Table 3.

Synergistic effect of 5,6-ECs associated with BTZ.

Cell	BTZ [nM]	5,6 α-EC [µg/mL]	5,6 β-EC [µg/mL]	CI (Mean ± SD)	Effect
U266	2	10	–	0.35 ± 0.087	Synergistic
	2	20	–	0.60 ± 0.024	Synergistic
	4	5	–	0.16 ± 0.037	Synergistic
	4	10	–	0.31 ± 0.039	Synergistic
	4	20	–	0.59 ± 0.014	Synergistic
	6	5	–	0.16 ± 0.019	Synergistic
	6	10	–	0.31 ± 0.015	Synergistic
	6	20	–	0.61 ± 0.012	Synergistic
	2	–	5	0.12 ± 0.02	Synergistic
	2	–	10	0.24 ± 0.02	Synergistic
	2	–	20	0.41 ± 0.02	Synergistic
	4	–	5	0.12 ± 0.01	Synergistic
	4	–	10	0.23 ± 0.01	Synergistic
	4	–	20	0.51 ± 0.01	Synergistic
	6	–	5	0.11 ± 0.02	Synergistic
	6	–	10	0.23 ± 0.03	Synergistic
	6	–	20	0.2 ± 0.21	Synergistic
JJN3	1.25	15	–	0.84 ± 0.05	Synergistic
	1.25	30	–	0.81 ± 0.02	Synergistic
	2.5	30	–	0.34 ± 0.01	Synergistic
	5	15	–	0.07 ± 0.04	Synergistic
	5	30	–	0.001 ± 0.01	Synergistic
	2	–	5	0.034 ± 0.05	Synergistic
	2	–	10	0.035 ± 0.01	Synergistic
	2	–	20	0.001 ± 0.02	Synergistic
	4	–	5	0.05 ± 0.01	Synergistic
	4	–	10	0.049 ±0.01	Synergistic
	4	–	20	0.001 ± 0.01	Synergistic
	6	–	5	0.05 ± 0.02	Synergistic
	6	–	10	0.50 ± 0.03	Synergistic
	6	–	20	${2.7}^{-13}$ ± 0.21	Synergistic

MM cell lines were seeded in 96-well plates at the density of 5 × 10⁴ cells per well, then treated with the vehicle or 5,6 α-EC (5–30 µg/mL), 5,6 β-EC (5–20 µg/mL), BTZ (1.25–6 nM) alone or with 5,6 α-EC /BTZ, 5,6 β-EC/BTZ combination. Viability was revealed with an MTT assay after 48 h. The results were analyzed by the CompuSyn software to evaluate the combination index. The Chou–Talalay index offers a quantitative definition for additive effects (CI = 1.0), synergism (CI < 1.0), and antagonism (CI > 1.0) for drugs combination.