Kim T W, Porter K L, Foley J F, Maronpot R R, Smart R C
Molecular and Cellular Toxicology, Department of Toxicology, North Carolina State University, Raleigh 27695-7633, USA.
Mol Carcinog. 1997 Sep;20(1):115-24.
Mirex is a potent tumor promoter in 7,1 2-dimethylbenz[a]anthracene (DMBA)-initiated female CD-1 mouse skin. Like 12-O-tetradecanoylphorbol-13-acetate (TPA), mirex promotes papillomas that have a Ha-ras mutation; however, unlike TPA promotion, mirex promotion does not involve a general hyperplastic response. We used proliferating cell nuclear antigen (PCNA) and 5-bromo-2'-deoxyuridine (BrdU) immunohistochemical staining to further examine the proliferative capacity of mirex. The numbers of PCNA- and BrdU-positive epidermal S-phase cells were highly concordant in all treatment groups. Unlike a single application of TPA, a single application of mirex had little or no effect on the number of S-phase epidermal cells, and chronic application of mirex to mouse skin produced only minimal increases in S-phase cells. Moreover, mirex did not significantly alter the growth of BALB/MK-2 keratinocytes in media containing either 0.05 or 1.2 mM Ca++. These results suggest that mirex may have highly specific effects on the proliferation of initiated cells and support the existence of a unique mirex mechanism and/or distinct population of mirex-promotable mutant Ha-ras epidermal cells. To begin to address this issue of a distinct population of mirex-promotable mutant Ha-ras cells, we conducted a tandem experiment in which DMBA-initiated mice were treated twice weekly with a maximal promoting dose of mirex. Then, when the number of papillomas reached a plateau, these same mice were treated twice weekly with a maximal promoting dose of TPA. Mice treated with mirex developed a maximum of 6.4 papillomas/mouse. These mice were then promoted with TPA, which produced 8.9 additional papillomas/mouse for a total of 15.3 papillomas/mouse. The maximum tumor yields from other groups of mice treated with only TPA or mirex were 9.8 and 7.3 papillomas/mouse, respectively. Therefore, under these tandem conditions, tumor yields were additive, indicating that there are at least two distinct populations of mutant Ha-ras cells: one promoted by mirex and the other by TPA.
灭蚁灵是一种强效的肿瘤促进剂，可作用于经7,12-二甲基苯并[a]蒽（DMBA）启动的雌性CD-1小鼠皮肤。与12-O-十四烷酰佛波醇-13-乙酸酯（TPA）一样，灭蚁灵可促进具有Ha-ras突变的乳头状瘤生长；然而，与TPA促进作用不同的是，灭蚁灵促进作用并不涉及一般的增生反应。我们使用增殖细胞核抗原（PCNA）和5-溴-2'-脱氧尿苷（BrdU）免疫组织化学染色来进一步检测灭蚁灵的增殖能力。在所有治疗组中，PCNA和BrdU阳性的表皮S期细胞数量高度一致。与单次应用TPA不同，单次应用灭蚁灵对S期表皮细胞数量几乎没有影响，而长期将灭蚁灵应用于小鼠皮肤只会使S期细胞数量有极小的增加。此外，在含有0.05或1.2 mM Ca++的培养基中，灭蚁灵对BALB/MK-2角质形成细胞的生长没有显著影响。这些结果表明，灭蚁灵可能对启动细胞的增殖具有高度特异性作用，并支持存在独特的灭蚁灵作用机制和/或不同群体的可被灭蚁灵促进的突变型Ha-ras表皮细胞。为了开始研究这一不同群体的可被灭蚁灵促进的突变型Ha-ras细胞问题，我们进行了一项串联实验，即对经DMBA启动的小鼠每周两次给予最大促进剂量的灭蚁灵。然后，当乳头状瘤数量达到平台期时，对这些相同的小鼠每周两次给予最大促进剂量的TPA。用灭蚁灵治疗的小鼠每只最多长出6.4个乳头状瘤。然后用TPA对这些小鼠进行促进，每只小鼠又长出8.9个乳头状瘤，总共每只小鼠有15.3个乳头状瘤。仅用TPA或灭蚁灵治疗的其他组小鼠的最大肿瘤产量分别为每只小鼠9.8个和7.3个乳头状瘤。因此，在这些串联条件下，肿瘤产量是相加的，这表明至少存在两个不同群体的突变型Ha-ras细胞：一个由灭蚁灵促进，另一个由TPA促进。
