O6-methylguanine-DNA methyltransferase (MGMT) transfectants of a 1,3- bis(2-chloroethyl)-1-nitrosourea (BCNU)-sensitive colon cancer cell line selectively repopulate heterogeneous MGMT+/MGMT- xenografts after BCNU and O6-benzylguanine plus BCNU

Weldon P. Phillips, James K V Willson, Sanford D. Markowitz, Elizabeth Zborowska, Nasir H. Zaidi, Lili Liu, Nahida H. Gordon, Stanton L. Gerson

Research output: Contribution to journalArticle

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Abstract

To evaluate the role of O6-alkylguanine-DNA alkyltransferase (AGT) in colon tumor chloroethylnitrosourea (CENU) resistance, AGT-deficient VACO 8 cells were transfected with a vector containing or lacking the human O6- methylguanine-DNA methyltransferase (MGMT) cDNA. VACO 8MGMT (V8MGMT) sublines possessed high levels of AGT activity in cell culture and were > 10-fold resistant to the CENU 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU). V8MGMT cells, VACO 8neo cells, and mixtures of both were grown as xenografts in nude mice. MGMT expression in VACO 8 xenografts reflected the percentage of V8MGMT cells present in the tumor inoculum. Xenografts originally containing 0-10% V8MGMT cells were sensitive to BCNU, although partial resistance was observed as the percentage of V8MGMT cells increased. Tumors containing 30-100% V8MGMT cells were completely resistant to BCNU with no regressions and no growth delays. Pretreatment with O6-benzylguanine (BG) depleted tumor AGT activity for at least 6 h and sensitized xenografts containing 1 and 100% V8MGMT cells to BCNU. After BCNU or BG + BCNU, xenografts growing from inoculums containing as low as 0.1% V8MGMT cells had high AGT activities similar to that found in V8MGMT xenografts, with the majority of the cells expressing MGMT. These results provide evidence that MGMT expression influences both intrinsic and acquired colon tumor CENU resistance, that selective expansion of AGT+ colon tumor cells commonly occurs after CENU exposure, and that BG is effective in sensitizing colon tumors to CENUs, even when only a small fraction of the cells in a heterogeneous tumor express MGMT.

Original languageEnglish (US)
Pages (from-to)4817-4823
Number of pages7
JournalCancer Research
Volume57
Issue number21
StatePublished - Nov 1 1997

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Carmustine
Methyltransferases
Heterografts
Colonic Neoplasms
Cell Line
DNA
Neoplasms
Colon
O(6)-benzylguanine
O-(6)-methylguanine
Nude Mice
Complementary DNA
Cell Culture Techniques

ASJC Scopus subject areas

  • Cancer Research
  • Oncology

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O6-methylguanine-DNA methyltransferase (MGMT) transfectants of a 1,3- bis(2-chloroethyl)-1-nitrosourea (BCNU)-sensitive colon cancer cell line selectively repopulate heterogeneous MGMT+/MGMT- xenografts after BCNU and O6-benzylguanine plus BCNU. / Phillips, Weldon P.; Willson, James K V; Markowitz, Sanford D.; Zborowska, Elizabeth; Zaidi, Nasir H.; Liu, Lili; Gordon, Nahida H.; Gerson, Stanton L.

In: Cancer Research, Vol. 57, No. 21, 01.11.1997, p. 4817-4823.

