V
`
`A
`
`MYLAN PHARMS. INC. EXHIBIT 1028 PAGE 1
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`

`
`Breast Cancer Research and Treatment
`
`Marc E. Lippman, M.D.! (Editor-in-Chief), Gary C. Chamness, Ph.Dj/Robert L. Dickson, Ph.D.! (Editors),
`C. Kent Osborne, M.D.2/Gary M. Clark, Ph.D.2 (Associate Editors)
`1Vincent T. Lombardi Cancer Research Center, Georgetown University, Washington DC, USA
`2 University of Texas Health Science Center at San Antonio, San Antonio TX, USA
`Editorial office address:
`Karen S. Cullen, BREA Editorial Office, Kluwer Academic Publishers, 101 Philip Drive, Assinippi Park,
`Norwell, MA 02061, USA; Tel: 617-871-6300; Fax: 617-871-6528; E-mail; Karen @ world. std. com.
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`MYLAN PHARMS. INC. EXHIBIT 1028 PAGE 2
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`

`
`Breast Cancer Research and Treatment
`
`t (Editors),
`
`Marc E. Lippman, M.D. 1 (Editor-in-Chief), Gary C. Chamness, Ph.D. 2/ Robert L. Dickson, Ph.D.
`C. Kent Osborne, M.D. 2/ Gary M. Clark, Ph.D. 2 (Associate Editors)
`I Vincent T. Lombardi Cancer Research Center. Georgetown University. Washington DC. USA
`2 University of Texas Health Science Center at Scm Antonio. San Antonio. TX. USA
`Editorial office address:
`Karen S. Cullen, BREA Editorial Office, Kluwer Academic Publishers, 101 Philip Drive, Assinippi Park,
`Norwell, MA 02061, USA; Tel: 617-871-6300; Fax: 617-871-6528; E-mail: Karen@world.std.com.
`EDITORIAL ADVISORY BOARD
`George Blumenschein (Arlington,
`Texas)
`Gianni Bonadonna (Milan, Italy)
`Paul P. Carbone (Madison,
`Wisconsin)
`Dean P. Edwards (Denver,
`Colorado)
`Evert Engelsman (Amsterdam, The
`Neth:rlands)
`.':
`.
`Bernard Fisher (Pittsburgh,
`Pennsylvania)
`
`Edwin Fisher (Pittsburgh,
`Pennsylvania)
`Jan-Ake Gustafsson (Stockholm.
`Sweden)
`Kathryn Horwitz (Denver,
`Colorado)
`Elwood V. Jensen (Hamburg.
`Germany)
`V. Craig Jordan (Madison, Wisconsin)
`Roger King (London, United Kingdom)
`Heinrich Maass (Hamburg, Germany)
`
`Kenneth S. McCarty, Jr. (Durham,
`North Carolina)
`Daniel Medina (Houston, Texas)
`Henri Rochefort (Montpellier, France)
`Richard Santen (Hershey.
`Pennsylvania)
`Jeffrey Schlom (Bethesda. Maryland)
`Haruo Sugano (Tokyo. Japan)
`Jeffrey M. Trent (Tucson, Arizona)
`
`All Rights Reserved
`© 1992 by Kluwer Academic Publishers
`No part of the material protected by this copyright notice may be reproduced or utilised in any form or by any means, electronic or
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`copyright owner
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`Netherlands
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`MYLAN PHARMS. INC. EXHIBIT 1028 PAGE 3
`
`

`
`BreastCancerResearch and Treatment 25: 1-9, 1993.
`© 1993 Kluwer Academic Publishers. Printed in the Netherlands.
`
`15thSan Antonio Breast Cancer Symposium - Plenary lecture
`
`The future of new pure antiestrogens in clinical breast cancer
`
`Alan E. Wake ling
`Bioscience I, ICI Pharmaceuticals,
`
`Alderley Park, Macclesfield, Cheshire SKIO 4TG, United Kingdom
`
`Key words: breast cancer, antiestrogens,
`
`tamoxifen,
`
`resistance
`
`Summary
`
`The rationale for seeking to identify new pure antiestrogens was based on the recognition that existing
`antiestrogens, exemplified
`by tamoxifen,
`all possess partial agonist
`(estrogenic)
`activity. Conceptually,
`pure antiestrogens
`should be more effective than tamoxifen in ablating the mitogenic action of estrogens
`on breast tumor growth.
