Comparison of the Effects of a
`Pure Steroidal Antiestrogen
`With Those of Tamoxifen in a
`Model of Human Breast Cancer
`
`C. Kent Osborne, Ester 8.
`Coronado-Heinsohn, Susan G.
`Hilsenbeck, Bryant L. McCue,
`Alan E. Wakeling, Richard A.
`McClelland, David L. Manning,
`Robert/. Nicholson*
`
`non(cid:173)
`a
`Background: Tamoxifen,
`steroidal estrogen antagonist, is the
`most prescribed drug for the treatment
`of breast cancer. The use of tamoxifen
`is limited, however, by the development
`of resistance to this compound in most
`patients. Although tamoxifen behaves
`primarily as an estrogen antagonist, iJ
`has agonist (or growth-stimulatory) ac(cid:173)
`tivity as well. ICI 182,780 is a 7a-alkyl(cid:173)
`sulfinyl analogue of estradiol lacking
`agonist activity. The absence of agonist
`activity may make this steroidal an(cid:173)
`tiestrogen superior to tamoxifen in sup(cid:173)
`pressing tumor cell growth. Purpose:
`We compared the inhibitory effects of
`ICI 182,780, tamoxifen, and estrogen
`withdrawal on the growth of estab·
`lished tumors and on tumorigenesis in
`a model system that uses estrogen-de(cid:173)
`pendent, human MCF-7 breast tumor
`cells growing in athymic nude mice.
`We also studied the hormonal respon(cid:173)
`siveness of tumors that became resis(cid:173)
`tant to the two estrogen antagonists
`and the effects of these drugs on
`estrogen-regulated gene expression.
`Methods: MCF-7 cells were injected
`the flanks of
`subcutaneously
`into
`castrated, female nude mice. The ef(cid:173)
`fects of repeated doses of tamoxifen
`and ICI 182,780 (500 µg and S mg,
`respectively) on the growth of estab(cid:173)
`lished tumors (8-10 mm in size) were
`determined after supplemental estro(cid:173)
`gen was removed. The effects of anti(cid:173)
`estrogen treatments on the process of
`tumorigenesis, in the absence of estro(cid:173)
`gen supplementation, were determined
`by initiating drug administration on
`
`the same day as tumor cell inoculation.
`To evaluate the hormonal responsive(cid:173)
`ness of tumors resistant to tamoxifen
`and ICI 182,780, 1-mm3 segments of
`the tumors were transplanted onto the
`flanks of new recipient mice, which
`were then treated with estrogen or the
`antiestrogens-elone or in combina(cid:173)
`tion. Tumor growth was monitored by
`measuring
`tumor volumes twice a
`week. Expression of the estrogen(cid:173)
`responsive genes, pLIV 1 and pS2, in
`the tumors of treated animals was
`analyzed using blots of total cellular
`RNA and complementary DNA probes.
`Results: Treatment with ICI 182, 780
`suppressed the growth of established
`tumors twice as long as treatment with
`tamoxifen or estrogen withdrawal.
`Tumorigenesis, in the absence of sup(cid:173)
`plemental estrogen, was delayed to a
`greater extent in ICI 182,780-treated
`mice than in tamoxifen-treated mice.
`ICI 182,780 was found to be more ef(cid:173)
`fective than tamoxifen in reducing the
`expression of estrogen-regulated genes.
`Most tumors eventually became resis(cid:173)
`tant to ICI 182,780 and grew inde(cid:173)
`pendently of estrogen. Conclusions: ICI
`182,780 is a more effective estrogen an(cid:173)
`tagonist than tamoxifen in the MCF-7
`tumor cell/nude mouse model system.
`[J Natl Cancer Inst 87:746-750, 1995)
`
`Tamoxifen, a nonsteroidal antiestro(cid:173)
`gen, is the most prescribed drug for the
`treatment of breast cancer. When used in
`the adjuvant setting after surgery for
`primary breast cancer, about one fifth of
`the deaths at lO years are avoided by 2
`years or more of treatment (/). Tamox(cid:173)
`ifen is also effective in inducing remis(cid:173)
`sions in women with estrogen receptor
`(ER)-positive metastatic breast cancer.
`Invariably, however, tumors become re(cid:173)
`sistant to tamoxifen, and tumor progres(cid:173)
`sion and death ensue. The evolution to
`tamoxifen resistance in metastatic breast
`cancer occurs after an average treatment
`duration of only 10-12 months, severely
`limiting the usefulness of this approach.
