Cross-Resistance of Triphenylethylene-Type Antiestrogens but Not ICI 182,780 in Tamoxifen-Stimulated Breast Tumors Grown in Athymic Mice1

Vol. 6, 4893–4899, December 2000 Clinical Cancer Research 4893

Cross-Resistance of Triphenylethylene-type Antiestrogens but not ICI 182,780 in Tamoxifen-stimulated Breast Tumors Grown in Athymic Mice1

Eun Sook Lee,2, 3 Jennifer MacGregor Schafer,2 MCF-7 tumor model, which implied that neither Idox nor Kathy Yao, Gale England, Ruth M. O’Regan, Tor would be effective as a second-line endocrine therapy Alexander De Los Reyes, and V. Craig Jordan4 after Tam failure and may offer no therapeutic advantages over Tam as adjuvant therapies. In contrast, ICI 182,780, a Robert H. Lurie Comprehensive Cancer Center [E. S. L., J. M. S., pure antiestrogen currently being tested as a treatment for A. D. L. R., V. C. J.], Division of Medical Oncology [R. M. O.], and Department of Surgery [G. E., K. Y.], Northwestern University breast cancer after Tam failure, had no growth-stimulatory Medical School, Chicago, Illinois 60611 effect on the MCF-7 Tam-stimulated breast tumor line. This agent may provide an advantage as an adjuvant therapy and increase the time to treatment failure. ABSTRACT The triphenylethylene antiestrogens, idoxifene (Idox) and toremifene (Tor), are structurally related analogues of INTRODUCTION 5 tamoxifen (Tam) and were developed to improve the thera- Tam is the endocrine treatment of choice for all stages of peutic index for advanced breast cancer patients. However, ER-positive breast cancer (1, 2) and the first agent used to the issue of cross-resistance with Tam for these new agents reduce the incidence of breast cancer in high-risk women (3). is critical for clinical testing because the majority of breast Although Tam is proven to provide survival advantages after cancer patients have already received or failed adjuvant adjuvant therapy, the development of drug resistance is a po- Tam. The goal of this study was to determine the effective- tentially limiting factor to extending therapy and to enhancing ness of Idox as an antitumor agent in three models of the beneficial actions of the drug (4). Tam-stimulated breast cancer in athymic mice and compare Clearly, any new antiestrogen that is developed for breast the results with the actions of Tor and ICI 182,780 in a cancer therapy must not produce premature drug resistance and Tam-stimulated MCF-7 tumor model. We first compared must have a better toxicological profile than Tam. A new ␤ antiestrogen that has the advantage of being used for extended the activities of Tam and Idox in the 17 -estradiol (E2)- therapy (Ͼ5 years) and has fewer serious side effects than Tam stimulated MCF-7 tumor line MT2:E2. Tam and Idox re- .would have broad applications as a treatment and preventative ؍ duced E2-stimulated growth by 65–70% (week 9: P 0.0009 Thus, a new antiestrogen must be proven to be superior to Tam ؍ for Tam, P 0.0005 for Idox versus E2 alone). However, Tam (1.5 mg daily) and Idox (1.0 mg daily) both produced in the laboratory before a commitment can be made for wide- T47D breast tumors in athymic mice during 23 weeks of spread clinical testing. However, any new agent must be tested treatment (12 tumors/22 sites and 15 tumors/18 sites, respec- clinically in a population of patients with recurrent breast cancer tively). Tam and Idox stimulated tumor growth equally in who may already have been exposed to Tam during adjuvant two different Tam-stimulated MCF-7 models and in a T47D therapy. As a result, there is a high probability that the disease model. Tor was completely cross-resistant with Tam in the will already be resistant to Tam. The issue of cross-resistance for the new agent will be critical for the success of clinical testing and ultimately the advancement of the drug for testing as an adjuvant therapy. The triphenylethylene derivatives, Idox and Tor, are struc- Received 7/7/00; revised 10/13/00; accepted 10/26/00. turally related analogues of Tam and have been studied to The costs of publication of this article were defrayed in part by the improve the therapeutic index (5). Idox differs from Tam in that payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to it contains an iodine atom located at position 4. This substitution indicate this fact. affords this compound a higher affinity for the ER and higher 1 These studies were funded by NIH Specialized Program of Research metabolic stability than Tam (6, 7). There is evidence that Idox Excellence in breast cancer 1P50 CA89018-01; a grant from Smith is more effective than Tam at inhibiting both MCF-7 cell growth Kline Beecham (Philadelphia); the generous support of the Lynn Sage Breast Cancer Foundation of Northwestern Memorial Hospital; and the in vitro (8) and rat mammary tumor growth in vivo (9), and in Avon Products Foundation. addition, Idox is less likely to develop drug resistance (10, 11). 2 Both of these authors contributed equally to this work. These data resulted in the clinical testing of Idox as a breast 3 Present address: Department of General Surgery, Korea University cancer treatment; however, it remains unclear whether structural Ansan Hospital, 516 Kojan-Dong Ansan City Kyunggi-Do, 425-020 South Korea. 4 To whom requests for reprints should be addressed, at Northwestern University Medical School, Robert H. Lurie Comprehensive Cancer Center, 8258 Olson Pavilion, 303 East Chicago Avenue, Chicago, IL 60611. Phone: (312) 908-5148; Fax: (312) 908-1372; E-mail: vcjordan@ 5 The abbreviations used are: Tam, tamoxifen; ER, estrogen receptor; ␤ nwu.edu. E2,17 -estradiol; Idox, idoxifene; Tor, toremifene.

