Targeting mTOR for fighting diseases: A revisited review of mTOR inhibitors.

mTOR (mammalian target of rapamycin), which is a serine/threonine kinase, has been well-established as being closely correlated with the occurrence of various human diseases, such as tumors and neurodegenerative diseases. Inhibition of the mTOR signaling pathways may effectively block the abnormal signal transduction of various growth factors and thereby block the occurrence and development of diseases. Of note, first-generation mTOR inhibitors are mainly reported to be rapamycin and its derivatives and second-generation mTOR inhibitors that consist of several ATP-competitive kinase inhibitors. Interestingly, the third-generation mTOR inhibitor, RapaLink-1, mediates rapamycin and mTOR kinase inhibitors via the same molecule and shows much higher efficiency. In addition, there are many mTOR inhibitors that have potential therapeutic effects for tumors and other types of diseases. Thus, we focus on summarizing the basic structures of mTOR and its complexes, some key upstream and downstream signaling pathways, and the structures and characteristics of the three generations of mTOR inhibitors in disease. Together, these findings may provide a better understanding of mTOR-regulated mechanisms and their inhibitors for fighting human diseases in the near future.