`The mechanisms by which tumors ac(cid:173)
`quire resistance to tamoxifen are poorly
`understood. Loss of ER from the tumor
`can occur by selection of an ER-negative
`clone or by suppression of receptor ex(cid:173)
`pression, but this loss explains only a
`minority of cases (2). Growing experi-
`
`mental and clinical evidence suggests that
`resistance in some patients may be caused
`by the intrinsic estrogen agonist proper(cid:173)
`ties of tamoxifen. Although tamoxifen is
`predominantly an estrogen antagonist in
`breast cancer cells, acquisition of increas(cid:173)
`ingly dominant agonist activity over time
`may result in clinical resistance because
`of the acquired ability of the drug to
`stimulate, rather than to inhibit, tumor
`growth (3-7). The mechanisms for ta(cid:173)
`moxifen-stimulated tumor growth are not
`clear, but these data suggest that an(cid:173)
`tiestrogens with pure antagonist proper(cid:173)
`ties might have superior antitumor
`activity.
`ICI 182,780 is a 7a.-alkylsulfinyl ana(cid:173)
`logue of estradiol that differs substantial(cid:173)
`ly
`from
`tamoxifen
`in
`tenns of its
`chemical, phannacologic, and biologic
`properties. This agent has no intrinsic
`is
`estrogen-agonist activity and, thus,
`considered a ''pure" antiestrogen (8,9). It
`has potent antiestrogenic activity
`in
`preclinical in vitro and in vivo model sys(cid:173)
`tems (10). We recently reported (7) that
`treating nude mice with ICI 182,780 in(cid:173)
`hibits the growth ofMCF-7 human breast
`tumor implants that had acquired ta(cid:173)
`moxifen resistance through the mechanism
`of tamoxifen-stimulated growth. Similar
`results were obtained with another
`analogue, ICI 164,384, studied earlier
`(/ 1). These data suggest the possibility
`that pure steroidal antiestrogens may be
`in some
`tamoxifen-resistant
`effective
`patients.
`In the present study, we have inves(cid:173)
`tigated the preclinical activity of ICI
`182,780 in more detail. We compared the
`inhibitory effects of ICI 182,780, tamox(cid:173)
`ifen, and estrogen withdrawal on the
`
`•Affiliations of authors: C. K. Osborne, E. B.
`Coronado-Heinsohn, S. G. Hilsenbeck, B. L.
`McCue, Depanrnent of Medicine, Division of Medi·
`cal Oncology, The University of Texas Health
`Science Center at San Antonio, San Antonio, Tex.
`A. E. Wakeling, 2.eneca Phannaceuticals,
`Mercside Alderley Part, Macclesfield, Oieshire,
`England. U.K.
`R. A. McClelland. D. L. Manning, R. I. Nichol(cid:173)
`son, Tenovus Cancer Research Center, University of
`Wales College of Medicine, Heath Park, Cardiff,
`Wales,U.K.
`Com~spond~nct to: C. Kent Osborne, M.D.,
`Department of Medicine, Division of Medical On·
`cology, The Universiry of Texas Health Science
`Center Bl San Antonio, 7703 Aoyd Curl Dr., San
`Antonio, TX 78284-7884.
`Stt "Notes" section following "References."
`
`746 REPORTS
`
`Journal of the National Cancer lnstilute, Vol. 87, No. 10, May 17, 1995
`
`MYLAN PHARMS. INC. EXHIBIT 1018 PAGE 1
`
`

`
`growth of established tumors and on
`tumorigenesis in a model system that uses
`estrogen-dependent,
`human MCF-7
`breast tumor cells growing in athymic
`nude mice. We also studied the hormonal
`responsiveness of tumors that had be(cid:173)
`come resistant to the two estrogen an(cid:173)
`tagonists and the effects of these drugs on
`estrogen-regulated gene expression.
`
`Materials and Methods
`
`Nude Mouse Model System
`
`ER-positive MCF-7 human bmlst cancer cells
`(passage I 00-200) were cultured as described pre(cid:173)
`viously (/2). The athymic nude mice used in these
`experiments were 4- to 5-week-old female castrated
`BALB/c-nu+/nu+ mice purchased
`from Harlan
`(Madison, Wis.). The
`Sprague-Dawley,
`Inc.
`methods for maintenance and housing of the mice
`and for growing MCF-7 tumors from cell suspen(cid:173)
`sions and from tumor transplants have been pu~
`lished in detail (J,7). Animal care was in accordance
`with institutional guidelines.
