PIK3CB and Familial prostate cancer: Signaling downstream of PI3K in cells that harbor mutations in PIK3CA is dependent on p110α,23 whereas PI3K signaling in PTEN-null prostate cancer cell lines is dependent on p110β.16,17,29 In agreement with these data, p-AKT in PTEN-null PC-3 cells was more sensitive to inhibition with TGX-221 than BYL-719 in a multiplex ELISA assay using specific antibodies to detect phospho-S473 and total AKT.