Targeting cytosolic phospholipase A(2) α in colorectal cancer cells inhibits constitutively activated protein kinase B (AKT) and cell proliferation

A constitutive activation of protein kinase B (AKT) in a hyper-phosphorylated status at Ser(473) is one of the hallmarks of anti-EGFR therapy-resistant colorectal cancer (CRC). The aim of this study was to examine the role of cytosolic phospholipase A(2)α (cPLA(2)α) on AKT phosphorylation at Ser(473) and cell proliferation in CRC cells with mutation in phosphoinositide 3-kinase (PI3K). AKT phosphorylation at Ser(473) was resistant to EGF stimulation in CRC cell lines of DLD-1 (PIK3CA(E545K) mutation) and HT-29 (PIK3CA(P499T) mutation). Over-expression of cPLA(2)α by stable transfection increased basal and EGF-stimulated AKT phosphorylation and proliferation in DLD-1 cells. In contrast, silencing of cPLA(2)α with siRNA or inhibition with Efipladib decreased basal and EGF-stimulated AKT phosphorylation and proliferation in HT-29. Treating animals transplanted with DLD-1 with Efipladib (10 mg/kg, i.p. daily) over 14 days reduced xenograft growth by >90% with a concomitant decrease in AKT phosphorylation. In human CRC tissue, cPLA(2)α expression and phosphorylation were increased in 63% (77/120) compared with adjacent normal mucosa determined by immunohistochemistry. We conclude that cPLA(2)α is required for sustaining AKT phosphorylation at Ser(473) and cell proliferation in CRC cells with PI3K mutation, and may serve as a potential therapeutic target for treatment of CRC resistant to anti-EGFR therapy.