Furthering the design and the discovery of small molecule ATP-competitive mTOR inhibitors as an effective cancer treatment

Introduction: The mammalian target of rapamycin (mTOR) is a serine/ threonine kinase, which is the key component of two distinct signaling complexes in cells; these complexes are the mTOR complex 1 (mTORC1) and the mTOR complex 2 (mTORC2). Given the importance of these complexes in cellular growth, survival, motility, proliferation, protein synthesis and transcription, it is not surprising that they are impacted in multiple types of cancer. Studies on a number of ATP-competitive mTOR inhibitors have suggested that these inhibitors have a therapeutic superiority to rapalogs (rapamycin analogs) in a number of cancers. Areas covered: This review provides insight into the binding of mTOR inhibitors with the ATP-binding site, for the benefit of future mTOR inhibitor design and discovery. The authors, furthermore, deduce that a hypothetical binding mode is from docking studies, co-crystal structures and the structure-activity relationships (SARs). The authors also highlight the preclinical and clinical development of hit/lead compounds, and the selectivity for representative mTOR inhibitors. Expert opinion: The structural analysis of mTOR is hampered by its large size and complexity. Further exploration of mTOR inhibitors may therefore require the combination of structure-based drug design (SBDD, based on the mTOR homology models), fragment-based drug design (FBDD) and analog synthesis. Recent studies suggested that the global inhibition of PI3Ks may be harmful to organisms. Therefore, the future discovery of dual mTOR/PI3K inhibitors needs to ensure that inhibitors are both efficacious and have reduced adverse effects.