Abstract 4551: A novel MET antibody-drug conjugate based combination therapy to overcome colorectal cancer plasticity and drug resistance

Abstract Despite therapeutic advancements, colorectal cancer (CRC) remains the second deadliest malignancy in the United States. Challenges encountered in CRC treatment may be attributed to cancer stem cells (CSC), an immortal tumor cell population. CSCs potentiate tumor relapse by exploiting its infinite replicative potential and inherent drug resistance. Moreover, CSCs exhibit plasticity, allowing them to transition between differentiated and undifferentiated states in response to environmental cues to evade therapy and drive metastatic progression. MET is a receptor tyrosine kinase frequently upregulated in CRCs. We previously demonstrated that treatment with chemotherapies or antibody-drug conjugates (ADCs) targeting the CSC marker LGR5 led to the loss of LGR5 expression with concomitant MET-STAT3 pathway activation in therapy-resistant CRC cells. Further, we showed that LGR5 couples to the scaffold protein IQGAP1, which correlates with poor prognosis in several cancer types. Interestingly, our new data revealed that LGR5 knockdown enhances IQGAP1 interaction with MET and STAT3 via co-immunoprecipitation assays, suggesting a role for IQGAP1 in mediating MET-STAT3 activation and plasticity of LGR5+ CRC cells. To overcome therapy-induced plasticity, we generated MET-targeting ADCs conjugated to DNA-crosslinking payloads. First, we cloned and produced MET monoclonal antibodies (mAbs) and evaluated them for specificity and binding in a panel of CRC cell lines expressing different MET protein levels. MET mAbs demonstrated high selectivity for MET-expressing CRC cells and internalized to lysosomes, which is necessary for ADC payload release. To generate MET ADCs, we employed a site-specific conjugation methodology to attach cleavable peptide linker-drug moieties to the highest affinity MET mAb. MET ADCs were evaluated for cancer cell-killing efficacy in vitro in parallel with MET mAb, non-targeting control mAb (cmAb), and control ADC (cADC). Our MET ADC displayed high potency and efficacy in MET-expressing CRC cells, whereas MET mAb, cmAb, and cADC had minimal effects. MET ADCs were then tested in combination with chemotherapies or other targeted therapies. The combination of MET ADCs with 5-fluorouracil showed a synergistic effect in vitro. Future work involves investigating the safety and efficacy of MET ADCs alone and combined with chemotherapies in xenograft models of CRC. These findings present a mechanism underpinning CRC plasticity and the rationale for a novel treatment modality to potentially overcome CRC resistance and relapse. Citation Format: Shraddha Subramanian, Tressie A. Posey, Joan Jacob, Adela Aldana, Kendra S. Carmon. A novel MET antibody-drug conjugate based combination therapy to overcome colorectal cancer plasticity and drug resistance abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts) ; 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84 (6Suppl): Abstract nr 4551.