`The discovery
`and properties of the pure antiestrogens
`ICI 164,384 and ICI
`182,780 are described and contrasted with those of tamoxifen. Key characteristics
`of these compounds
`which may be of particular
`relevance
`to their therapeutic
`application in the treatment of breast cancer are
`described. These include experimental
`data which predict efficacy in patients whose disease recurs during
`tamoxifen treatment, and the potential
`for pure antiestrogens
`to demonstrate greater efficacy than tamoxifen
`in first-line treatment of advanced breast cancer. The data imply that gains in efficacy could emerge as
`morerapid, more complete, or longer-lasting
`tumor remissions. Clinical
`trials with ICI 182,780 will reveal
`whether one or more of these predictions
`is correct.
`
`IntrOduction
`
`('Nolva-
`Thenonsteroidal antiestrogen tamoxifen,
`dex'l, ICI 46,474),
`is established
`as the treatment
`of choice for the endocrine
`therapy of advanced
`breast cancer [1].
`Its ease of use and the absence
`of serious side effects in patients
`stimulated trials
`to assess the value of tamoxifen in adjuvant
`treat-
`ment of primary breast cancer
`[2,3] and, more re-
`cently, the initiation of trials to test
`its potential
`as a chemo-preventive
`agent
`in women at high
`risk of developing breast cancer
`[4,5]. The pro-
`portion of patients with advanced
`breast cancer
`
`who respond to Nolvadex, and the average dura-
`tion of response, are not significantly greater than
`those obtained with other endocrine
`treatments.
`Nolvadex treatment
`is palliative, and the majority
`of women who
`respond
`to
`treatment will
`experience relapse.
`In adjuvant
`therapy, Nolvad-
`ex extends
`the disease-free
`interval and overall
`survival compared with no treatment
`[3]. Current
`clinical practice in the adjuvant use of Nolvadex
`shows an increasing trend towards continuation of
`drug treatment until disease recurrence.
`These
`clinical
`observations
`pose
`several
`important
`questions
`about
`future directions
`for
`treatment,
`
`Address/or offprints and correspondence: Alan E. Wakeling, Bioscience I, ICI Pharmaceuticals. Alderley Park, Macclesfield,
`f?eshire SKIO 4TG, United Kingdom
`Nolvadex' is a Trade Mark, the property of Imperial Chemical Industries pIc
`
`III
`
`II
`
`1
`
`uric
`opY
`~en
`
`ring
`
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`
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`MYLAN PHARMS. INC. EXHIBIT 1028 PAGE 4
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`

`
`2
`
`AE Wakeling
`
`two of which are considered here. Firstly, what
`re-v-
`treatment(s)
`should be applied in patients
`lapsing
`during
`or
`after Nolvadex
`treatment?
`Secondly, will pure antiestrogens
`provide more
`effective treatment of advanced breast cancer than
`Nolvadex
`or
`other
`currently
`available
`drug
`treatments?
`It will be argued that pure anti-':
`estrogens have particular properties which will
`provide answers to these important questions.
`
`Rationale for pure anti estrogens
`
`tumor growth by binding to
`stimulate
`Estrogens
`(ER) in the cell nucleus. The
`estrogen receptors
`estrogen-ER complex then dimerizes and binds to
`"specific DNA sequences
`(estrogen response ele-
`ments, ERE),
`to activate
`the
`transcription
`of
`estrogen responsive genes which ultimately trigger
`cell proliferation. Tamoxifen disrupts this process
`by binding to ER and interfering with normal
`transcriptional
`responses
`to estrogens
`[11]. The
`estrogenic effects of tamoxifen strongly imply that
`the
`tamoxifen-receptorcomplex
`in the
`cell
`nucleus is not inert -
`it retains some capacity to
`transduce
`signals similar
`to those induced by the
`estrogen-ER complex [11].
