Table 2. Combination Index values (CI) of double combinations.

Double combination	Ratio	J89GFP				THP89GFP
		EC50	EC75	EC90	EC95	EC50	EC75	EC90	EC95
BRY:PNB	2.5:2	0.56 ± 0.11 (+++)	0.48 ± 0.1 (+++)	0.42 ± 0.09 (+++)	0.38 ± 0.09 (+++)	1.16 ± 0.24 (−)	0.65 ± 0.11 (+++)	0.44 ± 0.12 (+++)	0.35 ± 0.11 (+++)
	5:2	0.41 ± 0.3 (+++)	0.34 ± 0.21 (+++)	0.33 ± 0.19 (+++)	0.34 ± 0.2 (+++)	1.27 ± 0.29 (−)	0.69 ± 0.32 (+++)	0.39 ± 0.2 (+++)	0.29 ± 0.15 (++++)
PNB:RMD	2:1	1.11 ± 0.1 (−)	0.92 ± 0.08 (±)	0.76 ± 0.06 (++)	0.67 ± 0.05 (+++)	2.05 ± 0.58 (−)	2.3 ± 0.37 (−)	2.71 ± 0.45 (−)	3.09 ± 0.79 (−)
BRY:RMD	2.5:1	0.47 ± 0.04 (+++)	0.26 ± 0.07 (++++)	0.16 ± 0.07 (++++)	0.11 ± 0.06 (++++)	0.88 ± 0.2 (+)	0.73 ± 0.29 (++)	0.64 ± 0.3 (+++)	0.63 ± 0.26 (+++)
	5:2	0.46 ± 0.04 (+++)	0.38 ± 0.05 (+++)	0.32 ± 0.05 (+++)	0.28 ± 0.05 (++++)	1.34 ± 0.42 (−)	0.87 ± 0.28 (+)	0.58 ± 0.18 (+++)	0.46 ± 0.15 (+++)

CI calculated at the EC₅₀, EC₇₅, and EC₉₀. CI < 0.9 indicates synergism; 0.9 < CI < 1.1 indicates additive effects, and CI > 1.1 indicates antagonism (−). Synergy level: ± indicates additive effects; 0.85 < CI < 0.9 + (slight synergism); 0.7 < CI < 0.85 ++ (moderate synergism); 0.3 < CI < 0.7 +++ (synergism); CI < 0.1 < 0.3 ++++ (potent synergism). Compound range concentration: BRY (12.5–50 nM), PNB (5–40 nM) and RMD (2.5–20 nM). Each experiment was performed in duplicate. Data are represented as the mean ± SD of at least three independent experiments. Abbreviations: CI, combination index; EC₅₀, 50% effective concentration; EC₇₅, 75% effective concentration; EC₉₀, 90% effective concentration; EC₉₅, 95% effective concentration; SD, standard deviation; BRY, bryostatin-1; PNB, panobinostat; RMD, romidepsin.