolia (Christm.) Swingle (Rutaceae) oil was significantly inhibitory to all three cancer cell lines, Origanum vulgare L. (Lamiaceae) and Teloxys ambrosioides (L.) W. A. Weber (Chenopodiaceae) oils were highly inhibitory to two cell lines, and Lippia graveolens Kunth (Verbenaceae) oil was highly inhibitory to one cell line. TI values equal to or greater than one showed significantly higher cytotoxicity to cancer cells compared to the Vero cell line for Ruta chalepensis L. (Rutaceae), Citrus limetta Risso (Rutaceae), C. aurantium L. (Rutaceae), Rosmarinus officinalis L. (Lamiaceae), and O. vulgare. Essential oils from L. graveolens, O. vulgare, and T. ambrosioides yielded high percentages (>96%) of decreased cell proliferation at low oil concentration (0.05 μL/mL). Results indicate that essential oils were more toxic to cancer cells than to cells from an established cell line, and such oils can be highly suppressive to DNA synthesis and cancer cell growth. Key words: Essential oils, medicinal plants, IC50, anticancer activity, Guatemala.