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and Prostatic Diseases (2007) 10, 378–383 & 2007 Nature Publishing Group All rights reserved 1365-7852/07 $30.00 www.nature.com/pcan ORIGINAL ARTICLE

Suppressive effects of , finasteride and on development of prostatic lesions in a transgenic rat model

Y-M Cho1, S Takahashi, M Asamoto, S Suzuki, M Tang and T Shirai Department of Experimental Pathology and Tumor Biology, Nagoya City University Graduate School of Medical Sciences, Mizuho-cho, Mizuho-ku, Nagoya, Japan

Transgenic (TG) rats bearing a probasin promoter/simian virus 40 T antigen (SV40 Tag) construct were treated with antiandrogens to examine their ability to suppress prostate carcinogenesis. Finasteride and flutamide were administered to 10-week-old TG rats five times a week for 2, 5 and 7 weeks. -treated exhibited atrophic glandular structures with almost no expression of SV40 Tag and only weak signals for receptors. Furthermore, quantitative data for ventral prostate adenocarcinomas showed significant decrease with antiandrogen treatment. Both finasteride and flutamide had the ability to suppress SV40 Tag-driven carcinogenesis through their different antiandrogenic mechanisms, suggesting that this TG model is suitable for exploring the potential of agents to inhibit development. Prostate Cancer and Prostatic Diseases (2007) 10, 378–383; doi:10.1038/sj.pcan.4500971; published online 24 April 2007