`In contrast
`it might
`be anticipatedthat
`pure antiestrogens
`should bind
`toER to formanER-complex
`which either does
`not bind to ERE's or, if DNA binding does occur,
`is unable to promote transcription.
`
`Discovery of novel antiestrogens
`
`In early animal studies it was shown that tamox-
`ifen antagonises
`the tropic actions of endogenous
`or exogenous estrogens but also, when adminis-
`tered alone to immature (or ovariectomised)
`rats
`and mice,
`itself has tropic
`(estrogenic)
`effects"
`[6,7]. Thus,
`tamoxifen has the characteristics' of-.
`an antiestrogen with partial agonist activity.
`In r
`animals and in man the balance between stimula-
`tory and inhibitory activities of tamoxifen varies
`The two key elements of the search for pure anti-
`widely depending on the organ, cell, or specific
`estrogens were.ifirstly.ca
`medicinal
`chemistry
`protein measured as an indicator of estrogenic
`strategy
`to identify
`novel ER ligands
`and,
`activity [8,9].
`Tamoxifen
`shares
`this property
`secondly,
`robust
`and
`reliable
`biological
`test
`with chemically similar, triphenylethylene-derived
`systems. The strategy chosen for initial chemistry
`agents, described earlier and more recently [10].
`is described elsewhere [12] andinvolved
`synthesis
`A consequence of this partial agonist activity is
`that complete blockade of the action of estrogens:
`of; estradiol
`analogues
`bearing C7-substituents
`which retain a high affinity for ER, an essential
`cannot be achieved with tamoxifen. Although it;::
`'''feature
`recognized in our drug target profile [13].
`is not known whether
`the partial agonist activity
`i.'Facile and reproducible
`testing-for both estrogen
`of tamoxifen in any way limits its clinical effi->
`: agonist and antagonist activity in vivo was provid-
`cacy, complete ablation of the estrogen-mediated'
`,.
`..../ ....ed by measurement
`of uter~tiopic
`and antiutero-
`tumor growth is a desirable objective
`since it\
`'tropic
`effects in immature rats [14].
`In this assay,
`might be anticipated to provide more rapid, moret"
`:,r'i\~j;tamoxifen alone maximallyincreases
`the uterine
`complete,
`or
`longer-lasting
`tumor
`responses.
`Conceptually,
`this objective could be achieved bY';)i~?'weight
`2-fold, compared with5-fold
`for estradiol.
`treatment with a pure antiestrogen'i:;~'i!{Correspondingly,
`coadministration
`of tamoxife~
`The profile of activity of a pure antiestrogen iSI;$\;:and
`estradiol demonstrates
`a maximum 60% inhl-
`easily understood in the pharmacological
`sense;
`.~\:;::;bition
`of
`the
`tropic
`action
`of estradiol.
`In
`developments
`in understanding
`the molecular
`'.,:':;,":'addition to this bioassay,
`the intrinsic potency ~f
`mode of action of estrogens
`and how this
`is
`·····new compounds
`could be monitored accuratelym
`.. ,~i;5yitro by receptor binding measurements
`affect~d by tamoxifen,
`also facilitated
`a bio-
`[15] and
`estrogen-
`chemical concept of how such agents might work .. '""~cel1
`growth
`.inhibition
`assays with
`
`MYLAN PHARMS. INC. EXHIBIT 1028 PAGE 5
`
`

`
`Clinical potential of pure antiestrogens
`
`3
`
`"~I
`
`action of ICI 164,384 have shown r that-it binds
`ER with a' substantially
`higher ';'affinity
`than
`tamoxifen (-lO-fold), but, unlike tamoxifen,
`fails
`to activate
`transcription
`of estrogen-responsive
`genes (see [18] for review).
`It is not yet clear
`whether
`the blockade ,of Ek-signaling
`bylCI
`164,384 is due to
`a failure '; of . the, receptor
`complex to dimerizearid
`bind to ERE [19] or to
`an inactivation of the transcriptional
`.activation
`function of
`the DNA-bound
`receptor
`complex
`[20]. Both mechanisms. may"contribitieto
`the
`of 'pure t antagonist -:activity:
`expression
`ICI
`164,384 treatment
`.leads '.to, a, rapid' reduction of
`cell and tissue ER concentration [21,22], an effect
`which is like1ytoseverety
`at~~~~atethecap~city
`of estrogen-responsive
`cells 'to respond to the
`natural hormone.
