Loss of PTEN function may account for reduced proliferation pathway sensitivity to LY294002 in human prostate and bladder cancer cells.

PURPOSE: Inhibition of phosphoinositide 3 (PI3)-kinase pathway is attractive for cancer treatment. To examine the role of the phosphatase and tensin homolog (PTEN) in the development of resistance to the treatment. METHODS: We cultured human prostate cancer cells (DU145 and PC-3 cells) and bladder cancer cells (EJ-1 and UM-UC-3 cells) with a PI3-kinase inhibitor, LY294002 for more than 6 weeks and cell proliferation was studied. Activation of Akt1 and ERK was examined by immunoblotting. We introduced the wild type PTEN in UM-UC-3 cells and their proliferation along with the signaling pathways was also examined. RESULTS: After 6 weeks, proliferation pathway sensitivity to LY294002 was reduced in cells expressing PTEN, but not in PTEN-null cells. PD98059, a MAPK/ERK kinase inhibitor, significantly inhibited proliferation of PTEN-expressing cells, but not PTEN-null cells. Stable PTEN expression in PTEN-null UM-UC-3 cells increased serum-induced ERK activation and sensitivity to PD98059-treatment, and reduced sensitivity to LY294002 after 6 weeks of exposure. CONCLUSIONS: Loss of PTEN function may protect against resistance to PI3-kinase inhibitors through an addiction to the PI3-kinase/Akt pathway