title: Methylthioadenosine phosphorylase cDNA transfection alters sensitivity to depletion of purine and methionine in A549 lung cancer cells.
abstract: Methylthioadenosine phosphorylase (MTAP), an enzyme involved in purine and methionine metabolism, is present in all normal tissues but is frequently deficient in a variety of cancers. It has been suggested that this metabolic difference between normal and cancer cells may be exploited to selectively treat MTAP-negative cancers by inhibiting de novo purine synthesis and by depleting L-methionine. However, these therapeutic strategies have only been tested in naturally occurring MTAP-positive and -negative cell lines, which might have additional genetic alterations that affect chemotherapeutic sensitivity. Therefore, it is of importance to examine the feasibility of enzyme-selective treatment using paired cell lines that have an identical genotype except for MTAP status. MTAP-negative A549 lung cancer cells were transfected with eukaryotic expression vectors encoding MTAP cDNA in sense and antisense orientations. The resultant stable transfectomas were treated with inhibitors of de novo purine synthesis such as methotrexate, 5,10-dideazatetrahydrofolate, and L-alanosine and by methionine depletion. The A549 cells transfected with an antisense construct (antisense transfectoma) expressed no MTAP protein and were more sensitive to both purine and methionine depletion than were cells expressing MTAP protein (sense transfectoma). Methylthioadenosine was able to completely rescue the sense transfectoma but not the antisense transfectoma from growth inhibition by depletion of purine and methionine. These results prove that MTAP deficiency contributes directly to the sensitivity of cancer cells to purine or methionine depletion. Inhibition of de novo purine synthesis, combined with methionine depletion in the presence of methylthioadenosine, is a highly selective treatment for MTAP-negative cancers.
authors.affiliation: The Sam and Rose Stein Institute for Research on Aging, Department of Medicine, University of California, San Diego, La Jolla 92093-0663, USA.
authors.forename: H
authors.initials: H
authors.lastname: Hori
authors.forename: P
authors.initials: P
authors.lastname: Tran
authors.forename: C J
authors.initials: CJ
authors.lastname: Carrera
authors.forename: Y
authors.initials: Y
authors.lastname: Hori
authors.forename: M D
authors.initials: MD
authors.lastname: Rosenbach
authors.forename: D A
authors.initials: DA
authors.lastname: Carson
authors.forename: T
authors.initials: T
authors.lastname: Nobori
mesh_terms: D000409:Alanine / Q000031:analogs & derivatives / Q000494:pharmacology; D000964:Antimetabolites, Antineoplastic / Q000494:pharmacology*; D019008:Drug Resistance, Neoplasm; D005240:Feasibility Studies; D005822:Genetic Vectors; D006801:Humans; D008175:Lung Neoplasms / Q000188:drug therapy / Q000235:genetics / Q000378:metabolism; D008715:Methionine / Q000378:metabolism*; D008727:Methotrexate / Q000494:pharmacology; D009363:Neoplasm Proteins / Q000172:deficiency / Q000235:genetics* / Q000378:metabolism; D011683:Purine-Nucleoside Phosphorylase / Q000172:deficiency / Q000235:genetics* / Q000378:metabolism; D011687:Purines / Q000378:metabolism*; D013763:Tetrahydrofolates / Q000494:pharmacology; D014158:Transcription, Genetic; D014162:Transfection; D014407:Tumor Cells, Cultured
chemical_list: D000964:Antimetabolites, Antineoplastic; D009363:Neoplasm Proteins; D011687:Purines; D013763:Tetrahydrofolates; C000082:alanosine; C045894:lometrexol; D008715:Methionine; D011683:Purine-Nucleoside Phosphorylase; C021784:5'-methylthioadenosine phosphorylase; D000409:Alanine; C030985:purine; D008727:Methotrexate