`Complete ablation of estiog~riacti~n
`by ICI
`164,384 in vivo requiredhighdosesof.drug
`[23]
`and, for this reason,
`ICIJ64,384
`did not merit
`serious consideratio? ~~ ardrug ..candidate ... More
`potent compounds~~resought
`which retained the
`pharm~s?logical,:, profile' Of ICI
`advantageous
`164,384, compare~ .\Viththe tamoxifen-like partial
`agonists. A ne\V compound,
`ICI 182,78Q,7~-[9-
`(4,4,5,5,5 -pentaflu()r0p.7I1tylsulfinyl)no?y
`1]-
`estra-1 ,3,5(1 0)-triene-3, 17P~diol(Figure1
`);was
`selected for intensive' study [2~]~:ICI\182,780
`differs from ICI 161,384jn.t\Vo'~ey·
`feat~res of
`the t« side-chain;the~mi~~"moietyof
`ICI
`164,384 was replaced by asulfinyl
`group and the
`terminal alkyl function was fluorinated to reduce
`the potential
`for metabolic,
`attack [12].
`ICI
`182,780 has a four to five-fold greater affinity for
`ER than ICI 164,384 and similarly is 5-fold more
`potent
`in inhibiting the growth of MCF-7 cells
`[24].
`In the rat uterotropic/antiuterotropic
`test,
`ICI 182,780 is
`lO-fold more potent
`than ICI
`164,384 [24].
`
`sensitive human breast cancer (MCF~7) cells [16].
`Synthesis of novel 7a-alkylamide
`analogues of
`estradiol provided
`the first
`examples
`of com-
`pounds devoid of estrogenic
`activity but capable,
`when administered
`together with estradiol," of
`blocking, completely the uterotropic
`effect of the
`natural hormone
`in rodents
`[12,17].
`Structure-
`activity analysis
`revealed the importance
`of the
`position,'length,
`and flexibility 'of the C7 side-
`chain in determining pure antagonist activity [12].
`it.was shown that receptor binding
`For example,
`and biological activity resides almost exclusively
`than the 7P isomers. Pure anti-
`in the 7a rather
`estrogens were found amongst compounds with an
`overall chain length of 16-18 atoms, and tertiary
`rather than secondary amides are preferred.
`''[he
`most potent pure antagonist
`amongst
`the alkyl-
`amideswas
`Nen-butyl-Ncmethyl-Ll-GdZp-di-
`hydroxyestra-I ,3,5( 10)-trien-7 a-yl)uridecanamide,
`leI 164,384 (Figure
`I). Studies of the mode of
`
`OH
`
`,.cl 164,~84
`
`,
`
`,,'.
`
`'i
`
`OH
`
`HQ
`
`HQ
`
`IC1182,780
`
`Figure 1. Structures of pure' antiestrogens
`
`MYLAN PHARMS. INC. EXHIBIT 1028 PAGE 6
`
`

`
`4
`
`AE Wakeling
`
`Comparative pharmacology of tamoxifen and
`pure anti estrogens
`
`Animal studies
`
`The most graphic distinction between pure and
`partial-agonist antiestrogens is provided by rodent
`tissue response assays where tamoxifen is a full
`or partial agonist. Thus, when tamoxifen rather
`than estradiol is used to stimulate the uterus, both
`ICI 164,384 and ICI 182,780 can block complete-
`ly its trophic action [17,24]. A similar bioassay
`in which full, normal mammary ductal elongation
`in ovariectomised pubertal rats is induced by
`either estrogen or tamoxifen treatment, showed
`that ICI 164,384 alone had no stimulatory effect
`but could completely block the tropic action of
`estrogen or tamoxifen [25]. These pharmaco-
`logical observations strongly support a common
`biochemical mode of action for estradiol, tamoxi-
`fen, and the pure antiestrogens through the ER.
