Identification of small-molecule inhibitors of human Golgi mannosidase via a drug repositioning screen.

Three Golgi mannosidases (GMs), namely Golgi a-mannosidases IA, IB, and IC, remove mannose residues from N-glycans and regulate the quality control and transportation of nascent proteins. GM inhibitors regulate several biological events such as cell-cell communication, differentiation, and apoptosis in cancer cells. As a result, GM inhibitor-based therapies have gained significant attention for cancer treatment. However, to date, no GM inhibitor has been approved and none is in clinical development for anti-cancer treatment. Meanwhile, drug repositioning plays an important role in identifying potential inhibitors that vary in molecular structure and properties to bypass much of the early cost and time. We performed a drug repositioning screen of a compound library that included approved drugs. The estrogen receptor antagonists tamoxifen and raloxifene inhibited human GMs at the cellular level. Sulindac, a nonsteroidal anti-inflammatory drug, also inhibited GMs. Our results demonstrated the efficacy of this screening strategy and revealed lead compounds for anti-cancer drug development.