Table 1 Classification of breast tumors based on hormone Hormone and Drug Treatments. Mice were divided responsiveness into groups of 10 and were treated with E2, antiestrogen, or

Tumor Derived from E2-stimulated Tam-stimulated combinations. Silastic E2 capsules (0.3 or 1 cm in length) were MCF-7:Tam MCF-7 cells No Yes made as described previously (22), implanted s.c., and replaced MT2:E2 MCF-7 cells Yes No after 8–10 weeks of treatment. The 0.3-cm E2 capsule produced MT2:Tam MCF-7 cells Yes Yes a mean of 83.8 pg/ml of serum E2, whereas the 1.0-cm capsule T47D:E T47D cells Yes No 2 produced 379.5 pg/ml of serum E (23). Each was designed to T47D:Tam T47D cells Yes Yes 2 represent the E2 levels observed in post- or premenopausal women, respectively. Tam (Sigma Chemical Co., St. Louis, MO), Tor (a gift from Orion Pharmaceutical, Oula, Finland), or Idox (a gift from Smith Kline Beecham, Philadelphia, PA) were analogues of Tam with less agonist effect are effective at inhib- first dissolved in ethanol and suspended in a solution of 90% iting the growth of Tam-resistant tumors. carboxymethylcellulose (1% carboxymethylcellulose in double- Tor, a chlorinated derivative of Tam, is approved for the distilled water) and 10% polyethylene glycol 400/Tween 80 treatment of advanced breast cancer in postmenopausal women (99.5% polyethylene glycol and 0.5% Tween 80). Ethanol was (12) and has been evaluated as an adjuvant therapy (13). Tor has evaporated under nitrogen before use. Tam, Tor, or Idox was a similar pharmacological profile to Tam, but it is less potent. administered p.o. at various doses: 0.5, 1.0, or 1.5 mg/mouse/ Tor is recommended at a dose of 60 mg daily, whereas Tam is day 5 days/week. ICI 182,780, a generous gift from Zeneca recommended at a dose of 20 mg daily. The primary reason for Pharmaceuticals, was dissolved in ethanol and suspended in developing Tor was to assuage concerns about rat liver carci- peanut oil to a final concentration of 50 mg/ml. Ethanol was nogenesis with Tam (14). An investigation of the mechanism of evaporated under nitrogen. ICI 182,780 was injected s.c. at a carcinogenesis suggests that the metabolic pathways necessary dose of 5 mg/mouse once a week. to induce DNA adducts are specific to the rat (15); therefore, the Tumor Measurements. Tumor measurements were per- results from these laboratory studies may have little relevance formed weekly using Vernier calipers. The cross-sectional area for humans. was calculated using the formula: length ϫ width/4 ϫ␲. We have developed a series of human models of drug Statistical Analysis. Comparisons in mean tumor be- resistance to Tam in the laboratory that may mimic drug resist- tween the animal groups were analyzed by ANOVA at each ance to Tam in the clinic (16–19). The initial goal of this study week and followed by unpaired Student’s t test. The two tailed was to compare and contrast the effectiveness of Idox as an P of the last week of each experiment was reported using antitumor agent in the MCF-7 and T47D models of Tam- StatMost 2.5 (Datamost Corp., Salt Lake City, UT). stimulated breast cancer. Our aim was not only to test the veracity of the view (10) that Idox is not cross-resistant with Tam so that clinical testing could proceed but also to build on RESULTS our experience in predicting clinical outcomes. Where possible, An initial study was carried out to determine the dose of we have compared our findings with Tor and the pure anties- Idox equivalent to that of Tam, which has been well established trogen ICI 182,780. The pure antiestrogen is not cross-resistant in our athymic nude mice model. Because Idox is metabolized with Tam (20) and is showing promise as a new treatment after at a 2–3-fold slower rate than Tam in the rat (6, 7), the same the development of drug resistance to Tam-stimulated cancers dose of Idox, such as 0.5 or 1.5 mg/day, is more than enough to (21). compare with these doses of Tam for effectiveness. However, our early experiments performed with 1.5 mg of Idox showed that this high dose is lethally toxic to the mice. Thus, we treated MATERIALS AND METHODS mice with 0.5 mg/day for low-dose Idox or 1.0 mg/day for Athymic Mouse Model. The MCF-7 and T47D tumors high-dose Idox. used in these experiments originated from an inoculation of To determine whether Idox inhibits the tumor growth more

