Table 2.

Binding of [³H]paclitaxel or [³H]peloruside A, but not [³H](−)-rhazinilam or [³H]NSC 613241 to gMTs^a

Radiolabeled ligandb	Potential inhibitorc	Ligand bound/tubulin in gMTs ± SD
Paclitaxel		0.53 ± 0.094
Paclitaxel	Epothilone B	0.16 ± 0.043
Paclitaxel	Laulimalide	0.50 ± 0.018
Paclitaxel	(−)-Rhazinilam	0.62 ± 0.17
Paclitaxel	NSC 613241	0.59 ± 0.24
Peloruside A		0.67 ± 0.12
Peloruside A	Epothilone B	0.78 ± 0.033
Peloruside A	Laulimalide	0.088 ± 0.0023
Peloruside A	(−)-Rhazinilam	0.69 ± 0.039
Peloruside A	NSC 613241	0.63 ± 0.030
(−)-Rhazinilam		0.038 ± 0.0071
NSC 613241		0.035 ± 0.014

^aReaction mixtures (100 μL) contained 0.25 mg/mL gMTs (equivalent to 2.5 μM tubulin), 3.4 M glycerol, 6.0 mM MgCl₂, 1.0 mM GTP, 1.0 mM EGTA, 10 mM phosphate buffered saline (pH 6.8), 3% dimethyl sulfoxide, and radiolabeled ligand and inhibitor as indicated. Incubation was at room temperature (about 22 °C) for 10 min, and centrifugation was at 45,000 rpm for 10 min at 22 °C. Pellets were dissolved in 110 μL 8.0 M urea. Radiolabel and protein (Lowry assay) were each determined on 50 μL of the urea solution.

^bRadiolabeled ligands, all tritiated, were at 2.5 μM. ^cPotential inhibitors, all nonradiolabeled, were at 25 μM.