The Bi-steric Inhibitor RMC-5552 Reduces mTORC1 Signaling and Growth in Lymphangioleiomyomatosis.

Mutations in the TSC (tuberous sclerosis complex) genes result in the hyperactivation of the mTORC1 (mechanistic/mammalian target of rapamycin 1) growth pathway in mesenchymal pulmonary cells. Rapamycin (sirolimus), a naturally occurring macrolide, is the only therapeutic approved for women with lymphangioleiomyomatosis (LAM), a progressive, destructive lung disease caused by TSC gene mutations and mTORC1 hyperactivation. However, on cessation of the drug, lung function decline continues. We demonstrated here that pulmonary LAM cancer stem-like state (SLS) cells most highly expressed the eIF4E (eukaryotic translation initiation factor 4E)-dependent translation initiation genes. We also showed that the 4E-BP1 (eukaryotic initiation factor 4E-binding protein 1) gene has the lowest expression in these cells, indicating that the 4E-BP1/eIF4E ratio in LAM SLS cells favors unrestrained eIF4E oncogenic mRNA translation. The bi-steric mTORC1-selective compound RMC-5552 prevented growth of LAM-associated fibroblasts and phosphorylation of proteins in the ribosomal protein S6K1/ribosomal protein S6 (S6K1/S6) and 4E-BP1/eIF4E translation mTORC1-driven pathways, whereas rapamycin only blocked the S6K/S6 axis. Rapamycin inhibition of LAM-associated fibroblast growth was rapidly reversed, but RMC-5552 inhibition was more durable. RMC-5552, through its potential to eradicate LAM cancer SLS cells, may have therapeutic benefit in LAM and other diseases with mTORC1 hyperactivity.