title: NTP Initiation/Promotion Study of o-Benzyl-p-Chlorophenol (CAS No. 120-32-1) in Swiss (CD-1(R)) Mice (Mouse Skin Study).
abstract: o-Benzyl-p-chlorophenol (BCP), an aryl halide, is a broad spectrum germicide used in disinfectant solutions and soap formulations in United States hospitals and households. Human exposure to BCP occurs by absorption through the skin and mucous membranes and by ingestion. BCP was studied because of the widespread human exposure and because BCP is an irritant and certain phenolic compounds are weak promoters of skin neoplasia. Groups of Swiss (CD-1(R)) mice were used to study BCP in a 1-year mouse skin initiation/promotion protocol. Genetic toxicology studies were conducted in Salmonella typhimurium and cultured Chinese hamster ovary cells. 1-YEAR INITIATION/PROMOTION STUDY: Groups of 50 male and 50 female Swiss (CD-1(R)) mice were topically exposed to BCP to study its effect as an initiator, promoter, and complete carcinogen. A number of control groups were included in these studies as a reference for the responses of the mouse skin to o -benzyl- p -chlorophenol (see following table). See report abstract or full report for Dose Regimen for Reference Controls in the 1-Year Initiation/Promotion Study of o -Benzyl- p - Chlorophenol. BCP in acetone was tested as an initiator with the promoter 12- O -tetradecanoylphorbol-13-acetate (TPA). The potential of BCP as an initiator was studied by applying a single 100 mL dose of BCP in acetone at a concentration of 10 mg/mL to the dorsal interscapular region of the backs of mice during week 1 of the study. Following the initial BCP application, mice were administered promoting doses of 5 mg TPA three times per week in 100 mL acetone for the first 6 months of the study and once weekly for the final 6 months of the study. BCP in acetone was tested as a promoter with the initiator 7,12-dimethylbenz(a)anthracene (DMBA). Mice were administered a single initiating dose of 50 mL DMBA in 100 mL acetone. Beginning on the second week of the study, mice received 100 mL applications of 0.1, 1.0, or 3.0 mg BCP in acetone three times weekly for up to 51 weeks. Comparative control groups used during the study of BCP as a promoter included: vehicle control (acetone/acetone); promoter control (TPA/TPA); and initiator control (DMBA/acetone). The potential for BCP to act as a complete carcinogen was studied by applying a single initiating dose of 10 mg BCP in 100 mL of acetone, followed by tri-weekly 100 mL applications of 0.1, 1.0, or 3.0 mg BCP to 50 male and 50 female Swiss (CD-1(R)) mice for 52 weeks. The responses of these groups were compared to vehicle control (acetone/acetone) and complete carcinogen control (acetone/DMBA) groups. The following table shows the various groups with BCP as a promoter, an initiator, and as a complete carcinogen. See full report or abstract for Dose Regimen in the 1-Year Initiation/Promotion Study of o - Benzyl- p -Chlorophenol. Results in the Study of BCP as a Complete Carcinogen: BCP acted as an irritant when tested as a complete carcinogen using a single initiating dose of 10 mg BCP followed by repetitive applications of 0.1, 1.0, or 3.0 mg BCP for up to 52 weeks, and many of the mice developed cutaneous lesions of scaling/crusts and ulceration. During the course of the study, a single papilloma was first observed after 12 weeks in one 0.1 mg BCP male mouse. One 3.0 mg BCP female was observed with a papilloma at week 10, and three 0.1 mg BCP females were observed with papillomas between weeks 22 and 27. No mice administered BCP/BCP had papillomas at the end of the study, and no malignant cutaneous epithelial tumors were observed at the application sites on any BCP/BCP mice. Thus, in the present study, BCP was not a complete carcinogen. Results in the Study of BCP as an Initiator: One vehicle control (acetone/acetone) male mouse had developed crusts at the site of application at necropsy, but no male or female vehicle controls had developed papillomas. Mice administered BCP/TPA developed application site lesions including scaling/crusts, ulceration, and irritation; the incidences of these lesions were similar to those in the initiator/promoter control (DMBA/TPA) /TPA) groups. After 22 weeks papillomas were observed in 12/50 male mice administered BCP/TPA. After 12 weeks papillomas were observed in 7/50 female mice administered BCP/TPA. However, the incidences of papillomas in mice administered BCP/TPA were lower than those in mice administered TPA/TPA (males, 16/50; females, 16/50) and were much lower than those in DMBA/TPA mice (males, 40/50; females, 48/50). Although the incidences of papillomas in mice administered BCP as an initiator were significantly greater than those in the vehicle controls, the incidences were not significantly different from those in TPA/TPA mice. Thus, in the present study, BCP did not demonstrate initiating potential. Results in the Study of BCP as a Promoter: During the course of the study, incidences of scaling and/or crusts, ulceration, and irritation were observed at the site of application in DMBA/BCP male and female mice, and the incidences were dose-related. Incidences of scaling and/or crusts, ulceration, and irritation in 3.0 mg BCP mice were similar to the incidences of these lesions in initiator/promoter control (DMBA/TPA) group, but much higher than the incidences of these lesions in the initiator control (DMBA/acetone) group. A dose-related increased incidence of papillomas was observed in males (DMBA/acetone, 8/50; DMBA/0.1 mg BCP, 3/50;DMBA/1.0 mg BCP, 5/50; and DMBA/3.0 mg BCP, 14/50) and females (2/50, 6/50, 6/50, and 18/50). The incidence of papillomas in DMBA/3.0 mg BCP females was significantly greater (P&lt;0.001) than that in DMBA/acetone females; the incidence of papillomas in DMBA/3.0 mg BCP males was marginally increased (P=0.077). No acetone/acetone mice developed papillomas. Although a higher percentage of DMBA/3.0 mg BCP mice developed papillomas over the course of the study than did DMBA/acetone controls, the time it took for half of the number of responding animals to develop papillomas was similar between DMBA/acetone groups and DMBA/3.0 mg BCP groups (DMBA/acetone males, week 38; DMBA/acetone females, week 34; DMBA/3.0 mg BCP males, week 36; DMBA/3.0 mg BCP females, week 37). However, the time to appearance of the first papilloma was shorter in DMBA/3.0 mg BCP mice (males, week 18; females, week 10) than in DMBA/acetone mice (males, week 26; females, week 27). BCP was considered to have promotion potential because the incidences of papillomas in mice treated with DMBA/3.0 mg BCP were greater than those in DMBA/acetone (initiator control) mice and because topical exposure to BCP alone caused no significant increased incidence of papillomas. However, the incidences of papillomas in DMBA/3.0 mg BCP mice (males, 14/50; females, 18/50) were much less than the incidences in DMBA/TPA (promoter control) mice (males, 40/50; females, 48/50); thus, BCP was classified as a weak promoter. GENETIC TOXICOLOGY: o -Benzyl- p -chlorophenol did not induce gene mutations in Salmonella typhimurium strains TA98, TA100, TA1535, or TA1537, and it did not induce sister chromatid exchanges or chromosomal aberrations in cultured Chinese hamster ovary cells. All tests were performed with and without S9 activation. CONCLUSIONS: Under the conditions of this 1-year mouse skin initiation/promotion study in Swiss (CD-1&reg;) mice, o -benzyl- p -chlorophenol was a cutaneous irritant and a weak skin tumor promoter relative to strong promoters such as TPA. BCP had no activity as an initiator or as a complete carcinogen.