Methotrexate Resistance in an in vivo Mouse Tumor Due to a Non-Active-Site Dihydrofolate Reductase Mutation
A series of methotrexate (MTX)-resistant L1210 leukemia murine ascites tumors were developed in vivo and analyzed for drug resistance. Three of 20 tumors studied expressed an altered dihydrofolate reductase (DHFR) and each was identical, having a C to T base transition at nucleotide 46 in the DHFR g...
Gespeichert in:
| Veröffentlicht in: | Proceedings of the National Academy of Sciences - PNAS 1993-12, Vol.90 (24), p.11797-11801 |
|---|---|
| Hauptverfasser: | , , , , , , , |
| Format: | Artikel |
| Sprache: | eng |
| Schlagworte: | |
| Online-Zugang: | Volltext |
| Tags: |
Tag hinzufügen
Keine Tags, Fügen Sie den ersten Tag hinzu!
|
| container_end_page | 11801 |
|---|---|
| container_issue | 24 |
| container_start_page | 11797 |
| container_title | Proceedings of the National Academy of Sciences - PNAS |
| container_volume | 90 |
| creator | Dicker, Adam P. Waltham, Mark C. Volkenandt, Matthias Schweitzer, Barry I. Otter, Glenys M. Schmid, Franz a. Sirotnak, Francis M. Bertino, Joseph R. |
| description | A series of methotrexate (MTX)-resistant L1210 leukemia murine ascites tumors were developed in vivo and analyzed for drug resistance. Three of 20 tumors studied expressed an altered dihydrofolate reductase (DHFR) and each was identical, having a C to T base transition at nucleotide 46 in the DHFR gene as demonstrated by PCR and direct sequencing. This transition results in a Gly to Trp substitution at amino acid 15 of the enzyme. Purified altered enzyme displays significantly lower binding affinity for the antifolates MTX, trimetrexate, edatrexate, and trimethoprim with respective Kivalues 165-, 76-, 30-, and 28-fold higher than values obtained for enzyme isolated from parental tumor (wild-type enzyme). Substrate (dihydrofolate) and cofactor (NADPH) binding is also diminished for the mutant enzyme, although to a lesser extent (17.3- and 3.6-fold higher Km, respectively). Gly-15 is highly conserved for all vertebrate species of DHFR but has no known interaction(s), either directly or indirectly, with bound cofactor, substrate, or inhibitor. Protein molecular modeling reveals that the affected residue is 9-12 Å away from the enzyme active site and located in a region analogous to the mobile Met-20 loop domain characterized for Escherichia coli DHFR. |
| doi_str_mv | 10.1073/pnas.90.24.11797 |
| format | Article |
| fullrecord | <record><control><sourceid>jstor_pnas_</sourceid><recordid>TN_cdi_pnas_primary_90_24_11797</recordid><sourceformat>XML</sourceformat><sourcesystem>PC</sourcesystem><jstor_id>2363550</jstor_id><sourcerecordid>2363550</sourcerecordid><originalsourceid>FETCH-LOGICAL-c554t-3490a69231c8f3e7442644c73914ced454631d3f246cecdd1fce155af2c210363</originalsourceid><addsrcrecordid>eNqFkUtvEzEUhS0EKqGwZwFihBBiM-H6OR6JTdVSQGpAgrK2jMdDHCZ2sD1R--9xmiGiLGBjL8537usg9BjDHENDX2-8TvMW5oTNMW7a5g6aYWhxLVgLd9EMgDS1ZITdRw9SWgFAyyUcoSNJBBdEztCPhc3LkKO90tlWn21yKWtvbOV8pf3u3bptqBZhTLa6HNchVmejrXKodPUx-PrEZLe19RdX3Gdued3F0IdhX6sbTdbFthizzi74h-her4dkH03_Mfp6_vby9H198endh9OTi9pwznJNy-xatIRiI3tqG8aIYMw0tMXM2I5xJijuaE-YMNZ0He6NxZzrnhiCgQp6jN7s627Gb2vbGetz1IPaRLfW8VoF7dRtxbul-h62iklocLG_nOwx_BxtymrtkrHDoL0tZ1CNKKfnAP8FsWg4kZQX8Plf4CqM0ZcbKAKYNCUhWSDYQyaGlKLtDwNjULuw1S5s1YIiTN2EXSxP_1z0YJjSLfqLSdfJ6KGPJVmXDhiVEhhmBXs2YbsGv9XbjV79m1D9OAzZXuWCPtmjq5RDPLCk5MI50F85j9SD</addsrcrecordid><sourcetype>Open