A recent study released on Aug. 7 investigates the mechanisms behind resistance to mTOR inhibitors and evaluates the effectiveness of multidrug combinations in treating β-catenin-mutant hepatocellular carcinoma (HCC).
Researchers conducted experiments using MHCC97H and SNU449 cell lines, which were transfected with various expression plasmids, including 4EBP1WT, 4EBP1A4, or HSP90β. The cells were then treated with rapamycin to assess their sensitivity to ferroptosis and chemotherapy. Further analysis involved Western blotting, co-immunoprecipitation, and immunofluorescence techniques to explore the regulatory role of 4EBP1 in ferroptosis.
The study found that rapamycin more effectively inhibited mTOR/RPS6 than mTOR/4EBP1 and induced ferroptosis. The presence of 4EBP1A4 enhanced this effect by promoting ferroptosis and increasing rapamycin's efficacy. According to the findings, "Mechanistically, 4EBP1A4 competitively bound HSP90β, displacing Keap1, thereby increasing Keap1–Nrf2 complex formation and promoting Nrf2 degradation." The combination of mTOR inhibitors (rapamycin or MLN0128) with an ERK inhibitor (PD901) was tested both individually and together in cell models as well as mouse models generated through hydrodynamic tail vein injection.
Results indicated that all treatments reduced p-4EBP1 levels, induced ferroptosis, inhibited tumor cell proliferation, and suppressed tumor growth. However, "the combination [MLN0128 + PD901] exhibited the strongest effect." The authors state that activation of both mTORC1/mTORC2 and ERK signaling inhibits ferroptosis by increasing phosphorylation of 4EBP1—a process contributing to HCC progression in β-catenin-mutant tumors.
The research highlights a mechanism where "4EBP1 serves as a critical downstream effector common to both ERK and mTOR pathways," suggesting its importance for targeted therapies. Combination therapy not only suppresses compensatory activation within these pathways but also synergistically induces ferroptosis for improved therapeutic outcomes.
According to the authors, "This study provides novel insights for advancing therapeutic strategies and targeted drug development in HCC."