MCF-7 or T47D cells (American Type Culture Collection) into effectively than Tam, we implanted 50 mice with MT2:E2 the mammary fat pads of old ovariectomized BALB/c nu/nu tumors that grew with E2 and were inhibited by Tam. The athymic mice (Harlan Sprague Dawley, Madison, WI), 4–6 animals were divided into a control (no drug) and four treated weeks of age, as described previously (16, 19). The MT2 tumors groups. The four treated groups of mice were implanted with

were derived from MCF-7 breast cancer cells that had been 0.3-cm E2 capsules and treated with 0.5 mg Tam, 0.5 mg Idox, injected into athymic mice and serially passaged with E2 or Tam 1.0 mg Idox, or E2 capsules alone for 9 weeks. As shown in Fig. capsule. The tumors contain a point mutation in the ligand 1, the abilities of Tam and Idox to inhibit tumor growth were domain of the ER, which results in a tyrosine for aspartate almost identical. Both drugs reduced 65–70% of tumor growth ϭ ϭ substitution at amino acid 351 (17). The characteristics of the compared with E2 capsule alone (P 0.0009 for Tam; P individual tumors are summarized in Table 1. 0.0005 for Idox). Interestingly, there was no difference in high- Ovariectomized athymic mice were implanted with 1-mm3 or low-dose Idox in inhibiting tumor growth (P ϭ 0.589). pieces of the relevant tumor into the mammary fat pads using a In the next experiment, we determined whether high-dose trocar and randomized as described in “Results.” The Animal Idox is capable of stimulating tumor growth to the same extent Care and Use Committee of Northwestern University approved as high-dose Tam in our previous Tam-stimulated T47D tumors

all procedures involving animals. (19). T47D:E2 tumors were transplanted into 40 mice, which

Fig. 2 Growth of T47D:E2 tumors in ovariectomized athymic mice (data are means; bars, SE). Forty mice (10/group) were bilaterally Fig. 1 Comparison of Tam-sensitive MT2:E2 tumor growth in re- implanted with T47D:E2 tumors and were treated for 23 weeks with sponse to Tam and Idox treatment (data are means; bars, SE). Fifty 0.3-cm E capsule, 1.5 mg Tam or 1.0 mg Idox. The mean sizes of Tam- ovariectomized athymic mice were bilaterally implanted with MT2:E 2 2 or Idox-stimulated tumor growth were similar (P ϭ 0.3662). tumors (10/group) and were treated for 9 weeks with 0.3-cm E2 capsule alone or combination with 0.5 mg oral Tam, 0.5 mg or 1.0 mg oral Idox. Tam (P ϭ 0.0009) and Idox (P ϭ 0.0005) significantly inhibited tumor growth compared with the E2 group. However, there was no difference ϭ Ϯ Ϯ ϭ between E2 in combination with Tam and two doses of Idox (P Tam, 0.93 0.12 versus Idox, 0.73 0.08 P 0.23), whereas 0.589). tumors in the control group did not grow. Experiments performed with 1.0 mg Idox showed no difference compared with 0.5 mg Idox in the MT2:Tam tumors; therefore, a lower dose (0.5 mg Idox) was chosen for the experiment using T47D:Tam. were divided into four groups: control, 1-cm E2 capsule, 1.5-mg In this experiment, 30 mice were transplanted with T47D:TAM Tam, or 1.0-mg Idox (Fig. 2). Over the course of 8 weeks, the tumors and separated into three groups: control, 1.5 mg Tam,

