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Molecular Pharmacology, Volume 52, Issue 5, 903-911
, MTAP
Malignant Cells: Restoration of Methylthioadenosine
Phosphorylase-Dependent Salvage Pathways and Alterations of Sensitivity
to Inhibitors of Purine de novo Synthesis
Cancer Center, University of Massachusetts Medical Center, Worcester, Massachusetts 01655 (Z.-H.C., T.M.S.), and Section of Hematology/Oncology, Department of Medicine, University of Chicago, Chicago, Illinois 60637 (O.I.O.)
5
-Deoxy-5
-methylthioadenosine phosphorylase (MTAP) is involved in the
salvage of adenine and methylthio moieties of
5
-deoxy-5
-methylthioadenosine, a byproduct of polyamine synthesis, to
adenine nucleotides and methionine, respectively. The gene encoding
MTAP, MTAP, is frequently codeleted along with the tumor
suppressor gene p16 in malignant cells bearing
homozygous deletions in the chromosome 9p21 region. p16
, MTAP
malignant cells have been shown to be more susceptible to the purine
de novo inhibitory actions of antifolates such as
methotrexate than are p16+,
MTAP+ cells. To understand the underlying
mechanism, we reintroduced MTAP activity into two
p16
, MTAP
cell model systems, the MiaPaCa-2 and PANC-1 human pancreatic carcinoma
cell lines, by transfection with MTAP cDNA. It was found that transfection with MTAP cDNA (i) restored both the
MTAP-dependent adenine and methionine salvage pathways, (ii) decreased
the rates of purine de novo synthesis (18-47% lower
than the wild-type or sham-transfected counterparts), and (iii)
decreased cellular sensitivity to the antipurine-related
growth-inhibitory actions of methotrexate and azaserine. These data
support the hypothesis that operation of the MTAP-dependent adenine
salvage pathway renders MTAP+ cells less
dependent on de novo purine synthesis and hence less susceptible than MTAP
malignant cells to
the growth-inhibitory actions of agents (e.g. antifolates) whose
mechanism of action in part involves the de novo purine
pathway. These findings provide a theoretical basis for the relatively
selective action certain antifolates may have against MTAP-deficient
malignancies.
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