Abstract 3402: THSD7B loss is associated with oxaliplatin resistance in colorectal cancer patient-derived tumor organoids

Abstract Despite significant advances in systemic therapies for colorectal cancer (CRC), this tumor remains the second leading cause of cancer-related mortality worldwide. Among the chemotherapeutic agents most widely used in CRC, oxaliplatin (OX) represents a cornerstone of both single-agent and combination regimens. However, the acquisition of drug resistance mechanisms leads to the failure of these treatments, underscoring the need to elucidate the molecular determinants underlying chemoresistance. Therefore, this study aimed to identify the molecular determinants associated with resistance to OX-based therapies through integrated genomic and transcriptomic approaches performed on drug-sensitive and OX-resistant CRC patient-derived tumor organoids (PDTOs). OX- and FOLFOX-resistant CRC PDTOs (5. 24-fold increment of drug resistance) were generated through the administration of increasing and sublethal doses of the drug for at least 90 days and integrated transcriptomic and exomic profiling were performed to characterize the molecular mechanisms sustaining chemoresistance. RNA-sequencing analyses revealed profound dysregulation of pathways involved in cytoskeletal regulation, extracellular space and cell death in both OX and FOLFOX-resistant models, while whole-exome sequencing identified newly acquired variants affecting genes related primarily to cell adhesion and extracellular matrix organization, with notable alterations affecting LARGE1 and Thrombospondin Type-1 Domain-Containing Protein 7B (THSD7B), both genes potentially implicated in OX resistance. Particularly, the presence of the THSD7B NM₀01080427. 1: c. 465dup, p. (Pro156ThrfsTer6) frameshift variant was first confirmed in OX-resistant PDTOs by droplet digital PCR (VAF=20. 9%). RT-qPCR analyses performed in drug-sensitive and OX and FOLFOX-resistant PDTOs revealed markedly reduced THSD7B transcript levels in resistant models. Functional silencing of THSD7B using small interfering RNAs performed on Caco2, HT29, and HCT116 CRC cell lines led to a significant downregulation of THSD7B expression (from 27% to 90% reduction) and resulted in increased OX resistance, particularly in the more differentiated lines (Caco2 and HT29), whereas no substantial effect was observed in the undifferentiated HCT116 line. Overall, our data show for the first time that THSD7B loss mediates OX resistance in CRC. Intriguingly, this evidence has been recently associated with platinum resistance also in lung cancer; therefore, the evaluation of THSD7B status may represent a valuable strategy for the early identification of platinum-resistant patients to avoid the administration of ineffective and potentially harmful treatments. Citation Format: Graziana Spoto, Luca Falzone, Marco Fichera, Massimo Libra. THSD7B loss is associated with oxaliplatin resistance in colorectal cancer patient-derived tumor organoids abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 1 (Regular Abstracts) ; 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86 (7 Suppl): Abstract nr 3402.