Table 2.

Inhibition (IC₅₀ values or % of inhibition at 10 µM) of the chymotrypsin-like (ChT-L), trypsin-like (T-L) and peptidyl-glutamyl peptide-hydrolyzing (PGPH or caspase-like C-L) activities of human 20S proteasome by panel compounds. Inhibition includes standard deviation from three independent experiments, each performed in duplicate.

[IC50 Value (µM) or Inhibition (%) at 10 µM]
Compound	ChT-L	T-L	PGPH (C-L)
auranofin	n.i. a	n.i.	n.i.
Au(PEt3)Cl	2.6 ± 0.3 µM	1.25 ± 0.05 µM	>10 µM
Au(PEt3)Br	1.4 ± 0.8 µM	1.26 ± 0.12 µM	>10 µM
Au(PEt3)I	6.1 ± 0.4 µM	5.80 ± 0.30 µM	>10 µM
[Au(PEt3)2]Cl	21 ± 1.1 %	n.i.	n.i.
Ag(PEt3)Cl	28 ± 0.5 %	2.20 ± 1.30 µM	n.i.
Ag(PEt3)Br	22 ± 0.4 %	2.65 ± 0.15 µM	n.i.
Ag(PEt3)I	25 ± 0.2 %	2.27 ± 0.78 µM	n.i.
[Ag(PEt3)2]NO3	38 ± 5.0 %	n.i.	n.i.

[a] n.i. = no inhibition. IC₅₀ values for the reference compound bortezomib: ChT-L: 38 ± 5.9 nM (ref. [25] 7 nM); T-L: 2206 ± 246 nM (ref. [25] 4200 nM); PGPH (C-L): 84 nM (ref. [25] 74 nM). IC₅₀ values in ref. [25] were determined after 1 h; the IC₅₀ values for bortezomib in the present study were determined immediately after substrate addition, and are—due to the covalent, time-dependent inhibition by bortezomib—higher for the ChT-L and PGPH (C-L) activities, which are more susceptible to bortezomib.