Pharmacologic inhibition of eIF4A blocks NRF2 synthesis to prevent osteosarcoma metastasis.

ABSTRACT

PURPOSE: Effective therapies for metastatic osteosarcoma (OS) remain a critical unmet need. Targeting mRNA translation in metastatic OS offers a promising option, as selective translation drives synthesis of cytoprotective proteins under harsh microenvironmental conditions to facilitate metastatic competence. EXPERIMENTAL DESIGN: We assessed expression levels of eukaryotic translation factors in OS, revealing high expression of the eIF4A1 initiation factor. Using a panel of metastatic OS cell lines and PDX models, eIF4A1 inhibitors were evaluated for their ability to block proliferation and reduce survival under oxidative stress, mimicking harsh conditions of the lung microenvironment. Inhibitors were also evaluated for their anti-metastatic activity using the ex vivo pulmonary metastasis assay (PuMA) and in vivo metastasis models. Proteomics were performed to catalog which cytoprotective proteins or pathways were affected by eIF4A1 inhibition. RESULTS: CR-1-31B, a rocaglate-based eIF4A1 inhibitor, exhibited nanomolar cytotoxicity against all metastatic OS models tested. CR-1-31B exacerbated oxidative stress and apoptosis when OS cells were co-treated with a tert-butylhydroquinone (tBHQ), a chemical oxidative stress inducer. CR-1-31B potently inhibited OS growth in the PuMA model and in experimental and spontaneous models of OS lung metastasis. Proteomic analysis revealed that tBHQ-mediated upregulation of the NRF2 antioxidant factor was blocked by co-treatment with CR-1-31B. Genetic inactivation of NRF2 phenocopied the anti-metastatic activity of CR-1-31B. Finally, the clinical grade eIF4A1 phase 1-2 inhibitor, Zotatifin, similarly blocked NRF2 synthesis and the OS metastatic phenotype. CONCLUSIONS: Collectively, our data reveal that pharmacologic targeting of eIF4A1 is highly effective in blocking OS metastasis by blunting the NRF2 antioxidant response.