Sildenafil (Viagra) sensitizes prostate cancer cells to doxorubicin-mediated apoptosis through CD95
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Anindita Das1, David Durrant1, Clint Mitchell2, Paul Dent2, Surinder K. Batra3, Rakesh C. Kukreja1
1Department of Internal Medicine, Pauley Heart Center, Virginia Commonwealth University, Richmond, VA, USA
2Department of Biochemistry and Molecular Biology, Virginia Commonwealth University, Richmond, VA, USA
3Department of Biochemistry and Molecular Biology, Buffett Cancer Center, University of Nebraska Medical Center, Omaha, NE, USA
Anindita Das, e-mail: firstname.lastname@example.org
Rakesh C. Kukreja, e-mail: email@example.com
Keywords: PDE5, doxorubicin, CD95, FLIP, prostate cancer
Received: September 14, 2015 Accepted: November 26, 2015 Published: December 24, 2015
We previously reported that Sildenafil enhances apoptosis and antitumor efficacy of doxorubicin (DOX) while attenuating its cardiotoxic effect in prostate cancer. In the present study, we investigated the mechanism by which sildenafil sensitizes DOX in killing of prostate cancer (PCa) cells, DU145. The death receptor Fas (APO-1 or CD95) induces apoptosis in many carcinoma cells, which is negatively regulated by anti-apoptotic molecules such as FLIP (Fas-associated death domain (FADD) interleukin-1-converting enzyme (FLICE)-like inhibitory protein). Co-treatment of PCa cells with sildenafil and DOX for 48 hours showed reduced expression of both long and short forms of FLIP (FLIP-L and -S) as compared to individual drug treatment. Over-expression of FLIP-s with an adenoviral vector attentuated the enhanced cell-killing effect of DOX and sildenafil. Colony formation assays also confirmed that FLIP-S over-expression inhibited the DOX and sildenafil-induced synergistic killing effect as compared to the cells infected with an empty vector. Moreover, siRNA knock-down of CD95 abolished the effect of sildenafil in enhancing DOX lethality in cells, but had no effect on cell killing after treatment with a single agent. Sildenafil co-treatment with DOX inhibited DOX-induced NF-κB activity by reducing phosphorylation of IκB and nuclear translocation of the p65 subunit, in addition to down regulation of FAP-1 (Fas associated phosphatase-1, a known inhibitor of CD95-mediated apoptosis) expression. This data provides evidence that the CD95 is a key regulator of sildenafil and DOX mediated enhanced cell death in prostate cancer.
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