Table 3. Cytotoxic Activity of 1a–1c against Human Cancer Cells and Normal Cells (IC₅₀, μM) and Their Selective Indexes^a.

	IC50 (μM)
compounds	HL-60	A549	MRC-5	SIc
1a	5.82 ± 0.133	5.52 ± 0.280	21.8 ± 2.550	3.95
1b	3.07 ± 0.080	2.59 ± 0.056	3.36 ± 0.204	1.30
1c	3.56 ± 0.052	0.76 ± 0.065	4.41 ± 0.069	5.80
SN-38b	<0.05	0.038 ± 0.003	<0.1

^aThe concentration of the compound needed to reduce cell viability by 50% (IC₅₀) was determined using the WST-8 assay. IC₅₀ values are expressed as the mean ± SD of triplicate experiments.

^bSN-38 was used as a positive control.

^cThe SI is defined as the IC₅₀ value against normal MRC-5 cells divided by the IC₅₀ value against A549 cells.