`Approximately 5 x 1<1' MCF-7 cells were in(cid:173)
`jected subcutaneously.into the flanks, just under the
`forelimb, of female nude mice to initiate tumor for(cid:173)
`mation. Estrogen supplementation was provided in
`the form of a 0.2S-mg estradiol (J:i) pellet (lnnov•
`tive Research, Rockville, Md.) placed subcutaneous(cid:173)
`ly in the interscapular region of the mice. The
`effects of tamoxifen and ICI 182, 780 on the growth
`of established tumors were studied after the tumors
`had reached a size of 8-10 mm (3-5 weeks). At this
`time, the animals were randomly allocated into four
`treatment groups: I) continued estrogen supplemen(cid:173)
`tation, 2) removal of the E2 pellet, 3) removal of the
`Ei pellet plus treatment with 500-µg tamoxifen
`citrate (Zcneca Pharmaceuticals, Wilmington, Del.)
`in peanut oil (injected subcutaneously each day,
`Monday through Friday), or 4) removal of the J:i
`pellet and treatment with !he indicated doses of
`ICI 182, 780 (Zeneca Pharmaceuticals, Macclesfield,
`England) in castor oil (subcutaneous injections once
`a week). Initial dose-response studies with ICI
`182,780 were performed in the presence of con(cid:173)
`tinued estrogen supplementation. Tumor growth was
`assessed, and tumor volumes were measured twice a
`week as described previously (12).
`In tumorigenesis experiments, various treatments
`were begun on the same day tumor cells were in(cid:173)
`jected. Inoculated mice were randomly allocated im(cid:173)
`mediately into four treatment groups: I) estrogen
`supplementation, 2) 500 µg tamoxifen once a day,
`Monday through Friday, 3) 5 mg ICI 182.780 once a
`week, or 4) drug vehicle (peanut oil and/or castor
`oil). Tumor volumes were measured twice a week.
`To investigate the hormonal responsiveness of
`tumors thai had become resistanl to ICI 182, 780,
`mice with resistant tumors were killed by cervical
`dislocation, and the tumors were resected and cut
`into 1-mm3 fragments. The fragments were then
`transplanted subcutaneously on !he flank just under
`the forelimb of new 4- to 5-week-old recipient mice
`that were then treated with esuogen, tamoxifen, ICI
`182, 780, or vehicle alone.
`
`Estrogen and Progesterone Receptor
`Assays
`
`ER content was determined in tumors homo(cid:173)
`genized in 0.4 M KCl-Tris buffer, using the ER an(cid:173)
`tibody kit (ER-EIA; Abbon U:boriitories, North
`Chicago, Ill.). Progesterone receptor (PgR) levels
`were measuml by a ligand-binding, dextran<e>ated
`charcoal method (3).
`
`mg to IO.O mg. Inhibitory activity was
`modest with doses of 0.5 mg or l.O mg,
`while more dramatic-but approximately
`equivalent-inhibitory effects were ob(cid:173)
`served with 5.0-mg and I0.0-mg doses
`(data not shown). For subsequent experi(cid:173)
`ments, a dose of 5.0 mg per mouse, given
`once a week, was used.
`
`Estrogen-Regulated Gene Expression
`
`Expression of the estrogen-responsive genes,
`pLIV I and pS2, was determined by nonhem blot
`(cDNA)
`analysis, using comllementary DNA
`probes labeled with c3 P)deoxycytidine triphosphate
`(3000 Ci/mmol; Amersham Ltd., Amersham,
`England, U.K.) by the random-priming method as
`described previously (/3). Briefly, total RNA was
`obtained from the tumors of treated mice by cell
`lysis in 4 M guanidinium thiocyanate and I% 2-mer(cid:173)
`captoethanol and centrifugation through 5.7 M
`caesium chloride (Beckman L-80 uluacentrifuge,
`SW50 rotor, 34 000 rpm at 20 'C for 17 hours).
`Purified samples were stored in RNase-free water at
`-70 'C before electrophoresis (10 µg/lane), bloning,
`and hybridization. Densitometric analysis of auto(cid:173)
`radiographs was perfonned using a model 620 video
`densitometer (Bio-Rad Laboratories, Richmond,
`Calif.), and values obtained were corrected for
`equivalence of RNA loading by comparison with the
`signals generated using a cDNA probe to human
`glyceraldeyhyde
`3-phosphate
`dehydrogenase
`(G3PDH) (Clontech Laboratories, Inc., Palo Alto,
`Calif.).
`Recorded densitometry values represent the area
`of peak values obtained. following background su~
`traction, from equivalently exposed autoradiographs
`(where x =band width in mm and y =optical den(cid:173)
`sity value). Hybridizations of each set of filters in
`the study were carried out simultaneously with the
`same labeled probes. The reponed values represent
`least
`two separate
`means of groups, and at
`hybridizations of different tilters were performed for
`each probe (stripping the previous probe with high(cid:173)
`stringency washes and checking for clearance by
`autoradiography).
