Previous studies showed that primary and acquired resistance to anti- Epidermal Growth Factor Receptor (EGFR) drugs used in colorectal cancer (CRC) could be overcome by the concomitant use of either regorafenib or MEK-inhibitors with anti-EGFR antibodies, such as cetuximab. However, little is known about the mechanisms leading to the acquired resistance to these agents used in combination.
We generated CRC cell lines (HCT15 and HCT116) resistant to either a combination of cetuximab and regorafenib or cetuximab and refametinib (BAY 86-9766, a selective MEK-inhibitor), after continuous exposure to the drugs for 8 months. Resistant clones had an IC50 100-fold higher than parental cells. We evaluated by Western Blot (WB) analysis and quantitative Reverse Transcriptase Polymerase Chain Reaction (qRT-PCR) the expression and activation status of a panel of membrane receptors including HER2, EGFR, AXL, EphA2, VEGFRs, intracellular transducers of MAPK and AKT pathways and Epithelial-Mesenchymal Transition (EMT) markers such as Vimentin, E-cadherin, Snail, Slug.
We found different activation patterns for some of the transmembrane receptors and intracellular transducers among HCT15 and HCT116 resistant clones. In particular, HER2 protein was overexpressed and activated in both Cetuximab-Regorafenib resistant (CR-res) and Cetuximab-Refametinib resistant (CM-res) cell populations compared to the parental cell lines. Moreover, there was evidence of Epithelial-Mesenchymal Transition in the CR-res cell population, suggesting the role of this process in acquired resistance to regorafenib. Experiments to test anti-HER2 drugs in resistant cell lines, as well as Next Generation Sequencing (NGS) approaches in order to detect de novo genomic rearrangements, are currently ongoing and will be presented.
Our in vitro preliminary data demonstrated, at least in part, that HER2 protein activation and EMT might play a role in the development of acquired resistance to cetuximab in combination with either regorafenib or refametinib, suggesting a possible role of anti-HER2 therapies in this setting.
Clinical trial identification
Legal entity responsible for the study
Associazione Italiana Ricerca sul Cancro (AIRC)
All authors have declared no conflicts of interest.