Table 2.

Comparison of in vitro growth inhibition potency of epothilone derivatives against various parent and drug-resistant tumor cell lines

Compound	DC-3F	DC-3F/ADX	P388/0	P388/Adr	SK-N-As	SK-N-FI	MCF-7	MCF-7/Adr
	IC50, μM*
1	0.0037	0.053	0.0018	0.0010	0.012	0.023	0.0030	0.0094
		(14.5×)		(5.3×)		(1.9×)		(3.1×)
2	0.0006	0.017	0.00029	0.0016	0.004	0.010	0.0005	0.0027
		(28×)		(5.5×)		(25×)		(5.4×)
3	0.011	0.042	0.0213	0.0125	0.073	0.223	0.032	0.144
		(3.9×)		(0.59×)		(3.1×)		(4.5×)
4	0.00097	0.00091	0.0068	0.0042	0.021	0.046	0.0029	0.0071
		(0.9×)		(0.62×)		(2.2×)		(2.4×)
Paclitaxel	0.095	32.0	0.0029	0.326	0.0016	0.130	0.0033	0.150
		(338×)		(111×)		(80×)		(46×)
Actinomycin D	0.00044	0.572	0.00015	0.0012	0.00085	0.0119	0.00068	0.00167
		(13,000×)		(8×)		(14×)		(2.5×)
Adriamycin	0.018	2.236	0.0055	2.65	0.077	1.42	0.057	0.216
		(124×)		(482×)		(18.4×)		(3.8×)

 Numbers in parentheses are folds of resistance based on the IC₅₀ ratio when compared with the corresponding parent cell lines except for P388/0 and P388/Adr, and XTT assay (21) was used. 

^*Cell growth inhibition was measured by protein-staining SRB assay (22) after 72-h incubation as described previously. The IC₅₀ values were determined with six to seven concentrations of each drug using a computer program. (23, 24).