`
`Statistical Analysis
`
`Analyses were performed using either the Krus(cid:173)
`kal-Wallis one-way analysis of variance (when
`there were more than two groups) or the Wilcoxon
`signed rank test for two samples. All statistical teslS
`were two-sided.
`
`Results
`
`ICI 182,780 Dose-Response
`
`ICI 182, 780 inhibited estrogen-induced
`growth of MCF-7 tumors in a dose-de(cid:173)
`pendent manner. Estrogen-supplemented
`mice with established MCF-7 tumors
`were randomly allocated to receive either
`continued estrogen treatment or estrogen
`treatment plus injections of ICI 182,780
`once a week in doses ranging from 0.5
`
`Effect of Estrogen Withdrawal,
`Tamoxifen, and ICI 182, 780 on
`MCF-7 Tumor Growth
`
`Treatment of mice by removal of the
`~ pellet alone or with tamoxifen or ICI
`182,780 significantly inhibited MCF-7
`tumor growth (Fig. 1). In this experiment,
`tumor volumes remained stable for nearly
`100 days after estrogen withdrawal before
`progression ensued. In contrast, tumor
`volumes decreased slightly with tamoxi(cid:173)
`fen and ICI 182,780 treatment, and tumor
`size remained stable for variable periods
`of time. A consistent observation was the
`delayed time to progression that was evi(cid:173)
`dent in mice treated with ICI 182,780.
`With estrogen withdrawal alone or with
`tamoxifen, tumors developed resistance,
`and progression was evident in all mice
`after 3-4 months of treatment (median, 97
`and 104 days, respectively). However, the
`median time to progression was nearly
`twice as long with ICI 182,780, and the
`growth of some tumors remained con(cid:173)
`trolled for extended periods of time
`(median, 200 days). In fact, two of the 10
`tumors from ICI 182, 780-treated mice
`still had not progressed after 11 months
`and one small tumor (4 mm diameter)
`completely regressed and did not reap(cid:173)
`pear during the course of the experiment
`(data not shown).
`
`Effect of ICI 182, 780 on Tumorigenesis
`
`ICI 182,780 also had a greater impact
`on tumor formation in mice in which drug
`treatments were begun on the day of
`tumor cell inoculation (Fig. 2). Tumors
`grew rapidly in mice treated with es(cid:173)
`trogen. Tumor growth was substantially
`delayed in mice treated with tamoxifen,
`but after 2 months, the growth rate in(cid:173)
`creased. Tumors grew very slowly, or not
`at all, in mice treated with ICI 182,78()(cid:173)
`similar to the growth pattern observed in
`estrogen-deprived mice (/2). By day 70,
`barely measurable tumors were present in
`the majority of mice. In another experi(cid:173)
`ment (data not shown), three of six mice
`
`J oumal of the National Cancer Institute, Vol. 87, No. 10, May 17. 1995
`
`REPORTS
`
`747
`
`MYLAN PHARMS. INC. EXHIBIT 1018 PAGE 2
`
`

`
`1200
`
`1000
`
`800
`
`600
`
`400
`
`20D
`
`"'
`E
`.§.
`GI
`E
`:II
`~
`~
`:II ...
`E
`
`·E2
`
`ICI 182,780
`
`DAYS
`
`4DD
`
`Fig. 1. Effects of estrogen (estradiol [E21) withdrawal, tamoxifen. and ICI 182,780 on MCF-7 tumor growth.
`Estrogen-supplemented mice were inoculated with MCF-7 cells. On day 36 when tumors had formed. mice
`were randomly allocaied to treatment by withdrawal of estrogen (-E2; - c:J-); wi1hdrawal of estrogen and
`treatment with 500 µg tamoxifen given once a day, Monday through Friday(-•-); or 5 mg ICI 182,780
`given once a week (-II·). Tumor volumes were determined at the times shown. n = 10 mice per group; means
`±SE.
`
`2000
`
`1500
`
`1000
`
`500
`
`ICI 182,780
`
`ol-~::t;:~;;i=!:=:!~=-:.--~-------
`o
`40
`100
`120
`80
`20
`6D
`
`DAYS
`
`Fig. l. Effect of estrogen, tamoxifen, and ICI 182,780 on MCF-7 tumorigenesis. Mice were inoculated with
`MCF-7 cells on day 0 and randomly allocated immediately 10 receive treatment with a I 7P estradiol (E2) pel(cid:173)
`let (+E2; -1!1-); 500 µg tamoxifen given once a day, Monday lhrough Friday(·•-); or S mg ICI 182,780
`given once a week (-II·). Tumor volumes were determined at the times shown. n = 8 mice per group; means
`±SE.
`
`treated with ICI 182,780 failed to grow
`measurable tumors even after 6 months of
`treatment.
