Combined mTOR/MEK inhibition prevents proliferation and induces apoptosis in NF2-mutant tumors
Abstract
Objective
Merlin, a tumor suppressor protein encoded by the Neurofibromatosis type 2 (NF2) gene, plays a critical role in maintaining normal cellular homeostasis within the nervous system. Loss of function mutations in NF2 are associated with the development of multiple tumor types, including schwannomas and meningiomas. Bioinformatic analyses have indicated that NF2 mutations are correlated with poor clinical outcomes and increased activation of the PI3K/mTOR signaling pathway, suggesting dysregulated apoptotic mechanisms in NF2-mutant tumors. Based on these observations, we hypothesized that pharmacological inhibition of the PI3K/mTOR pathway could suppress tumor cell proliferation in NF2-mutant models by promoting apoptotic activity.
Materials and Methods
To investigate the therapeutic potential of PI3K/mTOR pathway inhibition, we utilized two representative NF2-mutant tumor cell lines: NCI-H2452 (mesothelioma) and HEI193 (schwannoma). Two targeted inhibitors were selected: Trametinib, a MEK inhibitor, and Vistusertib, a dual mTORC1/2 inhibitor. In vitro experiments included cell proliferation assays (CCK-8), apoptosis analysis via flow cytometry, and western blotting for pathway analysis. In vivo antitumor efficacy was evaluated using xenograft models, with tumor volume and weight as primary endpoints.
Results
The CCK-8 assays demonstrated that both Trametinib and Vistusertib significantly reduced the proliferation of NCI-H2452 cells, with the combination treatment producing the most pronounced inhibitory effect. Flow cytometric analysis revealed a marked increase in apoptotic cell populations upon treatment with either drug, with the combination therapy yielding the highest apoptotic index. Parallel findings were observed in HEI193 cells, confirming the generalizability of the effect across different NF2-mutant models. In vivo xenograft studies further substantiated these results, showing substantial reductions in both tumor volume and weight following treatment, with the combination regimen demonstrating the most potent tumor suppression. Western blot analyses indicated that both Trametinib and Vistusertib effectively inhibited components of the PI3K/mTOR/MEK signaling axis and led to increased expression of merlin, suggesting a potential restoration of tumor suppressive signaling.
Conclusion
Our findings provide strong evidence that inhibition of the PI3K/mTOR signaling pathway can suppress the growth of NF2-mutant tumor cells through the induction of apoptosis. The combined administration of Trametinib and Vistusertib yielded superior anti-proliferative and pro-apoptotic effects compared to either agent alone. These results highlight the potential of dual-targeted therapy as a promising strategy for treating tumors harboring NF2 mutations.