Abstract A033: Targeting ROR2 with an antibody-drug conjugate to overcome MYOD1L122R-driven therapy resistance in rhabdomyosarcoma

Abstract Rhabdomyosarcoma (RMS) is the most common pediatric soft tissue sarcoma in the United States. Beyond the well-characterized embryonal (fusion-negative) and alveolar (fusion-positive) subtypes, a recently defined third subtype—spindle cell/sclerosing rhabdomyosarcoma (SS-RMS) —is found to be frequently associated with a recurrent L122R mutation in the DNA-binding domain of the MYOD1 transcription factor. This oncogenic variant, MYOD1L122R, is strongly linked to poor clinical outcomes, enhanced tumor aggressiveness, enrichment of tumor-propagating cancer stem cells, and resistance to multimodal therapies. We previously identified that MYOD1L122R directly engages regulatory elements of Receptor Tyrosine Kinase-Like Orphan Receptor 2 (ROR2), thereby enhancing stem-like properties and driving resistance to both chemotherapy and radiation. We show that the loss of ROR2 in our mutant MYOD1 models re-sensitizes in vitro models to therapy. Considering the importance of ROR2 in SS-RMS, we utilized an antibody-drug conjugate (ADC) to target ROR2 (Ozuriftamab vedotin) which is in clinical evaluation (NCT05271604). Using engineered cell line models and patient derived xenograft 3D explants, we observe a potent and significant effect on cell viability by the ADC in MYOD1L122R expressing cells but not MYOD1WT expressing cells. Ozuriftamab vedotin also promoted differentiation in the SS-RMS models, which appears to re-sensitize these cells to therapy. We next tested the ADC in vivo and found that the ADC significantly suppressed tumorigenic potential of engrafted MYOD1L122R expressing cells. Together, our findings highlight ROR2-directed therapies as a promising avenue for treatment in MYOD1-mutant SS-RMS and other aggressive RMS subtypes co-opting this pathway. Citation Format: Jihee Lee, Sabateeshan Mathavarajah, Yun Wei, Luis A Corchete Sanchez, Devika D Kannambadi, Esther Rheinbay, David M Langenau. Targeting ROR2 with an antibody-drug conjugate to overcome MYOD1L122R-driven therapy resistance in rhabdomyosarcoma abstract. In: Proceedings of the AACR Special Conference in Cancer Research: Discovery and Innovation in Pediatric Cancer— From Biology to Breakthrough Therapies; 2025 Sep 25-28; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2025;85 (18Suppl₂): Abstract nr A033.