Chemopreventive Activity of Tamoxifen, N-(4-Hydroxyphenyl

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[CANCERRESEARCH55. 5621-5627. December 1. 1995] Chemopreventive Activity of Tamoxifen, N-(4-Hydroxyphenyl)retinamide, and the Vitamin D Analogue Ro24-5531 for Androgen-promoted Carcinomas of the Rat Seminal Vesicle and Prostate

@ M. Scott 2 Mario A. Anzano,' Michael V. Miriam R. Anver, Darlene M. Green, Mark W. Shrader, Daniel L. Logsdon, Craig L. Driver, Charles C. Brown, Christopher W. Peer, Anita B. Roberts, and Michael B. Sporn4

Laboratory of Chemoprevention (M. S. L, M. A. A., C. W. P.. A. B. R., M. B. S.] and Biometry Branch (C. C. B.]. National Cancer Institute, NIH, Bethesda, Maryland 20892; Department of Veterinary Pathology. Armed Forces Institute of Pathology, Washington DC 20306 (M. V. S.]; and Science Applications International Corporation-Frederick, Frederick, Maryland 21702 (M. R. A.. D. M. G., M. W. S., D. L L, C. L D.]

ABSTRACT genitally deficient in Sa-reductase, which converts testosterone to Sa-dihydrotestosterone, have poorly developed prostates and have not We evaluated the ability of dietary N-(4-hydroxyphenyl)retinamide; been reported to develop prostatic carcinoma (9). Likewise, men who lcv,25-dihydroxy-16-ene-23-yne-26,27-hexafluorocholecalciferol (Ro24- are castrated before the age of 40 have a much lower than expected 5531); and tamoxifen to inhibit the development of androgen-promoted carcinomas of the accessory sex organs of male Lobund-Wistar rats. incidence rate for prostatic carcinoma as they age (10). With this in Invasive carcinomas ofthe seminal vesicle (SV) and anterior prostate (AP) mind, a chemoprevention strategy aimed at inhibiting androgen-pro were induced in Lobund-Wistar rats with three different combinations of moted carcinogenesis may be effective in reducing the incidence of initiator [N-nitroso-N-methylurea (NMU)] and promoter [testosterone invasive prostatic carcinoma. propionate (TP)]: (a) high-dose NMU (30 mg/kg) + high-dose TP (20 mg A major obstacle for carcinogenesis and chemoprevention studies via implant every 2 months); (b) high-dose NMU + low-dose TP (10 mg for prostate carcinoma has been the development of a suitable animal implanted every 2 months); or (c) low-dose NMU (15 mg/kg) + low-dose model (I 1, 12). The LW5 rat has been shown to develop tumors in the TP. During the period of TP administration, rats were fed a diet supple â€œprostatecomplexâ€•after initiation with NMU and promotion with TP mented with either N-(4-hydroxyphenyl)retinamide (1 or 2 mmol/kg diet), (13,14).AlthoughmanyofthesetumorsarisefromtheSV,whichhas Ro24-5531 (L25 or 2.5 nmol/kg diet), tamoxifen (0.5 or 5 mg(kg diet), or vehicle alone. After sacrifice at 8.5 or 11 months, the prostate-seminal been considered a major drawback to this model, it nevertheless vesicle complex from each rat was processed in toto and histologically represents a defined example of androgen-promoted carcinoma. Using staged as to the extent of tumor involvement. In animals given low-dose the LW rat model, we have evaluated three potential chemopreventive TP, all three agents were significantly effective at reducing the incidence agents: 4-HPR (fenretinide); Ro24-S53l (a synthetic vitamin D asia of invasive carcinomas of the SV and, to a lesser degree, the AP. Of the logue); and the estrogen response modifier tamoxifen. three agents, tamoxifen given in high dose (5 mg/kg) had the strongest The potential efficacy of these agents for chemoprevention has activity, reducing the occurrence of invasive SV carcinomas from 72â€”83% been reported in a variety of systems. In clinical studies, retinoids in controls to 6% (P 0.0001) and the occurrence of invasive AP have been shown to have chemopreventive activity for carcinomas carcinomas from 