E2 group grew robustly, whereas neither Tam nor Idox groups and 0.5 mg Idox (Fig. 3C). As expected, the tumors in Tam grew. The experiment was extended to 23 weeks, where 7 and treated mice grew, whereas the tumors in controls did not. The 4 large tumors (Ͼ0.5 cm2) grew in the Tam (12 of 22 sites) and Idox-treated mice produced only three larger tumors (Ͼ0.5 Idox (15 of 18 sites) groups, respectively. There was no signif- cm2), suggesting that there is partial cross-resistance for Idox icant difference between the mean tumor size or tumor inci- with Tam in the T47D:Tam tumor. dence (P ϭ 0.3662). To confirm that the triphenylethylene derivatives have sim- To verify whether Idox is effective after Tam failure in ilar effects on Tam-stimulated breast tumor growth, we tested advanced breast cancer, we tested the cross-resistance between the effect of Tor on MT2:Tam tumors (Fig. 4). Forty athymic Idox and Tam in our Tam-stimulated tumor models: MT2:Tam, mice were implanted with MT2:Tam tumors and treated with MCF-7:Tam, and T47D:Tam. Then, we extended this cross- 0.5 mg Tam, 0.5 mg Tor, or 1.5 mg Tor daily. A control group resistance experiment with Tor or with the pure antiestrogen ICI of mice received vehicle alone. Similar growth rates were seen 182,780. in the 0.5 mg Tam- and 1.5 mg Tor-treated mice (1.00 Ϯ 0.16 For the evaluation of the impact of Idox on the growth of versus 1.46 Ϯ 0.14; P ϭ 0.73). Tam-stimulated breast tumors, all three tumors were tested. In As shown previously, the pure antiestrogen ICI 182,780 the first experiment, 40 athymic mice were implanted with can inhibit Tam-stimulated tumor growth (20); therefore, we MT2:Tam and treated with 0.5 mg Tam, 0.5 mg Idox, or 1.0 mg confirmed that ICI 182,780 had no growth-stimulatory effect on Idox, or control (no drug). As expected, Tam resulted in rapid another type of Tam-stimulated breast tumor. Thirty mice were growth of these tumors, which reached an average tumor area of implanted with MT2:Tam tumors and treated with 0.5 mg Tam, 1cm2 by 9 weeks (Fig. 3A). Interestingly, 0.5 mg (P ϭ 0.4346) ICI 182,780 at a dose of 5 mg weekly or control. As shown in or 1.0 mg (P ϭ 0.8947) Idox produced a similar growth rate Fig. 5, ICI 182,780 did not stimulate tumor growth by 17 weeks, compared with Tam. The same experiment was performed using whereas control tumor started to grow at 13 weeks. the MCF-7:Tam tumors implanted into 30 athymic mice (Fig. Overall, Idox or Tor was partially or totally cross-resistant 3B). High-dose Tam or Idox stimulated growth of MCF-7:Tam with Tam; therefore, these drugs had similar growth-stimulatory tumors at a similar rate by 12 weeks (mean tumor area Ϯ SE: effects on Tam-stimulated breast tumors. In contrast, ICI

Fig. 3 Stimulatory effect of Tam or Idox on Tam-stimulated MT2:Tam (A), MCF-7:Tam (B), and T47D:Tam (C) tumor growth in ovariectomized athymic mice (data are means; bars, SE). Mice were implanted with MT2:Tam, MCF-7: Tam, or T47D:Tam tumors and treated with Tam or Idox. The magnitude of growth stimulation was the same as that of Tam in the MCF-7 model, MT2:Tam (P ϭ 0.4346 for 0.5 mg, P ϭ 0.8947 for 1.0 mg) and MCF-7:Tam (P ϭ 0.23). Although the magnitude was ϳ50% less than Tam in T47D:Tam, Idox had significant growth-stimulatory effect on tumor growth compared with control group (P ϭ 0.0055), which had no tumors at all.

182,780 had no growth-stimulatory effect on tamoxifen-stimu- synthesized in an attempt to overcome the drawbacks of Tam or lated breast tumors. to improve therapeutic efficacy (5). In the present study, we have used the athymic mouse breast tumor xenograft model to DISCUSSION evaluate the potential of Idox, Tor, and ICI 182,780 for clinical Although Tam is the endocrine therapy of choice for all use and to build our understanding of the mechanism of drug stages of breast cancer (2), most tumors that initially respond to resistance to Tam in vivo (16, 22, 29). The comparative studies Tam eventually develop acquired resistance and regrow (24, of cross-resistance in three novel models of drug resistance to 25). However, at least two-thirds of the tumors that become Tam were based on prior experience with Tam in this setting. In resistant to Tam continue to express ER (26–28), and many of an earlier study (23), we examined the circulating levels of Tam these respond to a second-line endocrine therapy. and found that a dose of 0.5 and 1.5 mg Tam/day produced In recent years, a number of new compounds have been serum levels of 58 Ϯ 7 ng/ml and 203 Ϯ 100 ng/ml, respec-

