The aromatase inhibitor letrozole and inhibitors of insulin-like growth factor I receptor synergistically induce apoptosis in in vitro models of estrogen-dependent breast cancer

Table 2 Summary of combination index values for AEW541 and letrozole

Cell line	Fa	Compound	IC₅₀ (nmol/l)	DRI	CI
MCF7/Aro	0.5	AEW541	33	5.9	0.888
		Letrozole	158	1.6
	0.75	AEW541	55	7.7	0.597
		Letrozole	265	2.4
	0.9	AEW541	92	10.0	0.406
		Letrozole	445	3.6
T47D/Aro	0.5	AEW541	268	7.9	0.513
		Letrozole	13	3.0
	0.75	AEW541	3326	10.0^a	0.284
		Letrozole	166	4.4

Combination index (CI) values above 1.1 indicate antagonistic, 0.9 to 1.1 additive, 0.7 to 0.9 moderately synergistic, 0.3 to 0.7 synergistic, and under <0.3 strongly synergistic. Note that the effective dose at 50%, 75% and 90% inhibition is decreased when both agents are combined. ^aDRI is greater than 10 (outside of concentration range). DRI, dose response index; Fa, fraction affected; IC50, 50% inhibitory concentration.

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