50â€”72%to18â€”22%(P< 0.05). arising in the head and neck (15, 16). In the laboratory, 4-HPR has shown chemopreventive activity for carcinomas of the mouse urinary INTRODUCTION bladder (17) and the rat mammary gland (18) and prostate (19). Dietary 4-HPR has been reported to decrease the incidence and mass Over the last 25 years, despite aggressive efforts toward earlier of ras- and myc-induced carcinomas in a mouse prostate reconstitu detection and treatment, the mortality rate for prostatic carcinoma has tion model (20). Several prostatic carcinoma cell lines have receptors steadily increased (1). The high mortality rate, now the second highest for vitamin D (21, 22), and the active form of vitamin D, 1,25-D3, has among cancers of males in the United States, is due largely to the fact growth-inhibitory activity for these cell lines in serum-based cell that the majority of patients have advanced disease beyond the con culture growth assays (21), as well as for primary cultures derived fines of the prostate by the time of diagnosis (2). The identification of from normal or carcinomatous human prostates (23). A variety of androgens as the major regulator of prostatic epithelial proliferation, vitamin D analogues (deltanoids) have also been shown to inhibit both in the normal prostate and in prostatic carcinomas, was originally growth in a similar fashion (24, 25) and to stimulate the secretion of hoped to offer a target for therapeutic intervention for such advanced prostate-specific antigen in the human LNCaP prostate carcinoma cell tumors (3â€”5).However, in practice, the concept of â€œtotalandrogen line (24). 1,25-D3 has also shown some chemopreventive activity for ablationâ€•therapy has found only limited success (2, 4). As treatment colon adenocarcinomas induced with l,2-dimethylhydrazine (26). failures for advanced carcinoma continue to frustrate clinicians, more The estrogen response modifier tamoxifen has for some time been emphasis has recently been focused on possible strategies to prevent used in the hormonal therapy of breast carcinomas in women. There the development of invasive prostatic carcinoma (6 â€”8).Testosterone are no reports of its use in males for prostate cancer. However, it has or its more active metabolite (Sce-dihydrotestosterone) is recognized as the major promoter for prostatic malignancy. As such, men con been shown that the promoting activity of testosterone for prostate carcinogenesis in rats is potentiated by E2 (27). This potentiation may be a result of up-regulation of androgen receptor in the prostate by E@ Received 6/19/95; accepted 9/26/95. The costs of publication of this article were defrayed in part by the payment of page (28, 29), an increased Vmaxfor nuclear 5a-reductase (30), or an as yet charges. This article must therefore be hereby marked advertisement in accordance with unidentified mechanism. 18 U.S.C. Section 1734 solely to indicate this fact. I These authors are all considered first authors on the work described herein. 2 To whom requests for reprints should be addressed, at Department of Pathology, Box 5 The abbreviations used are: LW, Lobund-Wistar, 4-HPR, N-(4-hydroxyphenyl)reti B-216,UniversityofColoradoMedicalCenter,Denver,CO80262. namide (fenretinide); Ro24-5531, la,25-dihydroxy-l6-ene-23-yne-26,27-hexafiuoro 3 Present address: Stine-Haskell Research Center, DuPont Merck Pharmaceutical cholecalciferol; l,25-D3, la,25-dihydroxycholecalciferol (1,23-dihydroxyvitamin D3); Company, Newark, DE 19714. E2, estradiol; NMU, N-nitroso-N-methylurea; TP, testosterone propionate; SV, seminal 4 Present address: Department of Pharmacology, Dartmouth Medical School, Hanover, vesicle; AP, anterior prostate; DLP, dorsolateral prostate; VP, ventral prostate; TGF-@, NH 03755. transforming growth factor 13. 5621

