Background: Prostate cancer is the second most prevalent cancer among men. Despite different treatments, including surgery, chemotherapy, radiation therapy, hormone therapy and immunotherapy for this disease, patients ultimately progress to advanced states. Thus, there is a need for new treatment options targeting cell growth and apoptosis to better control the proliferation and metastasis of these cells. Introduction: There are many reports indicating overexpression of the 15-lipoxygenase-1 (15-LOX-1) enzyme in prostate tumors. Studies have also shown that inhibition of this enzyme prevents the progression of prostate cancer. Methods: In this study, the activity of 15-LOX-1 was evaluated in PC-3 cells by a spectrophotometric assay. In addition, due to high similarity between the 15-LOX-1 and soybean 15-lipoxygenase (SLO) (L1; EC 1, 13, 11, 12) active sites, the soybean SLO was used to investigate inhibitory effects of synthetic coumarin compounds 8-isopentenyloxycoumarin (8-IC), 8-isopentenyloxy-3-carboxycoumarin (8-ICC), 8-geranyloxycoumarin (8-GC), 8-geranyloxy-3-carboxycoumarin (8-GCC), and 8-farnesyloxy-3-carboxycoumarin (8-FCC) on this enzyme. Moreover, the cytotoxic and anticancer effects of the coumarin compounds were examined on PC-3 (Prostate Cancer) and HDF-1 (Human Dermal Fibroblast) cells by alamarBlue assay. Finally, apoptosis-inducing effects of all synthetic compounds were determined by flow cytometry. Results: The IC50 values obtained by the alamarBlue test revealed that 8-IC, 8-GC and 8-GCC had cytotoxic effects on PC-3 cells. Treating both PC-3 and HDF-1 cells with 8-ICC and 8-FCC did not significantly reduce cell number. Furthermore, the IC50 values of 8-IC on HDF-1 cells showed cytotoxic effects, while treating these cells with 8-GC and 8-GCC did not show any significant cytotoxicity on these normal human fibroblasts. Assessing the ability of 4-MMPB (as a specific inhibitor of 15-LOX-1), 8-GC, and 8-GCC compounds to inhibit SLO revealed that these compounds exerted strong 15-LOX-1 inhibitory activity, while 8-IC and 8-FCC had a weak inhibitory effect and also 8-ICC showed no inhibitory effect on SLO enzyme. In addition, flow cytometric analysis by FITC (fluorescein isothiocyanate)-annexin V and propidium iodide showed that treatment with IC50 values of 8-GC and 8-GCC induced apoptosis in 35.2% and 30.8% of PC-3 cells, respectively. Conclusion: Thus, 8-GC and 8-GCC can be introduced as effective anticancer agents with apoptosis-inducing properties. Furthermore, our results suggest that the cytotoxic effects of these compounds might be related to the inhibition of 15-LOX-1 enzyme in PC-3 cells. On the other hand, the cytotoxic effects of 8-IC might be due to the inhibition of other signaling pathways in PC-3 cells. However, further in vivo experiments are required to determine the exact mechanism involved in the anticancer effects of these coumarin compounds.

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