Feedback Suppression of PI3Kα Signaling in PTEN-Mutated Tumors Is Relieved by Selective Inhibition of PI3Kβ
Menée in vitro et in vivo, cette étude met en évidence des mécanismes suggérant l'intérêt d'une stratégie combinant l'inhibition de deux isoformes de PI3K et du récepteur des androgènes pour le traitement des patients atteints d'un cancer de la prostate présentant un gène PTEN muté
In PTEN-mutated tumors, we show that PI3K
α activity is suppressed and PI3K signaling is driven by PI3Kβ. A selective inhibitor of PI3Kβ inhibits the Akt/mTOR pathway in these tumors but not in those driven by receptor tyrosine kinases. However, inhibition of PI3Kβ only transiently inhibits Akt/mTOR signaling because it relieves feedback inhibition of IGF1R and other receptors and thus causes activation of PI3Kα and a rebound in downstream signaling. This rebound is suppressed and tumor growth inhibition enhanced with combined inhibition of PI3Kα and PI3Kβ. In PTEN-deficient models of prostate cancer, this effective inhibition of PI3K causes marked activation of androgen receptor activity. Combined inhibition of both PI3K isoforms and androgen receptor results in major tumor regressions.