HTR1D triggers osteosarcoma metastasis and doxorubicin resistance via c-MYC/MAPK feedback and CCL2/5-HT-mediated M2 polarization

Osteosarcoma (OS) treatment remains hindered by frequent metastasis and resistance to doxorubicin, the standard chemotherapeutic. Despite multimodal therapy, survival for advanced disease is dismal. Identifying molecular drivers that concurrently regulate invasion and chemoresistance is urgently required. Clinical samples were analyzed for HTR1D expression. In vitro migration and invasion assays and in vivo xenograft models were used to explore HTR1D function. Co-IP, GST pull-down, and point mutation assays verified HTR1D-GNAI1 interaction; luciferase assay and IF-FISH confirmed c-MYC-mediated HTR1D transcription. Knockdown and rescue assays of CCL2 and flow cytometry were performed to characterize CCL2/5-HT-dependent M2 macrophage polarization. Functional experiments validated the anti-tumor activity of Poliumoside. High HTR1D expression correlated with metastasis and poor chemotherapy outcome in OS patients. HTR1D knockdown suppressed OS cell metastasis in vitro and reversed DOX resistance and tumor metastasis in vivo. Mechanistically, HTR1D interacts with GNAI1 to activate MAPK signaling, and c-MYC transcriptionally upregulates HTR1D to form a positive feedback loop. Meanwhile, HTR1D induces CCL2 secretion to trigger M2 macrophage polarization, and M2-derived 5-HT sustains this chemoresistant loop; in vivo CCL2 depletion inhibits metastasis and improves DOX sensitivity. Poliumoside blocks HTR1D-GNAI1 binding to suppress OS metastasis and DOX resistance. HTR1D drives OS metastasis and DOX resistance through intracellular c-MYC/HTR1D/MAPK feedback and CCL2/5-HT-mediated M2 polarization. Poliumoside, by targeting this interaction, represents a promising dual-action therapeutic candidate capable of simultaneously overcoming metastatic progression and acquired drug resistance.