Proteasome Inhibition as a Cancer Type-Specific Off-Target Effect of Everolimus in Cancer Cells.

Everolimus, an mTORC1 inhibitor, may also affect proteasome activity in a manner similar to bortezomib, necessitating further investigation. In this study, we employed ultrafast expression proteomics in combination with cell viability and proteasome activity assays to identify potential secondary targets of everolimus and to obtain a more comprehensive understanding of its mechanism of action across the proteomes of multiple cancer cell lines. The results were compared with those obtained for bortezomib and lonidamine, which were used as positive and negative controls for proteasome inhibition, respectively. Our findings reveal that everolimus inhibits 20S proteasome in lung (A549) and colon (HCT116) cancer cells, while having no detectable effect in breast cancer cells (MCF-7). An in silico model of everolimus interaction with 20S proteasome was built suggesting an allosteric mechanism of inhibition.