Nordic Soc Paediat Haematology On; Nersting, Jacob; Nielsen, Stine Nygaard; Grell, Kathrine; Paerregaard, Maria; Abrahamsson, Jonas; Lund, Bendik; Jonsson, Olafur Gisli; Pruunsild, Kaie; Vaitkeviciene, Goda; Kanerva, Jukka; Schmiegelow, Kjeld
(2019)
PurposeMethotrexate polyglutamates (MTXpg) facilitate incorporation of thioguanine nucleotides into DNA (DNA-TG, the primary cytotoxic thiopurine metabolite and outcome determinant in MTX/6-mercaptopurine treatment of childhood ALL). We hypothesized that mapping erythrocyte levels of MTXpg with 1-6 glutamates and their associations with DNA-TG formation would facilitate future guidelines for maintenance therapy dosing.Methods and resultsSummed MTX with 1-6 glutamates resolved by LCMS [median (interquartile): 5.47 (3.58-7.69) nmol/mmol hemoglobin] was in agreement with total MTX by radio ligand assay. In 16,389 blood samples from 1426 ALL maintenance therapy patients, MTXpg3 21.0 (15.2-27.4)% was the predominant metabolite, and MTXpg1 (the maternal drug) constituted 38.6 (27.2-50.2)% of MTXpg1-6. All subsets correlated; the strongest associations were between metabolites with similar polyglutamate lengths. Correlations of MTXpg1 with MTXpg2 and MTXpg3,4,5,6 were r(s)=0.68 and r(s)=0.25-0.42, respectively. Intercorrelations of MTXpg3,4,5,6 were all r(s)0.51. MTXpg4 accounted for 29.8 (24.7-33.3)% of MTXpg3-6, yet explained 96% of the summed MTXpg3-6 variation. MTXpg1-4, MTXpg1-6, MTXpg2-6 and MTXpg3 were all associated with DNA-TG levels (p