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Table 3 Correlation of the TSIA assay (continuous and short exposure) with accumulation of MTX polyglutamates and TS mRNA expression

From: Methotrexate resistance in relation to treatment outcome in childhood acute lymphoblastic leukemia

  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
  1. 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-Glu1–6 and MTX-Glu4–6) is expressed as pmol MTX-Glun/109 cells; TS mRNA level is expressed as ratio normalized to β-actin. The asterisk denotes significant (P < 0.05) associations