Platelet
12-lipoxygenase (P-12-LOX) is overexpressed in different types of
cancers, including
prostate cancer, and the level of expression is correlated with the grade of this
cancer.
Arachidonic acid is metabolized by 12-LOX to 12(S)-hydroxyeicosatetraenoic
acid [12(S)-
HETE], and this biologically active metabolite is involved in
prostate cancer progression by modulating cell proliferation in multiple
cancer-related pathways inducing angiogenesis and
metastasis. Thus, inhibition of P-12-LOX can reduce these two processes. Several
lipoxygenase inhibitors are known, including plant and mammalian
lipoxygenases, but only a few of them are known inhibitors of P-12-LOX.
Curcumin is one of these
lipoxygenase inhibitors. Using a homology model of the three-dimensional structure of human P-12-LOX, we did computational docking of synthetic
curcuminoids (
curcumin derivatives) to identify inhibitors superior to
curcumin. Docking of the known inhibitors
curcumin and NDGA to P-12-LOX was used to optimize the docking protocol for the system in study. Over 75% of the compounds of interest were successfully docked into the active site of P-12-LOX, many of them sharing similar binding modes.
Curcuminoids that did not dock into the active site did not inhibit P-12-LOX. From a set of the
curcuminoids that were successfully docked and selected for testing, two were found to inhibit human
lipoxygenase better than
curcumin. False-positive
curcuminoids showed high LogP (theoretical) values, indicating poor water solubility, a possible reason for lack of inhibitory activity or/and nonrealistic binding. Additionally, the
curcuminoids inhibiting P-12-LOX were tested for their ability to reduce sprout formation of endothelial cells (in vitro model of angiogenesis). We found that only
curcuminoids inhibiting human P-12-LOX and the known inhibitor NDGA reduced sprout formation. Only limited inhibition of sprout formation at approximately IC(50) concentrations has been seen. At IC(50), a substantial amount of
12-HETE can be produced by
lipoxygenase, providing a stimulus for angiogenic sprouting of endothelial cells. Increasing the concentration of
lipoxygenase inhibitors above IC(50), thus decreasing the concentration of 12(S)-HETE produced, greatly reduced sprout formation for all inhibitors tested. This universal event for all tested
lipoxygenase inhibitors suggests that the inhibition of sprout formation was most likely due to the inhibition of human P-12-LOX but not other
cancer-related pathways.