Targeted intracellular protein degradation induced by a small molecule: En route to chemical proteomics

Abstract

We have developed a heterobifunctional all-small molecule PROTAC (PROteolysis TArgeting Chimera) capable of inducing proteasomal degradation of the androgen receptor. This cell-permeable PROTAC consists of a non-steroidal androgen receptor ligand (SARM) and the MDM2 ligand known as nutlin, connected by a PEG-based linker. The SARM-nutlin PROTAC recruits the androgen receptor to MDM2, which functions as an E3 ubiquitin ligase. This leads to the ubiquitination of the androgen receptor, and its subsequent degradation by the proteasome. Upon treatment of HeLa cells with 10 μM PROTAC for 7h, we were able to observe a decrease in androgen receptor levels. This degradation is proteasome dependent, as it is mitigated in cells pre-treated with 10 μM epoxomicin, a specific protease inhibitor. These results have implications for the potential study and treatment of various cancers with increased androgen receptor levels.

Identification and Characterization of a Peptidic Ligand for Ras

“…Building on these results, optimized Ras ligands could then provide access to a number of chemical tools and possible therapeutics, including utilizing the ligands in a PROTAC approach to recruit Ras for cellular degradation in disease states. [31][32][33] Taken together, our data show that peptide 7 is a novel Ras ligand that binds Ras with low micromolar dissociation constants, does not alter the biochemical activity of Ras, and can potentially serve in the development of future chemical tools targeting Ras.…”

BET Bromodomain as a Target of Epigenetic Therapy

“…For example, posttranslational degradation of target protein can be achieved through the recruitment of E3 ubiquitin ligases with PROTACs, which bear a peptide E3 ligase-recognition structure. [42][43][44][45][46] Another strategy is called SNIPER (specific and non-genetic inhibitor of apoptosis protein (IAP)-dependent protein eraser) [47][48][49][50][51] ; SNIPERs are bifunctional compounds in which a small IAP-recognition structure, such as MeBS or MV-1, is conjugated with a target protein-recognition structure [47][48][49][50][51] (Fig. 8).…”

Chemical Inducers of Targeted Protein Degradation

“…Cell-permeable PROTACs consisting of fumagillin, apigenin, and estrogen derivatives conjugated via a linker to the HIF1␣ peptide sequence, designed to target MetAP-2, the aryl hydrocarbon receptor, and the ER, respectively, have subsequently been reported by Kim and co-workers (24,25). To address the cell permeability issue associated with the high molecular weight of earlier PROTACs, our group reported the first all-small molecule PROTAC targeting the AR in HeLa cells (26). This PROTAC consisted of a selective androgen receptor modulator (SARM) ligand attached via a soluble polyethylene glycol linker to an imidazoline derivative known to bind the E3 ligase MDM2.…”