Dual PI3K/mTOR inhibitor, XL765 (SAR245409), shows superior effects to sole PI3K [XL147 (SAR245408)] or mTOR [rapamycin] inhibition in prostate cancer cell models.

Deregulation of phosphatidylinositol-3-kinase (PI3K)/protein kinase B (Akt)/mammalian target of rapamycin (mTOR) signaling pathway contributes to prostate cancer development and progression. Here, we compared the in vitro effects of the dual PI3K/mTOR inhibitor (XL765) with those observed with the sole PI3K (XL147) or mTOR (rapamycin) inhibition in 2 non-tumor prostate epithelial cell lines, 8 prostate cancer cell lines, and 11 prostate cancer cell derivatives. We demonstrated that the XL765 treatment showed superior and proliferative effects of XL147 or rapamycin. The XL765 effects were associated to increasing the chromosome region maintenance 1 (CRM1)-mediated nuclear localization of glycogen synthase kinase 3 beta (GSK3ß) and Foxo-1a with higher induction of apoptosis when compared to those observed in XL147 and rapamycin treatments. IC50 values were calculated in phosphatase and tensin homologue deleted on chromosome 10 (PTEN)-positive and PTEN-negative cell lines as well as after PTEN transfection or PTEN downmodulation by siRNA strategy revealing that the presence of this protein was associated with reduced sensitivity to PI3K and mTOR inhibitors. The comparison of IC50 values was also calculated for androgen-dependent and -independent cell lines as well as after androgen receptor (AR) transfection or the AR downmodulation by siRNA strategy revealing that androgen independence was associated with enhanced responsiveness. Our results provide a rationale to use the dual PI3K/Akt/mTOR inhibitors in hormone-insensitive prostate cancer models due to the overactivity of PI3K/Akt/mTOR in this disease condition.

Increased expression and activity of p75NTR are crucial events in azacitidine-induced cell death in prostate cancer.

The high affinity nerve growth factor (NGF) NGF receptor, p75NTR, is a member of the tumor necrosis factor (TNF) receptor superfamily that shares a conserved intracellular death domain capable of inducing apoptosis and suppressing growth in prostate epithelial cells. Expression of this receptor is lost as prostate cancer progresses and is minimal in established prostate cancer cell lines. We aimed to verify the role of p75NTR in the azacitidine-mediated antitumor effects on 22Rv1 and PC3 androgen-independent prostate cancer cells. In the present study, we reported that the antiproliferative and pro-apoptotic effects of 5-azacytidine (azacitidine) were more marked in the presence of physiological concentrations of NGF and were reduced when a blocking p75NTR antibody or the selective p75NTR inhibitor, Ro 08-2750, were used. Azacitidine increased the expression of p75NTR without interfering with the expression of the low affinity NGF receptor TrkA and induced caspase 9-dependent caspase 3 activity. Taken together, our results suggest that the NGF network could be a candidate for future pharmacological manipulation in aggressive prostate cancer.