Keywords: chemoprevention; transgenic rat; finasteride; flutamide

Introduction Approaches to influence androgen levels in prostatic tissue include (a) inhibition of the pituitary secretion of Among US men, prostate cancer is the most common luteinizing hormone (LH) by LH-releasing hormone non-cutaneous neoplasm and the second leading cause (LHRH) analogs, (b) prevention of the conversion of of cancer death. It has been estimated that there will be to (DHT) by 5a-reduc- approximately 234 460 new cases of prostate cancer and tase in the prostate and (c) blocking prostatic androgen 27 350 associated deaths in the United States in 2006.1 receptors (ARs) using -like antagonists with no Over 60% of these newly diagnosed cases of prostate intrinsic activity, to reduce potentially unacceptable cancer will be pathologically advanced; at this stage, systemic toxicity.6 One such is the azasteroid there is no cure and the prognosis is dismal. Since the finasteride.7 Another potential suppressive agent is frequency of latent prostatic tumors has been shown to the nonsteroidal antiandrogen flutamide, which exerts increase with each decade of life from the 50s (5.3–14%) to effects by interfering with the binding of DHT or the 90s (40–80%)2 and relatively long time periods are testosterone to the AR.5 necessary for progression to actual prostate cancer, the The study of prostate cancer chemoprevention and concept of chemoprevention has attracted much attention. treatment has been hindered by the lack of appropriate The majority of prostate initially respond to animal models. Recently, we have established transgenic androgen ablation therapy because of hormone-depen- (TG) rats, designated TRAP (Transgenic Rat for Adeno- dent growth,3 but relapse with generation of hormone- carcinoma of the Prostate), bearing a probasin promoter/ independent cancer cell occurs and eventually leads to a simian virus 40 T antigen (SV40 Tag) construct in which fatal outcome in many cases.4,5 Although androgen androgen-dependent prostate cancers develop rapidly.8–10 ablation at this hormone refractory stage is ineffective, In our TRAP model, high-grade prostatic intraepithe- androgen deprivation strategy as an early intervention lial neoplasia (PINs) are found from 4 weeks of age, and may delay the promotion and/or progression of prostate prostate adenocarcinomas in the ventral, dorsolateral cancer, resulting in reduced morbidity and mortality. and anterior lobes are observed at 100% incidences before 15 weeks of age. Prostate adenocarcinomas Correspondence: Dr S Takahashi, Department of Experimental developing in TRAP are strictly androgen dependent in Pathology and Tumor Biology, Nagoya City University Graduate a pattern similar to that of human primary prostate School of Medical Sciences, 1 Kawasumi, Mizuho-cho, Mizuho-ku, cancer. TRAP lesions have many advantages, for Nagoya 467-8601, Japan. example, their large size allows adequate materials to E-mail: [email protected] be obtained and development of prostate cancer occurs 1Current address: Division of Pathology, National Institute of Health Sciences, Setagaya-ku, Tokyo, Japan in a shorter experimental period and more efficiently Received 20 December 2006; revised and accepted 26 March 2007; compared with several other rat prostate carcinogenesis 11–19 published online 24 April 2007 models. These characteristics of TRAP may make it Suppressive effects of antiandrogens, finasteride and flutamide Y-M Cho et al particularly suitable for evaluation of strategies for were demonstrated with diaminobenzidine as the 379 chemoprevention and treatment. The present study was substrate. conducted to assess whether finasteride and flutamide have the ability to suppress prostate carcinogenesis in our TRAP model. Statistical analysis Statistical analysis of differences between means and incidences was carried out using analysis of variance and Materials and methods the Kruskal–Wallis test, respectively. When positive results were obtained, the Mann–Whitney U-test with Animal and treatment Bonferroni correction was applied to evaluate the Male heterozygous TRAP rats established in our labora- statistical significance between treatment groups. tory with a Sprague–Dawley genetic background were used in the present study.8,9 They were housed three/ cage on wood-chip bedding in an air-conditioned animal Results room at 23721C and 50710% humidity, with food (Oriental MF, Oriental Yeast Co., Tokyo, Japan) and tap TRAP rats treated with finasteride or the high dose of water available ad libitum. Finasteride (Merck KGaA, flutamide for 5 and 7 weeks showed significantly Darmstadt, Germany) and flutamide (Nippon Kayaku (Po0.001) lower prostate weights relative to body Co. Ltd, Tokyo, Japan) were suspended in 0.5% methyl- weights as compared to controls (Table 1). Macroscopi- cellulose 400 cP (Wako Pure Chemical Industries Ltd, cally, prostates of TRAP in the non-treated group showed Osaka, Japan) and administrated to 10-week-old TG rats slight enlargement and irregular surfaces but no appar- five times a week via intragastric route at concentrations ent nodule or mass formation. In contrast, antiandrogen of 10 and 5 or 20 mg/kg, respectively. Animals were treatment was associated with obvious prostate and then killed at weeks 2, 5 and 7, and lesions in the prostate seminal vesicle . Histopathological findings for were histopathologically classified as described pre- prostatic lesions are summarized in Table 2. Antiandro- viously into PIN and adenocarcinoma categories.8 The gen treatment for 2 weeks caused destruction of areas of lesions in each prostate sample were quantita- glandular structure with inflammatory cell infiltration tively measured with an Image Processor for Analytical (Figure 1a). After treatment for 7 weeks, atrophic glands Pathology (Sumika Technos Co., Osaka). Testosterone were frequently observed with minimal nuclear atypia levels in serum were also analyzed by radioimmuno- (Figures 1b and 2). PINs and/or adenocarcinomas were assay at a commercial laboratory (SRL, Tokyo). detected in all lobes. There were no statistically sig- The present experiment was performed under proto- nificant differences in the incidences of PINs or cols approved by the Institutional Animal Care and Use adenocarcinomas among the groups. However, the areas Committee of Nagoya City University Graduate School of lesions were significantly reduced in finasteride- and of Medical Sciences. high dose of flutamide-treated groups in the ventral and lateral lobes, but not the dorsal lobe. The lesions also tended to be suppressed without significance by low- Immunohistochemistry analysis dose flutamide in all lobes (Table 3). The avidin–biotin–peroxidase complex (ABC) method Almost no expression of the SV40 Tag and only weak was used to determine the expression of the SV40 signals for AR were detected in involuted glands of rats Tag and the AR in prostate epithelial cells. Prostate treated with antiandrogens (Figure 3). Serum testoster- sections were treated with mouse anti-SV40 Tag (1:250, one levels were not influenced by finasteride treatment. Pharmingen, San Diego, CA, USA), or rabbit anti-AR On the other hand, the levels of testosterone were (1:200, Affinity Bioreagents, Golden, CO, USA) and significantly (Po0.001) increased in the flutamide-trea- then sequentially with secondary antibody and ABC ted groups in a dose-dependent manner at week 5. At (Vectastain ABC Elite kit, Vector Laboratories, week 7, however, levels had returned to normal level Burlingame, CA, USA). The sites of peroxidase binding (Figure 4).

