mTOR, p70S6K, AKT, and ERK1/2 levels predict sensitivity to mTOR and PI3K/mTOR inhibitors in human bronchial carcinoids

Abstract

Bronchial carcinoids (BCs) are rare neuroendocrine tumors that are still orphans of medical treatment. Human BC primary cultures may display resistance to everolimus, an inhibitor of the mammalian target of rapamycin (mTOR), in terms of cell viability reduction. Our aim was to assess whether the novel dual phosphatidylinositol 3-kinase (PI3K)/mTOR inhibitor NVP-BEZ235 is effective in everolimus-resistant human BC tissues and cell lines. In addition, we searched for possible markers of the efficacy of mTOR inhibitors that may help in identifying the patients who may benefit from treatment with mTOR inhibitors, sparing them from ineffective therapy. We found that NVP-BEZ235 is twice as potent as everolimus in reducing cell viability and activating apoptosis in human BC tissues that display sensitivity to mTOR inhibitors, but is not effective in everolimus-resistant BC tissues and cell lines that bypass cyclin D1 downregulation and escape G0/G1 blockade. Rebound AKT activation was not observed in response to treatment with either mTOR inhibitor in the 'resistant' BC cells. In addition to total mTOR levels, putative markers of the sensitivity of BCs to mTOR inhibitors are represented by AKT, p70S6K (RPS6KB2), and ERK1/2 (MAPK3/1) protein levels. Finally, we validated these markers in an independent BC group. These data indicate that the dual PI3K/mTOR inhibitor NVP-BEZ235 is more potent than everolimus in reducing the proliferation of human BC cells. 'Resistant' cells display lower levels of mTOR, p70S6K, AKT, and ERK1/2, indicating that these proteins may be useful as predictive markers of resistance to mTOR and PI3K/mTOR inhibitors in human BCs.

Gly388Arg FGFR4 Polymorphism Is Not Predictive of Everolimus Efficacy in Well-Differentiated Digestive Neuroendocrine Tumors

“…Despite the retrospective nature of our study and its limited size due to the rarity of the disease, our results do not encourage performing further assessment. In contrast, expression, activation and mutations of mTOR pathway may be good candidates for predictive biomarkers and thus merit further investigation in the treatment of digestive NET with everolimus [5]. …”

“…Thus, they might allow defining a subgroup of tumors particularly sensitive to everolimus. Similarly, while PNET displaying an activated mTOR pathway, as evaluated by immunochemistry, seem to have a worse prognosis, they may also be more sensitive to everolimus, as it was suggested in bronchial carcinoid cell lines [4,5]. Those displaying low expression of mTOR, p70S6, AKT and ERK1/2 were resistant to everolimus [5].…”

Everolimus in the treatment of neuroendocrine tumors: efficacy, side-effects, resistance, and factors affecting its place in the treatment sequence

“…In 17 patients with NETs treated with everolimus and octreotide, high tumor p-Akt levels in pre-treatment ( R = 0.476, P = 0.053) and on-treatment ( R = 0.604, P = 0.015) tumor biopsy specimens correlated with longer PFS[144]. In an immunohistochemical analysis of bronchial NETs in 21 patients, protein levels of the total and phosphorylated form of mTOR and its component (p70S6K [ribosomal protein S6 kinase, 70 kDa], Akt and ERK 1/2) were upregulated in everolimus sensitive patients compared to everolimus resistant patients[145]. The efficacy of monitoring intra-tumor p-p70S6K [80,146–148] was suggested by other groups, however, the relationship to PFS and tumor response with everolimus were conflicting.…”

“…In addition, overexpression p70S6K was reported to be associated with shorter PFS[10,146]. Discrepancies between these studies may partly result from the small number of patients, and due to the heterogeneity in patient’s background, especially their genetic profile[8,16,145,184]. …”

Predictive factors of response to mTOR inhibitors in neuroendocrine tumours

“…In addition, AKT/mTOR pathway signalling molecules in their active form (i.e. phosphorylated), such as basal mTOR, p70S6K, AKT and ERK1/2, are expressed at higher levels in human bronchial carcinoids responding to everolimus treatment in vitro, as compared to those resistant (Gagliano et al 2013). Therefore, these markers may be useful to identify human NETs that may benefit from medical therapy with mTOR inhibitors.…”