An oriental medicinal plant derived from the bark of the magnolia tree shows promise as a treatment for prostate cancer. In traditional Asian medicine, extracts of magnolia have been used for pain relief and as a treatment for anxiety and depression, and the plant is marketed widely as an alternative medicine. Honokoi (HNK) is a bioactive natural product obtained from magnolia and research has shown that it has a range of potentially therapeutic effects on the body, including anti-tumor, promotion of neural growth, inhibition of platelet aggregation, anti-inflammatory, antioxidant, and others that have attracted interest in it as a drug candidate.
Honokiol has shown activity against a number of solid tumor types including breast, prostate, gastric, and ovarian cancers. In order to demonstrate activity of honokiol against prostate cancer, investigators from the University of Pittsburgh and Kagoshima University in Japan exposed human and mouse prostate cancer cells to pharmacologic doses of HNK and observed the cells for evidence of autophagy (cellular self-degradation), cell viability, and reactive oxygen species that would indicate apoptosis (programmed cell death).
They assessed autophagy by transmission electron microscopy, immunofluorescence, and immunoblotting for the presence of LC3BII, a protein marker for autophagy, and determined cell viability by trypan blue assay, and apoptosis by DNA fragmentation and Annexin V/propidium iodide assay.
EPR was performed on a Bruker X-band benchtop EPR spectrometer as one of several methods to identify reactive oxygen species in the cells treated with honokiol. EPR signals in the human cells were measured after four hours of treatment with honokiol or a control DMSO solution. The treated cells had a significantly higher EPR signal than the DMSO-treated cells. The results were confirmed by fluorescence.