Access Repository</sourcetype><iscdi>true</iscdi><recordtype>article</recordtype><pqid>201278428</pqid></control><display><type>article</type><title>Methotrexate Resistance in an in vivo Mouse Tumor Due to a Non-Active-Site Dihydrofolate Reductase Mutation</title><source>MEDLINE</source><source>JSTOR Archive Collection A-Z Listing</source><source>PubMed Central</source><source>Alma/SFX Local Collection</source><source>Free Full-Text Journals in Chemistry</source><creator>Dicker, Adam P. ; Waltham, Mark C. ; Volkenandt, Matthias ; Schweitzer, Barry I. ; Otter, Glenys M. ; Schmid, Franz a. ; Sirotnak, Francis M. ; Bertino, Joseph R.</creator><creatorcontrib>Dicker, Adam P. ; Waltham, Mark C. ; Volkenandt, Matthias ; Schweitzer, Barry I. ; Otter, Glenys M. ; Schmid, Franz a. ; Sirotnak, Francis M. ; Bertino, Joseph R.</creatorcontrib><description>A series of methotrexate (MTX)-resistant L1210 leukemia murine ascites tumors were developed in vivo and analyzed for drug resistance. Three of 20 tumors studied expressed an altered dihydrofolate reductase (DHFR) and each was identical, having a C to T base transition at nucleotide 46 in the DHFR gene as demonstrated by PCR and direct sequencing. This transition results in a Gly to Trp substitution at amino acid 15 of the enzyme. Purified altered enzyme displays significantly lower binding affinity for the antifolates MTX, trimetrexate, edatrexate, and trimethoprim with respective Kivalues 165-, 76-, 30-, and 28-fold higher than values obtained for enzyme isolated from parental tumor (wild-type enzyme). Substrate (dihydrofolate) and cofactor (NADPH) binding is also diminished for the mutant enzyme, although to a lesser extent (17.3- and 3.6-fold higher Km, respectively). Gly-15 is highly conserved for all vertebrate species of DHFR but has no known interaction(s), either directly or indirectly, with bound cofactor, substrate, or inhibitor. Protein molecular modeling reveals that the affected residue is 9-12 Å away from the enzyme active site and located in a region analogous to the mobile Met-20 loop domain characterized for Escherichia coli DHFR.</description><identifier>ISSN: 0027-8424</identifier><identifier>EISSN: 1091-6490</identifier><identifier>DOI: 10.1073/pnas.90.24.11797</identifier><identifier>PMID: 8265628</identifier><identifier>CODEN: PNASA6</identifier><language>eng</language><publisher>Washington, DC: National Academy of Sciences of the United States of America</publisher><subject>Active sites ; Amino Acid Sequence ; Amino acids ; Animals ; Antineoplastic agents ; Base Sequence ; Binding Sites ; Biochemistry ; Biological and medical sciences ; Cell lines ; Chromatography, Affinity ; Complementary DNA ; DNA ; DNA Primers ; DNA, Neoplasm - chemistry ; DNA, Neoplasm - isolation & purification ; Drug Resistance - genetics ; Enzyme Stability ; Enzymes ; Escherichia coli - enzymology ; Folic acid antagonists ; General aspects ; Genetic mutation ; Humans ; Kinetics ; Leukemia ; Leukemia L1210 - drug