`
`ICI 182,780-Resistant Tumors
`
`As indicated above, tumor resistance
`eventually occurred in most, but not all,
`
`mice treated with ICI 182,780. This resis(cid:173)
`tance was manifested by regrowth of
`tumors, usually after many months of
`treatment. To investigate the honnonal
`sensitivity of these resistant tumors, frag(cid:173)
`ments of a tumor that had progressed
`after months
`of
`treatment with
`
`ICI 182,780 were transplanted into new
`castrated, recipient mice that were then
`treated with estrogen, tamoxifen, ICI
`182,780, tamoxifen plus ICI 182,780, or
`vehicle alone. This experiment was con(cid:173)
`ducted five times with different tumor
`transplants, and a representative result is
`shown in Fig. 3. Transplanted tumor frag(cid:173)
`ments. grew well in all mice, even those
`treated with vehicle alone(-~), suggest(cid:173)
`ing estrogen independence. However, in
`four of five experiments, tumor growth
`was slightly· increased by estrogen treat(cid:173)
`ment ( +~. indicating continued sen(cid:173)
`sitivity to the honnone. As expected,
`growth of these transplanted I Cl 182, 780-
`resistant tumors was also observed in
`recipient mice treated with ICI 182,780.
`Interestingly, in four of the five experi(cid:173)
`ments, treatment of recipient mice with
`tamoxifen alone or
`tamoxifen plus
`ICI 182,780 resulted in a slight retarda(cid:173)
`tion of tumor growth compared with
`treatment
`using
`vehicle
`alone
`or
`ICI 182,780 alone, although the observed
`differences in the individual experiments
`were modest and not statistically sig(cid:173)
`nificant. A total of six of the 25 mice in
`these experiments showed slower tumor
`growth with tamoxifen treatment, indicat(cid:173)
`ing some heterogeneity among the trans(cid:173)
`planted
`fragments
`in
`response
`to
`tamoxifen. However, most mice resistant
`to ICI 182,780 showed cross-resistance to
`tamoxifen.
`··
`Resistance to ICI 182,780 was not due
`to a complete loss of tumor ER, although
`treatment with this drug reduced expres(cid:173)
`sion of both ER and PgR. Tumors har(cid:173)
`vested 4 weeks after initiating treatment
`with ICI 182,780 (ER = 37 ± 3 fmol/mg
`protein; PgR = 27 ± 7 fmoVmg protein)
`as well as those harvested at the time of
`resistance to ICI 182,780 (ER = 16 ± 4
`fmol/mg protein; PgR = 17 ± 8 fmol/mg
`protein) expressed both ER and PgR at
`markedly reduced levels compared with
`estrogen-treated controls (ER = 208 ± 81
`fmol/mg protein; PgR = I 03 ± 20
`fmol/mg protein) (P = .024).
`Expression of two estrogen-responsive
`genes, pS2 and pUV I, was also mea(cid:173)
`sured in these tumors (Table I). pS2 and
`pLIVI messenger RNA (mRNA) expres(cid:173)
`sion was reduced by 20%-74% in tumors
`from tamoxifen-treated mice (P = .013).
`It is interesting that pS2 and pLIVI ex(cid:173)
`pression remained suppressed even after
`
`748 REPORTS
`
`Journal of the National Cancer Institute, Vol. 87, No. 10, May 17, 1995
`
`MYLAN PHARMS. INC. EXHIBIT 1018 PAGE 3
`
`

`
`3000
`
`2500
`
`2000
`
`1000
`
`...
`I
`J 1500
`0 > ..
`
`0
`E
`~
`
`ICl112,71D
`
`Tama•lfen+ICl112, 710
`T•ma•lfen
`
`than treaunent by estrogen withdrawal
`alone or with tamoxifen. Finally, expres(cid:173)
`sion of the estrogen-regulated genes pS2
`and pLIV I was nearly abolished by treat(cid:173)
`ment with ICI 182,780.
`Previous reports by us and by other in(cid:173)
`vestigators (7,/ I ,14-16) have also shown
`that the growth of tumors with acquired
`tamoxifen resistance can be inhibited or
`blocked by treatment with a pure an(cid:173)
`tiestrogen such as ICI 182,780, suggest(cid:173)
`ing that the pure antiestrogens work by a
`different mechanism of action
`than
`tamoxifen and other similar antiestrogens. ·
`Tamoxifen resistance in our model sys(cid:173)
`tem
`is associated with drug-induced
`tumor growth stimulation that occurs
`after an initial period of growth suppres(cid:173)
`sion (3). The ability of tamoxifen alone to
`stimulate the growth of these tumors is
`less than that of estrogen. Interestingly,
`when combined with estrogen, tamoxifen
`can
`still
`inhibit
`estrogen-stimulated
`growth, indicating that it continues to
`possess both estrogen-agonist and an(cid:173)
`tagonist properties (7). The increasingly
`dominant agonist properties of tamoxifen
`that develop after prolonged treatment
`can be blocked by the addition of pure
`antiestrogens
`(7,/ /}. Evidence
`for
`tamoxifen-stimulated tumor growth as a
`mechanism for acquired tamoxifen resis(cid:173)
`tance in patients has also been presented
`(5,6J7). On the basis of these preclinical
`studies, it has been suggested that treat(cid:173)
`ment with ICI 182,780 might induce
`tumor regression in some patients who
`have developed
`tamoxifen
`resistance.
