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Neuroblastoma (NB) is a cancer of the peripheral nervous system found in children under 15 years of age. It is the most frequently diagnosed cancer during infancy, accounting for ~12% of all cancer-related deaths in children. Leucine-rich repeat-containing G-protein-coupled receptor 5 (LGR5) is a membrane receptor that is associated with the primary tumor formation and metastasis of cancers in the gastrointestinal system. Remarkably, high levels of LGR5 are found in NB tumor cells, and high LGR5 expression is strongly correlated with poor survival. Antibody–drug conjugates (ADCs) are monoclonal antibodies that are covalently linked to cell-killing cytotoxins to deliver the payloads into cancer cells. We generated an ADC with an anti-LGR5 antibody and pyrrolobenzodiazepine (PBD) dimer-based payload SG3199 using a chemoenzymatic conjugation method. The resulting anti-LGR5 ADC was able to inhibit the growth of NB cells expressing LGR5 with high potency and specificity. Importantly, the ADC was able to completely inhibit the growth of NB xenograft tumors in vivo at a clinically relevant dose for the PBD class of ADCs. The findings support the potential of targeting LGR5 using the PBD class of payload for the treatment of high-risk NBs. [ABSTRACT FROM AUTHOR]

Antibody-drug conjugates (ADCs) have emerged as a major modality of targeted cancer therapy, yet no ADC has been approved for colorectal cancer (CRC). LGR4/5/6 (leucine-rich repeat containing, G protein-coupled receptor 4, 5, 6) are three related receptors that are expressed at high levels together or alternately in nearly all cases of CRC. ADCs targeting LGR5 have been shown to have robust anti-tumor potency, but not all CRC cells express LGR5 and LGR5-positive tumor cells may lose LGR5 expression due to cancer cell plasticity. R-spondin 4 (RSPO4) is a natural protein ligand of LGR4/5/6 with high affinity for all three receptors. We fused a mutant form of RSPO4 that retains high affinity binding to LGR4/5/6 to IgG1 Fc to create a peptibody designated R462. Conjugation of R462 with a camptothecin analog (CPT2) at eight drugs per peptibody led to the synthesis of R462-CPT2 that showed highly potent cytotoxic activity in vitro in CRC cell lines expressing any of LG4/5/6. In cell line xenograft and PDX models of CRC, R462-CPT2 demonstrated robust anti-tumor effect. Importantly, R462-CPT2 showed no major adverse effect at therapeutically effective dose levels. These results strongly support the use of RSPO ligand drug-conjugates that target LGR4/5/6 simultaneously for the treatment of CRC.