Abstract 4411: Effects of novel PI3K/mTOR inhibitors BKM120 and BEZ235 in comparison to everolimus in Head & Neck Squamous cell carcinomas (HNSCC).
Authors: Hesbert Aurelie , Serova Marie , de Gramont Armand , Slimane Khemaies , Raymond Eric , Faivre Sandrine 
Published: August 2014

Background: Current management of advanced HNSCC is limited to surgery, radiotherapy, and chemotherapy. The frequent activation of the PI3K/AKT/mTOR signaling pathway in HNSCC has suggested that inhibition of PI3K/mTOR may have potential therapeutic activity. Preliminary results of the phase I/II CAPRA clinical trial combining the mTOR inhibitor everolimus with paclitaxel and carboplatin have shown promising antitumor activity. Experimental evidences have suggested that mTOR inhibition using rapalogues may be hampered by a negative feedback resulting in PI3K activation. The aim of our study was to evaluate the antiproliferative effects of novel PI3K/mTOR inhibitors in comparison to everolimus in a panel of three HNSCC cell lines.

Materials and Methods: HNSCC cell lines (SQ20B, HEP2, and SCC61) were treated with mTORC1 specific inhibitor everolimus, the dual PI3K/mTOR inhibitor BEZ235, and the specific PI3K inhibitor BKM120. Antiproliferative effects were assessed using MTT assay. Protein expression and phoshorylation were assessed by western blot.

Results: HNSCC cancer cells were characterized for predictive factors of mTOR inhibitors. SQ20B and SCC61 cells displayed an epithelial phenotype whereas HEP2 cells displayed mesenchymal characteristics. SQ20B and SCC61 cells also had a constitutively activated AKT pathway in contrast to HEP2 cells. Others potentials predictive factors of mTOR inhibitors (Bcl2, Cyclin D1, p27, c-Myc) were differentially expressed in HEP2, SCC61, and SQ20B cells. In all cell lines, everolimus displayed IC50 over 6 μM. Novel mTOR inhibitors were 2-30 times more potent with IC50 ranging from 0.2 to 0.8 μM for BEZ235 and from 2.1 to 2.4 μM for BKM120. Everolimus and BEZ235 were less potent in HEP2 compared to SQ20B and SCC61 cells. In SQ20B and SCC61 cell lines everolimus displayed low IC25 (0.02μM) close to BEZ235 (0.1μM) and lower than BKM120 (1.4μM). All inhibitors displayed potent inhibition of S6 phosphorylation in all cells. Everolimus and the novel mTOR inhibitors inhibited the constitutive AKT activation observed in SQ20B and SCC61. In contrast, everolimus but not the novel mTOR inhibitors, significantly increased AKT activation in HEP2 cells. In combinations with carboplatin or paclitaxel, everolimus and BEZ235 displayed synergistic antiproliferative effects in HEP2 and additive effects in SQ20B, whereas BKM120 displayed mostly additive effects in both cell lines.

Conclusion: Novel generation of PI3K/mTOR inhibitors displayed more potent antiproliferative effects than everolimus in HNSCC cell lines. Everolimus and BEZ235 were more active in epithelial cells with constitutionally activated AKT pathway whereas BKM120 potently inhibited cell proliferation in all HNSCC models. Several combinations with chemotherapies were shown to be synergistic and may be regarded as an attractive strategy in HNSCC patients.

Citation Format: Aurelie Hesbert, Marie Serova, Armand de Gramont, Khemaies Slimane, Eric Raymond, Sandrine Faivre. Effects of novel PI3K/mTOR inhibitors BKM120 and BEZ235 in comparison to everolimus in Head & Neck Squamous cell carcinomas (HNSCC). [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 4411. doi:10.1158/1538-7445.AM2013-4411