`One recent study (/8) has shown that
`short-term
`ICI 182, 780
`treatment of
`patients who have ER-positive tumors
`causes statistically significant reductions
`in the Ki67 labeling index and reductions
`in the expression of estrogen-regulated
`genes such as PgR and pS2. In addition,
`remissions have now been reported in
`tamoxifen-resistant patients treated with
`this drug (19).
`Although ICI 182,780 controls MCF-7
`tumor growth for longer durations than
`tamoxifen, eventual resistance
`to
`this
`agent is common. MCF-7 tumors that
`progress after prolonged treatment are
`estrogen-independent (grow in the ab(cid:173)
`sence of estrogen supplementation) al(cid:173)
`though they are still estrogen-sensitive
`(growth is enhanced by estrogen). The
`mechanisms by which
`resistance
`to
`
`500
`
`0
`
`0
`
`20
`
`4D
`
`ID
`
`1DD
`
`DAYS
`
`Fig. 3. Hormonal sensitivity of ICI 182, 780.resistanl tlllDOIS. Fragments of a tumor that had developed resis(cid:173)
`tance in a mouse treatcd with IC 182,780 were transplanted into new recipienl female castrated nude mice.
`The recipienl mice were then randomly allocated to receive vehicle alone C-Ei; -ID-), an estradiol (El) pellet
`(+E2; -+-); wnoxifen alone(-£-); ICI 182,780 alone<+>. or a combination oftamoxifen plus ICI 182,780
`( .... ). Tumor volumes were calculated on the days shown. n = 6 mice per group; means ±SE.
`
`evolution to tamoxifen resistance when
`the drug was stimulating tumor growth
`(3). In fact, pS2 was significantly lower
`in
`tamoxifen-resistant tumors than
`in
`tamoxifen-scnsitive tumors (P = .012).
`This finding suggests that the agonist ac(cid:173)
`tivity of tamoxifen, if responsible for
`tamoxifen-stimulated tumor growth, may
`be specific to genes associated with cell
`proliferation, while its antagonist activity
`continues to suppress the activity of
`genes less crucial for tumor survival. In
`contrast to the results obtained with
`tamoxifen, mRNA expression was nearly
`
`Table I. Exiession of estrogen-sensitive genes•
`
`Treatment group
`(No. of blots analyzed)
`
`Gene, relative
`mRNAlevel
`
`pS2
`
`pLIVI
`
`Estrogen ( 4)
`Tamoxifen-sensitive (S)
`Tamoxifen-resistant (S)
`!Cl-sensitive (S)
`!Cl-resistant (8)
`
`12.2±0.7
`9.8±0.S
`3.2±0.4
`03±0.0S
`0.6±0.23
`
`12.2±0.6
`6.0± l.S
`7.s ± 1.8
`0±0
`2.3± 1.3
`
`•mRNA expression was measured by nonhem
`blot analysis of total RNA extracted from MCF-7
`tumors taken from mice treated with estrogen (con(cid:173)
`trols), tamoxifen for 3 weeks (tamOxifen-sensitive),
`lhe time of tumor progression
`wnoxifen until
`(wnoxifen-resiswu), ICI 182, 780 for4 weeks (ICl(cid:173)
`sensitive), or ICI 182, 780 until 1umor progression
`(ICl-resistanl). Values shown are the means± SE of
`scanning densitometry uniu corrected for RNA
`loading.
`
`abrogated by treatment with ICI 182,780
`(P<.004), and there was no difference be(cid:173)
`tween sensitive and resistant tumors. It is
`unlikely, therefore, that ICI 182,780 resis(cid:173)
`tance is caused by metabolic conversion
`of the drug to Ei. since expression of
`these estrogen-regulated genes remained
`low.
`
`Discussion
`
`Oinical data demonstrate that, in some
`patients, the current endocrine therapies
`for breast cancer result in temporary
`tumor regression or growth stabilization,
`tumor regrowth, usually
`followed by
`within 6-18 months of treatment. We
`have developed an experimental in vivo
`model that mimics this clinical scenario.