MATERIALS AND METHODS

LW rats were obtained and housed at the National Cancer Institute Fred crick Cancer Research and Development Center (Frederick, MD) from an original breeding stock provided as a gift by Dr. Morris Pollard (University of Notre Dame).Three animals per cage were housed in polycarbonatecages with Sani-Chips bedding in a controlled environment with lighting between 6 a.m. and 6 p.m. At all times, water and diet were provided ad !ibitum.The animals were 3 months old at the beginning of the experiments. The procedure for tumor induction was the same as described previously (14), with the following exceptions. Three different combinations of the carcinogen (NMU) and promoter (TP) were used. In Experiment A, the i.v. dose of NMU (Ash Stevens, Detroit, MI) was 30 mg/kg body weight, whereas the implanted dose of TP (Sigma Chemical Co., St. Louis, MO) was 20 mg. In Experiment B, the implanted dose of TP was decreased to 10 mg, whereas the dose of NMU remained at 30 mg/kg body weight. In Experiment C, the dose of NMU was decreased to 15 mg/kg body weight, and the implanted dose of TP was reduced to 10 mg. The TP implants were replaced every 2 months for the duration of the experiments. In each of the 3 experiments, a total of 126 animals were divided into 7 treatment groups of 18 animals each: group 1, control diet; group 2, Ro24-5531 (2.5 nmollkg diet, Hoffmann-LaRoche, Nutley, NJ); group 3, Ro24-553l (1.25 nmol/kg diet); group 4, 4-HPR (2 mmol/kg diet, R. W. Johnson Pharmaceutical Research Institute, Spring House, PA); group 5, 4-HPR (I mmol/kg diet); group 6, tamoxifen (5 mg/kg diet, Sigma); and group 7, tamoxifen (0.5 mg/kg diet). All the test compounds were dissolved in ethanol and incorporated into Purina 5002 diet (Purina Mills, Inc., St. Louis, MO), along with Neobee M-5 oil (37.5 mi/kg diet, Stepan Chemical, Maywood, NJ) and Tenox 5 (1 mI/kg diet, Eastman Chemical, Kingsport, TN). Control diet consisted of ethanol vehicle, along with Neobee oil and Tenox 5. At the end of the experimental time period (either 8.5 or 11 months), the animals were euthanized with CO2. and the accessory sex organs were re moved, weighed, and fixed in 10% neutral buffered formalin. The AP (coag ulating gland), DLP, and SVs were step-sectioned at 50 @mthroughthe entire organ. A single section was taken of the VP. Hematoxylin and eosin-stained sections were examined and staged as described previously (14). Briefly, stages 1 and 2 are lesions with intraepithelial neoplastic changes (stage 1, one or two foci; stage 2, three or more foci), stages 3 and 4 lesions are characterized by stromal invasion (stage 3, one or two foci; stage 4, two or more foci), stage Fig. 1. A, AP: control diet, stage 3 carcinoma. Variably-sized, irregular glands invade the stroma H & E. X200. B, SV: control diet, stage 3 carcinoma. Infiltrating glands and S lesions are characterized by a marked scirrhous reaction confined to the cords of cells abutting, but not penetrating, the capsule. H&E. X 100. gland of origin, and stage 6 lesions are characterized by a markedly invasive scirrhous tumor that can no longer be traced to a particular organ of origin. Stage 0 represents histologically normal tissue. The results were analyzed for Histologically, there was glandular atrophy manifested by attenuation differences in the development of invasive tumors in all regions of the of the epithelium and a decrease in secretion accompanied by a prostate-SV complex between the test groups and control using Fisher's exact general shrinkage in size in all portions of the prostate complex. The test. Animals were also evaluated stage-for-stage using Wilcoxon's rank sum Sv, AP, and central areas of the DLP appeared to be the most severely test. involved(Fig.3). Tables 1â€”3summarize the results for three separate experiments RESULTS (A, B, and C). In Experiment A, rats were initiated with a 30 mg/kg i.v. dose of NMU, followed by s.c. implantation of 20 mg TP every Histopathological assessment of hematoxylin and eosin-stained se 2 months for the duration of the experiment. Using this dosage ml sectionsthroughtheentireprostate-SVcomplexofeveryanimal regimen, a substantial number of rats developed large palpable was made for each of three separate experiments. The three experi tumors within 8Â½months, which histologically corresponded to ments were reviewed by separate pathologists: Experiment A by stage 5 and 6 lesions (Table 1). None of the three chemopreventive M. R. A.; Experiment B by M. V. S.; and Experiment C by M. S. L. agents were particularly effective in Experiment A, and there were In all experiments, the SV showed the largest numbers of invasive no statistically significant trends in the data, with the exception of carcinomas followed by the AP (Fig. 1). Invasive tumors definitively high-dose tamoxifen (S mg/kg of diet), which decreased the num arising in the DLP were rare and were seen only with high doses of ber of invasive tumors (stage 3â€”6)of the SV by 28% over control NMU and TP (see below). No tumors were seen in the VP. The (P = 0.04). It was postulated that the dosage of carcinogen and concentrations of the respective chemopreventive agents were the promoter were too high to allow evidence of any potential inhib same for all three experiments. Body weights of the rats in all itory effect of the chemopreventive agents. Furthermore, because treatment groups showed minor reductions compared to control, the the origin of large stage 6 tumors could not be accurately deter largest of which were seen in the high-dose tamoxifen and high-dose mined, a stage 6 value was assigned to all the accessory sex organs, 4-HPR treatment groups having a 21 and 19% reduction in mean body thereby skewing the data toward higher stages in those organs in weight, respectively (Fig. 2A). However, no signs of toxicity were which the tumors did not actually arise. manifest. Tamoxifen also caused a marked reduction in the size and In Experiments B and C, this problem was addressed by decreasing weight of the prostate complex, specifically as shown in Fig. 2B. the dosages of NMU and/or TP. In Experiment B, the dose of NMU 5622

