935. Anti-PI3K/Akt Cell Survival Pathway Gene Therapy Supplemented with Plant Sterol Diet for Prostate Cancer Treatment

Abstract

Prostate cancer is the most frequently diagnosed malignancy and the second leading cause of cancer deaths in American men today. The dietary animal and plant sterols appear to play critical roles in prostate cancer formation/progression, or prevention, respectively. Cholesterol, the animal sterol that is enriched in red meat and dietary fat, is implicated in promoting prostate cancer formation and progression. On the other hand, plant sterols (such as |[beta]|-sitosterol or |[beta]|-SIT) that are enriched in nuts, cereals and soy products, induce cancer cells to apoptosis and inhibit tumor formation and progression. To examine whether dietary sterols have effects on prostate cancer cell proliferation and migration, we treated human prostate cancer PC-3 and DU145 cells with cholesterol and |[beta]|-SIT for 4 days. We found that |[beta]|-SIT effectively inhibited cell proliferation of PC-3 and DU145 cells at 38.3% and 36.3%, respectively, when compared to untreated control cells, whereas cholesterol stimulated proliferation of PC-3 and DU145 cells, at 50% and 62.5%, respectively. Moreover, |[beta]|-SIT also inhibited migration of PC-3 and DU145 cells, at 80.9% and 18.0%, respectively, when compared to the control cells. In contrast, cholesterol stimulated migration of PC-3 and DU145 cells, at 33. 8% and 23.8%, respectively. In an animal study, mice fed with cholesterol-rich diet had a larger implanted xenograft C4-2B prostate tumor and increased tumor progression in terms of metastasis to the bone, by comparing with control mice fed with regular diet, whereas mice fed with plant sterol-rich diet had a smaller C4-2B xenograft tumor and decreased tumor progression. Activation of phosphoinositide 3 kinase (PI3K)/Akt pathway protects cancer cells from apoptosis induced by anticancer therapies and chemotherapeutic agents. Activity of PI3K/Akt kinases is often increased in prostate cancer and is associated with poor prognosis. To test whether blocking of PI3K/Akt cell survival pathway would sensitize prostate cancer cells to |[beta]|-SIT mediated apoptosis, a recombinant adenoviral viral vector, Ad-PI3K-DN, which expresses a PI3K dominant-negative mutant, was generated. In vitro assays demonstrated that Ad-PI3K-DN effectively inhibited PC-3 cell growth. To examine the combinative anti-tumor effects by Ad-PI3K- DN and plant sterol diet, we treated mice with implanted C4-2B prostate tumor with both plant sterol diet and Ad-PI3K-DN. An additive inhibitory effect was observed in mouse group treated with both plant sterol diet and Ad-PI3K-DN. In summary, our results showed that plant sterols inhibit prostate cancer proliferation and migration in vitro and tumor progression in vivo. Gene therapy targeting PI3K/Akt cell survival pathway effectively inhibits prostate cancer growth. A novel approach is being investigated for effective treatment of prostate cancer by combining gene therapy in blocking cancer cell survival pathway and diet supplement in prevention of tumor progression.