Abstract A39: Dosage-dependent regulation of caspase 8 activation in LNCaP and DU-145 human prostate cancer cell lines by the Chinese medicinal herb scutellaria barbata.

Abstract

Abstract A39 Scutellaria barbata (SB) (known in traditional Chinese medicine as Ban-Zhi-Lian) is a perennial herb. It has been used to treat appendicitis, hepatitis, pulmonary abscess, and several cancers. LNCaP cells are derived from a human prostate cancer cell line with mutated androgen receptors (AR) while DU-145 is a classical human prostate cell line without androgen receptors. Our previous data indicated that SB activated apoptosis in LNCaP cells via caspases 3, 8, and 9. Histopathological data revealed that the herb had the ability to delay tumor progression and development in TRAMP mice. Recent Western blot data from LNCaP cells undergoing treatment with SB showed increased expression of Akt protein while decreased phosphorylation of Akt in the cells. In this study, we compared the effect of AR-dependence on the herb's apoptosis activation through caspase 8 on these two different cell lines. The two cell lines were incubated with distilled water as a control group and 100 µL and 200µL of SB as experimental groups for 2 and 8 hours separately. A specific carboxyfluorescein (FAM) labeled peptide fluoromethyl ketone (FMK) caspase inhibitor (FAM-Peptide-FMK) was used to label caspase 8- activated cells. Caspase positive (+) cells appeared green whereas necrotic cells were stained red with propidium iodide and observed under a fluorescent microscope. Pictures were taken and the activation/necrosis ratio (A/N ratio) was analyzed using ImageJ software (developed by the National Institutes of Health). Significant induction of caspase 8 by SB was observed in androgen receptor positive LNCaP cells. In both 2 and 8 hour incubation, SB activated more caspase 8 in LNCaP cells than in DU-145 cells treated at 100 µL and 200 µL concentrations ( A/NLNCaP > A/NDU-145 ). In addition, DU-145 exhibited significant dosage-dependent induction of caspase 8 by SB, while dosage-dependence was not observed in LNCaP cells (A/N100µL = A/N200µL). These data indicate that SB might activate apoptosis through an up-stream androgen receptor pathway, thus suggesting a plausible mechanism for this herb’s activation of the apoptotic pathway in prostate cancer cells. Citation Information: Cancer Prev Res 2008;1(7 Suppl):A39.