A mmol/kg diet). A trend toward fewer tumors was seen in the low-dose tamoxifen group as well, reaching significance only in the AP. Al though there was an apparent reduction of invasive lesions in the DLP for high-dose tamoxifen and 4HPR, these numbers were considered 500 inaccurate due to the number of stage 6 lesions obscuring the DLP of controls; such lesions likely did not actually arise within the DLP. No

400 significant differences could be seen in any of the treatment groups for the DLP. In Experiment C, the dosages of NMU and TP were reduced to 15 â€¢g,300 mg/kg and 10 mg/implant, respectively. This regimen resulted in far a fewer advanced lesions at 11 months, allowing for improved stratifi

â€¢g200 cation of the data (Table 3). Control animals still showed a high number of invasive lesions arising in the SV (83% stage 3) and the AP (50% stage 3). No invasive tumors were seen in the DLP, 100 although areas of in situ neoplasia (stage 1 and 2) were apparent. The efficacy for all chemopreventive agents tested was much more appar 0 ent with this protocol. For tumors arising in the SV, all three corn Control Ro24- Ro24- 4-HPR 4-HPR Tam Tam pounds gave significant inhibition of tumor incidence and progres 5531 5531 High Low High Low High Low sion; the most dramatic effects again occurred with high-dose tamoxifen. In this case, high-dose tamoxifen decreased the incidence B of invasive SV carcinomas from 83 to 6% (P = 0.0001). High-dose tamoxifen also had significant efficacy in the AP, reducing the mci dence of invasive tumors from 50 to 18% (P = 0.05). As in Exper iment B, there were regressive changes in the prostate complex with high-dose tamoxifen and lesser degrees of regression with low-dose â€¢0 0 tamoxifen. In contrast to Experiment B, low-dose tamoxifen had 0 substantial antitumor activity in both the SV and AP. Low-dose and high-dose 4-HPR reduced the incidence of invasive SV tumors from 83 to 39% (P = 0.01) and 47% (P = 0.03), respectively. However, â€˜C a tumors of the AP were not significantly effected by 4-HPR. Ro24- E 5531 had significant anticarcinogenicactivity in the SV and AP as 0 C-) well; however, a dosage effect could not be clearly demonstrated. a a 0 0@ DISCUSSION One of the major drawbacks to any animal model is their limited analogy to human disease. For the prostate, this is especially true Control Ro24- Ro24- 4-HPR 4-HPR Tam Tam 5531 5531 High Low High Low because no satisfactory spontaneous animal model exists (12). The High Low required use of carcinogens that elicit extensive damage to DNA to

