Table 1.

In vitro activity profile of compounds binding at the allosteric binding site

Cmpd	Structure	Kd ITC (μM)	FL IC50 (μM)	LE	PD IC50 (μM)	EC50 (μM)	CC50 (μM)
1		ND	> 5000	< 0.30	Inactive	ND	ND
2		ND	55% I ± 3 @ 500 μM	0.30	Inactive	ND	ND
3		29	20 ± 4	0.38	54 ± 4% I @ 1000 μM	Inactive	40
4		ND	1.3 ± 0.1	0.42	Inactive	Inactive	11
5		0.062	0.10 ± 0.03	0.38	Inactive	0.4±0.2	>10
6		0.022	68% I ± 6 @ 0.01	~ 0.39	Inactive	0.0083± 0.001	4.5
7		24	59% I ± 5 @ 300	< 0.25	ND	Inactive	>30

K_d refers to the binding affinity of the ligand to the full length protein measured by isothermal titration calorimetry (ITC); IC₅₀’s reflect the inhibition of protease activity of the full length (FL) and protease domain (PD) proteins respectively. Assay conditions for FL and PD are optimised for maximum signal and differ from each other (see methods for details). LE (ligand efficiency) is defined as the binding affinity in kcal per heavy atom, in this instance the IC₅₀ value from the full length protease assay have been used rather than the K_d to allow comparison of all of the compounds. EC₅₀ is the cell based replicon activity of the compounds and CC₅₀ reflects the cytotoxicity index. Compounds were assayed independently 3 or more times, and the reported value is either the geometric or arithmetic mean ± the standard deviation (SD). All ITC data is n = 1.