Kurian P, Kumari H L, Milo G E
Ohio State University Comprehensive Cancer Center, Columbus 43210.
Carcinogenesis. 1992 Mar;13(3):489-91. doi: 10.1093/carcin/13.3.489.
Treatment of human skin fibroblasts in early S-phase with (+-)7 beta,8 alpha-dihydroxy-9 alpha,10 alpha-epoxy-7,8,9,10- tetrahydrobenzo[a]pyrene (BPDE-I) results in more extensive modification of early replicating DNA than parental DNA. We have investigated the effects of benzamide (BZ) and 3-aminobenzamide (3-ABZ), inhibitors of transformation, on the modification of parental and replicating DNA of cells in early S-phase by BPDE-I. Synchronized cells were exposed to 5-bromodeoxyuridine at S-phase entry and treated 3 h later with 0.114 microM BPDE-I for 30 min. The cells at the time of treatment represent a radiolabeling index of 40 +/- 5% of the total number of cells. The replicated DNA was isolated from the non-replicated parental DNA on a CsCl gradient. A 32P-postlabeling procedure was used to quantitate the carcinogen-DNA adducts. The level of modification per nucleotide residue of the early replicated DNA was 1.6-2.2 times higher compared to the level of modification of the parental DNA. Addition of BZ inhibited the BPDE-I modification of the replicated DNA by 27-53%. There was no significant effect on the parental DNA modification. The major adduct that was quantitatively suppressed in the early replicated DNA was BPDE-I-trans-N2-dG. The addition of 3-ABZ also inhibited the modification of the dG by approximately 50% without significantly inhibiting the BPDE-I-dG adducts in the parental DNA. The data suggest that BZ and 3-ABZ inhibit the modification of specific sites in the replicating DNA leading to inhibition of transformation.
用（±）7β，8α-二羟基-9α，10α-环氧-7,8,9,10-四氢苯并[a]芘（BPDE-I）处理处于S期早期的人皮肤成纤维细胞，会导致早期复制DNA比亲本DNA发生更广泛的修饰。我们研究了转化抑制剂苯甲酰胺（BZ）和3-氨基苯甲酰胺（3-ABZ）对BPDE-I对S期早期细胞的亲本DNA和复制DNA修饰的影响。同步化的细胞在进入S期时暴露于5-溴脱氧尿苷，3小时后用0.114 microM BPDE-I处理30分钟。处理时的细胞放射性标记指数占细胞总数的40±5%。通过氯化铯梯度从未复制的亲本DNA中分离出复制的DNA。采用32P后标记程序定量致癌物-DNA加合物。早期复制DNA每个核苷酸残基的修饰水平比亲本DNA的修饰水平高1.6-2.2倍。添加BZ可使复制DNA的BPDE-I修饰降低27-53%。对亲本DNA修饰没有显著影响。在早期复制DNA中被定量抑制的主要加合物是BPDE-I-反式-N2-dG。添加3-ABZ也使dG的修饰降低了约50%，而对亲本DNA中的BPDE-I-dG加合物没有显著抑制作用。数据表明，BZ和3-ABZ抑制复制DNA中特定位点的修饰，从而导致转化受到抑制。
