Life science
Medical & healthcare, Drug development

Discovery of protein degraders targetinga multi-functional protein
Department of Complex Molecular Chemistry, SANKEN (The Institute of Scientific and Industrial Research)
Associate Professor Yukihiro Itohhttps://researchmap.jp/itohy?lang=en

Life science

Abstract
Proteolysis targeting chimeras (PROTACs), which induce selective
degradation of their target protein in cells or in vivo, are of interest as
novel drug modalities. Unlike conventional enzyme inhibitors and receptor antagonists that inhibit a specific protein function, PROTACs
reduce the protein through degradation, inhibiting all of its functions.
This characteristic of PROTACs inspired us to apply this techniqueto multi-functional enzymes that possess both catalytic and scaffolding functions. So far, we have identified several PROTACs, including
one for protein lysine deacetylase HDAC8, and demonstrated its
advantages over conventional enzyme inhibitors.

▍ Background & Results
HDAC8 catalyzes protein deacetylation such as acetylated
SMC3. Additionally, HDAC8 serves a scaffolding function, interacting with some transcriptional factors such as STAT3 and CREB.
Furthermore, dysregulation and overexpression of HDAC8 are associated with the growth of T-cell leukemia. In other words, HDAC8PROTACs are of interest as therapeutic agents for T-cell leukemia
because they can inhibit both catalytic and scaffolding functions ofHDAC8. Therefore, we endeavored to identify HDAC8 PROTACs.
PROTACs are designed by linking a binder of a target protein toa binder of ubiquitin ligase (E3) and induce degradation of the protein via the ubiquitin-proteasome system. Thus, we designed andsynthesized HDAC8 PROTAC candidates based on compound 1,which binds to HDAC8 to inhibit its catalytic function, and thalidomide derivative 2, which is one of the E3 binders.
We evaluated the HDAC8 degradation activity of the candidates
in T-cell leukemia Jurkat cells. As a result, we found that compound 3 reduced the level of HDAC8 in does- and time-dependent
manner. We also confirmed that a proteasome inhibitor disrupted the reducing activity of 3, which indicated that 3 induced thedegradation of HDAC8 dependently on the ubiquitin-proteasome
system. Additionally, we found that 3 inhibited the growth of Jurkat
cells more strongly than conventional HDAC8 inhibitor 1, which
only inhibits the catalytic function (1: GI50 = 7.1 μM, 3: GI50 = 0.78μM). These results suggest that the inhibition of both catalytic andscaffolding functions by the HDAC8 PROTAC is more effective forthe treatment of T-cell leukemia than only catalytic inhibition by theconventional inhibitor.

▍ Significance of the research and Future perspective
PROTACs are adaptable to various proteins and have garneredsignificant attention as molecules that expand the druggability ofproteins. In fact, several PROTACs targeting disease-related proteins have been reported and studies on their application havebeen conducted for drug development. Currently, more than ten
PROTACs are in clinical stages as potential therapeutic agents fordiseases such as cancer. Some of them may receive pharmaceutical approval.

P a t e n t Japanese Patent Application No.2023-143583
Chotitumnavee, Jiranan; Itoh, Yukihiro; Suzuki, Takayoshi et al. Selective degradation of histone deacetylase 8 mediated by a proteolysis targeting chimera(PROTAC). Chem. Commun. 2022, 58, 4635-4638. doi: 10.1039/d2cc00272h
Tr e a t i s e
Tetsuya, Iida; Itoh, Yukihiro; Suzuki, Takayoshi et al. Design, synthesis, and biological evaluation of lysine demethylase 5 C degraders. ChemMedChem
2021, 16, 1609-1618. doi: 10.1002/cmdc.202000933
URLK e y w o r d target protein degradation, PROTAC, HDAC8, enzyme