Inhibitors of farnesyltransferase (e.g., R115777) are being developed for therapy and prevention of various cancers. The efficacy of R115777 [Zarnestra; (B)-6-[amino(4-chlorophenyl)(1-methyl-1H-imidazol-5-yl)-methyl]-4-(3-chlorophenyl)-1-methyl-2(1H)-quinolinone] to prevent the development of lung tumors in mice was determined. Female strain A mice (7-8 weeks of age) were given 100 mg/kg benzo(a)pyrene [B(a)P] by i.p. injection, and 4 or 14 weeks later, they were given 50 or 100 mg/kg R115777

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... oral gavage 5 days/week. The mice were sacrificed 22 weeks after they received the B(a)P. Tumor multiplicity was 5.0 +/- 0.85, 4.5 +/- 0.52, 2.1 +/- 0.31, and 1.5 +/- 0.31 tumors/mouse in mice that received 0, 50, 100 (weeks 4-22), or 100 (weeks 14-22) mg/kg R115777. Thus, 100 mg/kg R115777 was similarly effective in preventing lung tumors when administered during the promotional phase of carcinogenesis [that is, either 4 or 14 weeks after B(a)P], whereas the lower dose of 50 mg/kg R115777 was ineffective. The proliferating cell nuclear antigen labeling index was also significantly reduced in lung tumors from mice treated with 100 mg/kg R115777 starting at 4 or 14 weeks. These results demonstrated that R115777 can prevent the development of lung tumors in the A/J mouse model, where tumors routinely have mutations in the Ki-Rasoncogene.