Fig. 4 Cross-resistant effect of Tam and Tor on Tam-stimulated MT2: Fig. 5 A pure antiestrogen ICI 182,780 had no growth-stimulatory

Tam tumor growth in ovariectomized athymic mice (data are means; effect on Tam-stimulated MT2:E2 tumors (data are means; bars, SE). bars, SE). Forty ovariectomized athymic mice (10/group) were bilater- Thirty ovariectomized athymic mice (10/group) were bilaterally im- ally implanted with MT2:Tam tumors and treated for 13 weeks with 0.5 planted with MT2:Tam tumors and treated for 17 weeks with 0.5 mg mg Tam, 0.5 mg Tor, or 1.5 mg Tor. Both 0.5 mg Tam and 1.5 mg Tor Tam or ICI 182,780 at a dose of 5 mg/week given as a single s.c. dose. stimulated tumor growth to a similar extent (P ϭ 0.73). Tam significantly stimulated tumor growth compared with control (P Ͻ 0.0001). However, ICI 182,780 did not stimulate tumor growth by 17 weeks, whereas control tumors grew at 13 weeks. tively. Because the metabolism is different between the two species, it is difficult to relate administered doses between humans and mice. Nevertheless, the animal model has been Idox will result in development of an Idox-stimulated tumor; we validated because the level of circulating Tam in the mouse is compared and contrasted the activities of Tam and Idox using equivalent to that observed in patients receiving 20 mg daily the T47D tumor line transplanted into athymic mice (Fig. 2). (30). Thus, the experimental doses of Idox or Tor were selected There was no difference between the rate of drug resistance for evaluation based on the dose ratio proposed for patients. demonstrated by Tam and Idox. Naturally, we believed that Idox is more metabolically stable than Tam and binds the different tumor models could explain the contradictory result ER with a higher affinity (6, 7). However, the fact that Tam is with the report by Johnston et al. (11); therefore, we decided to converted to 4-hydroxytamoxifen in athymic mice (31), which evaluate the cross-resistance between the Tam and Idox in both has high affinity for the ER, implies that higher doses of Idox MCF-7 and T47D models. The evaluation of Idox in the two should be tested. We initially compared the magnitude of Tam-stimulated models would then test the hypothesis of growth inhibition on Tam-sensitive tumors treated with the whether the modest decrease in estrogenic properties of Idox is same dose of 1.5 mg/day Idox as that of Tam. Unfortunately, relevant to neutralize the drug-resistance mechanism. this dose was lethal to mice; therefore, the dose was reduced to Idox stimulated tumor growth in both Tam-stimulated 1.0 mg/day. Because Idox has an approximately 2–3-fold longer MCF-7 and T47D tumors (Fig. 3). The magnitude of growth half-life (32), we determined that the 1.0 mg dose was sufficient stimulation was the same as that with Tam in two MCF-7 to compare the efficacy of Idox with Tam. In fact, Tam and Idox models, MT2:Tam and MCF-7:Tam. Although the magnitude of produced comparable antiestrogenic effects on the growth of the tumor growth was around half that of Tam in the T47D:Tam

MT2:E2 tumor (Fig. 1). model, Idox had a significant growth-stimulatory effect on tu- The acquisition of resistance during prolonged therapy of mor growth compared with the control group (P ϭ 0.0055). Tam can be explained by the estrogenic activities of Tam. Additionally, we believe that the action of triphenylethylene- Tam-stimulated, ER-positive tumors are selected by the weak type antiestrogens to stimulate tumor growth is dose related. We estrogenic effect of Tam, which may be amplified by an alter- have shown this previously with the MCF-7 (16) and T47D (19) ation in the complement of coactivators and corepressors pres- models. The effect is illustrated with different doses of Tor in ent in the cells (33, 34). Johnston et al. (11) have shown that the MCF-7 tumor model (Fig. 4). Although using higher doses Idox is unlikely to produce an Idox-stimulated tumor because of Idox in the T47D model would test our hypothesis, we the drug is less estrogenic and produces sustained apoptosis in believe that a dose-related principal is already established, and the MCF-7 xenograft. It has also been shown that Idox is less no further useful information about Idox would be obtained. estrogenic in rat uterus (8). To address the question of whether Idox appears to offer no therapeutic advantages over Tam, and

