In a recent paper published online in Cell Discovery, JI Guangju's group from Institute of Biophysics of Chinese Academy of Sciences, cooperating with researchers from Tsinghua University and Peking University, achieved a rapid and reversible knockdown of FKBP12 protein in animals by chemical design of protein-degrading molecules (PROTACs), and realized rapid knockdown of protein in rhesus monkeys for the first time.

Traditionally, Loss of gene function studies have mainly been achieved through genetic modifications. The approaches have failed in a certain degree to achieve acute and reversible changes of gene function. The complications of potential genetic compensation and/or spontaneous mutations arising in gene-knockout models may lead to misinterpretations.

Proteolysis-targeting chimeras (PROTACs) contain a specific ligand for a target protein of interest that is connected to a ligand for an E3 ubiquitin ligase via a linker. Through binding the Ca²+-release channel (ryanodine receptor), FKBP12 regulates Ca²⁺ signaling to carry out important functions, particularly in the heart. The global knockdown of FKBP12 via prevalent approaches is embryonic-lethal due to severe developmental heart defects such as ventricular septal defects.

In this study, researchers developed a chemical approach for the global knockdown of targeted proteins using PROTACs. It is a novel, fast, and effective method for generating protein depletion animal models such as mice, rats, pigs, and rhesus monkeys.

The strategy can also achieve conditional protein knockdown in the brain via i.c.v. administration.

When the PROTAC probe is administered orally, this approach is very effective. After withdrawal of the PROTAC, the FKBP12 protein level recovers in a certain period of time.

The models are suitable for self-controlled biomedical studies. Mice and rhesus monkeys with FKBP12 knockdown via the chemical strategy exhibited Ca²⁺-leakage and increased Ca²⁺ sparks in cardiomyocytes, and cardiac dysfunctions. Thus, these models may be developed for cardiac drug screening.

Additionally, this strategy can be applied to other targets such as BTK.

It may be a challenge to develop PROTAC for those targeted proteins without well-documented specific binders. Thus, PROTACs hold the promise to be employed as a complementary approach for currently available tools in a quick, controllable and reversible way for both in vitro and in vivo studies.

"This strategy not only provides a powerful tool for protein function studies in vivo, but also highlights the potential of using PROTAC in future human cancer therapies,” said WEI Wenyi from Harvard Medical School.

Although FDA has approved the first oral PROTAC (arv-110) into a phase I clinical study at present, the PROTAC system research and animal level of preclinical research, especially large animals is lacking. Therefore, this study realized the systematic exploration of PROTAC technology from mice, pigs to rhesus monkeys, filled in the blank of PROTAC technology preclinical research, and provided guidance for its application in clinical treatment of human diseases.