Table 1 Relative prostate weights in TRAP rats treated with finasteride or flutamide for 5 and 7 weeks Duration Treatment No. of rats Final body weight (g) Relative prostate weight (%)

Dorsolateral lobe Anterior lobe and

5 weeks Finasteride 10 mg/kg 5 429.4715.9 0.1570.02 0.2470.03*** Flutamide 20 mg/kg 5 397.7753.2 0.1170.02** 0.2170.07*** Flutamide 5 mg/kg 5 424.8743.5 0.1570.02 0.3570.05* Control 5 407.8756.1 0.1770.06 0.4070.16

7 weeks Finasteride 10 mg/kg 5 478.4754.9 0.1270.01*** 0.1870.02*** Flutamide 20 mg/kg 5 449.4725.8 0.1170.02*** 0.2270.09*** Flutamide 5 mg/kg 5 469.3748.3 0.1970.01 0.3870.07 Control 5 462.7727.1 0.2270.03 0.4370.06

Values are mean7s.d. *, **, ***: significantly different from the control group at Po0.05, 0.01 and 0.001, respectively.

Prostate Cancer and Prostatic Diseases Suppressive effects of antiandrogens, finasteride and flutamide Y-M Cho et al 380 Table 2 Histopathological findings of neoplastic lesions in TRAP rats Duration Treatment No. of rats No. of rats with prostatic lesion

Ventral Dorsal Lateral Anterior

PIN Ca PIN Ca PIN Ca Ca

2 weeks Finasteride 10 mg/kg 5 0 5 3 2 1 4 5 Flutamide 20 mg/kg 4 0 4 3 1 0 4 4 Flutamide 5 mg/kg 5 1 4 3 2 1 4 5 Control 5 0 5 3 2 3 2 5

5 weeks Finasteride 10 mg/kg 5 1 4 1 4 1 4 5 Flutamide 20 mg/kg 5 1 4 2 3 0 5 5 Flutamide 5 mg/kg 5 0 5 3 2 0 5 5 Control 5 1 4 2 3 1 4 5

7 weeks Finasteride 10 mg/kg 5 0 5 3 2 0 5 5 Flutamide 20 mg/kg 5 0 5 4 1 2 3 5 Flutamide 5 mg/kg 5 0 5 1 4 0 5 5 Control 5 1 4 2 3 1 4 5

Abbreviations: Ca, carcinoma; PIN, prostatic intraepithelial neoplasia; TRAP, TG rat for adenocarcinoma of the prostate.

Figure 1 Representative findings for involuted prostate cancer lesions in TRAP rats treated with antiandrogen flutamide for 2 (a) and 7 (b) weeks. Original magnification, Â 400. TRAP, TG rat for adenocarcinoma of the prostate.

Discussion orchiectomy at 5 or 20 weeks of age causes severe involution or regression, and inhibition of prostate TG animal models are powerful tools for screening carcinoma development, in clear contrast to the case chemopreventive or therapeutic agents against cancer with TRAMP mice that demonstrated the development because cancer lesions develop uniformly and rapidly in of poorly differentiated prostate cancer with 80% TG animals. To date, a number TG animals for prostate incidence at 12 weeks after castration.8,23 Oral adminis- cancer research have been established and all of them are tration of finasteride for 2 months to methylnitrosourea/ mice except our TRAP rats.20,21 Among them, TG -inoculated male Wistar rats adenocarcinoma mouse prostate (TRAMP) model, har- reduced the tumor incidence to 10%, as compared with boring rat probasin promoter/SV40 Tag gene construct, the 64.3% of the control group.24 Recently, the National is widely used. TRAMP mice demonstrated the devel- Cancer Institute-sponsored Prostate Cancer Prevention opment of well-differentiated adenocarcinomas in pros- Trial designed to investigate the efficacy of a variety of tate by 10 weeks of age and of poorly differentiated agents ranging from dietary supplements to laboratory metastatic, androgen-independent tumors by 28 weeks manufactured drugs for the primary chemoprevention of of age.22,23 In our TRAP rats, well-moderately differ- prostate cancer demonstrated that finasteride can pre- entiated adenocarcinomas similarly developed in pros- vent prostate cancer.25 The observed 25% reduction in tate by 10–15 weeks of age. However, all the 7-year period prevalence of prostate cancer in men adenocarcinomas in TRAP rats were completely andro- over age 55 years and few side effects25 provides strong gen dependent and did not metastasize.9 support for the importance of hormonal control for Hormonal factors play important roles in carcinogen- primary prostate cancer. esis as well as the homeostasis in the prostate gland. In the present study, there were massive or partial Because promote prostate carcinogenesis, pathologic responses by flutamide or finasteride treat- inhibition of androgenic functions is a fundamental ment as demonstrated by the reduction of prostatic approach to control prostate cancer. Our previous studies neoplastic lesions in TRAP rats. However, these re- on the initiation and progression of prostate cancer using sponses were not complete, that is, small or tiny foci of TRAP rats demonstrated that androgen depletion by carcinoma were still remaining. Reflecting these findings,

