Table 2. Cytotoxic activity of 1 and derivatives 4-19 in three different cell lines (MCF-7, DU145, STO).

Data are reported as IC₅₀ values (concentration of drug required to inhibit growth by 50%) determined by MTS assay after 72 h of continuous exposure to each compound; data represent mean values±SD of at least three independent experiments. n.a.: not assessed.

	IC50 (μM)
Compound	MCF-7	DU145	STO	STO-17AAG
1	58.9±7.4	63.2±2.0	57.0±2.1
4	57.6±3.9	66.3±6.6	59.7±1.5
5	60.0±4.3	61.5±3.4	59.5±5.1
6	82.3±6.2	64.8±2.8	68.4±6.2
7	70.3±9.5	68.2±8.2	60.6±8.4
8	n.a.	n.a.	n.a.
9	54.5±5.7	59.4±4.7	40.9±3.2
10	56.4±4.6	50.7±7.1	29.9±1.4
11	n.a.	n.a.	n.a.
12	77.2±0.4	60.9±5.8	74.9±1.8
13	41.4±4.2	55.3±1.6	43.6±4.5
14	61.8±5.4	58.8±4.9	50.0±1.3
15	62.0±6.3	63.3±5.3	60.4±.3.0
16	61.2±2.7	52.5±5.7	61.9±4.7
17	n.a.	n.a.	n.a.
18	56.6±3.9	17.3±2.6	8.9±1.1	7.1±1.6
19	51.3±4.0	12.7±2.5	9.1±1.1	7.5±1.2
17-AAG			0.08±0.01	2.6±0.1