PTEN expression controls cellular response to cetuximab by mediating PI3K/AKT and RAS/RAF/MAPK downstream signaling in KRAS wild-type, hormone refractory prostate cancer cells

Overexpression of epidermal growth factor receptor (EGFR) and mutation of pten tumor suppressor gene in human cancer cells leads to activated EGFR downstream signaling including PI3-kinase/AKT (PI3K/AKT) and/or mitogen-activated protein kinases (RAS/RAF/MAPK) and have been linked to resistance to anti-EGFR targeted therapies. Cetuximab is a chimeric IgG1 monoclonal antibody that binds the EGFR with high specificity and have been developed as promising therapeutic anticancer treatments in several solid tumors, including colorectal and head and neck squamous cell carcinomas. Cetuximab activity is related to PI3K/AKT and RAS/RAF/MAPK signaling pathways functionality and its activity has been shown to be higher in wild-type KRAS tumors. To study the influence of PTEN expression on cell response to cetuximab, we used wild-type KRAS, PTEN-null, EGFR overexpressing PC3 prostate cancer cells. Reintroduction of PTEN significantly reduced the constitutive overexpression of phosphorylated-AKT (p-AKT) and downstream kinases (p-GSK3 beta and p-P70S6 kinase) as well as phosphorylated-ERK1/2 (p-ERK1/2) and consequently significantly restored cetuximab-induced cell growth inhibition and apoptosis induction. Taken together, the results achieved in the present study show that PTEN controls the cellular response to cetuximab in KRAS wild-type prostate carcinoma PC3 cells through the regulation of AKT phosphorylation and restoration of the functionality of EGFR downstream signaling. Extrapolation of these findings to clinical situation, suggests that the assessment of EGFR downstream signaling functionality could be proposed as a diagnostic response predictive marker for anti-EGFR targeted therapies.