EIF4EBP1 and neoplasm: To determine the extent of class I PI3K kinase pathway activation in these five canine tumour cell lines, we employed western blot analysis to examine the presence of active (phosphorylated) forms of several components of the class I PI3K pathway, including phosphorylated Akt, mTOR, S6RP, 4EBP1 and eIF4E.