Abstract 3812: Overcoming de novo and acquired modes of cetuximab resistance by broad-spectrum receptor tyrosine kinase inhibitors

MEK inhibition has been shown to delay emergence of cetuximab resistance in colorectal cancer (CRC) (Nat Commun 22;6:8305, 2015). By exploiting a novel 3D culture system, we herein show that three broad-spectrum tyrosine kinase inhibitors overcome de novo and acquired resistance to cetuximab. By culturing a CRC cell line, HCA-7 in 3D in type I collagen, we previously identified two novel modes of cetuximab resistance. In 3D culture, HCA-7-derived CC are sensitive to cetuximab, while SC exhibit de novo cetuximab resistance (PNAS 114:E2852-E2861, 2017). Continuous exposure of CC to cetuximab resulted in colonies that acquired resistance to cetuximab, designated CC-CR, which was dependent in part on increased levels of lncRNA MIR100HG that leads to increased WNT signaling (Nat Med 23:1331-1341, 2017). We previously showed increased MET and RON tyrosine phosphorylation in SC cells and that MET/RON inhibitor, crizotinib overcomes SC cetuximab resistance. We now show that crizotinib also overcomes acquired cetuximab resistance in CC-CR. A phospho-RTK array showed increased phosphorylation of several RTKs, including MET and RON, in SC and CC-CR cells compared to cetuximab-sensitive CC counterparts. Furthermore, other multi-RTK inhibitors cabozantinib and BMS-777607 helped overcome cetuximab resistance, as measured by 3D colony growth and activation state of key signaling molecules. Conversely, addition of RTK ligands HGF and NRG1 induced cetuximab resistance in CC cells, which could be blocked by addition of crizotinib and this was associated with disorganized spindle positioning during cell division, leading to multi-layering of CC cultures. By FACS analysis, we observed increased cell cycle arrest in G1 phase in SC and CC-CR cultures treated with cetuximab and crizotinib. Furthermore, we show that crizotinib overcomes cetuximab resistance in vivo in SC nude mice xenografts. Finally, in a direct comparison between vertical suppression (EGFR/MEK inhibition) and parallel inhibition (EGFR/multi-RTK inhibition), we observed a higher degree of synergy with the latter strategy. The non-overlapping toxicities of cetuximab and crizotinib warrants consideration for its clinical deployment. Note: This abstract was not presented at the meeting. Citation Format: Bhuminder Singh, Ramona Graves-Deal, Galina Bogatcheva, Robert J. Coffey. Overcoming de novo and acquired modes of cetuximab resistance by broad-spectrum receptor tyrosine kinase inhibitors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 3812.