GSE138417
Selective Inhibitors of mTORC1 Activate 4EBP1 and Suppress Tumor Growth
The clinical benefit of current mTOR inhibitors is limited, perhaps reflecting their intrinsic pharmacological profiles. Rapamycin analogs selectively inhibit mTORC1, but fail to suppress phosphorylation of the mTORC1 substrate 4EBP1, a translational repressor that is a key driver of oncogenic mTORC1 signaling. mTOR kinase active-site inhibitors fully suppress mTORC1 and phosphorylation of its substrates, but are active against mTORC2 and additional kinases, potentially contributing to tolerability limitations. The prototype bi-steric inhibitor RapaLink-1 exploits the selective mTORC1 interactions of rapamycin and the broad mTOR kinase inhibitory effects of an active-site inhibitor, through covalent linkage of the two pharmacophores to achieve complete mTORC1/2 inhibition. We demonstrate that the anti-proliferative activity of RapaLink-1 is dependent upon mTORC1 and suppression of 4EBP1 phosphorylation. Using a rational design strategy, we tuned the affinities of the rapamycin core and ATP-mimetic moieties to create novel bi-steric inhibitors with enhanced mTORC1 selectivity and potency against 4EBP1 phosphorylation. mTORC1-selective bi-steric compounds produced durable inhibition of 4EBP1 phosphorylation in vitro and in vivo, and drove tumor regressions at well-tolerated doses in xenograft models of breast cancer. Overall design: 4 biological replicates of MCF7 cells under one of the following conditions: Starvation, Full serum + DMSO, Full serum + MLN0128, Full serum + RMC-4627, Full serum + RMC-4745. RMC-4627 and RMC-4745 are selective inhibitors of mTORC1 developed within this study. For one of the biological replicate (replicate 1), we provided 2 technical replicates (1A and 1B)