`Our data suggest that, in this experimen(cid:173)
`tal model system, ICI 182,780 possesses a
`greater ability to suppress estrogen-sensi(cid:173)
`tive gene expression and greater an(cid:173)
`titumor activity than the partial estrogen
`antagonist tamoxifen. In addition, MCF-7
`tumorigenesis was significantly delayed
`by ICI 182,780 when compared with
`tamoxifen. Moreover, a proportion of
`treated mice failed to develop tumors
`even after prolonged follow-up, an event
`rarely encountered
`in our experience
`treating mice with tamoxifen. ICI 182,780
`also suppressed growth of established
`tumors for a significantly longer duration
`
`Journal of the National Cancer Institute, Vol. 87, No. 10, May 17, 1995
`
`REPORTS 749
`
`MYLAN PHARMS. INC. EXHIBIT 1018 PAGE 4
`
`

`
`ICI 182,780 develops are not clear, but
`reduced levels of ER and reduced expres(cid:173)
`sion of estrogen-regulated genes (com(cid:173)
`pared with tamoxifen-sensitive or with
`tamoxifen-resistant tumors) are evident.
`Reduced ER levels have also been seen in
`tumors
`from
`patients
`treated with
`ICI 182, 780, in cultured breast cancer
`cells; and in mouse uterine tissue follow(cid:173)
`ing the administration of the prototype
`pure antiestrogen ICI 164,384 (18-20).
`Other data suggest that the pure anti(cid:173)
`estrogen-ER complex may be more
`fragile and more susceptible to receptor
`degradative pathways (16). In contrast,
`ER levels are high in tamoxifen-resistant
`tumors obtained with our model system
`(3). On the basis of our data, we would
`predict
`that most
`patients with
`ICI 182,780-resistant tumors would not
`respond well
`to subsequent treatment
`with tamoxifen.
`Even if pure antiestrogens are shown to
`have superior antitumor activity
`in
`women with breast cancer, they may not
`be the optimal antiestrogens for clinical
`use. The estrogenic properties of ta(cid:173)
`moxifen in bone and on blood lipids may
`help to reduce bone loss and prevent car(cid:173)
`diovascular disease, which are added
`benefits when
`treating breast cancer
`patients
`for prolonged periods after
`surgery for primary tumors or for breast
`cancer prevention (2 I ,22). The effect of
`ICI 182,780 on these parameters is not
`yet known, but it might be deleterious
`given its lack of estrogenic qualities.
`However, treatment with ICI 182,780
`might not be associated with the in(cid:173)
`creased risk of endometrial cancer recent(cid:173)
`ly attributed to tamoxifen (23). Further
`clinical study of pure antiestrogens in
`tamoxifen-resistant and
`in
`tamoxifen(cid:173)
`naive patients is clearly indicated.
`
`References
`(/) Systemic treatment of early breast cancer by
`honnonal, cytotoxic, or immune therapy. 133
`randomised trials involving 31,000 recurrences
`and 24,000 deaths among 75,000 women.
`Early Breast Cancer Trialists' Collaborative
`Group [stt comment citations in Medline].
`Lancet 339: 1-15, 71-85, 1992
`(2) Encarnacion CA, Ciocca DR, McGuire WL, et
`al: Measurement of steroid honnone receptors
`in breast cancer patients on tamoxifen. Breast
`Cancer Res Treat 26:237-246, 1993
`(J) Osborne CK, Coronado E, Allred DC, et al:
`Acquired tamoxifen resistance: correlation
`with reduced breast tumor levels of tamoxifen
`and isomerization of trans-4-hydroxytamoxi(cid:173)
`fen [see comment ciwion in Medline]. J Natl
`Cancer lnst83:1477-1482, 1991
`(4) Gottardis MM, Jordan VC: Development of
`tamoxifen-stimulated growth of MCF-7
`tumors in athymic mice after long-tenn anti(cid:173)
`estrogen administration. Cancer Res 48:5183-
`5187, 1988
`(5) Pritchard Kl, Thomson DB, Myers RE, et al:
`Tamoxifen therapy in premenopausal patients
`with metastatic breast cancer. Cancer Treat
`Rep64:787-796, 1980
`(6) Hoogstraten B, Gad-el-Mawla N, Maloney TR,
`et al: Combined modality therapy for first recur(cid:173)
`rence of breast cancer. A Southwest Oncology
`Group Study. Cancer 54:2248-2256, 1984
`(7) Osbome CK, Jarman M, McCague R, et al:
`The importance of tamoxifen metabolism in
`tamoxifen-stimulated breast tumor growth.
