Table 3.

Correlation of the TSIA assay (continuous and short exposure) with accumulation of MTX polyglutamates and TS mRNA expression

	Precursor B cell ALL		T cell ALL		Total ALL
	TSIA cont.	TSIA short	TSIA cont.	TSIA short	TSIA cont.	TSIA short
MTX-Glu1–6
Correlation coefficient	−0.547*	−0.495*	−0.094	−0.128	−0.432*	−0.524*
P value	<0.001	<0.001	0.685	0.612	<0.001	<0.001
Number of patients	64	58	21	18	85	76
MTX-Glu4–6
Correlation coefficient	−0.494*	−0.503*	−0.258	0.046	−0.399*	−0.568*
P value	<0.001	<0.001	0.336	0.875	0.001	<0.001
Number of patients	54	50	16	14	70	64
TS mRNA
Correlation coefficient	0.591	0.678*	0.139	0.483	0.466*	0.693*
P value	0.056	0.045	0.701	0.187	0.033	0.001
Number of patients	11	9	10	9	21	18

P value was estimated using Spearman’s Rho test; TSIA continuous (TSIA cont.) and short-term exposure (TSIA short) are expressed as the concentration of MTX (in μM) necessary to inhibit 50 % of the TS activity (TSI₅₀) compared to the controls incubated without MTX (in triplicate); the concentration of MTX polyglutamates (MTX-Glu_1–6 and MTX-Glu_4–6) is expressed as pmol MTX-Glu_n/10⁹ cells; TS mRNA level is expressed as ratio normalized to β-actin. The asterisk denotes significant (P < 0.05) associations