therapy ; Leukemia L1210 - enzymology ; Leukemia L1210 - genetics ; Medical sciences ; Methotrexate - therapeutic use ; Mice ; Models, Molecular ; Molecular Sequence Data ; NADP - metabolism ; Pharmacology ; Pharmacology. Drug treatments ; Point Mutation ; Polymerase Chain Reaction ; Protein Conformation ; Tetrahydrofolate Dehydrogenase - genetics ; Tetrahydrofolate Dehydrogenase - isolation & purification ; Tetrahydrofolate Dehydrogenase - metabolism ; Time Factors ; Tumors</subject><ispartof>Proceedings of the National Academy of Sciences - PNAS, 1993-12, Vol.90 (24), p.11797-11801</ispartof><rights>Copyright 1993 The National Academy of Sciences of the United States of America</rights><rights>1994 INIST-CNRS</rights><rights>Copyright National Academy of Sciences Dec 15, 1993</rights><lds50>peer_reviewed</lds50><oa>free_for_read</oa><woscitedreferencessubscribed>false</woscitedreferencessubscribed><citedby>FETCH-LOGICAL-c554t-3490a69231c8f3e7442644c73914ced454631d3f246cecdd1fce155af2c210363</citedby></display><links><openurl>$$Topenurl_article</openurl><openurlfulltext>$$Topenurlfull_article</openurlfulltext><thumbnail>$$Uhttp://www.pnas.org/content/90/24.cover.gif</thumbnail><linktopdf>$$Uhttps://www.jstor.org/stable/pdf/2363550$$EPDF$$P50$$Gjstor$$H</linktopdf><linktohtml>$$Uhttps://www.jstor.org/stable/2363550$$EHTML$$P50$$Gjstor$$H</linktohtml><link.rule.ids>230,314,727,780,784,803,885,27924,27925,53791,53793,58017,58250</link.rule.ids><backlink>$$Uhttp://pascal-francis.inist.fr/vibad/index.php?action=getRecordDetail&idt=3880414$$DView record in Pascal Francis$$Hfree_for_read</backlink><backlink>$$Uhttps://www.ncbi.nlm.nih.gov/pubmed/8265628$$D View this record in MEDLINE/PubMed$$Hfree_for_read</backlink></links><search><creatorcontrib>Dicker, Adam P.</creatorcontrib><creatorcontrib>Waltham, Mark C.</creatorcontrib><creatorcontrib>Volkenandt, Matthias</creatorcontrib><creatorcontrib>Schweitzer, Barry I.</creatorcontrib><creatorcontrib>Otter, Glenys M.</creatorcontrib><creatorcontrib>Schmid, Franz a.</creatorcontrib><creatorcontrib>Sirotnak, Francis M.</creatorcontrib><creatorcontrib>Bertino, Joseph R.</creatorcontrib><title>Methotrexate Resistance in an in vivo Mouse Tumor Due to a Non-Active-Site Dihydrofolate Reductase Mutation</title><title>Proceedings of the National Academy of Sciences - PNAS</title><addtitle>Proc Natl Acad Sci U S A</addtitle><description>A series of methotrexate (MTX)-resistant L1210 leukemia murine ascites tumors were developed in vivo and analyzed for drug resistance. Three of 20 tumors studied expressed an altered dihydrofolate reductase (DHFR) and each was identical, having a C to T base transition at nucleotide 46 in the DHFR gene as demonstrated by PCR and direct sequencing. This transition results in a Gly to Trp substitution at amino acid 15 of the enzyme. Purified altered enzyme displays significantly lower binding affinity for the antifolates MTX, trimetrexate, edatrexate, and trimethoprim with respective Kivalues 165-, 76-, 30-, and 28-fold higher than values obtained for enzyme isolated from parental tumor (wild-type enzyme). Substrate (dihydrofolate) and cofactor (NADPH) binding is also diminished for the mutant enzyme, although to a lesser extent (17.3- and 3.6-fold higher Km, respectively). Gly-15 is highly conserved for all vertebrate species of DHFR but has no known interaction(s), either directly or indirectly, with bound cofactor, substrate, or inhibitor. Protein molecular modeling reveals that the affected residue is 9-12 Å away from the enzyme active site and located in a region analogous to the mobile Met-20 loop domain characterized for Escherichia coli DHFR.