Login to Access Video or Poster Abstract: MP83-05
Sources of Funding: None

Introduction

We conducted a bioinformatic study querying genes involved in cholesterol homeostasis and prostate cancer (PC) outcomes. We found sterol hydroxylase CYP27A1 is correlated with PC progression and is consistently lower in PC vs. normal tissue. Preclinically, we found CYP27A1 overexpression, which metabolizes cholesterol to 27-hydroxycholesterol (27HC), decreased intracellular cholesterol and inhibited PC cell growth in vitro and in vivo. Likewise, treating PC cells with 27HC reduced intracellular cholesterol and decreased in vitro cell proliferation. This has not been tested in vivo. Cellular cholesterol is predominantly concentrated in plasma membrane micro-domains known as lipid rafts, which localize various membrane receptors and facilitate cellular signaling. Preliminarily, we found 27HC causes lipid raft depletion and disorganization reducing JAK2/STAT3 signaling. We hypothesize 27HC mediates its anti-PC activity by inhibiting STAT3-driven PC.

Methods

In vitro : Cell proliferation, immunoblots, immunoprecipitation, immunofluorescence (IF), matrigel based prostasphere assays and fluorescence activated cell sorting (FACS) techniques were used. In vivo : DU145 PC cells were injected subQ in mice fed a high fat high cholesterol diet for 6 weeks. After tumors grew to an average of 200mm³, mice were randomized on tumor size and serum cholesterol into two groups and injected daily with vehicle (cyclodextrin) or 27HC (40mg/kg) for 40 days.

Results

27HC reduced active phosphorylated STAT3 (p-STAT3) levels in DU145 PC cells in vitro. 27HC inhibited STAT3 dimerization and reduced nuclear STAT3 levels. Adding exogenous cholesterol rescued p-STAT3 levels. Likewise, upstream of STAT3, phosphorylation of JAK2 was reduced by 27HC. Assessment of lipid rafts by IF and FACS showed a decrease and disorganization of lipid rafts after 27HC treatment. 27HC also reduced the number of PC cell-derived prostaspheres, which was rescued by cholesterol addback. Finally, our in vivo study showed that 27HC reduced tumor volume over time in a DU145 xenograft model.

Conclusions

27HC reduced STAT3 signaling in PC cells by inhibiting STAT3 phosphorylation, dimerization and nuclear localization, likely due to reduced lipid raft JAK/STAT signaling. We also observed that 27HC reduces prostasphere numbers in vitro. These 27HC-mediated effects were rescued by cholesterol addback. Lastly, our in vivo study showed that 27HC treatment slowed tumor growth. These data suggest that 27HC may be a novel treatment for STAT3-driven PC.

Funding

None