PI3K Signaling Pathway Activation Predicts Class I PI3K Inhibitor GDC-0941 Sensitivity in AML.

Abstract 1057

Poster Board I-79

The PI3K-Akt signal transduction pathway plays a key role in the pathogenesis of many human cancers. In AML malignancy, deregulation of upstream receptor tyrosine kinases such as FLT3, c-Kit, and c-FMS or mutations in K-Ras, N-Ras, B-Raf and CEBPA genes lead to activation of PI3K-Akt signaling to promote cell survival and cell growth. A highly selective Class I PI3K inhibitor, GDC-0941, provides exciting therapeutic opportunities for targeting this pathway in AML. Here we show that GDC-0941 significantly inhibits the viability of the majority of a large panel of AML cell lines tested in vitro (80% or 19/24) at a concentration of < 1 uM. Because not all AML cell lines responded to GDC-0941, we show that PI3K-Akt pathway activation, evidenced by basal pAkt level, can serve as a potential predictive biomarker for GDC-0941 in AML in that sensitive cell lines displayed higher level of pAkt relative to resistant cell lines. Consistently, GDC-0941 treatment leads to decreased pAkt, and therefore the down-regulation of this important pro-survival signaling. Our further analysis shows that GDC-0941 treatment can induce apoptosis and/or cell cycle arrest. We also obtained fresh AML tumor samples to test whether GDC-0941 can similarly induces apoptosis in blast cells and showed that GDC-0941 treatment results in a down-regulation of pAkt level and increased apoptosis. Other PD biomarkers such as phospho-BAD level and Bim expression are both consistent with the observed apoptotic responses. Furthermore, the mammalian target of rapamycin complex 1 (mTORC1) inhibitor, rapamycin, synergizes with GDC-0941 to produce an increased amount of apoptosis in several AML cell lines tested. This is likely due to the fact that long-term treatment with rapamycin induces the sensitivity of the PI3K –Akt signaling pathway by releasing the negative feedback loop of mTORC1-S6K-IRS1/2 module. Importantly, in some AML cell lines we observe synergies between GDC-0941 and AraC. Interestingly, while AraC alone does not induce apoptosis in AML cell lines with PTEN loss or mutation, the synergy between AraC and GDC-0941 comes from increased apoptotic response, suggesting that GDC-0941 can synergize with chemo agents that induces S/G₂ cell cycle arrest. Together, our preclinical data suggest that GDC-0941 may be used as a targeted therapy in AML patients as a single agent or in combination with other chemotherapies in clinic.