Structural mechanisms of the mTOR pathway

Design, Synthesis, Formulation, and Bioevaluation of Trisubstituted Triazines as Highly Selective mTOR Inhibitors for the Treatment of Human Breast Cancer

The aberrant activation of the PI3K/mTOR signaling pathway is implicated in various human cancers. Thus, the development of inhibitors targeting mTOR has attracted considerable attention. In this study, we used a structure-based drug design strategy to discover a highly potent and kinase-selective mTOR inhibitor 24 (PT-88), which demonstrated an mTOR inhibitory IC50 value of 1.2 nM without obvious inhibition against another 195 kinases from the kinase profiling screening. PT-88 displayed selective inhibition against MCF-7 cells (IC50: 0.74 μM) with high biosafety against normal cells, in which autophagy induced by mTOR inhibition was implicated. After successful encapsulation in a lipodisc formulation, PT-88 demonstrated favorable pharmacokinetic and biosafety profiles and exerted a large antitumor effect in an MCF-7 subcutaneous bearing nude mice model. Our study shows the discovery of a highly selective mTOR inhibitor using a structure-based drug discovery strategy and provides a promising antitumor candidate for future study and development.

OTUB1-mediated inhibition of ubiquitination: a growing list of effectors, multiplex mechanisms, and versatile functions

Protein ubiquitination plays a pivotal role in protein homeostasis. Ubiquitination may regulate the stability, activity, protein-protein interaction, and localization of a protein. Ubiquitination is subject to regulation by two groups of counteracting enzymes, the E3 ubiquitin ligases and deubiquitinases. Consistently, deubiquitinases are involved in essentially all biological processes. OTUB1, an OTU-family deubiquitinase, is a critical regulator of development, cancer, DNA damage response, and immune response. OTUB1 antagonizes the ubiquitination of a wide-spectrum of proteins through at least two different mechanisms. Besides direct deubiquitination, OTUB1 can also inhibit ubiquitination by non-canonically blocking ubiquitin transfer from certain ubiquitin-conjugases (E2). In this review, we start with a general background of protein ubiquitination and deubiquitination. Next, we introduce the basic characteristics of OTUB1 and then elaborate on the updated biological functions of OTUB1. Afterwards, we discuss potential mechanisms underlying the versatility and specificity of OTUB1 functions. In the end, we discuss the perspective that OTUB1 can be a potential therapeutic target for cancer.