Abstract
Iva hayesiana, also known as San Diego poverty weed, is a California native plant that grows in the San Diego coastal region and Baja California. I. hayesiana contains the flavone hispidulin, which has been shown to be cytotoxic to human pancreatic cancer cells. A previous screen indicated that an extract of the leaves and stems of I. hayesiana is cytotoxic to the human breast cancer cell line MDA-MB-231. However, with repeated extractions over several months, the cytotoxic properties became negligible. The goal of this study was threefold: first, to optimize the extraction conditions for I. hayesiana, second, to determine whether the cytotoxicity is seasonal, and third, to determine whether hispidulin is responsible for the cytotoxicity towards MDA-MB-231. Results showed that hexane extracts of fresh aerial parts of I. hayesiana were the most effective against MDA-MB-231, with an IC50 of 56 ± 3 µg/mL. Vacuum distillation of the leaves and stems showed that the cytotoxic constituents are not volatile; therefore, HPLC was used for chromatographic analysis. Monthly extracts from February thru July showed that the cytotoxicity returned in April and dissipated in June, when the plant flowered, which supports the hypothesis that the cytotoxicity is seasonal and is therefore related to the life cycle of the plant. HPLC of these extracts indicate that there are distinct chemical differences between the active and inactive extracts. Most notably, there is one HPLC peak of interest that requires further analysis. Lastly, it was determined that hispidulin is present in I. hayesiana however; it was not found to be responsible for the cytotoxicity seen towards MDA-MB-231. In fact the IC50 of the pure compound dissolved in ethanol was greater than 100 µg/mL, which was the highest concentration tested.