we predict that the drug would be unsuitable for testing after ence of antiestrogenicity on the 4-substituent. J. Med. Chem., 32: Tam failure. Idox has recently been withdrawn from clinical 2527–2533, 1989. testing. 7. McCague, R., Parr, I. B., and Haynes, B. P. Metabolism of the 4-iodo To confirm and validate our models with clinical outcome, derivative of tamoxifen by isolated rat hepatocytes. Demonstration that the iodine atom reduces metabolic conversion and identification of four a cross-resistance experiment was designed using MT2:Tam metabolites. Biochem. Pharmacol., 40: 2277–2283, 1990. tumor treated with another Tam analogue, Tor, and the pure 8. Chander, S. K., McCague, R., Luqmani, Y., Newton, C., Dowsett, antiestrogen ICI 182,780. Tor is known to be cross-resistant M., Jarman, M., and Coombes, R. C. Pyrrolidino-4-iodotamoxifen and with Tam in clinical trials (35, 36) and produce Tor-stimulated 4-iodotamoxifen, new analogues of the antiestrogen tamoxifen for the tumors in animal models (37). The laboratory studies showed treatment of breast cancer. Cancer Res., 51: 5851–5858, 1991. clearly that Tor and Tam are cross-resistant, but ICI 182,780 is 9. Pace, P., Jarman, M., Phillips, D., Hewer, A., Bliss, J., and Coombes, not. These data suggest that in women who fail Tam neither R. C. Idoxifene is equipotent to tamoxifen in inhibiting mammary Idox nor Tor would be effective as a second-line endocrine carcinogenesis but forms lower levels of hepatic DNA adducts. Br. J. Cancer, 76: 700–704, 1997. therapy. ICI 182,780 has shown promising results clinically, 10. Johnston, S. R., Riddler, S., Haynes, B. P., A’Hern, R., Smith, I. E., with high response rates of ϳ70% after Tam failure in advanced Jarman, M., and Dowsett, M. The novel anti-oestrogen idoxifene inhib- breast cancer (21). It has also been shown in the laboratory that its the growth of human MCF-7 breast cancer xenografts and reduces the ICI 182,780 does not stimulate the growth of Tam-resistant frequency of acquired anti-oestrogen resistance. Br. J. Cancer, 75: breast and endometrial tumors (20, 23). 804–809, 1997. These laboratory models of drug resistance to Tam have 11. Johnston, S. R., Boeddinghaus, I. M., Riddler, S., Haynes, B. P., extended previous studies with Idox (10, 11) and shown that a Hardcastle, I. R., Rowlands, M., Grimshaw, R., Jarman, M., and Dow- triphenylethylene-like antiestrogen is unlikely to reduce the risk sett, M. Idoxifene antagonizes estradiol-dependent MCF-7 breast cancer xenograft growth through sustained induction of apoptosis. Cancer Res., of premature drug resistance compared with Tam. A goal of our 59: 3646–3651, 1999. laboratory is to build a database of model systems with a clinical 12. Hayes, D. F., Van Zyl, J. A., Hacking, A., Goedhals, L., Bezwoda, correlation. The array of models of drug resistance to Tam we W. R., Mailliard, J. A., Jones, S. E., Vogel, C. L., Berris, R. F., have used show cross-resistance with Idox and Tor but not ICI Shemano, I., et al. Randomized comparison of tamoxifen and two 182,780, which parallels clinical experience. Although these separate doses of toremifene in postmenopausal patients with metastatic model systems may prove to be useful for testing any new breast cancer. J. Clin. Oncol., 13: 2556–2566, 1995. selective ER modulator, an understanding of the mechanism of 13. Holli, K. Toxicity and early survival results of a prospective, randomized adjuvant trial comparing toremifene and tamoxifen in node- drug resistance must remain a priority for further study. A positive breast cancer. Proc. Am. Soc. Clin. Oncol., 87: 334, 2000. systematic investigation of