Momordicine I induces ER stress and inhibits OSCC by targeting ribosomal proteins

Oral squamous cell carcinoma (OSCC) is one of the most common malignant tumors worldwide. This necessitates the development of innovative drugs with high efficiency, low toxicity, and good tolerance. Bitter melon extract has been reported to have potent anticancer activity against OSCC. We evaluated the effects of nine triterpenoids from bitter melon extract on OSCC using cell counting kit-8 (CCK-8) proliferation and Transwell migration assays. Among the nine triterpenoids, momordicine I (MI) exhibited the strongest anticancer activity against OSCC. Animal experiments also showed that MI inhibited OSCC cell growth in vivo. Additionally, MI decreased the mitochondrial membrane potential and promoted apoptosis in OSCC. RNA-sequencing (RNA-seq) analysis revealed that MI induced an unfolded protein response (UPR) and endoplasmic reticulum (ER) stress, which was confirmed by western blotting and reverse transcription-quantitative polymerase chain reaction (RT-qPCR). Cellular thermal shift assay (CETSA) and mass spectrometry (MS) analysis, combined with molecular docking, identified ribosomal proteins (ribosomal protein L7 (RPL7), RPL11, RPL12, RPL18, RPL30, RPL38, RPS13, and RPS25) as MI targets. By targeting ribosomal proteins, MI likely disrupts ribosome-mediated protein folding, leading to the UPR and ER stress. In summary, MI targets ribosomal proteins to induce ER stress and inhibit OSCC, highlighting its therapeutic potential.