Prostate Cancer and Prostatic Diseases Suppressive effects of antiandrogens, finasteride and flutamide Y-M Cho et al 381

Figure 2 Representative findings for involuted prostate cancer lesions in TRAP rats treated with finasteride 10 mg/kg/day (a), flutamide 20 mg/kg/day (b), flutamide 5 mg/kg/day (c) or vehicle (d) five times a week for 7 weeks. Original magnification, Â 40. TRAP, TG rat for adenocarcinoma of the prostate.

Table 3 Quantitative data for proliferative lesions in prostate of TRAP rats treated with finasteride or flutamide for 7 weeks Treatment No. of rats Epithelial area/acinus (%) examined Ventral Dorsal Lateral

Finasteride 10 mg/kg 5 80.173.2* 60.273.9 56.973.5** Flutamide 20 mg/kg 5 77.879.1* 63.273.6 65.274.7** Flutamide 5 mg/kg 5 87.772.0 59.773.9 71.4710.0 Control 4 93.374.0 66.071.9 81.576.4

Abbreviation: TG rat for adenocarcinoma of the prostate. Values are mean7s.d. *, **: significantly different from the control group at Po0.05 and 0.01, respectively.

Figure 3 Representative findings for AR and SV40Tag protein expression in serial sections of partially involuted prostate glands in TRAP rats treated with antiandrogen finasteride for 7 weeks. Similar expression was evident in rats treated with flutamide. (a) H&E. (b) AR. (c) SV40 Tag. Original magnification, Â 400. AR, ; H&E, hematoxylin and eosin; TRAP, TG Rat for adenocarcinoma of the prostate. there were no significant differences in the incidences of tumors although well-differentiated tumors were ob- PIN or adenocarcinoma in the prostate of TRAP rats. In served more frequently,6 suggesting that it is difficult to TRAMP mice, high-dose flutamide significantly de- exert complete pathologic responses by flutamide alone creased the incidence of only poorly differentiated against well-differentiated prostate tumors induced by

Prostate Cancer and Prostatic Diseases Suppressive effects of antiandrogens, finasteride and flutamide Y-M Cho et al