drug mechanisms in model systems 14. Hard, G. C., Iatropoulos, M. J., Jordan, K., Radi, L., Kaltenberg, will potentially provide valuable clues to improve the efficacy O. P., Imondi, A. R., and Williams, G. M. Major difference in the of breast cancer therapy. hepatocarcinogenicity and DNA adduct forming ability between toremifene and tamoxifen in female Crl:CD(BR) rats. Cancer Res., 53: 4534–4541, 1993. ACKNOWLEDGMENTS 15. White, I. N., de Matteis, F., Davies, A., Smith, L. L., Crofton- We thank Dr. Fred Rademaker for assistance with statistical anal- Sleigh, C., Venitt, S., Hewer, A., and Phillips, D. H. Genotoxic potential ysis. of tamoxifen and analogues in female Fischer F344/n rats, DBA/2 and C57BL/6 mice and in human MCL-5 cells. Carcinogenesis (Lond.)., 13: 2197–2203, 1992. REFERENCES 16. Gottardis, M. M., and Jordan, V. C. Development of tamoxifen- stimulated growth of MCF-7 tumors in athymic mice after long-term 1. Early Breast Cancer Trialists’ Collaborative Group. Tamoxifen for antiestrogen administration. Cancer Res., 48: 5183–5187, 1988. early breast cancer: an overview of the randomised trials. [see comments]. Lancet, 351: 1451–1467, 1998. 17. Wolf, D. M., and Jordan, V. C. Characterization of tamoxifen stimulated MCF-7 tumor variants grown in athymic mice. Breast Cancer 2. Osborne, C. K. Tamoxifen in the treatment of breast cancer. N. Engl. Res Treat., 31: 117–127, 1994. J. Med., 339: 1609–1618, 1998. 18. Yao, K., Lee, E., Bentrem, D. J., England, G., Schafer, J. I. M., 3. Fisher, B., Costantino, J. P., Wickerham, D. L., Redmond, C. K., O’Regan, R., and Jordan, V. C. Antitumor action of physiological Kavanah, M., Cronin, W. M., Vogel, V., Robidoux, A., Dimitrov, N., Atkins, J., Daly, M., Wieand, S., Tan-Chiu, E., Ford, L., and Wolmark, estradiol on tamoxifen-stimulated breast tumors grown in athymic mice. N. Tamoxifen for prevention of breast cancer: report of the National Clin. Cancer Res., 6: 2028–2036, 2000. Surgical Adjuvant Breast and Bowel Project P-1 Study. J. Natl. Cancer 19. MacGregor Schafer, J., Lee, E-S., O’Regan, R. M., Yao, K., and Inst., 90: 1371–1388, 1998. Jordan, V. C. Rapid development of tamoxifen stimulated mutant p53 4. Fisher, B., Dignam, J., Bryant, J., DeCillis, A., Wickerham, D. L., breast tumors (T47D) in athymic mice. Clin. Cancer Res., 6: 4374– Wolmark, N., Costantino, J., Redmond, C., Fisher, E. R., Bowman, 4381, 2000. D. M., Deschenes, L., Dimitrov, N. V., Margolese, R. G., Robidoux, A., 20. Osborne, C. K., Coronado-Heinsohn, E. B., Hilsenbeck, S. G., Shibata, H., Terz, J., Paterson, A. H., Feldman, M. I., Farrar, W., Evans, McCue, B. L., Wakeling, A. E., McClelland, R. A., Manning, D. L., and J., and Lickley, H. L. Five versus more than five years of tamoxifen Nicholson, R. I. Comparison of the effects of a pure steroidal antiestro- therapy for breast cancer patients with negative lymph nodes and estrogen with those of tamoxifen in a model of human breast cancer. J. Natl. gen receptor-positive tumors [see comments]. J. Natl. Cancer Inst., 88: Cancer Inst., 87: 746–750, 1995. 1529–1542, 1996. 21. Howell, A., DeFriend, D. J., Robertson, J. F., Blamey, R. W., 5. Gradishar, W. J., and Jordan, V. C. Clinical potential of new anties- Anderson, L., Anderson, E., Sutcliffe, F. A., and Walton, P. Pharmaco- trogens. J. Clin. Oncol., 15: 840–852, 1997. kinetics, pharmacological and anti-tumour effects of the specific anti- 6. McCague, R., Leclercq, G., Legros, N., Goodman, J., Blackburn, oestrogen ICI 182780 in women with advanced breast cancer. Br. J. G. M., Jarman, M., and Foster, A. B. Derivatives of tamoxifen. Depend- Cancer, 74: 300–308, 1996.