Fig. 2. A, body weights of the rats at termination, Experiment C. Columns, mean; bars, invoke carcinoma causes the natural history of rat tumors to differ SEM. Ro24-5531 high = 2.5 nmollkg diet; Ro24-5531 low = I.25 nmol/kg diet; 4-HPR dramatically from that of human prostatic cancer. Furthermore, the high = 2 mmol/kg diet; 4-HPR low = I mmol/kg diet; tamoxifen high 5.0 mg/kg diet; two species have markedly dissimilar anatomy. The DLP of rats is tamoxifen low = 0.5 mg/kg diet. B, wet weight of prostate-SV complex at termination, Experiment C. Columns, mean expressed as a percentage of body weight; bars, SEM. considered to be most similar to the human posterior prostate lobes, Significance analyzed by Student's t test. whereas the rat AP may be homologous with the median lobe (31, 32). In terms of function, the differences between the rat accessory sex organs and those of the human may be more dramatic (33). Despite remained at 30 mg/kg, whereas the implanted dose of TP was de these differences, the two systems share an important property (i.e., creased to 10 mg. This experiment was terminated after 11 months, their dependence on androgen for development and function; Ref. 32). rather than the 8Â½months in Experiment A. Despite the lower dose of Similarly, the development of invasive carcinomas in the two systems TP, there were still substantial numbers of stage 5 and 6 lesions using appears to be facilitated by androgen (3, 13, 27). Thus, the value of the this regimen (Table 2). However, the chemopreventive effects of rat model used in the present study lies in its dependence on androgen high-dose tamoxifen were much more pronounced, showing a marked as a tumor promoter, rather than its physiological and anatomical reduction of tumor development in the SV and AP. For SV, the resemblance to human prostate carcinoma. number of invasive carcinomas (Stage 3â€”6)fell from 72% in the NMU acts as an initiator in the LW rat model, whereas androgen is control group to 6% in the high-dose tamoxifen group (P = 0.0001). believed to operate as a promoter. In the three experiments of the Invasive carcinomas arising in the AP fell from 72% in the control present study, the rate of tumor growth and, therefore, overall tumor group to 22% (P = 0.003). A stage-for-stage assessment using Wil burden could be controlled by altering the dose of androgen, as well coxon's rank sum test showed P values of 0.0001 and 0.001 for the as that of the carcinogen. The efficacies of the tested chemopreventive effect of the high dose of tamoxifen on carcinogenesis in the SV and agents were optimized when relatively low doses of both the carcin AP, respectively. 4-HPR and Ro24-5531 showed less effective but ogen, NMU (15 mg/kg), and the promoter, TP (10 mg/kg replaced statistically significant suppression of development of invasive tumors every 2 months), were administered. Using this protocol, tumors of the AP (Table 2). It was of interest that the lower dose of 4-HPR remained largely confined to the organ of origin, and the effects of the (1 mmol/kg diet) was much more effective than high-dose 4-HPR (2 tested agents were more dramatic. Because administration of the test 5623

