PHSCN, a novel anticancer peptide, inhibits prostate tumor growth and metastasis by down-regulating the FAK/PI3K/AKT-mediated signaling pathway

Proc Amer Assoc Cancer Res, Volume 45, 2004 3982 We have previously reported that PHSCN, a synthetic pentapeptide structurally related to the PHSRN sequence of fibronectin, blocks α5β1 integrin-mediated DU145 invasion in vitro and inhibits prostate cancer growth, metastasis, and recurrence in animal models of the disease. Based on these results, a PHSCN Phase I clinical trial is currently underway at Fox Chase Cancer Center in Philadelphia. However, the mechanism that underlies these inhibitory effects of PHSCN on prostate cancer is not well understood. In the current studies, we investigated the effect of PHSCN on the α5β1 integrin-mediated signaling pathway functioning in the regulation of cancer cell survival and invasion. We observed that at a concentration of 100 μg/20,000 cells, PHSCN significantly deceases DU145 proliferation and increases the presence of apoptotic markers, cytokeratin 18 epitope and phosphatidyl serine on the outer membrane leaflet, which suggested that PHSCN might induce prostate cancer cell apoptosis. Thus, we examined molecules that are recognized as the key regulators in the integrin-mediated cell invasion and survival pathway including FAK, PI3K and AKT. The effect of PHSCN on these molecules was evaluated in the presence of PHSRN. We have demonstrated that under serum free conditions, PHSRN induces DU145 cell invasion through the activation of integrin α5β1/PI3K signal pathway. At a concentration of 1 μg/20,000 cells, PHSRN induces phosphorylation of FAK (Y397) and the binding of PI3K to FAK, followed by an increased PI3K activity and AKT phosphorylation on both T308 and S473. These are rapid and transient effects: FAK phosphorylation occurs within 30 minutes and increased PI3K activity and Akt phosphorylation are evident within an hour remained for 4-6 hours. However, when added simultaneously at the equal molar concentration, PHSCN abolishes PHSRN-induced FAK and AKT phosphorylation, as well as PI3K activity. Inhibition of FAK/PI3K activity may contribute to the blocking effect of PHSCN on cancer cell invasion, as well as the induction apoptosis. Inhibition of AKT phosphorylation has been linked with increased apoptosis in many cell types via its effect on the phosphorylation and activation of several apoptotic factors. Consistent with the inhibition of AKT activity, activated Caspases 3 was detected in DU145 cells treated with PHSCN at 100 μg/20,000 cells, after 5 days of exposure. The effect of PHSCN on other apoptosis-related molecules is currently under investigation. These results suggest that the inhibitory effect of PHSCN on prostate cancer progression is mediated, at least partially, through the AKT-regulated Caspase pathway and provide the potential molecular targets for the development of combination therapies to further improve the efficacy of PHSCN in treating human prostate cancers.