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90th Annual Meeting Abstracts

Honokiol Induces Apoptosis in Melanoma Cells Through Mitochondrial Depolarization
*Abhilasha Tangada, MD, *Debbie McDonald, BS, *John G Schneider, MD, David W McFadden, MD
University of Vermont, Burlington, VT

Background: Natural polyphenols have demonstrated significant anti-tumor properties. Honokiol is a polyphenol derived from the Magnolia officinalis plant. Studies have shown it has anti-tumor effects on leukemia, prostate, and breast cancer in vitro. Our goal was to examine the effects of honokiol on melanoma, a chemotherapy resistant tumor, and investigate its mechanism of action.
Methods: Two melanoma cell lines, SK-MEL-2 and MeWo, were cultured and passaged using standard techniques. Cells were treated with increasing doses of honokiol (20-100 μM). MTT colorimetric assay was performed to assess cell viability. Cell-Death Detection ELISAPLUS was used to determine type of cell death. Caspase activity was evaluated to determine the apoptotic mechanism using the Apo-ONETM Caspase 3/7 Assay. Pan-caspase and caspase 3/7-specific inhibitors were used to investigate the effects of caspase inhibition. Mitochondrial depolarization and its inhibition by cyclosporine A were evaluated using the MitoProbe JC-1 assay.
Results: Honokiol induced cell death in a dose-dependent manner (P<0.001). Melanoma cells preferentially underwent apoptosis after treatment with honokiol (P< 0.05). Honokiol treatment increased caspase activity (P<0.05), although caspase inhibition did not prevent honokiol-induced cell death. Honokiol produced significant mitochondrial membrane depolarization (P<0.05). Cyclosporine-A treatment protected cells from mitochondrial membrane depolarization demonstrated by decreased honokiol-induced growth inhibition (P<0.05). Similar results were observed in both cell lines.
Conclusions: Our study demonstrated for the first time that the naturally occurring polyphenol honokiol inhibits melanoma growth in vitro by induction of mitochondrial initiated apoptosis. These results suggest a potential therapeutic or adjuvant role for honokiol in the treatment of melanoma. Further in vitro studies are warranted to confirm the mechanism of action and development of an in vivo model is planned.


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