CHEMOPREVENTIONOF ANDROGEN-PROMOTEDCARCINOMA

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Fig. 3. A. SV: control diet. B, SV: high-dose tamoxifen. There is a decrease in epithelial height and amount of secretory material compared to A. C, AP: control diet. D: AP, high-dose tamoxifen. There is a decrease in the epithelial cell height and relative paucity of secretions compared to C. E, DLP: control diet. F, DLP: high-dose tamoxifen. The epithelium is markedly attenuated. Note increase in thickness of smooth muscle surrounding glands in comparison to E (arrows). H&E. X400.

compounds did not commence until 1 week after NMU treatment and Ro24-553l has been shown to significantly inhibit the incidence of during the period of androgen administration, the observed results can mammary carcinomas in rats initiated with NMU (35). This effect was be attributed to inhibitory actions of the agents on androgen-promoted synergistic with tamoxifen. In the current study, Ro24-553l was carcinogenesis. moderately effective at inhibiting the development of carcinomas of We have examined the effects of three compounds (Ro24-5531, the rat SV and AP, reaching statistical significance in Experiment C 4-HPR, and tamoxifen) used individually at two dosage regimens on when the dosage of both the carcinogen and the promoter were inhibition of the development of carcinomas within the prostate corn reduced. However, a dosage effect for this agent could not be dem plex of rats. The DLP, AP, VP, and SVs were separately analyzed. In onstrated. this system, the SV developed the greatest numbers of invasive Fenretinide (or 4-HPR) also showed moderate chemopreventive tumors, followed by the AP, whereas invasive tumors of the DLP activity predominantly for SV tumors (Tables 2 and 3). Again, effi were distinctly rare. No tumors developed in the VP. Therefore, cacy was lost if the dose of TP was too high. This retinoid has shown adequate numbers of invasive tumors for satisfactory statistical anal chernopreventive activity in a number of animal organ systems, in ysis were found only in the SV and AP. cluding the mammary gland (18), bladder (17), and prostate (19). Ro24-553l is a synthetic vitamin D analogue that is about 80-fold Pollard et a!. (19) showed substantial activity for 4-HPR in preventing more active than 1,25-D3 in terms of its ability to inhibit the prolif palpable tumors in the prostate complex. Although the protocol used eration and induce the differentiation of HL-60 leukemia cells (34). in the Pollard et a!. (19) study was similar to ours, it differed in several Additionally, this compound has reduced toxicity (induction of hy major aspects. The diets used differed, which, as previously specu percalcemia) compared to 1,25-D3. In terms of chemoprevention, lated (14), may impact on tumorigenicity. More important, however, 5624

Table I Experiment A: effectsof Ro24-5531.withStageControl5531 4-HPR.and tamoxifenon development of accessory sex organ carcinomas in initiated withNMU (30 mg/kg)and promoted TP (20 mg every 2 monthsf'rats

loweNumberofrats(18)(18) highb 5531 lowc4-HPR highÂ°@4-HPR loweTam highTam (18)(18)(17)(18)(18)DLP0

22 1â€”2 61 78 61 56 59 61 67 3â€”4 0 11 0 6 6 6 0 11AP0 5â€”628 116 6 1733 618 1822 II22

0 1â€”2 39 33 44 22 6 33 28 3â€”4 28 50 39 50 53 50 28 39sv0 5â€”617 II0 17 170 286 350 176

0 1â€”2 0 11 11 6 6 28 0 3â€”4 17 28 17 33 24 11 22 72P/I'0.02P2'0.04 5â€”66 7817 44 726 5612 596 566

Total % with invasive tumor 94 83 83 94 94 78 100

a Numbers in the table are the percentages of rats with lesions of any defined stage. Duration of the experiment was 8.5 months. b Ro24-553 1 , 2.5 nmol/kg diet.

