Abstract A165: Determining drug inhibition profiles and opportunities for synergistic combination therapies in head and neck cancer cell lines

Abstract

Abstract Background: Metastatic head and neck cancer (HNC) remains poorly treatable and novel therapies are needed. We explored drug inhibition profiles in a large panel of head and neck cancer cell lines in order to select better therapies in the future and explore synergistic combinations. Methods: We measured the IC50 values of 23 clinically relevant small molecule inhibitors in 30 HNC cell lines by viability (resazurin). Hierarchical cluster analysis of single agent profiles was performed. Two cell lines were treated with combinations of two inhibitors to evaluate synergy via combinatorial index calculation (Chou). Signaling pathways were interrogated by immunoblot. Results: Single agents with a high degree of activity included bortezomib (lowest IC50 for SCC74: 15pM), dasatinib (HN13: 36pM), NVP-BEZ235 (SCC74: 50pM). However cluster analysis did not show consistent groupings, but similar agents clustered together. In both cell lines investigated for synergy — combinations of MET inhibitors with agents blocking GSK3-ß, Proteasome, src, EGFR, and PKC-β, as well as combinations of src inhibition with PI3K, HDAC, IGF1R, or PKC-β inhibition showed strong synergy by CI values. In SCC58 (non-HPV) inhibitors of EGFR, MET, IGF1-R, and HIF1 synergized with each other or with src or PKC-ß inhibition. In OSCC3 (HPV(+) MET inhibition synergized with everolimus (mTOR) or NVP-BEZ235 (PI3K/mTOR). Specific combinations with high degrees of synergy include: SU11274 (MET)/Erlotinib (EGFR): SCC58 CI50=0.29; OSCC3: CI50=0.53; PHA665752 (MET)/Bortezomib (Proteasome): OSCC3 CI50=0.41; IGF1-R-Inh./HIF1-Inh.: SCC58 CI50=0.33; IGF1-R-Inh./Enzastaurin (PKC-s): SCC58 CI50=0.15; Bortezomib (Proteasome)/Enzastaurin (PKC-ß): SCC58 CI50=0.38; Enzastaurin(PKC-ßs)/IGF-R-Inh.: OSCC3 CI50=0.72; Enzastaurin (PKC-ß):/SU11274 (MET): OSCC3 CI50=0.47; SB216763(GSK3-ß)/SU11274: OSCC3 CI50=0.52; Dasatinib (src)/Wortmannin (PI3K): OSCC3 CI50=0.64; SAHA/Dasatinib(src): OSCC3 CI50=0.58; SB216763 (GSK3-ß)/SU11274 (MET): OSCC3 CI50=0.5. Immunoblotting showed varying effects on several downstream signaling cascades. E.g. after combined treatment with PF-2341066 and Enzastaurin p-ERK signaling was reduced significantly more than after treatment with either agent alone. Conclusion: HNC cell lines show differential sensitivity to targeted agents and do not readily cluster based on drug inhibition. Nevertheless remarkable sensitivity in multiple cell lines was observed for certain inhibitors targeting src, the proteasome, and PI3K. Furthermore synergy was noted combining inhibitors of established targets in HNC (MET, EGFR, IGFR, and HIF1). Furthermore HPV-infected cell lines appear to be sensitive to combined inhibition of MET and the downstream PI3K/Akt/mTOR pathway. We are in the process of investigating the underlying etiology of specific drug sensitivities. Citation Information: Mol Cancer Ther 2009;8(12 Suppl):A165.