22. Robinson, S. P., and Jordan, V. C. Antiestrogenic action of 30. Langan-Fahey, S. M., Tormey, D. C., and Jordan, V. C. Tamoxifen toremifene on hormone-dependent, -independent, and heterogeneous metabolites in patients on long-term adjuvant therapy for breast cancer. breast tumor growth in the athymic mouse. Cancer Res., 49: 1758– Eur. J. Cancer, 26: 883–888, 1990. 1762, 1989. 31. Robinson, S. P., Langan-Fahey, S. M., and Jordan, V. C. Implica- 23. O’Regan, R. M., Cisneros, A., England, G. M., MacGregor, J. I., tions of tamoxifen metabolism in the athymic mouse for the study of Muenzner, H. D., Assikis, V. J., Bilimoria, M. M., Piette, M., Dragan, antitumor effects upon human breast cancer xenografts. Eur. J. Cancer Y. P., Pitot, H. C., Chatterton, R., and Jordan, V. C. Effects of the Clin. Oncol., 25: 1769–1776, 1989. antiestrogens tamoxifen, toremifene, and ICI 182,780 on endometrial 32. Coombes, R. C., Haynes, B. P., Dowsett, M., Quigley, M., English, cancer growth [see comments]. J. Natl. Cancer Inst., 90: 1552–1558, 1998. J., Judson, I. R., Griggs, L. J., Potter, G. A., McCague, R., and Jarman, M. Idoxifene: report of a Phase I study in patients with metastatic breast 24. Osborne, C. K. Mechanisms for tamoxifen resistance in breast cancer. Cancer Res., 55: 1070–1074, 1995. cancer: possible role of tamoxifen metabolism. J. Steroid Biochem. Mol. Biol., 47: 83–89, 1993. 33. Jordan, V. C. Molecular mechanism of action of raloxifene and tamoxifen: today and tomorrow. J. Natl. Cancer Inst., 90: 967–971, 25. Tonetti, D. A., and Jordan, V. C. The role of estrogen receptor 1998. mutations in tamoxifen-stimulated breast cancer. J. Steroid Biochem. Mol. Biol., 62: 119–128, 1997. 34. Lavinsky, R. M., Jepsen, K., Heinzel, T., Torchia, J., Mullen, T. M., Schiff, R., Del-Rio, A. L., Ricote, M., Ngo, S., Gemsch, J., Hilsenbeck, 26. Encarnacion, C. A., Ciocca, D. R., McGuire, W. L., Clark, G. M., Fuqua, S. A., and Osborne, C. K. Measurement of steroid hormone S. G., Osborne, C. K., Glass, C. K., Rosenfeld, M. G., and Rose, D. W. receptors in breast cancer patients on tamoxifen. Breast Cancer Res. Diverse signaling pathways modulate nuclear receptor recruitment of Treat., 26: 237–246, 1993. N-CoR and SMRT complexes. Proc. Natl. Acad. Sci. USA, 95: 2920– 2925, 1998. 27. Chang, J., Powles, T. J., Allred, D. C., Ashley, S. E., Makris, A., Gregory, R. K., Osborne, C. K., and Dowsett, M. Prediction of clinical 35. Stenbygaard, L. E., Herrstedt, J., Thomsen, J. F., Svendsen, K. R., outcome from primary tamoxifen by expression of biologic markers in Engelholm, S. A., and Dombernowsky, P. Toremifene and tamoxifen in breast cancer patients. Clin. Cancer Res., 6: 616–621, 2000. advanced breast cancer–a double-blind cross-over trial. Breast Cancer Res Treat., 25: 57–63, 1993. 28. Johnston, S. R., Lu, B., Dowsett, M., Liang, X., Kaufmann, M., Scott, G. K., Osborne, C. K., and Benz, C. C. Comparison of estrogen 36. Vogel, C. L., Shemano, I., Schoenfelder, J., Gams, R. A., and receptor DNA binding in untreated and acquired antiestrogen-resistant Green, M. R. Multicenter Phase II efficacy trial of toremifene in tamox- human breast tumors. Cancer Res., 57: 3723–3727, 1997. ifen- refractory patients with advanced breast cancer. J. Clin. Oncol., 11: 29. Osborne, C. K., Coronado, E., Allred, D. C., Wiebe, V., and 345–350, 1993. DeGregorio, M. Acquired tamoxifen resistance: correlation with re- 37. Osborne, C. K., Wiebe, V. J., McGuire, W. L., Ciocca, D. R., and duced breast tumor levels of tamoxifen and isomerization of trans-4- DeGregorio, M. W. Tamoxifen and the isomers of 4-hydroxytamoxifen hydroxytamoxifen [see comments]. J. Natl. Cancer Inst., 83: 1477– in tamoxifen-resistant tumors from breast cancer patients. J. Clin. On- 1482, 1991. col., 10: 304–310, 1992.

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