C Ro24-5531, 1.25 nmollkg diet. d 4-HPR, 2 mmol/kg diet.

e 4-HPR, I mmollkg diet. -@Tamoxifen,5.0mg/kggTamoxifen,0.5mg/kgdiet. diet. h pj Wilcoxon's rank sum test (stage-for-stage).

â€˜P2 = Fisher's exact test [invasive (stages 3â€”6) versus noninvasive (stages 0â€”2)].

Table2 EeperimentB:effectsofRo24-5531,withStageControl5531 4-HPR,and tamox(fenon development of accessory sex organ carcinomas in initiated withNMU (30 mg/kg)and promoted TP (10 mg every 2 months!'rats

low'@Numberofrats(18)(18) highb 5531 lOwc4-HPR highâ€•4HPR loweTam highTam (18)(18)(18)(18)(18)DLP0

67 1â€”2 6 0 0 17 6 39 28 3â€”4 0 6 0 0 0 0 0 6AP0 5â€”672 2278 17 3383 072 2261 067

17 1â€”2 6 6 0 6 12 6 6 3â€”4 50 17 50 61 28 22 39 11P1â€•0.050.040.0010.05P2'0.050.003Sv05â€”622 2256 22 3322 1150 1172 044

28 1â€”2 II 6 0 0 0 0 17 3â€”4 II 17 6 11 0 0 6 44pjh0.020.0001P2'0.0001 5â€”617 6128 50 6756 3350 5094 633

Total % with invasive tumor 83 72 100 83 72 22 78

a Numbers in the table are the percentages of rats with lesions of any defined stage. Duration of the experiment was 1 1 months. S Ro24-553 1, 2.5 nmol/kg diet.

C Ro24-5531, 1.25 nmol/kg diet. d 4-HPR, 2 mmol/kg diet. e 4-HPR, 1 mmol/kg diet. 1Tamoxifen,gTamoxifen,0.5mg/kgdiet. 5.0 mg/kg diet. h pj Wilcoxon's rank sum test (stage-for-stage).

â€˜P2 = Fisher's exact test [invasive (stages 3â€”6) versus noninvasive (stages 0â€”2)]. 5625

Table 3 Experiment C: effects of Ro24-5531,withStageControl55314-HPR, and tamox:fen on development of accessory sex organ carcinomas in initiated with NMU (15 mg/kg) arid promoted TP (10 mg every 2 months!'rats loweNumberofrats(18)(17) highâ€• 5531 lowc4-HPR higW'4-HPR loweTam highTam (18)(17)(18)(17)(17)DLP0

72 1â€”2 22 29 28 29 33 29 24 3â€”4 0 0 0 0 0 0 0 0AP0 5â€”678 071 0 065 667 071 076

61 1â€”2 22 6 6 12 39 0 6 3â€”4 50 18 33 35 33 18 24 0P1â€•0.050.0020.011P2'0.05Sv05â€”628 065 12 047 628 082 071

28 1-2 6 24 28 18 0 0 12 3-4 44 24 44 41 28 6 47 0P150.01 5â€”611 3935 18 035 661 1194 041 0.00040.0050.0030.00010.0003P2'0.01 0.020.030.010.00010.03Total

% with invasive tumor10059 6165611853months. a Numbers in the table are the percentages of rats with lesions of any defined stage. Duration of the experiment was 11 b Ro24-553l, 2.5 nmollkg diet.

C Ro24-553 1, 1.25 nmol/kg diet. e4-HPR,1mmollkgdiet.d 4-HPR, 2 mmol/kg diet. 1lamoxifen,gTamoxifen,0.5mg/kgdiet. 5.0 mg/kg diet. h pj Wilcoxon's rank sum test (stage-for-stage).

