Phillips W P, Willson J K, Markowitz S D, Zborowska E, Zaidi N H, Liu L, Gordon N H, Gerson S L
Division of Hematology-Oncology, Case Western Reserve University, University Hospitals' Ireland Cancer Center, Cleveland, Ohio 44106-4937, USA.
Cancer Res. 1997 Nov 1;57(21):4817-23.
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.
为评估O6-烷基鸟嘌呤-DNA烷基转移酶（AGT）在结肠肿瘤对氯乙基亚硝脲（CENU）耐药性中的作用，将缺乏AGT的VACO 8细胞用含有或不含人O6-甲基鸟嘌呤-DNA甲基转移酶（MGMT）cDNA的载体进行转染。VACO 8MGMT（V8MGMT）亚系在细胞培养中具有高水平的AGT活性，并且对CENU 1,3-双（2-氯乙基）-1-亚硝脲（BCNU）的耐药性>10倍。V8MGMT细胞、VACO 8neo细胞以及两者的混合物在裸鼠中作为异种移植物生长。VACO 8异种移植物中的MGMT表达反映了肿瘤接种物中存在的V8MGMT细胞的百分比。最初含有0-10% V8MGMT细胞的异种移植物对BCNU敏感，尽管随着V8MGMT细胞百分比的增加观察到部分耐药性。含有30-100% V8MGMT细胞的肿瘤对BCNU完全耐药，没有消退且没有生长延迟。用O6-苄基鸟嘌呤（BG）预处理可使肿瘤AGT活性至少耗尽6小时，并使含有1%和100% V8MGMT细胞的异种移植物对BCNU敏感。在给予BCNU或BG + BCNU后，从含有低至0.1% V8MGMT细胞的接种物中生长的异种移植物具有与V8MGMT异种移植物中发现的相似的高AGT活性，大多数细胞表达MGMT。这些结果提供了证据，表明MGMT表达影响结肠肿瘤对CENU的固有耐药性和获得性耐药性，AGT+结肠肿瘤细胞在CENU暴露后通常会选择性扩增，并且BG即使在异质性肿瘤中只有一小部分细胞表达MGMT时，也能有效地使结肠肿瘤对CENU敏感。
