XL147 is a selective and reversible class I PI3K inhibitor for PI3Kα/δ/γ with IC50 of 39 nM/36 nM/23 nM, less potent to PI3Kβ.

XL147 inhibits class I PI3K isoforms in an ATP-competitive manner. In a panel of HER2-overexpressing human breast cancer cell lines, treatment with XL147 abrogates AKT and S6 phosphorylation but also induces the expression and phosphorylation of HER3 and other RTKs. In HER2+ cells, phosphorylation of HER3 is maintained by the HER2 tyrosine kinase, leading to partial recovery of phosphorylated AKT (pAKT) and thereby limiting the antitumor action of XL 147. In addition, knockdown of HER3 or treatment with the anti-HER2 agents trastuzumab or lapatinib sensitizes HER2+ breast cancer cells to XL147 in vitro and in vivo. Treatment with XL147 inhibits the monolayer growth of all tested cell lines, including BT474, HCC1937 et al. in a dose-dependent manner. The main effect of XL147 is inhibition of cell proliferation. XL147 induces cell death at the concentration of 20 μM. Treatment with XL147 leads to dose-dependent inhibition of PI3K. Consistent with the inhibition of cell proliferation, XL147 induces a reduction in cyclin D1 and pRB and an increase in levels of the CDK inhibitor p27KIPI but no detectable change in levels off total or cleaved poly (ADP-ribose) polymerase (PARP). Treatment with XL147 leads to a dose-dependent reduction in pAKTS473/T308 and pS6S240/244. Surprisingly, XL147 also triggers up-regulation of total HER3 and/or pHER3Y1289 levels. In HER2-overexpressing cells, inhibition of PI3K is followed by up-regulation of expression and phosphorylation of multiple receptor tyrosine kinases, including HER3. Knockdown of FoxO1 and FoxO3a transcription factors prevents the induction of HER3, InsR, IGF1R, and FGFR2 mRNAs upon inhibition of PI3K. In HER2+ cells, knockdown of HER3 with siRNA or cotreatment with the HER2 inhibitors trastuzumab or lapatinib enhances XL147-induced cell death and inhibition of pAKT and pS6.

A66

AS-252424

AS-605240

AZD 6482

BAY 80-6946