I P2 = Fisher's exact test [invasive (stages 3â€”6) versus noninvasive (stages 0â€”2)].

our end points were chosen to be able to evaluate smaller (microscop human prostate organ cultures, E2 stimulates [3H]thymidine uptake ic) tumors and, therefore, as noted above, largely organ-confined (42, 43). In the case of human prostate organ cultures, this effect was lesions rather than palpable lesions. Because only grossly detectable localized to the basal epithelium and could be reversed by the estrogen lesions were evaluated in the Pollard et a!. (19) study, existing small antagonist toremifene (43). Furthermore, E2 can synergize with tes or microscopic lesions could have been missed. tosterone to induce growth of the rat VP and DLP, an effect associated Of the three agents tested, tamoxifen had the most profound and with elevated activity of the nuclear fraction of 5a-reductase (30). consistent effect on carcinogenesis (Tables 1â€”3).A clear dose Therefore, the actions of E2 and androgen may be intimately linked. dependency was also seen; high-dose tamoxifen (5 mg/kg diet) was In this respect, treatment with tamoxifen may influence both the significantly more effective than low-dose tamoxifen (0.5 mg/kg androgen- and estrogen-signaling systems. Similarly, the recently diet). Histopathologically, the effect of tamoxifen on the SV and developed estrogen response modifier Raloxifene has shown antian AP appeared similar to the changes induced by castration but to a drogenic activity in guinea pig SV, as well as rat prostate (44, 45). lesser extent (Fig. 3). It is not clear, however, if these changes are Tamoxifen may also have activity at the level of the pituitary to a result of antiandrogenic, antiestrogenic/estrogenic, or some non reduce the secretion of luteinizing hormone (46); however, in our hormonal actions (36) of tamoxifen. To our knowledge, this is the experiments, TP was administered by implant, thereby bypassing the first report of the use of an estrogen response modifier for the pituitary-testes axis. Castration causes an up-regulation of TGF-g3 in chemoprevention of an androgen-promoted carcinoma. Schneider the VP associated with apoptosis (47). Similarly, tamoxifen treatment et a!. (37) demonstrated antineoplastic activity for tamoxifen as up-regulates TGF-@3in breast stroma, a process which is reported to be well as zindoxifene, a 2-phenylinole-based estrogen response mod independent of estrogen receptor status (48). It is unknown whether ifier, on xenografted Dunning rat prostate adenocarcinomas and TGF-@3is involved in the observed effects of tamoxifen on rat pros Noble rat adenocarcinomas. In contrast, Pienta et a!. (38) have shown little or no activity for tamoxifen alone in suppressing the tate-complex carcinogenesis and regression. Experiments are cur growth of the Dunning rat prostate carcinoma cell line MLL rently under way in our laboratory to investigate this possibility. grafted into male Copenhagen rats, although it was synergistic with The results of our experiments are encouraging in that all three of the growth-inhibitory activity of vinblastine, a microtubule inhib the agents tested (a retinoid, a deltanoid, and an estrogen response itor (38). However, the experimental designs of these two studies modifier) were effective in reducing the development of tumors utilize previously established advanced carcinomas or carcinoma within the male rat accessory sex organs when administered as single cell lines and, therefore, are fundamentally different than the agents. Further investigation into the combined chemopreventive ef design of the current study, which embraces relatively early events ficacy in multiagent protocols is warranted. Ultimately, the aim of (promotion) in the process of carcinogenesis. such protocols would be to optimize the combined anticarcinogenic Estrogen receptors have been identified in the prostate, predomi activity while decreasing the required dosage and, therefore, toxicity nantly in the stroma (39â€”41). In both rat DLP organ cultures and of each agent. 5626

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Downloaded from cancerres.aacrjournals.org on September 25, 2021. © 1995 American Association for Cancer Research. Chemopreventive Activity of Tamoxifen, N -(4-Hydroxyphenyl)retinamide, and the Vitamin D Analogue Ro24-5531 for Androgen-promoted Carcinomas of the Rat Seminal Vesicle and Prostate

M. Scott Lucia, Mario A. Anzano, Michael V. Slayter, et al.

Cancer Res 1995;55:5621-5627.

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