Expression of
cyclooxygenase-2 (Cox-2), an inducible
enzyme responsible for the production of
prostaglandins from
arachidonic acid, is elevated in human prostate
tumor samples. The aim of this study was to investigate whether expression of Cox-2 is effective against
prostate cancer cell apoptosis triggered by
sanguinarine, the quaternary benzophenanthridine
alkaloid with
antineoplastic properties.
Sanguinarine effectively induced apoptosis in LNCaP human
prostate cancer epithelial cells as assessed by
caspase-3 activation assay,
Annexin V staining assay, or by visual analysis for the apoptotic morphology changes.
Sanguinarine-mediated apoptosis was associated with the increase of
nitric oxide (NO) formation in
prostate cancer cells as assessed by measurements of
nitrites with Sievers
nitric oxide analyzer as well as flow cytometry analysis using NO fluorescent sensor. Activation of
NO synthase (NOS) activity was crucial for
sanguinarine-induced cell death because NOS inhibitor
L-NMMA efficiently protected cells from apoptosis. Adenovirus-mediated transfer of Cox-2 into LNCaP cells inhibited
sanguinarine-induced apoptosis and prevented an increase in NO production. Surprisingly, NO donors failed to induce apoptosis in LNCaP cells, suggesting that constitutive NO generation is not sufficient for triggering apoptosis in these cells. Besides NO generation, NOS is also capable of producing
superoxide radicals.
Sanguinarine-induced production of
superoxide radicals, and the addition of
MnTBAP, a scavenger of
superoxide radicals, efficiently inhibited
sanguinarine-mediated apoptosis. These results suggest that Cox-2 expression rescues
prostate cancer cells from
sanguinarine-induced apoptosis by a mechanism involving inhibition of NOS activity, and that coadministration of
Cox-2 inhibitors with
sanguinarine may be developed as a strategy for the management of
prostate cancer.