Optimal targeting of BCL-family proteins in head and neck squamous cell carcinoma requires inhibition of both BCL-xL and MCL-1

Abstract

// Thomas J. Ow 1, 2, 12 , Cory D. Fulcher 1 , Carlos Thomas 2 , Pilib Ó Broin 3 , Andrea López 4 , Denis E. Reyna 4 , Richard V. Smith 1, 2, 5, 12 , Catherine Sarta 1 , Michael B. Prystowsky 2, 12 , Nicolas F. Schlecht 2, 6, 7, 8 , Bradley A. Schiff 1 , Gregory Rosenblatt 2 , Thomas J. Belbin 2, 9 , Thomas M. Harris 2 , Geoffrey C. Childs 2 , Nicole Kawachi 2 , Chandan Guha 2, 10, 12 and Evripidis Gavathiotis 4, 11, 12 1 Department of Otorhinolaryngology-Head and Neck Surgery, Montefiore Medical Center/Albert Einstein College of Medicine, Bronx, NY, USA 2 Department of Pathology, Montefiore Medical Center/Albert Einstein College of Medicine, Bronx, NY, USA 3 School of Mathematics, Statistics, and Applied Mathematics, National University of Ireland Galway, Galway, Ireland 4 Department of Biochemistry, Albert Einstein College of Medicine, Bronx, NY, USA 5 Department of Surgery, Montefiore Medical Center/Albert Einstein College of Medicine, Bronx, NY, USA 6 Department of Epidemiology & Population Health, Montefiore Medical Center/Albert Einstein College of Medicine, Bronx, NY, USA 7 Department of Medicine (Oncology), Montefiore Medical Center/Albert Einstein College of Medicine, Bronx, NY, USA 8 Department of Cancer Prevention & Control, Roswell Park Comprehensive Cancer Center, Buffalo, NY, USA 9 Discipline of Oncology, Memorial University of Newfoundland, St. John’s, NL, Canada 10 Department of Radiation Oncology, Montefiore Medical Center/Albert Einstein College of Medicine, Bronx, NY, USA 11 Department of Medicine (Cardiology), Montefiore Medical Center/Albert Einstein College of Medicine, Bronx, NY, USA 12 Albert Einstein Cancer Center, Bronx, NY, USA Correspondence to: Thomas J. Ow, email: thow@montefiore.org Keywords: head and neck squamous carcinoma; MCL-1; BCL-xL; navitoclax; A-1210477 Received: April 24, 2018     Accepted: December 16, 2018     Published: January 11, 2019 ABSTRACT Mechanisms of treatment resistance in head and neck squamous cell carcinoma (HNSCC) are not well characterized. In this study, HNSCC tumors from a cohort of prospectively enrolled subjects on an ongoing tissue banking study were divided into those that persisted or recurred locoregionally (n=23) and those that responded without recurrence (n=35). Gene expression was evaluated using llumina HumanHT-12-v3 Expression BeadChip microarrays. Sparse Partial Least Squares – Discriminant Analysis (sPLS-DA) identified 135 genes discriminating treatment-resistant from treatment-sensitive tumors. BCL-xL was identified among 23% of canonical pathways derived from this set of genes using Ingenuity Pathway analysis. The BCL-xL protein was expressed in 8 HNSCC cell lines examined. Cells were treated with the BCL-xL inhibitor, ABT-263 (navitoclax): the average half maximal inhibitory concentration (IC50) was 8.9μM (range 6.6μM – 13.9μM). Combining ABT-263 did not significantly increase responses to 2 Gy radiation or cisplatin in the majority of cell lines. MCL-1, a potential mediator of resistance to ABT-263, was expressed in all cell lines and HNSCC patient tumors, in addition to BCL-xL. Treatment with the MCL-1 inhibitor, A-1210477, in HNSCC cell lines showed an average IC50 of 10.7μM (range, 8.8μM to 12.7μM). Adding A-1210477 to ABT-263 (navitoclax) treatment resulted in an average 7-fold reduction in the required lethal dose of ABT-263 (navitoclax) when measured across all 8 cell lines. Synergistic activity was confirmed in PCI15B, Detroit 562, MDA686LN, and HN30 based on Bliss Independence analysis. This study demonstrates that targeting both BCL-xL and MCL-1 is required to optimally inhibit BCL-family pro-survival molecules in HNSCC, and co-inhibition is synergistic in HNSCC cancer cells.