</description><subject>Active sites</subject><subject>Amino Acid Sequence</subject><subject>Amino acids</subject><subject>Animals</subject><subject>Antineoplastic agents</subject><subject>Base Sequence</subject><subject>Binding Sites</subject><subject>Biochemistry</subject><subject>Biological and medical sciences</subject><subject>Cell lines</subject><subject>Chromatography, Affinity</subject><subject>Complementary DNA</subject><subject>DNA</subject><subject>DNA Primers</subject><subject>DNA, Neoplasm - chemistry</subject><subject>DNA, Neoplasm - isolation & purification</subject><subject>Drug Resistance - genetics</subject><subject>Enzyme Stability</subject><subject>Enzymes</subject><subject>Escherichia coli - enzymology</subject><subject>Folic acid antagonists</subject><subject>General aspects</subject><subject>Genetic mutation</subject><subject>Humans</subject><subject>Kinetics</subject><subject>Leukemia</subject><subject>Leukemia L1210 - drug therapy</subject><subject>Leukemia L1210 - enzymology</subject><subject>Leukemia L1210 - genetics</subject><subject>Medical sciences</subject><subject>Methotrexate - therapeutic use</subject><subject>Mice</subject><subject>Models, Molecular</subject><subject>Molecular Sequence Data</subject><subject>NADP - metabolism</subject><subject>Pharmacology</subject><subject>Pharmacology. Drug treatments</subject><subject>Point Mutation</subject><subject>Polymerase Chain Reaction</subject><subject>Protein Conformation</subject><subject>Tetrahydrofolate Dehydrogenase - genetics</subject><subject>Tetrahydrofolate Dehydrogenase - isolation & purification</subject><subject>Tetrahydrofolate Dehydrogenase - metabolism</subject><subject>Time Factors</subject><subject>Tumors</subject><issn>0027-8424</issn><issn>1091-6490</issn><fulltext>true</fulltext><rsrctype>article</rsrctype><creationdate>1993</creationdate><recordtype>article</recordtype><sourceid>EIF</sourceid><recordid>eNqFkUtvEzEUhS0EKqGwZwFihBBiM-H6OR6JTdVSQGpAgrK2jMdDHCZ2sD1R--9xmiGiLGBjL8537usg9BjDHENDX2-8TvMW5oTNMW7a5g6aYWhxLVgLd9EMgDS1ZITdRw9SWgFAyyUcoSNJBBdEztCPhc3LkKO90tlWn21yKWtvbOV8pf3u3bptqBZhTLa6HNchVmejrXKodPUx-PrEZLe19RdX3Gdued3F0IdhX6sbTdbFthizzi74h-her4dkH03_Mfp6_vby9H198endh9OTi9pwznJNy-xatIRiI3tqG8aIYMw0tMXM2I5xJijuaE-YMNZ0He6NxZzrnhiCgQp6jN7s627Gb2vbGetz1IPaRLfW8VoF7dRtxbul-h62iklocLG_nOwx_BxtymrtkrHDoL0tZ1CNKKfnAP8FsWg4kZQX8Plf4CqM0ZcbKAKYNCUhWSDYQyaGlKLtDwNjULuw1S5s1YIiTN2EXSxP_1z0YJjSLfqLSdfJ6KGPJVmXDhiVEhhmBXs2YbsGv9XbjV79m1D9OAzZXuWCPtmjq5RDPLCk5MI50F85j9SD</recordid><startdate>19931215</startdate><enddate>19931215</enddate><creator>Dicker, Adam P.</creator><creator>Waltham, Mark C.</creator><creator>Volkenandt, Matthias</creator><creator>Schweitzer, Barry I.</creator><creator>Otter, Glenys M.</creator><creator>Schmid, Franz a.