`It is also implicit in these observations that the
`pure antiestrogen-receptor complex, in contrast to
`the tamoxifen-receptor complex, is devoid of the
`capacity to induce the transcription of estrogen-
`responsive genes in vivo.
`Comparisons of the effects of ICI 164,384 and
`ICI 182,780 vs.
`those of tamoxifen in intact
`female rats [23,24] showed that tamoxifen reduces
`uterine weight, but maximally is much less
`effective than ovariectomy, whereas the pure
`antiestrogens are almost as effective as ovari-
`ectomy. The fact that pure antiestrogens were
`slightly less effective than ovariectomy could be
`evidence that the size of the uterus is influenced
`by non-estrogenic hormones rather than any lack
`of antiestrogenic potency in these compounds.
`Some evidence of this emerged from studies
`where rats were treated with a combination of an
`LHRH analog (chemical hypophysectomy) and
`ICI 164,384. Uterine weight was reduced below
`that achieved by the LHRH analog alone [26].
`Further interesting observations which may be
`relevant to clinical efficacy emerged from the
`
`in intact rats.
`studies of antiestrogen effects
`Firstly, pure antiestrogen treatment did not affect
`gonadotropin concentrations or the body weightof
`the animals (Table 1), whereas tamoxifen ex-
`hibited estrogenic effects by reducing both body
`weight and circulating gonadotropin concentra-
`tions [23]. Since ovariectomy causes increased
`body weight gain and gonadotropin secretion by
`removal of the negative feedback of estrogens on
`the brain,
`it can be argued that
`the pure anti-
`estrogens, unlike tamoxifen, do not block ER in
`the brain at doses which have profound effects on
`the uterus. This peripheral versus central selec-
`tivity of action could have highly beneficial
`effects in premenopausal patients where anti-
`uterotropic
`effects
`and breast
`tumor growth
`inhibition might be achieved without disturbing
`the hypothalamic-pituitary-ovarian
`axis. More
`recent studies in intact or ovariectomized/estro-
`gen-treated monkeys using magnetic resonance
`imaging of the uterus, have confirmed that leI
`182,780 is a pure
`antagonist
`and produces
`profound antiuterotropic effects achieved without
`concurrent "castration-like" increases of plasma
`gonadotropin concentration [27 and unpublished
`studies].
`If these observations are paralleled in
`patients, hot flashes or the psychosocial conse-
`quences of estrogen withdrawal should not occur
`in women treated with ICI 182,780. Tamoxifen
`does have central effects in patients, for example
`in inducing hot flashes [1], and concerns have
`also been expressed that its uterotropic action may
`increase the incidence of endometrial cancer [28];
`such concerns would be eliminated by treatment
`with pure antiestrogens.
`One predicted undesirable action of pure anti-
`estrogens in therapeutic use may be a tendency to
`reduce bone density and hence to precipitate .or
`exacerbate osteoporosis. Analysis of bone denSIty
`in rats treated with ICI 182,780 failed to reveal
`any effect whereas, in the same study, ovariec-
`tomy significantly reduced bone density (Table 1).
`This suggests that there are differentials in the
`sensitivity of peripheral estrogen target organs to
`
`MYLAN PHARMS. INC. EXHIBIT 1028 PAGE 7
`
`

`
`Clinical potential of pureantiestrogens
`
`5
`
`Table 1. Effects of ICI 182,780 in adult female rats
`
`Treatment
`
`Intact control
`
`OVX control
`
`ICI182,780
`(mg/kg/d x 28)
`0.1
`0.3
`1.0
`3.0
`
`Uterine weight'
`(mg)
`
`Body weight gain
`(g)
`
`70 ± I"
`
`208 ± 17
`174 ± 16·(
`94 ± 9
`103±2
`
`60 ±4
`114 ± 6
`
`68 ± 4
`67 ±4
`70 ±4
`71 ± 6
`
`1.2 ± 0.2
`
`33.5± 7.1
`
`1.2 ± 0.1
`1.3 ± 0.1"
`2.8 ± 0.3
`" 2,4± 0.6
`
`Bone density
`(g/ml)
`.
