Abstract 7873: In vivo preclinical efficacy of a novel “payload-bearing” peptide LX-101 targeting IGF-1R in Ewing sarcoma

Abstract Ewing sarcoma (ES) is an extremely aggressive and highly metastatic bone cancer in children and young adults, ranked as the second most frequent bone tumor in pediatric patients. With a survival of ∼80% for localized and regional tumors, which can drop down to ∼40% for metastatic cases, standard treatment for ES usually includes radiotherapy, surgery, and chemotherapy based on the VDC/IE regimen. Alternative therapeutic approaches targeting critical pathways with recognized roles in tumorigenesis, such as IGF-1, PI3K, and mTOR, have also demonstrated remarkable clinical activity as single agents or in combinations for several cancer types. For this reason, it is imperative to confirm and generate preclinical evidence of anticancer activity in ES. Here, we tested the in vitro and in vivo efficacy of LX-101, a next-generation therapy targeting IGF-1R, which couples a proprietary IGF-1 variant to a cytotoxic MTX payload, as a single agent or in combination with alpelisib (a PI3K inhibitor) and temsirolimus (an mTOR inhibitor) in various ES models. We tested the in vitro activity of LX-101 on the proliferation and viability of A-673, ES-8, and TC-71 cell lines. Once anti-proliferative activity was confirmed, we evaluated the sensitivity of all three ES cell lines to the combination of LX-101 with alpelisib and temsirolimus, estimating synergistic effects on the viability of the ES cultures. To consolidate that the cytotoxic effect on ES is mediated by on-target impact, we examined the changes in the expression and activation of IGF-1 downstream effectors by western blot, which were clearly reduced after LX-101 exposure in all three cell lines when compared with non-exposed cells, confirming that LX-101 inhibits the activation of IGF-1R, and indicating the suppression of the IGF-1 pathway. Finally, we tested the in vivo activity using three different PDX Ewing sarcoma models, with and without alpelisib or temsirolimus to assess synergistic preclinical efficacy. The pharmacodynamic effects were evaluated using a custom tissue microarray (TMA) analysis, using sequential multiplex immunofluorescence of 40 proteins related to the IGF/PI3K/mTOR signaling pathway.Our results indicate that LX-101 exhibits potent single-agent activity in the preclinical setting as an anti-cancer agent for ES, and even stronger activity when combined with agents that inhibit PI3K or mTOR. Collectively, the preclinical efficacy demonstrated provides a strong rationale for advancing LX-101 into clinical trials for ES. Citation Format: Roberto Cardenas-Zuniga, Jiaqian Fan, Asmaa G. Ahmed, Marcus Thurm, Kien Ryan Cao, Clement Agyemang, Danh Truong, Joseph A. Ludwig. In vivo preclinical efficacy of a novel “payload-bearing” peptide LX-101 targeting IGF-1R in Ewing sarcoma 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 7873.