Stepan Vyskocil

An inhibitor of NEDD8-activating enzyme as a new approach to treat cancer

The clinical development of an inhibitor of cellular proteasome function suggests that compounds targeting other components of the ubiquitin–proteasome system might prove useful for the treatment of human malignancies. NEDD8-activating enzyme (NAE) is an essential component of the NEDD8 conjugation pathway that controls the activity of the cullin-RING subtype of ubiquitin ligases, thereby regulating the turnover of a subset of proteins upstream of the proteasome. Substrates of cullin-RING ligases have important roles in cellular processes associated with cancer cell growth and survival pathways. Here we describe MLN4924, a potent and selective inhibitor of NAE. MLN4924 disrupts cullin-RING ligase-mediated protein turnover leading to apoptotic death in human tumour cells by a new mechanism of action, the deregulation of S-phase DNA synthesis. MLN4924 suppressed the growth of human tumour xenografts in mice at compound exposures that were well tolerated. Our data suggest that NAE inhibitors may hold promise for the treatment of cancer.

Substrate-assisted inhibition of ubiquitin-like protein-activating enzymes: the NEDD8 E1 inhibitor MLN4924 forms a NEDD8-AMP mimetic in situ.

The NEDD8-activating enzyme (NAE) initiates a protein homeostatic pathway essential for cancer cell growth and survival. MLN4924 is a selective inhibitor of NAE currently in clinical trials for the treatment of cancer. Here, we show that MLN4924 is a mechanism-based inhibitor of NAE and creates a covalent NEDD8-MLN4924 adduct catalyzed by the enzyme. The NEDD8-MLN4924 adduct resembles NEDD8 adenylate, the first intermediate in the NAE reaction cycle, but cannot be further utilized in subsequent intraenzyme reactions. The stability of the NEDD8-MLN4924 adduct within the NAE active site blocks enzyme activity, thereby accounting for the potent inhibition of the NEDD8 pathway by MLN4924. Importantly, we have determined that compounds resembling MLN4924 demonstrate the ability to form analogous adducts with other ubiquitin-like proteins (UBLs) catalyzed by their cognate-activating enzymes. These findings reveal insights into the mechanism of E1s and suggest a general strategy for selective inhibition of UBL conjugation pathways.

Design and Optimization of Potent and Orally Bioavailable Tetrahydronaphthalene Raf Inhibitors

Inhibition of mutant B-Raf signaling, through either direct inhibition of the enzyme or inhibition of MEK, the direct substrate of Raf, has been demonstrated preclinically to inhibit tumor growth. Very recently, treatment of B-Raf mutant melanoma patients with a selective B-Raf inhibitor has resulted in promising preliminary evidence of antitumor activity. This article describes the design and optimization of tetrahydronaphthalene-derived compounds as potent inhibitors of the Raf pathway in vitro and in vivo. These compounds possess good pharmacokinetic properties in rodents and inhibit B-Raf mutant tumor growth in mouse xenograft models.