Table III.

Cytotoxicity induced by CPA or IFA alone or in combination with 2-ME.

O2 (%)	2-ME	CPA	CPA+2-ME	R index	Effect
16.2	94.35±7.3	56.8±1.7a	54.2±3.3	0.99±0.06	No effect
1	95.6±7.0	54.3±1.9a	27.3±2.1b	1.92±0.13c	Additivity
0.1	93.2±3.0	55.5±1.5a	30.2±2.1b	1.74±0.11c	Additivity
	2-ME	IFA	IFA+2-ME	R index	Effect
16.2	93.9±1.0	53.7±2.2a	48.6±2.0	1.04±0.02	No effect
1	94.4±1.2	49.7±2.5a	23.6±2.3b	2.03±0.12c	Synergy
0.1	95.4±1.6	48.8±2.9a	26.5±1.9b	1.77±0.10c	Additivity

Cells were incubated for 24 h under normoxia (16.2% O₂) or hypoxia (1 or 0.1% O₂) with CPA or IFA in the absence and the presence of 2-ME (5 µM) and cell viability was determined with the MTT assay. Values are expressed as the percentage of the control cell viability (no drugs added) and are means ± SEM from five independent experiments.

^aP<0.001 vs. 2-ME

^bP<0.01 vs. CPA or IFA alone

^cP<0.01 vs. the R index of cells incubated under normoxia; one-way ANOVA and Tukey's test. The R index was calculated as described in Materials and methods. 2-ME, 2-methoxyestradiol; CPA, cyclophosphamide; IFA, ifosfamide.