Therapeutic Synergy of a MUC13-Targeted Radiopharmaceutical and ATR Inhibition in Colorectal Cancer
Ying Chen1#, Ha Tran1#, H. Charles, Manning1,2,3
1Department of Nuclear Medicine, The University of Texas MD Anderson Cancer Center, 1881 East Rd., Houston, TX 77054, USA.
2Radiopharmaceuticals for Advanced Diagnostic Imaging and Therapy R&D Platform, Therapeutics Discovery Division, The University of Texas MD Anderson Cancer Center, 1881 East Rd., Houston, TX 77054, USA.
3Cyclotron Radiochemistry Facility, The University of Texas MD Anderson Cancer Center, 1881 East Rd., Houston, TX 77054, USA.
Objectives: Colorectal cancer (CRC) remains a leading cause of cancer-related mortality, with metastatic disease characterized by limited durable responses and frequent therapeutic resistance. We have previously developed a MUC13-targeted radionuclide therapy (RNT) platform based on terbium-161 (161Tb), which demonstrates potent antitumor activity in preclinical CRC models1; however, response heterogeneity suggests the presence of intrinsic resistance mechanisms. DNA Damage Response (DDR)-associated signaling was implicated in MUC13-high CRC based on transcriptomic analysis of patient data, leading us to evaluate ATR inhibition using ART03802 in combination with radiolabeled MUC13-targeted antibody in MUC13-positive CRC models, supported by DNA damage and clonogenic survival assays.
Methods: MUC13 expression was evaluated using patient-derived transcriptomic datasets and validated in CRC cell lines and xenograft models. DDR pathway activity was evaluated using transcriptomic profiling and gene set enrichment analysis (GSEA). Radiolabeled MUC13-targeted antibodies were generated using standard chelator-based radiochemistry. For imaging studies, the antibody was conjugated with a DFO chelator and labeled with zirconium-89 (89Zr). For therapeutic studies, a DOTA-conjugated antibody was radiolabeled with terbium-161 (161Tb) or lutetium-177 (177Lu). Therapeutic efficacy of radiolabeled MUC13-targeted antibodies was evaluated in CRC PDX models alone or in combination with ART0380. DNA damage was assessed by gamma-H2AX immunofluorescence, and therapeutic response was measured using clonogenic survival assays.
Results: In our prior work, MUC13-targeted RNT induced significant DNA damage and tumor growth inhibition in CRC models. However, transcriptomic analysis of CRC patient data (n = 207) identified selective enrichment of ATR-related DDR signaling in MUC13-high tumors. Of all DNA Damage & Repair pathways evaluated, only the Full DNA Repair Network (NES = 1.771, p = 0.00015, FDR = 0.00024) and ATR Damage Response (NES = 1.656, p = 0.0028, FDR = 0.0028) reached significance (FDR < 0.05), with ATR consistently ranking as a top leading-edge gene across both gene sets. This nominated ATR pathway inhibition as a rational strategy to extend the therapeutic effect of 161Tb-labeled MUC13-targeted RNT, evaluated here using the clinical ATR inhibitor ART0380. Functionally, combination treatment with ART0380 increased radiation-induced DNA damage, which results in an estimated 4-fold increase in gamma-H2AX foci formation compared with RNT monotherapy after 4 hours of treatment. In clonogenic assays, 1.0 uM ATR inhibitor treatment for 4 h yielded a surviving fraction of 0.40, while combination with 177Lu-anti-MUC13 further reduced the surviving fraction to 0.10, consistent with enhanced treatment response.
Conclusions: Our findings identify ATR-mediated DNA damage repair response as a mechanistic resistance pathway limiting the efficacy of MUC13-targeted radionuclide therapy in CRC. These findings support combining ATR inhibitors with MUC13-directed RNT as a precision therapeutic strategy.
Acknowledgments: We acknowledge the support from the TRIUMPH Postdoctoral Fellowship Program and collaborators at MD Anderson Cancer Center.
References: [1] Aiko Yamaguchi, Ryan P. Coll, et al. Clin. Cancer Res. 2026, under review.
[2] Christopher L. Carroll, Michael G. Johnson, et al. J. Med. Chem. 2024, 67, 21890-21904.