</creator><creator>Sirotnak, Francis M.</creator><creator>Bertino, Joseph R.</creator><general>National Academy of Sciences of the United States of America</general><general>National Acad Sciences</general><general>National Academy of Sciences</general><scope>IQODW</scope><scope>CGR</scope><scope>CUY</scope><scope>CVF</scope><scope>ECM</scope><scope>EIF</scope><scope>NPM</scope><scope>AAYXX</scope><scope>CITATION</scope><scope>7QG</scope><scope>7QL</scope><scope>7QP</scope><scope>7QR</scope><scope>7SN</scope><scope>7SS</scope><scope>7T5</scope><scope>7TK</scope><scope>7TM</scope><scope>7TO</scope><scope>7U9</scope><scope>8FD</scope><scope>C1K</scope><scope>FR3</scope><scope>H94</scope><scope>M7N</scope><scope>P64</scope><scope>RC3</scope><scope>7X8</scope><scope>5PM</scope></search><sort><creationdate>19931215</creationdate><title>Methotrexate Resistance in an in vivo Mouse Tumor Due to a Non-Active-Site Dihydrofolate Reductase Mutation</title><author>Dicker, Adam P. ; Waltham, Mark C. ; Volkenandt, Matthias ; Schweitzer, Barry I. ; Otter, Glenys M. ; Schmid, Franz a. ; Sirotnak, Francis M. ; Bertino, Joseph R.</author></sort><facets><frbrtype>5</frbrtype><frbrgroupid>cdi_FETCH-LOGICAL-c554t-3490a69231c8f3e7442644c73914ced454631d3f246cecdd1fce155af2c210363</frbrgroupid><rsrctype>articles</rsrctype><prefilter>articles</prefilter><language>eng</language><creationdate>1993</creationdate><topic>Active sites</topic><topic>Amino Acid Sequence</topic><topic>Amino acids</topic><topic>Animals</topic><topic>Antineoplastic agents</topic><topic>Base Sequence</topic><topic>Binding Sites</topic><topic>Biochemistry</topic><topic>Biological and medical sciences</topic><topic>Cell lines</topic><topic>Chromatography, Affinity</topic><topic>Complementary DNA</topic><topic>DNA</topic><topic>DNA Primers</topic><topic>DNA, Neoplasm - chemistry</topic><topic>DNA, Neoplasm - isolation & purification</topic><topic>Drug Resistance - genetics</topic><topic>Enzyme Stability</topic><topic>Enzymes</topic><topic>Escherichia coli - enzymology</topic><topic>Folic acid antagonists</topic><topic>General aspects</topic><topic>Genetic mutation</topic><topic>Humans</topic><topic>Kinetics</topic><topic>Leukemia</topic><topic>Leukemia L1210 - drug therapy</topic><topic>Leukemia L1210 - enzymology</topic><topic>Leukemia L1210 - genetics</topic><topic>Medical sciences</topic><topic>Methotrexate - therapeutic use</topic><topic>Mice</topic><topic>Models, Molecular</topic><topic>Molecular Sequence Data</topic><topic>NADP - metabolism</topic><topic>Pharmacology</topic><topic>Pharmacology. Drug treatments</topic><topic>Point Mutation</topic><topic>Polymerase Chain Reaction</topic><topic>Protein Conformation</topic><topic>Tetrahydrofolate Dehydrogenase - genetics</topic><topic>Tetrahydrofolate Dehydrogenase - isolation & purification</topic><topic>Tetrahydrofolate Dehydrogenase - metabolism</topic><topic>Time Factors</topic><topic>Tumors</topic><toplevel>peer_reviewed</toplevel><toplevel>online_resources</toplevel><creatorcontrib>Dicker, Adam P.</creatorcontrib><creatorcontrib>Waltham, Mark C.</creatorcontrib><creatorcontrib>Volkenandt, Matthias</creatorcontrib><creatorcontrib>Schweitzer, Barry I.