Abstract P256: Pan-ErbB inhibition enhances activity of KRASG12C inhibitors in preclinical models of KRASG12C mutant cancers
Authors: Robichaux Jacqulyne P. , Galan-Cobo Ana , Powell Ried T. , Gale Kelly A. , He Jun , Zhang Fahao , Nilsson Monique B. , Zhang Xiang , Sobieski Mary M. , Nguyen Nghi , Clifford Stephan C. , Heymach John V. 
Published: December 2021

Abstract
Sotorasib (AMG 510) is the first KRAS inhibitor to be FDA-approved for the treatment of KRASG12C mutant lung adenocarcinomas which comprise ~42% of KRAS mutations in lung adenocarcinomas. Preclinical studies have shown that within hours of KRASG12C inhibition, synthesis of new KRASG12C protein and increased KRAS signaling was observed, leading to enhanced tumor cell growth and survival. This appeared to be due, at least in part, to a feeback loop leading to activation of EGFR signaling but the role of other ErbB family members including ErbB2 (HER2), ErbB3 (HER3), and ErbB4 (HER4) has not been fully evaluated. We hypothesize that short-term adaptation to KRAS inhibition is driven by multiple ErbB family members, and that the combination of pan-ErbB inhibitors with KRASG12C inhibitors could enhance KRASG12C inhibitor activity and prolong survival in preclinical models harboring KRASG12C mutations to a greater extent than more specific EGFR inhibitors. To investigate the role of different ErbB family members in this feedback signaling, we evaluated the impact of an EGFR specific inhibitor, erlotinib, an EGFR/HER2 inhibitor, afatinib, or pan-ErbB inhibitor (EGFR/HER2/3/4), poziotinib on anti-tumor activity of KRASG12C inhibitors in KRASG12C mutant NSCLC cell lines. We initially tested the different inhibitors in combination with sotorasib and adagrasib (MRTX849) and calculated the BLISS index (BI) for each drug pair matrix, using SynergyFinder. We found that when combined with either sotorasib or adagrasib, poziotinib had a synergistic effect (BI&gt;10) in H23 (BI: 17, p=0.01), HCC44 (BI: 11, p=0.04), and H1792 (BI: 13, p=0.01) and an additive effect (BI= -10–10) in H2122 (BI: 2.8). Afatinib and erlotinib were additive in H23 (BI: 9.2 & 9.4), HCC44 (BI:8.8 & 7.9), H2122 (BI: -4.5 & -3.3) and H1792 (BI: 6.6 & 3.3). Poziotinib yielded a higher BI across all four cell lines compared to afatinib (p&lt;0.0001) or erlotinib (p=0.0004). To determine if poziotinib prevented upregulation of ErbB-signaling after treatment with KRASG12C inhibitors, we treated KRASG12C mutant cell lines (NSCLC: H23 and Bladder Cancer: UM-UC-3) with KRASG12C inhibitors, sotorasib or adagrasib, for four hours and found by Western blotting that phosphorylated EGFR, HER2, HER3, and HER4 were increased after treatment. The addition of 10 nM poziotinib prevented the upregulation of phosphorylated EGFR, HER2, HER3, and HER4 in both cell lines. Together these data demonstrate that inhibition of EGFR, HER2, HER3, and HER4 signaling by the pan-ErbB inhibitor poziotinib resulted in greater synergy with KRASG12C inhibitors than EGFR or EGFR/HER2 inhibitors and highlight the potential importance of HER3 and HER4, in addition to EGFR and HER2, in feedback signaling after KRAS G12C inhibition. Additional studies of pan-ErbB and ErbB-specific inhibitors with KRASG12C inhibitors are warranted to determine tolerability and optimal dosing to prolong survival in KRAS mutant cancers.
Citation Format: Jacqulyne P. Robichaux, Ana Galan-Cobo, Ried T. Powell, Kelly A. Gale, Jun He, Fahao Zhang, Monique B. Nilsson, Xiang Zhang, Mary M. Sobieski, Nghi Nguyen, Stephan C. Clifford, John V. Heymach. Pan-ErbB inhibition enhances activity of KRASG12C inhibitors in preclinical models of KRASG12C mutant cancers [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2021 Oct 7-10. Philadelphia (PA): AACR; Mol Cancer Ther 2021;20(12 Suppl):Abstract nr P256.