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. 2020 Feb 25;13(3):34.
doi: 10.3390/ph13030034.

Targeted Protein Degradation by Chimeric Compounds Using Hydrophobic E3 Ligands and Adamantane Moiety

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Free PMC article

Targeted Protein Degradation by Chimeric Compounds Using Hydrophobic E3 Ligands and Adamantane Moiety

Takuji Shoda et al. Pharmaceuticals (Basel). .
Free PMC article

Abstract

Targeted protein degradation using small chimeric molecules, such as proteolysis-targeting chimeras (PROTACs) and specific and nongenetic inhibitors of apoptosis protein [IAP]-dependent protein erasers (SNIPERs), is a promising technology in drug discovery. We recently developed a novel class of chimeric compounds that recruit the aryl hydrocarbon receptor (AhR) E3 ligase complex and induce the AhR-dependent degradation of target proteins. However, these chimeras contain a hydrophobic AhR E3 ligand, and thus, degrade target proteins even in cells that do not express AhR. In this study, we synthesized new compounds in which the AhR ligands were replaced with a hydrophobic adamantane moiety to investigate the mechanisms of AhR-independent degradation. Our results showed that the compounds, 2, 3, and 16 induced significant degradation of some target proteins in cells that do not express AhR, similar to the chimeras containing AhR ligands. However, in cells expressing AhR, 2, 3, and 16 did not induce the degradation of other target proteins, in contrast with their response to chimeras containing AhR ligands. Overall, it was suggested that target proteins susceptible to the hydrophobic tagging system are degraded by chimeras containing hydrophobic AhR ligands even without AhR.

Keywords: adamantane; chimeric compound; hydrophobic tagging; protein degradation.

Conflict of interest statement

M.N. received a research fund from Daiichi Sankyo Pharmaceutical Co., Ltd. All other authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Chemical structure of β-NF-ATRA (1).
Figure 2
Figure 2
Chemical structures of designed compounds.
Scheme 1
Scheme 1
(a) 12, EDC-HCl, DMAP, CH2Cl2; (b) H2 gas, 10% Pd/C, EtOAc; (c) 13, EDC-HCl, DMAP, CH2Cl2; (d) TBAF, THF.
Scheme 2
Scheme 2
(a) 14, EDC-HCl, HOBt, CH2Cl2; (b) 4M HCl/1,4-dioxane; (c) 13, HATU, DIPEA, DMF; (d) TBAF, THF.
Scheme 3
Scheme 3
(a) 13, HATU, DIPEA, DMF; (b) TBAF, THF.
Figure 3
Figure 3
HyT compounds induce the degradation of CRABP-2 but not of CRABP-1. (AC) Protein knockdown activities of HyT 2, 3, and 4 or β-NF-ATRA 1 in MCF-7 (A), SH-SY5Y (B), or IMR-32 cells (C). Cells were treated with the indicated compounds for 24 h. Whole-cell lysates were analyzed by western blotting. The numbers below the CRABP-1 and CRABP-2 panels represent CRABP-1/actin and CRABP-2/actin ratios, respectively, normalized by designating the expression from the vehicle control condition as 100%.
Figure 4
Figure 4
Proteasomal inhibitor MG132 inhibits the reduction of CRABP-2 by HyT compounds. MCF-7 cells were incubated with the indicated concentrations of HyT compounds in the presence or absence of 10 µM MG132 for 18 h. Whole-cell lysates were analyzed by western blotting.
Scheme 4
Scheme 4
(a) HBTU, DIPEA, and DMF.
Figure 5
Figure 5
Ad-JQ1 (16) induces the degradation of BRD3 but not of BRD2 or BRD4. Protein knockdown activities of Ad-JQ1 in MCF-7 cells. Cells were treated with the indicated concentration of Ad-JQ1 for 48 h. Whole-cell lysates were analyzed by western blotting.

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