`
`1.523 ± 0.008
`
`1,491 ± 0.006
`
`1.528± 0.005
`1:528± 0.008
`1.532± 0.005
`1.533'± 0.005
`
`antiestrogens as well as central versusperipheral
`differences,and cautions against premature judge-
`menr of likely pharmacological actions of these
`agentsin man.
`
`Breast cancer cells
`
`the ERJsignalling
`Functional disablement of
`capacityby pure antiestrogens produces effects on
`human breast cancer cells which have' profound
`therapeutic implications. A comparison 'of the
`potency and efficacy of tamoxifen, ICI 164;384;
`and ICI 182,780 as inhibitors of the growth of
`estrogen-responsive MCF-7 human breast tumor-
`derived cells, showed that the pure antiestrog~~s
`are up to two orders of magnitude more:po"teIlt,
`reflecting in part
`their higher affinity J9I'ER
`[23,24]. More significantly, analysis'of.the<
`growth dynamics of the cultured cells' showed
`that, although both classes of agent share the
`ability,to block cell division in the G1 phase of
`the cell cycle [29], both ICI 164,384 and ICI
`182,780were much more effective than tamoxifen
`in reducing the proportion of cells which remain
`ableto synthesize DNA after prolonged exposure
`[24,30]. The proportion of cells which continued
`to synthesize DNA in a two day period at the end
`of five days exposure to the antiestrogeIls,'.'was
`reduced from 82% in control cultures to 37% by
`tamoxifen but to only 7% by ICI 182,780 [24].
`
`This difference may be due to the partial agonist
`activity of tamoxifeii which is amplified by inter:
`action with mitogenic signals provided by growth
`factors,' an"effect which is absent in the case of
`the pure antiestrogens [30].
`If the greater efficacy of pureversuspartial
`agonist antiestrogens against hum'anbreast cancer
`cell growth described above translates to' the
`clinical setting;' one, might anticipate significant
`benefits in the rate and extent of tumor remission
`following pure antiestrogen therapy compared
`with other;';alltiestrogenic"
`therapies.
`It
`is
`particular1yimp()~tant
`to recognize that
`if the
`synergistic growthstimulatory interactionbetween
`estradiol and.,insulin-like growth factors deIIlon-
`strated in vitro [16;30,31] occurs.in patients there
`may be a massive difference inefficacy.between
`treatments which only reduce estrogen action
`(tamoxifen, aromatase inhibitors, LHRH analogs)'
`compared with a. treatment which can potentially
`sustain 100% blockade. Thus, there is a powerful
`rationale which argues the superiority of pure
`antagonists over other treatments.
`The major cause of death from breast cancer
`is metastatic disease. rather
`than uncontrolled
`proliferation of the primary tumor. Metastatic
`spread depends on the capacity of the tumor cells
`to cross the basement membrane and invade into
`surrounding tissue. Experimental studies. with
`breast tumor-derived cell lines have ••shown that
`
`MYLAN PHARMS. INC. EXHIBIT 1028 PAGE 8
`
`

`
`6
`
`AE Wakeling
`
`invasive capacity and proliferative potential are
`independently variable [32].
`It
`is therefore
`important to know whether antiestrogens affect
`the phenotypic expression of invasive behavior by
`breast
`tumor cells.
`This question has been
`examined in comparative studies of the effects of
`estradiol and several antiestrogens on the capacity
`of MCF-7 cells to cross a re-constituted basement
`membrane in vitro [33]. Both estradiol and 4'-
`hydroxytamoxifen, but not ICI 164,384, stimu-
`lated this activity; ICI 164,384 was also able to
`block estrogen and 4' -hydroxytamoxifen-stimu-
`lated invasion.
`ICI 164,384 also demonstrated
`anti-invasive activity against MCF-7 cells in an
`alternative bioassay [34]. These data argue that
`early treatment of breast cancer with a pure
`antiestrogen might be particularly beneficial
`in
`limiting tumor spread.
