Therapeutic co-targeting of LGR5 and MET to overcome heterogeneity and therapy resistance in colorectal tumors - ABSTRACT: Tumor heterogeneity and therapy resistance remain challenges to the successful treatment of metastatic colorectal cancer (mCRC). Leucine-rich repeat containing G protein-coupled receptor 5 (LGR5) is upregulated in a large fraction of primary colorectal tumors and metastases with low expression in normal tissues. LGR5 has also been validated as a marker of cancer stem-like cells (CSCs) that self-renew and drive tumor growth and metastasis. We and others generated LGR5-targeted antibody-drug conjugates (ADCs) incorporating microtubule inhibitors to target CSCs and eliminate colorectal tumors. However, these first-generation LGR5 ADCs only led to tumor inhibition, followed by relapse once treatment was terminated, due in part to LGR5 downregulation and drug payload selection. Interestingly, we showed loss of LGR5 mediated by LGR5-targeted ADCs or genetic knockout in CRC cells resulted in activation of the receptor tyrosine kinase MET to enhance survival and therapy resistance of LGR5-negative CRC cells. MET is also highly expressed in primary colorectal tumors and metastases with lower expression in normal tissues and MET-targeted ADCs have shown great promise in clinical trials for different tumor types. Therefore, we hypothesize co-targeting LGR5 and MET with ADCs, incorporating two different drug payloads with different mechanisms of action, will overcome tumor heterogeneity and therapy resistance attributed to target downregulation and/or payload insensitivity. Recently, we utilized a site-specific conjugation approach to generate new LGR5- and MET-targeted ADCs with diverse payloads that are more potent in CRC models. Thus, we propose in Aim 1 to first scale-up production and characterize LGR5- and MET-targeted ADCs. The ADCs will then be tested as monotherapies and in combination to measure effects on tumor antigen binding, internalization, signaling pathways, and cytotoxicity in a panel of CRC cell lines and patient-derived tumor organoids that express different levels of LGR5 and MET. In Aim 2, ADCs will be evaluated as monotherapies and in combination for safety and toxicity studies in normal immunocompetent mice and therapeutic efficacy in patient-derived xenograft models of CRC. This project could have significant impact for the treatment of mCRC and lead to future studies toward the development of a novel LGR5/MET ADC combination to overcome tumor heterogeneity and therapy resistance to eliminate tumors and prevent relapse.
