Competition Abstracts

Poster 1  

Targeting MET–LGR5 Crosstalk using an Antibody-Drug Conjugate Combination with Diverse Payloads to Overcome Adaptive Resistance in Colorectal Cancer 
 Shraddha Subramanian^1,2, Zhengdong Liang¹, Peyton C. High^1,2, Cara Guernsey-Biddle^1,2, Adela M. Aldana¹, and Kendra S. Carmon^1,2
1Center for Translational Cancer Research, The University of Texas Health Science Center, Houston, TX, USA; ²The University of Texas MD Anderson Cancer Center UTHealth Houston Graduate School of Biomedical Sciences, Houston, TX, USA

Off-target side effects and drug resistance often hamper the therapeutic benefits of existing anti-cancer therapies against colorectal cancer (CRC), the second deadliest malignancy worldwide. CRCs contain tumor-initiating cancer stem cells (CSCs) that survive toxic drugs, thereby producing mortality-inducing metastases. Antibody-drug conjugates (ADCs) leverage monoclonal antibody (mAb) specificity to deliver cytotoxic payloads to cancer cells. We generated ADCs targeting leucine-rich repeat-containing G protein-coupled receptor 5 (LGR5), a bona fide CSC biomarker frequently overexpressed in CRCs. Our LGR5 ADC exhibited high potency in CRC xenograft models with minimal toxicity; however, it failed to prevent tumor relapse after treatment cessation. Interestingly, our findings demonstrated that recurrent tumors evade LGR5 ADC-mediated elimination through transient conversion into an LGR5-negative (LGR5^–) state, accompanied by concomitant MET upregulation and downstream pathway activation. MET is a receptor tyrosine kinase frequently upregulated in CRCs and promotes metastatic progression. Thus, this study aims to elucidate the mechanisms of MET-mediated resistance to LGR5 ADCs and to evaluate the therapeutic efficacy of combining MET-targeted therapies with next-generation LGR5 ADCs in preventing the recurrence and metastasis of CRC. We identified that the activation of STAT3, a downstream effector protein in the MET pathway, undermines LGR5 ADC efficacy in CRC cells. To eliminate drug-resistant LGR5^– cells, we generated MET-targeted ADCs by conjugating a highly selective MET mAb (ABT700) backbone to the pyrrolobenzodiazepine (PBD) dimer using a site-specific conjugation methodology. Our MET ADC (ABT700-PBD) demonstrated dose-dependent cytotoxicity in CRC cells. Furthermore, ABT700-PBD did not affect CRC cells with genetically induced MET ablation, demonstrating its specificity. Safety studies in immunocompetent mice showed that ABT700-PBD exhibited a favorable safety profile. Moreover, in CRC patient-derived xenograft (PDX) models, ABT700-PBD induced marked tumor regression. However, in tumors that recurred following dose-dependent ABT700-PBD monotherapy, LGR5 protein expression was upregulated. Together, these findings suggest that MET and LGR5 function within an epistatic pathway that governs cellular plasticity and therapeutic resistance in CRC. Cytotoxicity assays evaluating the combination of ABT700-PBD with our next-generation LGR5 ADC showed additive anti-proliferative activity in vitro. The LGR5 ADC was produced by attaching a previously characterized LGR5 mAb (8E11) backbone to a camptothecin (CPT2)-derived payload. Combination treatment with ABT700-PBD and 8E11-CPT2 in CRC PDX models extended survival compared to LGR5 or MET ADC monotherapies. These results provide a preclinical framework supporting combination therapy with MET and LGR5-targeted ADCs to overcome resistance-induced tumor relapse in advanced CRC.