Table 2. Endonuclease inhibition (FRET), anti-viral effect (CPE), cytotoxic dose and thermo-stabilisation (Tm) of pH1N1 PA-Nter by diketo compounds and EGCG.

Compound	FRETa IC50 [µM]	antiviral activity IC50 [µM]b	CC50c [µM]	Tme [°C]
none	-	-	-	53.5
DPBA	2.7±0.3	inactive	>200d	65
R05-1	0.13±0.04	20.4±3.0	>100d	69
R05-2	0.06±0.02	15.9±4.0	>50d	71
R05-3	1.1±0.5	19.9±2.0	79.8±11.5	69
EGCG	1.9±0.4	1.1±0.4	54.7±4.5	ndf

^aFluorescence resonance energy transfer (FRET) based endonuclease activity assay. FRET measurements were determined in quadruplicates with at least two independent sets. Mean values and 95% confidence limits (as indicated) were calculated.

^bReduction of virus induced cytopathic effect (CPE); inactive: no antiviral activity at the highest concentration tested. For CPE IC50 and CC50 values samples were applied in duplicates and IC50 values, CC50 values, and corresponding 95% confidence intervals were determined. The experiments were independently performed at least twice.

^c48 h cytotoxicity on MDCK cells.

^dNo cytotoxicity at the highest concentration tested (mainly limited by solubility).

^eApparent melting temperature Tm derived from Thermofluor measurements.

^fNot determined due to fluorescence quenching.