HA15 and 4μ8C combination as a novel therapeutic strategy in chondrosarcoma patient-derived xenograft models : exploiting grade-dependent ER stress vulnerabilities

Abstract

Background: Chondrosarcoma, the second most common primary bone cancer, remains challenging to treat due to its resistance to conventional chemotherapy and radiotherapy. This study investigates the role of endoplasmic reticulum (ER) stress in chondrosarcoma progression and explores novel therapeutic strategies targeting ER stress pathways. Methods: ER stress profiles in low-grade (LCHS) and high-grade chondrosarcoma (HCHS) were analyzed using single-cell RNA sequencing, Western blotting, and immunohistochemistry. The effects of the ER stress inducer HA15 and inhibitors ISRIB and 4μ8C were evaluated in vitro and in patient-derived xenograft (PDX) models. Cell viability, apoptosis, migration, and invasion assays were performed, along with gene expression analysis and protein quantification. Results: LCHS exhibited higher baseline ER stress levels compared to HCHS. HA15 induced apoptosis in LCHS through the PERK/eIF2α/ATF4/ATF5/DDIT3 pathway, while promoting survival and proliferation in HCHS via the IRE1α/XBP1s pathway. Knockdown experiments revealed crucial roles for both ATF5 and DDIT3 in mediating HA15-induced apoptosis. Combination treatment with HA15 and the IRE1α inhibitor 4μ8C synergistically induced apoptosis in HCHS by redirecting ER stress signaling from the IRE1α/XBP1s survival pathway to the IRE1α/JNK pro-apoptotic pathway. In PDX models, this combination significantly reduced tumour growth and improved survival in HCHS. Conclusions: Grade-dependent differences in ER stress profiles and responses to ER stress modulation in chondrosarcoma were demonstrated. The synergistic effect of combining HA15 and 4μ8C was shown to present a promising therapeutic strategy, particularly for high-grade chondrosarcomas. This study provides new insights into chondrosarcoma biology and identifies novel targets for therapeutic intervention.