382 Welfare of Japan, and a grant from the Society for Promotion of Toxicological Pathology in Nagoya, Japan.

References

1 Jemal A, Siegel R, Ward E, Murray T, Xu J, Smigal C et al. Cancer statistics, 2006. CA Cancer J Clin 2006; 56: 106–130. 2 Sheldon CA, Williams RD, Fraley EE. Incidental carcinoma of the prostate: a review of the literature and critical reappraisal of classification. JUrol1980; 124: 626–631. 3 Cunha GR, Donjacour AA, Cooke PS, Mee S, Bigsby RM, Higgins SJ et al. The endocrinology and developmental biology of the prostate. Endocr Rev 1987; 8: 338–362. Figure 4 Effects of finasteride and flutamide treatment on serum 4 Crawford ED, Eisenberger MA, McLeod DG, Spaulding JT, testosterone levels in TRAP rats. Control,& finasteride 10 mg/kg, Benson R, Dorr FA et al. A controlled trial of leuprolide with and flutamide 20 mg/kg,’ flutamide 5 mg/kg. * Significantly without flutamide in prostatic carcinoma. N Engl J Med 1989; different from the control value at Po0.001. TRAP, TG rat for 321: 419–424. adenocarcinoma of the prostate. 5 Denis LJ, Griffiths K. Endocrine treatment in prostate cancer. Semin Surg Oncol 2000; 18: 52–74. SV40 Tag in TG animals. Involution of the prostate 6 Raghow S, Kuliyev E, Steakley M, Greenberg N, Steiner MS. accompanied suppressed expression of transgene and Efficacious chemoprevention of primary prostate cancer by AR. Similar histopathological findings have been ob- flutamide in an autochthonous transgenic model. Cancer Res 2000; 60: 4093–4097. served in human prostate cancer cases who received 26 7 Steiner JF. Finasteride: a 5 alpha-reductase inhibitor. Clin Pharm hormonal therapy with finasteride or AR antagonists. 1993; 12: 15–23. Although there were no significant changes in serum 8 Asamoto M, Hokaiwado N, Cho YM, Takahashi S, Ikeda Y, testosterone concentration in the present study, relative Imaida K et al. Prostate carcinomas developing in transgenic rats prostate weights were obviously reduced by finasteride with SV40 T antigen expression under probasin promoter control administration and prostate adenocarcinoma develop- are strictly androgen dependent. Cancer Res 2001; 61: 4693–4700. ment was significantly suppressed. It is well known that 9 Cho YM, Takahashi S, Asamoto M, Suzuki S, Inaguma S, treatment with flutamide causes a marked increase of Hokaiwado N et al. Age-dependent histopathological findings in serum testosterone associated with inhibition of the the prostate of probasin/SV40 T antigen transgenic rats: lack of negative feedback response to testosterone by the influence of carcinogen or testosterone treatment. Cancer Sci 27 2003; 94: 153–157. hypothalamus. The reason for return to a normal 10 Asamoto M, Hokaiwado N, Cho YM, Shirai T. Effects of genetic testosterone level after flutamide treatment for 7 weeks background on prostate and taste bud carcinogenesis due to found here is unclear. It is plausible that continuous SV40 T antigen expression under probasin gene promoter flutamide treatment acts at the level of the anterior control. Carcinogenesis 2002; 23: 463–467. pituitary gland by blocking the secretion of bioactive LH, 11 Shirai T, Iwasaki S, Masui T, Mori T, Kato T, Ito N. Enhancing thus depriving the testes of their physiologic stimulus effect of cadmium on rat ventral prostate carcinogenesis induced and causing an arrest of androgen secretion. It has been by 3,20-dimethyl-4-aminobiphenyl. Jpn J Cancer Res 1993; 84: shown that LH-releasing hormone (LHRH) can 1023–1030. 12 Shirai T, Imaida K, Masui T, Iwasaki S, Mori T, Kato T et al. transitionally stimulate serum testosterone release, and 0 5 Effects of testosterone, dihydrotestosterone and on 3,2 - then reduce the level through blocking LH. dimethyl-4-aminobiphenyl-induced rat prostate carcinogenesis. Treatment with the two antiandrogens here resulted in Int J Cancer 1994; 57: 224–228. decreased expression of SV40 Tag via inhibition of AR 13 Shirai T, Tamano S, Sano M, Imaida K, Hagiwara A, Futakuchi M function. The SV40 Tag acts as an oncoprotein through et al. Site-specific effects of testosterone propionate on the interaction with both retinoblastoma (Rb)28 and p53 prostate of rat pretreated with 3,20-dimethyl-4-aminobiphenyl: tumor-suppressor gene products.29,30 Loss of p53 and dose-dependent induction of invasive carcinomas. Jpn J Cancer Rb genes has been implicated in the development of Res 1995; 86: 645–648. prostate cancer31,32 and in the TRAP model, SV40 Tag 14 Shirai T, Fukushima S, Ikawa E, Tagawa Y, Ito N. Induction of prostate carcinoma in situ at high incidence in F344 rats by a expression leads to abrogation of p53 and Rb functions, 0 predisposing these cells to genetic instability. Although combination of 3,2 -dimethyl-4-aminobiphenyl and ethinyl . Cancer Res 1986; 46: 6423–6426. the TRAP model significantly differs from human 15 Kawabe M, Shibata MA, Sano M, Takesada Y, Tamano S, Ito N prostate cancers regarding the status of p53 and Rb until et al. Decrease of prostaglandin E2 and 5-bromo-20-deoxyuridine late stages, it provides a very sensitive system to measure labeling but not prostate tumor development by indomethacin the consequence of hormone ablation in an in vivo model treatment of rats given 3,20-dimethyl-4-aminobiphenyl and and assess the efficacy of potential androgen analogs testosterone propionate. Jpn J Cancer Res 1997; 88: 350–355. because carcinogenesis in this model is primarily 16 Miyata E, Kawabe M, Sano M, Takesada Y, Takahashi S, Shirai T. androgen driven. Effects of , an , on rat prostate carcinogen- esis by 3,20-dimethyl-4-aminobiphenyl and testosterone do not support an estrogen role in testosterone promotion. Prostate 1997; 31: 9–13. 17 Cui L, Mori T, Takahashi S, Imaida K, Akagi K, Yada H et al. Acknowledgements Slight promotion effects of intermittent administration of testosterone propionate and/or on 3,20-di- This work was supported in part by a Grant-in Aid for methyl-4-aminobiphenyl- initiated rat prostate carcinogenesis. cancer research from the Ministry of Health, Labour and Cancer Lett 1998; 122: 195–199.

