Lentiviral vector neutral endopeptidase gene transfer suppresses prostate cancer tumor growth

Neprilysin (neutral endopeptidase, NEP) is a cell surface peptidase whose expression is lost in approximately 50% of prostate cancers (PC). NEP normally functions to inactivate peptides such as bombesin and endothelin-1, and potentiates the effects of the PTEN tumor suppressor via a direct protein - protein interaction. NEP loss contributes to PC progression. We investigated the therapeutic efficacy of using a lentiviral vector system to restore NEP expression in PC cells. Third-generation lentiviral vectors encoding wild-type NEP (L-NEP) or green fluorescent protein (L-GFP) were introduced into NEP- deficient 22RV1 PC cells. Cells infected with L-NEP or L- GFP at a multiplicity of infection of 10 demonstrated NEP enzyme activity of 1171.2 +/- 74.9 and 17.27 +/- 5.3 pmol/ mg/ min (P<0.0001), respectively. Cell viability, proliferation and invasion were each significantly inhibited in 22RV1 cells expressing NEP compared with control cells infected with L- GFP (P<0.01). Analysis of known downstream effects of NEP showed NEP- expressing cells exhibiting decreased Akt and focal adhesion kinase phosphorylation and increased PTEN protein expression. Finally, injection of L-NEP into established 22RV1 xenograft tumors significantly inhibited tumor growth (P<0.01). These experiments demonstrate that lentiviral NEP gene transfer is a novel targeted strategy for the treatment of NEP-deficient PC.