</creatorcontrib><creatorcontrib>Otter, Glenys M.</creatorcontrib><creatorcontrib>Schmid, Franz a.</creatorcontrib><creatorcontrib>Sirotnak, Francis M.</creatorcontrib><creatorcontrib>Bertino, Joseph R.</creatorcontrib><collection>Pascal-Francis</collection><collection>Medline</collection><collection>MEDLINE</collection><collection>MEDLINE (Ovid)</collection><collection>MEDLINE</collection><collection>MEDLINE</collection><collection>PubMed</collection><collection>CrossRef</collection><collection>Animal Behavior Abstracts</collection><collection>Bacteriology Abstracts (Microbiology B)</collection><collection>Calcium & Calcified Tissue Abstracts</collection><collection>Chemoreception Abstracts</collection><collection>Ecology Abstracts</collection><collection>Entomology Abstracts (Full archive)</collection><collection>Immunology Abstracts</collection><collection>Neurosciences Abstracts</collection><collection>Nucleic Acids Abstracts</collection><collection>Oncogenes and Growth Factors Abstracts</collection><collection>Virology and AIDS Abstracts</collection><collection>Technology Research Database</collection><collection>Environmental Sciences and Pollution Management</collection><collection>Engineering Research Database</collection><collection>AIDS and Cancer Research Abstracts</collection><collection>Algology Mycology and Protozoology Abstracts (Microbiology C)</collection><collection>Biotechnology and BioEngineering Abstracts</collection><collection>Genetics Abstracts</collection><collection>MEDLINE - Academic</collection><collection>PubMed Central (Full Participant titles)</collection><jtitle>Proceedings of the National Academy of Sciences - PNAS</jtitle></facets><delivery><delcategory>Remote Search Resource</delcategory><fulltext>fulltext</fulltext></delivery><addata><au>Dicker, Adam P.</au><au>Waltham, Mark C.</au><au>Volkenandt, Matthias</au><au>Schweitzer, Barry I.</au><au>Otter, Glenys M.</au><au>Schmid, Franz a.</au><au>Sirotnak, Francis M.</au><au>Bertino, Joseph R.</au><format>journal</format><genre>article</genre><ristype>JOUR</ristype><atitle>Methotrexate Resistance in an in vivo Mouse Tumor Due to a Non-Active-Site Dihydrofolate Reductase Mutation</atitle><jtitle>Proceedings of the National Academy of Sciences - PNAS</jtitle><addtitle>Proc Natl Acad Sci U S A</addtitle><date>1993-12-15</date><risdate>1993</risdate><volume>90</volume><issue>24</issue><spage>11797</spage><epage>11801</epage><pages>11797-11801</pages><issn>0027-8424</issn><eissn>1091-6490</eissn><coden>PNASA6</coden><abstract>A series of methotrexate (MTX)-resistant L1210 leukemia murine ascites tumors were developed in vivo and analyzed for drug resistance. Three of 20 tumors studied expressed an altered dihydrofolate reductase (DHFR) and each was identical, having a C to T base transition at nucleotide 46 in the DHFR gene as demonstrated by PCR and direct sequencing. This transition results in a Gly to Trp substitution at amino acid 15 of the enzyme. Purified altered enzyme displays significantly lower binding affinity for the antifolates MTX, trimetrexate, edatrexate, and trimethoprim with respective Kivalues 165-, 76-, 30-, and 28-fold higher than values obtained for enzyme isolated from parental tumor (wild-type enzyme). Substrate (dihydrofolate) and cofactor (NADPH) binding is also diminished for the mutant enzyme, although to a lesser extent (17.3- and 3.6-fold higher Km, respectively). Gly-15 is highly conserved for all vertebrate species of DHFR but has no known interaction(s), either directly or indirectly, with bound cofactor, substrate, or inhibitor. Protein molecular modeling reveals that the affected residue is 9-12 Å away from the enzyme active site and located in a region analogous to the mobile Met-20 loop domain characterized for Escherichia coli DHFR.</abstract><cop>Washington, DC</cop><pub>National Academy of Sciences of the United States of America</pub><pmid>8265628</pmid><doi>10.1073/pnas.90.24.11797</doi><tpages>5</tpages><oa>free_for_read</oa></addata></record> |
| fulltext | fulltext |
| identifier | ISSN: 0027-8424 |
| ispartof | Proceedings of the National Academy of Sciences - PNAS, 1993-12, Vol.90 (24), p.11797-11801 |
| issn | 0027-8424 1091-6490 |
| language | eng |
| recordid | cdi_pnas_primary_90_24_11797 |
| source | MEDLINE; JSTOR Archive Collection A-Z Listing; PubMed Central; Alma/SFX Local Collection; Free Full-Text Journals in Chemistry |
| subjects | Active sites Amino Acid Sequence Amino acids Animals Antineoplastic agents Base Sequence Binding Sites Biochemistry Biological and medical sciences Cell lines Chromatography, Affinity Complementary DNA DNA DNA Primers DNA, Neoplasm - chemistry DNA, Neoplasm - isolation & purification Drug Resistance - genetics Enzyme Stability Enzymes Escherichia coli - enzymology Folic acid antagonists General aspects Genetic mutation Humans Kinetics Leukemia Leukemia L1210 - drug therapy Leukemia L1210 - enzymology Leukemia L1210 - genetics Medical sciences Methotrexate - therapeutic use Mice Models, Molecular Molecular Sequence Data NADP - metabolism Pharmacology Pharmacology. Drug treatments Point Mutation Polymerase Chain Reaction Protein Conformation Tetrahydrofolate Dehydrogenase - genetics Tetrahydrofolate Dehydrogenase - isolation & purification Tetrahydrofolate Dehydrogenase - metabolism Time Factors Tumors |
| title | Methotrexate Resistance in an in vivo Mouse Tumor Due to a Non-Active-Site Dihydrofolate Reductase Mutation |
| url | https://sfx.bib-bvb.de/sfx_tum?ctx_ver=Z39.88-2004&ctx_enc=info:ofi/enc:UTF-8&ctx_tim=2024-12-29T11%3A22%3A10IST&url_ver=Z39.88-2004&url_ctx_fmt=infofi/fmt:kev:mtx:ctx&rfr_id=info:sid/primo.exlibrisgroup.com:primo3-Article-jstor_pnas_&rft_val_fmt=info:ofi/fmt:kev:mtx:journal&rft.genre=article&rft.atitle=Methotrexate%20Resistance%20in%20an%20in%20vivo%20Mouse%20Tumor%20Due%20to%20a%20Non-Active-Site%20Dihydrofolate%20Reductase%20Mutation&rft.jtitle=Proceedings%20of%20the%20National%20Academy%20of%20Sciences%20-%20PNAS&rft.au=Dicker,%20Adam%20P.&rft.date=1993-12-15&rft.volume=90&rft.issue=24&rft.spage=11797&rft.epage=11801&rft.pages=11797-11801&rft.issn=0027-8424&rft.eissn=1091-6490&rft.coden=PNASA6&rft_id=info:doi/10.1073/pnas.90.24.11797&rft_dat=%3Cjstor_pnas_%3E2363550%3C/jstor_pnas_%3E%3Curl%3E%3C/url%3E&disable_directlink=true&sfx.directlink=off&sfx.report_link=0&rft_id=info:oai/&rft_pqid=201278428&rft_id=info:pmid/8265628&rft_jstor_id=2363550&rfr_iscdi=true |