PIK3CA/PTEN Mutations and Akt Activation As Markers of Sensitivity to Allosteric mTOR Inhibitors

Abstract

Purpose We sought to determine whether PI3K pathway mutation or activation state and rapamycin-induced feedback-loop activation of Akt is associated with rapamycin sensitivity or resistance. Experimental Design Cancer cell lines were tested for rapamycin-sensitivity, Akt phosphorylation and mTOR target inhibition. Mice injected with breast or neuroendocrine cancer cells and patients with neuroendocrine tumor (NET) were treated with rapalogs, and Akt phosphorylation was assessed. Results 31 cell lines were rapamycin-sensitive (RS) and 12 were relatively rapamycin-resistant (RR; IC50>100 nM). Cells with PIK3CA and/or PTEN mutations were more likely to be RS (p=0.0123). Akt phosphorylation (S473 and T308) was significantly higher in RS cells (p<0.0001). Rapamycin led to a significantly greater pathway inhibition and greater increase in p-Akt T308 (p<0.0001) and p-Akt S473 (p=0.0009) in RS cells. Rapamycin and everolimus significantly increased Akt phosphorylation but inhibited growth in an in vivo NET model (BON). In patients with NETs treated with everolimus and octreotide, progression-free survival correlated with p-Akt T308 in pretreatment (R=0.4762, p=0.0533) and on-treatment tumor biopsies (R=0.6041, p=0.0102). Patients who had a documented partial response were more likely to have an increase in p-Akt T308 with treatment compared to non-responders (p=0.0146). Conclusion PIK3CA/PTEN genomic aberrations and high p-Akt levels are associated with rapamycin sensitivity in vitro. Rapamycin-mediated Akt activation is greater in RS cells, with a similar observation in patients with clinical responses on exploratory biomarker analysis; thus feedback-loop activation of Akt is not a marker of resistance but rather may function as an indicator of rapamycin activity.

WOMEN IN CANCER THEMATIC REVIEW: Systemic therapies in neuroendocrine tumors and novel approaches toward personalized medicine

“…In an in vivo NET model and in patients treated with everolimus and octreotide, an increased AKT activation was associated with rapamycin sensitivity (Meric-Bernstam et al 2012). In an exploratory biomarker analysis in more than 500 patients with human EGFR 2-positive advanced breast cancer, it could be demonstrated that patients with cancers showing PIK3CA mutations, PTEN loss or hyperactive PI3K pathway derive PFS benefit from everolimus (André et al 2016).…”

Everolimus as first line therapy for pancreatic neuroendocrine tumours: current knowledge and future perspectives

“…1 Simplified representation of the PI3K-AKT-mTOR pathway and mechanism of action of everolimus suggested as its direct target in humans (Sabatini et al 1994). Rapamycin and its analogs (i.e., everolimus) bind to an intracellular receptor, the FK506-binding protein (FKBP) (Harding et al 1989;Siekierka et al 1989), and this FKBP-rapamycin complex interacts with mTOR leading to inactivation of the mTOR signalling through dephosphorylation of both downstream effectors (4EBP1 and S6K1) of mTORC1 (Meric-Bernstam et al 2012). mTOR signalling is implicated in cancer proliferation and progression (Osaki et al 2004;Wullschleger et al 2006), and several studies documented that inhibition of the PI3K/AKT/mTOR pathway can be helpful for the treatment of patients with cancer, including pNETs.…”

“…Recently, effectiveness of everolimus was positively correlated to the IHC overexpression of phosphorylated p70S6K (Benslama et al 2016). Response to mTOR inhibitors seems to correlate with the presence of mutations of genes involved in the PI3K/AKT/mTOR pathway (Meric-Bernstam et al 2012). Sensitivity to rapamycin was related to genomic aberration of PIK3CA and/or PTEN (Meric-Bernstam et al 2012), while resistance to everolimus has been observed in patients with oncogenic KRAS mutation (Di Nicolantonio et al 2010).…”

“…Response to mTOR inhibitors seems to correlate with the presence of mutations of genes involved in the PI3K/AKT/mTOR pathway (Meric-Bernstam et al 2012). Sensitivity to rapamycin was related to genomic aberration of PIK3CA and/or PTEN (Meric-Bernstam et al 2012), while resistance to everolimus has been observed in patients with oncogenic KRAS mutation (Di Nicolantonio et al 2010). Recently, in patients with pNETs responsiveness to everolimus treatment has been correlated with a higher protein levels of the IGF1 downstream signalling involved in mTOR pathway (Falletta et al 2016).…”

Akt as a potential prognostic marker in neuroendocrine tumors: a possibility?

“…Meric-Bernstam et al [17] used paired pre-treatment and on-treatment fine needle aspirates from 17 neuroendocrine carcinoma patients on a phase II trial of everolimus and octreotide (a somatostatin analogue) to determine whether baseline p-Akt would be predictive of response and whether induction of p-Akt by everolimus would engender resistance. In this study, p-Akt(Thr308) was detected using a reverse phase protein array (RPPA).…”