Abstract 336: Mechanism of action of MCLA-129, a bispecific antibody that targets EGFR and c-MET and impairs growth of EGFR exon 20 insertion mutant non-small cell lung cancer
Authors: de Gorter David J. , O'Connor Marie , Deshiere Alexandre , van Rosmalen Martijn , Fatrai Szabolcs , van Bueren Jeroen Lammerts , Geuijen Cecile A. 
Published: June 2022

Abstract
Introduction: MCLA-129 is an ADCC-enhanced IgG1 bispecific antibody that targets epidermal growth factor receptor (EGFR) and c-MET. The HGF/c-MET pathway is frequently upregulated in tumors that are resistant to EGFR tyrosine kinase inhibitors (TKIs). This study investigated the MCLA-129 mechanism of action in vitro and effectiveness in vivo in an EGFR exon20 insertion (ex20ins) non-small cell lung cancer (NSCLC) model.
Methods: To study the effect of MCLA-129 on c-MET and EGFR dimerization, β-galactosidase enzyme complementation assays were performed. Ligand-dependent phosphorylation of EGFR and c-MET was assessed in vitro on the NCI-H1650 NSCLC cell line by immunoblotting. Shotgun mutagenesis epitope mapping was used to identify the binding epitope of MCLA-129 to EGFR. ADCC activity of MCLA-129 was determined in NSCLC cells expressing different levels of EGFR and c-MET using an ADCC reporter assay with high affinity FcγRIII 158V-variant and low affinity 158F-variant effector cells. ADCP was measured with monocyte-derived macrophages incubated with pHrodo-labeled HCC827 NSCLC target cells with readout of tumor cell phagocytosis on the Incucyte® system. For the evaluation of efficacy in vivo in the EGFR exon20ins PDX model, MCLA-129 was administered at 2.5, 8 or 25 mg/kg i.p. weekly.
Results: MCLA-129 blocks EGF and HGF binding to EGFR and c-MET, respectively, and prevents receptor dimerization. Consequently, MCLA-129 inhibits phosphorylation of EGFR and c-MET as demonstrated in NCI-H1650 cells. Mutagenesis analysis identified critical binding residues of domain III of EGFR for MCLA-129 binding that are distinct from cetuximab binding. MCLA-129 displayed potent ADCC activity on NSCLC cell lines using effector cells expressing either high or low affinity FcγRIII variant. MCLA-129 demonstrated potent dose-dependent ADCP of HCC827 NSCLC cells. Finally, MCLA-129 led to significant dose-dependent regression of a patient-derived EGFR exon20ins NSCLC tumor in a mouse PDX model.
Conclusion: MCLA-129 is a Biclonics® common light chain bispecific antibody with multiple mechanisms of action including potent inhibition of c-MET and EGFR ligand binding, ligand-induced receptor dimerization and phosphorylation, ADCC and ADCP. MCLA-129 demonstrates significant growth inhibition of a patient-derived EGFR exon20ins tumor in a preclinical xenograft model. A phase 1/2 clinical trial of MCLA-129 in solid tumors is ongoing. These data support the further clinical development of MCLA-129 in patients with NSCLC, including NSCLC with EGFR exon20ins, and other solid tumors.
Citation Format: David J. de Gorter, Marie O'Connor, Alexandre Deshiere, Martijn van Rosmalen, Szabolcs Fatrai, Jeroen Lammerts van Bueren, Cecile A. Geuijen. Mechanism of action of MCLA-129, a bispecific antibody that targets EGFR and c-MET and impairs growth of EGFR exon 20 insertion mutant non-small cell lung cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 336.