Prostate Cancer and Prostatic Diseases Suppressive effects of antiandrogens, finasteride and flutamide Y-M Cho et al 383 18 Tsukamoto S, Akaza H, Onozawa M, Shirai T, Ideyama Y. A five- 25 Thompson IM, Goodman PJ, Tangen CM, Lucia MS, Miller GJ, alpha reductase inhibitor or an antiandrogen prevents the Ford LG et al. The influence of finasteride on the development of progression of microscopic prostate carcinoma to macroscopic prostate cancer. N Engl J Med 2003; 349: 215–224. carcinoma in rats. Cancer 1998; 82: 531–537. 26 Bostwick DG, Qian J, Civantos F, Roehrborn CG, Montironi R. 19 Bosland MC. Use of animal models in defining efficacy of Does finasteride alter the pathology of the prostate and cancer chemoprevention agents against prostate cancer. Eur Urol 1999; grading? Clin Prostate Cancer 2004; 2: 228–235. 35: 459–463. 27 Marchetti B, Labrie F. Characteristics of flutamide action on 20 Kasper S, Smith Jr JA. Genetically modified mice and their use in prostatic and testicular functions in the rat. J Steroid Biochem developing therapeutic strategies for prostate cancer. JUrol2004; 1988; 29: 691–698. 172: 12–19. 28 DeCaprio JA, Ludlow JW, Figge J, Shew JY, Huang CM, Lee WH 21 Shappell SB, Thomas GV, Roberts RL, Herbert R, Ittmann MM, et al. SV40 large tumor antigen forms a specific complex with the Rubin MA et al. Prostate pathology of genetically engineered mice: product of the retinoblastoma susceptibility gene. Cell 1988; 54: definitions and classification. The concensus report from the Bar 275–283. Harbor Meeting of the Mouse Models of Human Cancer 29 Lane DP, Crawford LV. T antigen is bound to a host protein in Consortium Prostate Pathology Committee. Cancer Res 2004; SV40-transformed cells. Nature 1979; 278: 261–263. 64: 2270–2305. 30 Linzer DI, Levine AJ. Characterization of a 54K dalton 22 Gingrich JR, Barrios RJ, Morton RA, Boyce BF, DeMayo FJ, cellular SV40 tumor antigen present in SV40-transformed Finegold MJ et al. Metastatic prostate cancer in a transgenic cells and uninfected embryonal carcinoma cells. Cell 1979; 17: mouse. Cancer Res 1996; 56: 4096–4102. 43–52. 23 Gingrich JR, Barrios RJ, Kattan MW, Nahm HS, Finegold MJ, 31 Levine AJ, Momand J, Finlay CA. The p53 tumour suppressor Greenberg NM. Androgen-independent prostate cancer progres- gene. Nature 1991; 351: 453–456. sion in the TRAMP model. Cancer Res 1997; 57: 4687–4691. 32 Bookstein R, Rio P, Madreperla SA, Hong F, Allred C, Grizzle 24 Esmat AY, Refaie FM, Shaheen MH, Said MM. Chemoprevention WE et al. Promoter deletion and loss of retinoblastoma gene of prostate carcinogenesis by DFMO and/or finasteride treat- expression in human prostate carcinoma. Proc Natl Acad Sci USA ment in male Wistar rats. Tumori 2002; 88: 513–521. 1990; 87: 7762–7766.

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