Research output: Contribution to journalArticle

Phillips, Weldon P. ; Willson, James K V ; Markowitz, Sanford D. ; Zborowska, Elizabeth ; Zaidi, Nasir H. ; Liu, Lili ; Gordon, Nahida H. ; Gerson, Stanton L. / O6-methylguanine-DNA methyltransferase (MGMT) transfectants of a 1,3- bis(2-chloroethyl)-1-nitrosourea (BCNU)-sensitive colon cancer cell line selectively repopulate heterogeneous MGMT+/MGMT- xenografts after BCNU and O6-benzylguanine plus BCNU. In: Cancer Research. 1997 ; Vol. 57, No. 21. pp. 4817-4823.
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title = "O6-methylguanine-DNA methyltransferase (MGMT) transfectants of a 1,3- bis(2-chloroethyl)-1-nitrosourea (BCNU)-sensitive colon cancer cell line selectively repopulate heterogeneous MGMT+/MGMT- xenografts after BCNU and O6-benzylguanine plus BCNU",
abstract = "To evaluate the role of O6-alkylguanine-DNA alkyltransferase (AGT) in colon tumor chloroethylnitrosourea (CENU) resistance, AGT-deficient VACO 8 cells were transfected with a vector containing or lacking the human O6- methylguanine-DNA methyltransferase (MGMT) cDNA. VACO 8MGMT (V8MGMT) sublines possessed high levels of AGT activity in cell culture and were > 10-fold resistant to the CENU 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU). V8MGMT cells, VACO 8neo cells, and mixtures of both were grown as xenografts in nude mice. MGMT expression in VACO 8 xenografts reflected the percentage of V8MGMT cells present in the tumor inoculum. Xenografts originally containing 0-10{\%} V8MGMT cells were sensitive to BCNU, although partial resistance was observed as the percentage of V8MGMT cells increased. Tumors containing 30-100{\%} V8MGMT cells were completely resistant to BCNU with no regressions and no growth delays. Pretreatment with O6-benzylguanine (BG) depleted tumor AGT activity for at least 6 h and sensitized xenografts containing 1 and 100{\%} V8MGMT cells to BCNU. After BCNU or BG + BCNU, xenografts growing from inoculums containing as low as 0.1{\%} V8MGMT cells had high AGT activities similar to that found in V8MGMT xenografts, with the majority of the cells expressing MGMT. These results provide evidence that MGMT expression influences both intrinsic and acquired colon tumor CENU resistance, that selective expansion of AGT+ colon tumor cells commonly occurs after CENU exposure, and that BG is effective in sensitizing colon tumors to CENUs, even when only a small fraction of the cells in a heterogeneous tumor express MGMT.",
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AU - Phillips, Weldon P.

AU - Willson, James K V

AU - Markowitz, Sanford D.

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AU - Liu, Lili

AU - Gordon, Nahida H.

AU - Gerson, Stanton L.

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N2 - To evaluate the role of O6-alkylguanine-DNA alkyltransferase (AGT) in colon tumor chloroethylnitrosourea (CENU) resistance, AGT-deficient VACO 8 cells were transfected with a vector containing or lacking the human O6- methylguanine-DNA methyltransferase (MGMT) cDNA. VACO 8MGMT (V8MGMT) sublines possessed high levels of AGT activity in cell culture and were > 10-fold resistant to the CENU 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU). V8MGMT cells, VACO 8neo cells, and mixtures of both were grown as xenografts in nude mice. MGMT expression in VACO 8 xenografts reflected the percentage of V8MGMT cells present in the tumor inoculum. Xenografts originally containing 0-10% V8MGMT cells were sensitive to BCNU, although partial resistance was observed as the percentage of V8MGMT cells increased. Tumors containing 30-100% V8MGMT cells were completely resistant to BCNU with no regressions and no growth delays. Pretreatment with O6-benzylguanine (BG) depleted tumor AGT activity for at least 6 h and sensitized xenografts containing 1 and 100% V8MGMT cells to BCNU. After BCNU or BG + BCNU, xenografts growing from inoculums containing as low as 0.1% V8MGMT cells had high AGT activities similar to that found in V8MGMT xenografts, with the majority of the cells expressing MGMT. These results provide evidence that MGMT expression influences both intrinsic and acquired colon tumor CENU resistance, that selective expansion of AGT+ colon tumor cells commonly occurs after CENU exposure, and that BG is effective in sensitizing colon tumors to CENUs, even when only a small fraction of the cells in a heterogeneous tumor express MGMT.

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