In Vitro and In Vivo Synergistic Antitumor Activity of the Combination of BKM120 and Erlotinib in Head and Neck Cancer: Mechanism of Apoptosis and Resistance

Abstract

We previously reported that the EGFR-targeted inhibitor erlotinib induces G arrest of squamous cell carcinoma of the head and neck (SCCHN) cell lines without inducing significant apoptosis. Large-scale genomic studies suggest that >50% of SCCHN cases have activation of PI3K pathways. This study investigated whether cotargeting of EGFR and PI3K has synergistic antitumor effects and apoptosis induction. We examined growth suppression, apoptosis, and signaling pathway modulation resulting from single and combined targeting of EGFR and PI3K with erlotinib and BKM120, respectively, in a panel of SCCHN cell lines and a xenograft model of SCCHN. In a panel of 12 cell lines, single targeting of EGFR with erlotinib or PI3K with BKM120 suppressed cellular growth without inducing significant apoptosis. Cotargeting of EGFR and PI3K synergistically inhibited SCCHN cell line and xenograft tumor growth, but induced variable apoptosis; some lines were highly sensitive, others were resistant. Mechanistic studies revealed that the combination inhibited both axes of the mTORC1 (S6 and 4EBP1) pathway in apoptosis-sensitive cell lines along with translational inhibition of Bcl-2, Bcl-xL, and Mcl-1, but failed to inhibit p-4EBP1, Bcl-2, Bcl-xL, and Mcl-1 in an apoptosis-resistant cell line. siRNA-mediated knockdown of eIF4E inhibited Bcl-2 and Mcl-1 and sensitized this cell line to apoptosis. Our results strongly suggest that cotargeting of EGFR and PI3K is synergistic and induces apoptosis of SCCHN cell lines by inhibiting both axes of the AKT-mTOR pathway and translational regulation of antiapoptotic Bcl-2 proteins. These findings may guide the development of clinical trials using this combination of agents. .

Rationale for Using Irreversible Epidermal Growth Factor Receptor Inhibitors in Combination with Phosphatidylinositol 3-Kinase Inhibitors for Advanced Head and Neck Squamous Cell Carcinoma

“…Our data are consistent with previous studies showing the benefit of PI3K-and EGFR-inhibitor combination therapies (Rebucci et al, 2011;Young et al, 2013;D'Amato et al, 2014;Lattanzio et al, 2015;Michmerhuizen et al, 2016;Anisuzzaman et al, 2017;Silva-Oliveira et al, 2017) and also extend that work by discovering that PI3K inhibitors are much more effective in combination with irreversible than reversible EGFR inhibitors in HNSCC. In prior work comparing the classes of EGFR-targeting monotherapies in this cancer type, preclinical data demonstrated that irreversible EGFR inhibitors are superior to other EGFR-targeting agents, including cetuximab (Ather et al, 2013;Silva-Oliveira et al, 2017) and reversible inhibitor gefitinib (Young et al, 2015).…”

“…Comparisons for HS-173 and gefitinib combinations in each cell line and for HS-173 and afatinib combination in UM-SCC-59 were performed but are not shown given the lack of significant interaction term. (Rebucci et al, 2011;D'Amato et al, 2014;Lattanzio et al, 2015) or the reversible EGFR inhibitors (e.g., gefitinib, erlotinib) (Young et al, 2013;Anisuzzaman et al, 2017). One exception is a recent report from Silva-Oliveira et al (2017) that examined the responses to PI3K pathway inhibitors (including AKT inhibitor MK-2206) with two different irreversible EGFR inhibitors.…”

“…Preclinical data indicate that dual therapies directed against both PI3K and EGFR pathways might improve responses in HNSCC (Rebucci et al, 2011;Young et al, 2013;D'Amato et al, 2014;Lattanzio et al, 2015;Michmerhuizen et al, 2016;Anisuzzaman et al, 2017;Silva-Oliveira et al, 2017). Given these promising data, several clinical trials assessing the combination in HNSCC have been opened, most of which use the EGFR-targeting antibody cetuximab in combination with various inhibitors of PI3K (e.g., NCT01816984, NCT2282371, NCT02822482).…”

The influence of PI3K inhibition on the radiotherapy response of head and neck cancer cells

“…However, when we look at BKM120, the study of Kong et al investigated the effect of BKM120 in PIK3CA hotspot mutated and wild type cell lines and it was concluded that BKM120 exhibit potent activity in both 30 . Since the value of PIK3CA status as predictive biomarker is still unknown according to Anizussaman et al and we had limited availability of HNSCC cell lines with a PIK3CA mutation, we did not incorporate a PIK3CA-mutated cell line in our experimental set-up 15,[31][32][33][34][35] .…”

CDK 4/6 Inhibition Overcomes Acquired and Inherent Resistance to PI3Kα Inhibition in Pre-Clinical Models of Head and Neck Squamous Cell Carcinoma

“…The rationale for combining pathways inhibitors to prevent PI3Ki resistance has been shown to achieve extended response in pre-clinical HNSCC models. For example, by simultaneously blocking mTORC2 [ 30 , 31 ], human epidermal growth factor receptor 3 (HER3) [ 32 , 33 ], Epidermal growth factor receptor (EGFR) [ 34 , 35 ], Jun N-terminal kinases (JNK) [ 36 ], Extracellular signal-regulated kinases (ERK) [ 37 ], and AXL [ 22 ]. Previously, Vora et al [ 23 ] and others [ 26 ] described in both pre-clinical breast cancer models and in patients, that resistance to BYL719 is mediated by sustained activation of mTORC1 that regulates the CDK 4/6–Rb axis.…”