title: De novo purine synthesis inhibition and antileukemic effects of mercaptopurine alone or in combination with methotrexate in vivo.
abstract: Methotrexate (MTX) and mercaptopurine (MP) are widely used antileukemic agents that inhibit de novo purine synthesis (DNPS) as a mechanism of their antileukemic effects. To elucidate pharmacodynamic differences among children with acute lymphoblastic leukemia (ALL), DNPS was measured in leukemic blasts from newly diagnosed patients before and after therapy with these agents. Patients were randomized to receive low-dose MTX (LDMTX: 6 oral doses of 30 mg/m(2)) or high-dose MTX (HDMTX: intravenous 1 g/m(2)) followed by intravenous MP; or intravenous MP alone (1 g/m(2)), as initial therapy. At diagnosis, the rate of DNPS in bone marrow leukemia cells was 3-fold higher in patients with T-lineage ALL compared with those with B-lineage ALL (769 +/- 189 vs 250 +/- 38 fmol/nmol/h; P =.001). DNPS was not consistently inhibited following MP alone but was markedly inhibited following MTX plus MP (median decrease 3% vs 94%; P <.001). LDMTX plus MP and HDMTX plus MP produced greater antileukemic effects (percentage decrease in circulating leukocyte counts) compared with MP alone (-50% +/- 4%, -56% +/- 3%, and - 20% +/- 4%, respectively; P <.0001). Full DNPS inhibition was associated with greater antileukemic effects compared with partial or no inhibition (-63% +/- 4% vs -37% +/- 4%; P <.0001) in patients with nonhyperdiploid B-lineage and T-lineage ALL. HDMTX plus MP yielded 2-fold higher MTX polyglutamate concentrations than LDMTX plus MP (2148 +/- 298 vs 1075 +/- 114 pmol/10(9) cells; P <.01) and a higher percentage of patients with full DNPS inhibition (78% vs 53%; P <.001). Thus, the extent of DNPS inhibition was related to in vivo antileukemic effects, and a single dose of intravenous MP produced minimal DNPS inhibition and antileukemic effects, whereas MTX plus MP produced greater antileukemic effects and DNPS inhibition, with full inhibition more frequent after HDMTX.
authors.affiliation: Department of Pharmaceutical Sciences, St Jude Children's Research Hospital and University of Tennessee, Memphis, 38105, USA.
authors.forename: Thierry
authors.initials: T
authors.lastname: Dervieux
authors.forename: Timothy L
authors.initials: TL
authors.lastname: Brenner
authors.forename: Yuen Y
authors.initials: YY
authors.lastname: Hon
authors.forename: Yinmei
authors.initials: Y
authors.lastname: Zhou
authors.forename: Michael L
authors.initials: ML
authors.lastname: Hancock
authors.forename: John T
authors.initials: JT
authors.lastname: Sandlund
authors.forename: Gaston K
authors.initials: GK
authors.lastname: Rivera
authors.forename: Raul C
authors.initials: RC
authors.lastname: Ribeiro
authors.forename: James M
authors.initials: JM
authors.lastname: Boyett
authors.forename: Ching-Hon
authors.initials: CH
authors.lastname: Pui
authors.forename: Mary V
authors.initials: MV
authors.lastname: Relling
authors.forename: William E
authors.initials: WE
authors.lastname: Evans
mesh_terms: D000293:Adolescent; D000964:Antimetabolites, Antineoplastic / Q000008:administration & dosage / Q000627:therapeutic use*; D000971:Antineoplastic Combined Chemotherapy Protocols / Q000008:administration & dosage / Q000627:therapeutic use*; D001854:Bone Marrow Cells / Q000378:metabolism; D002051:Burkitt Lymphoma / Q000188:drug therapy / Q000378:metabolism / Q000473:pathology; D002648:Child; D002675:Child, Preschool; D005260:Female; D006801:Humans; D007223:Infant; D015459:Leukemia-Lymphoma, Adult T-Cell / Q000188:drug therapy / Q000378:metabolism / Q000473:pathology; D007958:Leukocyte Count; D008297:Male; D015122:Mercaptopurine / Q000008:administration & dosage / Q000627:therapeutic use*; D008727:Methotrexate / Q000008:administration & dosage / Q000627:therapeutic use*; D054198:Precursor Cell Lymphoblastic Leukemia-Lymphoma / Q000188:drug therapy* / Q000378:metabolism / Q000473:pathology; D011687:Purines / Q000037:antagonists & inhibitors* / Q000096:biosynthesis*
chemical_list: D000964:Antimetabolites, Antineoplastic; D011687:Purines; D015122:Mercaptopurine; D008727:Methotrexate