`Cancer Chemother Pharmacol· ·34:89-95, l 994
`(8) Wakeling AE, Bowler J: Novel antioestrogens
`without partial agonist activity. J Steroid
`Biochem 31 :645-653, 1988
`(9) Wakeling AE. Dukes M, Bowler J: A potent
`specific pure antiestrogen with clinical poten(cid:173)
`tial. CancerRes51:3867-3873, 1991
`(JO) Wakeling AE: Steroidal pure antiestrogens. Jn
`Regulatory Mechanisms in Breast Cancer
`(Lippman M, Dickson R, eds). Boston: Kluwer
`Acad Publ, 1991, pp 239-257
`(1 I) Gottardis MM, Jiang SY, Jeng MH, et al: In(cid:173)
`hibition of tamoxifen-stimulated growth of an
`MCF-7 tumor variant in athymic mice by
`novel steroidal antiestrogens. Cancer Res
`49:4090-4093, 1989
`(/2) Osborne CK, Hobbs K, Clark GM: Effect of
`estrogens and antiestrogens on growth of
`human breast cancer cells in athymic nude
`mice. Cancer Res 45:.584-.590, 198.5
`(/J) Manning DL, McClelland RA, Gee JM, et al:
`The role of four oestrogen-responsive genes,
`pUVI, pS2, pSYD3 and pSYD8, in predicting
`responsiveness to endocrine therapy in pri-
`
`mary breast cancer. Eur J Cancer 29A:l462-
`1468, 1993
`(14) Bri1nner N, Frandsen TI., Holst-Hansen C, et
`al: MCF7/LCC2: a 4-hydroxytamoxifen resis(cid:173)
`tant human breast cancer variant that retains
`sensitivity to the steroidal antiestrogen ICI
`182, 780. Cancer Res .53:3229-3232, 1993
`(15) Lyltkesfeldt AE, Sorensen EK: Effect of
`estrogen and antiestrogens on cell proliferation
`and synthesis of secreted proteins in the
`human breast cancer cell lines MCF-7 and a
`tamoxifen resistant variant subline, AL- I.
`Acta0ncol 31:131·138, l992
`(16) Parker MG: Action of pure antiestrogens in in(cid:173)
`hibiting estrogen receptor action. Breast Can(cid:173)
`cer Res Treat 26: 131·137, 1993
`(/7) Wiebe VJ, Osborne CK, Fuqua SA, et al:
`Tamoxifen resistance in breast cancer. Crit
`Rev Oncol Hematol 14:173-188, 1993
`(18) DeFriend DJ, Howell A, Nicholson RI, et al:
`Investigation of a new pure antiestrogen (ICI
`182780) in women with primary breast cancer.
`Cancer Res 54:408-414, 1994
`(/9) Defriend DJ, Blarney RW, Robertson JF, et
`al: Response to the pure antiestrogen ICI
`182780 after tamoxifen failure in advanced
`breast cancer. Breast Cancer Res Treat 17: 136,
`1993
`(20) Gibson MK, Nemmers LA, Beckman WC Jr,
`et al: The mechanism of JCJ 164,384 an(cid:173)
`tiestrogenicity involves rapid loss of estrogen
`in uterine
`tissue. Endocrinology
`receptor
`129:2000-2010, 1991
`(2/) Love RR, Mazess RB, Barden HW, et al: Ef(cid:173)
`fects of tamoxifen on bone mineral density in
`postmenopausal women with breast· cancer
`[stt comment ciwion in Medline]. N Engl J
`Med 326:852-856, 1992
`(22) Love RR, Newcombe PA, Wiebe DA, et al:
`Effects of tamoxifen · therapy on lipid and
`lipoprotein levels in postrnenopausal patients
`with node-negative breast cancer [stt com(cid:173)
`ment citation in Medline]. J Natl Cancer Inst
`82:1327-1332, 1990
`(23) Fomander T, HellstrOm AC, Moberger B:
`Descriptive clinicopathologic study of 17
`patients with endometri11l cancer during or
`after adjuvant tamoxifen in early breast can(cid:173)
`cer. J Natl Cancer Inst 85:1850-18.5.5, 1993
`
`Notes
`Supponed in pan by Public Health Service grant$
`CA30251, CA3019.5, CA58183, and CA54174 from
`the National Cancer Institute, National Institutes of
`Health, Department of Health and Human Services.
`Manuscript received September 19, 1994; revised
`December 27, 1994; accepted March 6, 1995.
`
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`750 REPORTS
`
`Journal oftheNaiional Cancer Institute, Vol. 87, No. 10, May 17, 1995
`
`MYLAN PHARMS. INC. EXHIBIT 1018 PAGE 5