Docetaxel (DTX) chemotherapy remains a standard-of-care for metastatic castration-resistant prostate cancer (CRPC). DTX modestly increases survival, yet results in frequent occurrence of side-effects and resistant disease. An alternate chemotherapy with greater efficacy and minimal side-effects is needed. Acquisition of metabolic aberrations promoting increased survival and metastasis in CRPC cells include constitutive activation of Akt, loss of adenosine monophosphate-activated protein kinase (AMPK) activity due to Ser-485/491 phosphorylation, and over-expression of 3-hydroxy-3-methylglutaryl-Coenzyme A reductase (HMG-CoAR). We report that combination of simvastatin (SIM) and metformin (MET), within pharmacological dose range (500nM to 4µM SIM and 250µM to 2mM MET), significantly and synergistically reduces C4-2B3/B4 CRPC cell viability and metastatic properties with minimal adverse effects on normal prostate epithelial cells. Combination of SIM and MET decreased Akt Ser-473 and Thr-308 phosphorylation and AMPKα Ser-485/491 phosphorylation, increased Thr-172 phosphorylation and AMPKα activity as assessed by increased Ser-79 and Ser-872 phosphorylation of acetyl-CoA carboxylase and HMG-CoAR, respectively; decreased HMG-CoAR activity, and reduced total cellular cholesterol and its synthesis in both cell lines. Studies of C4-2B4 orthotopic NCr-nu/nu mice further demonstrated that combination of SIM and MET (3.5–7.0µg/g body weight SIM and 175–350µg/g body weight MET) daily by oral gavage over 9-week period significantly inhibited primary ventral prostate tumor formation, cachexia, bone metastasis, and biochemical failure more effectively than 24µg/g body weight DTX intraperitoneally-injected every three weeks, 7.0µg/g/day SIM, or 350µg/g/day MET treatment alone, with significantly less toxicity and mortality than DTX, establishing combination SIM and MET as a promising chemotherapeutic alternative for metastatic CRPC.

Diosmetin, a plant flavonoid, has been shown to exert promising effects on prostate cancer cells as an anti-proliferative and anticancer agent. In this study, using western blot analysis for protein expression and flow cytometry for cell cycle analysis, we determined that the treatment of the LNCaP and PC-3 prostate cancer cells with diosmetin resulted in a marked decrease in cyclin D1, Cdk2 and Cdk4 expression levels (these proteins remain active in the G0-G1 phases of the cell cycle). These changes were accompanied by a decrease in c-Myc and Bcl-2 expression, and by an increase in Bax, p27Kip1 and FOXO3a protein expression, which suggests the potential modulatory effects of diosmetin on protein transcription. The treatment of prostate cancer cells with diosmetin set in motion an apoptotic machinery by inhibiting X-linked inhibitor of apoptosis (XIAP) and increasing cleaved PARP and cleaved caspase-3 expression levels. On the whole, the findings of this study provide an in-depth analysis of the molecular mechanisms responsible for the regulatory effects of diosmetin on key molecules that perturb the cell cycle to inhibit cell growth, and suggest that diosmetin may prove to be an effective anticancer agent for use in the treatment of prostate cancer in the future.

Persistent oxidative stress due to generation of reactive oxygen species (ROS) has been associated with malignancy and cancer progression. Using a panel of human prostate cancer cells, we observed increased production of intracellular ROS, compared to normal human prostate epithelial cells, accompanied by elevated expression of antioxidant enzymes viz. superoxide dismutase, catalase, peroxiredoxin-1 and thioredoxin that may be a likely mechanism to endure increased oxidative stress. There is a need for novel antioxidant agent that can effectively suppress the generation of increased ROS in cancer cells. Rhamnetin (3,5,3,4-tetrahydroxy-7-methoxyflavone), remains highest on oxygen radical absorbance capacity scale, however its anti-proliferative activities has not been assessed. Rhamnetin is an O-methylated flavonol, abundantly present in cloves, sweet annie, annual wormwood, green vegetables and orchard grass. Previous studies (Shukla et al. Proc. Amer. Assoc. Cancer Res. 102: 5576, 2011) using androgen-responsive human prostate cancer LNCaP and androgen-refractory PC-3 cells, we have demonstrated that rhamnetin possess anticancer activity, induces apoptosis, and inhibits cancer cell growth. In the present study we assessed the antioxidant and anti-proliferative ability of rhmanetin in prostate cancer. Treatment of LNCaP and PC-3 cells with 100μM paraquat, an oxidative stress-inducing agent, induced cellular proliferation in both these cells. Treatment of cells with 5-80μM rhamnetin significantly decreased paraquat-induced ROS production and inhibited cell proliferation in dose-dependent manner. Similar effects were noted with the addition of recombinant Klotho protein to these cells, which is known to offer resistance to oxidative stress at the cellular level. Rhamnetin treatment also increased Klotho protein levels in both cell lines, along with increase in the expression of p53 and p21/waf1. Furthermore, rhamnetin treatment resulted in the increased expression of caspase-3, caspase-9 causing induction of apoptosis, which may be one of the protective mechanism(s) to decrease cell proliferation and enhance resistance to oxidative stress in cancer cells. Taken together, these results demonstrate that rhamnetin acts as a potent antioxidant agent, reduces intracellular ROS levels, increases Klotho protein expression, induces apoptosis in prostate cancer cells, which may have a significant role in the inhibition of prostate cancer progression. Citation Format: Christine Oak, Natarajan Bhaskaran, Sanjay Gupta, Sanjeev Shukla. Antiproliferative, antioxidant and antiapoptotic effect of rhamnetin in human prostate cancer cells. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 1232. doi:10.1158/1538-7445.AM2014-1232

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