`
`Tamoxifen resistance
`
`The mechanisms which might underlie the devel-
`opment of resistance to tamoxifen among patients
`with advanced breast cancer who initially respond
`to treatment, has been studied using human breast
`cancer cells grown either in vitro or in vivo as
`xenografts in nude mice, and exposed continuous-
`ly to growth inhibitory concentrations of tam-
`In vitro,
`oxifen.
`long-term exposure of both
`MCF-7 and T47D cells to tamoxifen leads to a
`loss of sensitivity to the growth inhibitory activity
`of tamoxifen [35,36]. In T47D cells it was sug-
`gested that the mechanism underlying the devel-
`opment of tamoxifen resistance in vitro is the
`selection of subpopulations of cells which are
`growth stimulated bytamoxifen,
`rather than the
`selective outgrowth of cells which are unaffected
`by tamoxifen [36]. If these "tamoxifen-resistant"
`cells derive a growth advantage from tamoxifen
`exposure, one mechanism for such an effect could
`be the selective stimulation of a subpopulation of
`tumor cells in which the effect of tamoxifen is
`"interpreted" as predominantly estrogenic rather
`
`Is it likely that tumor cells
`than antiestrogenic.
`which respond differentially to tamoxifen coexist
`within a phenotypically homogeneous population?
`Differentials between estrogenic and antiestrogen-
`ic responses to tamoxifen at the organ, cell, and
`gene level alluded to earlier, are well-established
`[10]. Also, the differential efficacy of pure and
`partial agonist antiestrogens on the proliferative
`potential of MCF-7 cells described earlier has
`been attributed to the estrogenic activity of
`tamoxifen [30]; thus, the subpopulation of cells
`which continue to proliferate in the presence of
`tamoxifen, but not in the presence of pure anti-
`estrogens, may be that which eventually grows
`out as the dominant resistant line. An important
`prediction of this mechanism is that tumor cells
`growing because they "read" tamoxifen as an
`agonist, should remain sensitive to the growth-
`inhibitory effect of pure antiestrogens.
`In one
`case,
`that of
`the "tamoxifen-resistant" AL-l
`subline of MCF-7 cells, cell growth was still
`sensitive to inhibition by ICI 164,384 [37].
`Animal model studies have provided evidence
`that a similar positive
`selection pressure to
`generate "tamoxifen-resistant'' cells might operate
`in vivo. The growth of MCF-7 cells as solid
`tumors in nude mice is blocked initially by tam-
`oxifen but
`then resumes
`[38,39]. That
`those
`tumors which develop "resistance" to tamoxifen
`are not resistant in the sense generally understood
`in cancer therapeutics, was shown in two ways.
`Firstly, re-transplantation studies showed that such
`tumors would grow only if the host was treated
`with either tamoxifen or estradiol and, secondly,
`that
`the growth of these tamoxifen "resistant"
`tumors is attenuated by the pure antiestrogen leI
`164,384 [40]. Recent studies on the metabolism
`of tamoxifen in resistant
`tumors removed from
`nude mice indicate that responsive and resistant
`tumors differ in respect of concentrations of the
`parent drug and potentially estrogenic metabolites
`[41]. Tamoxifen-stimulated tumor growth may be
`explained by. metabolic adaptation of the tumor.
`This mechanism provides an alternative to the
`
`MYLAN PHARMS. INC. EXHIBIT 1028 PAGE 9
`
`

`
`Clinical potential of pure antiestrogens
`
`7
`
`likely to increase substantially in the future due to
`the trend to maintain adjuvant
`treatment
`until
`relapse.
`For patients who relapse at some time
`after completion of an adjuvant course of Nolvad-
`ex, there is no a priori reason to exclude a further
`trial of Nolvadex. However, based again on the
`arguments deployed above, that pure antiestrogens
`are the more effective
`inhibitors of
`tumor cell
`growth and are less likely to induce treatment
`failure,
`it can be argued that a better option is
`treatment with a pure antiestrogen.
`
`Clinical application
`
`ICI
`of
`low oral bioavailability
`The relatively
`182,780 [24] necessitated development of alterna-
`tive dosing regimens.
`Experimental
`studies
`in
`rats dosed parenterally with oil-based formulations
`of ICI 182,780, showed that antiestrogenic
`activ-
`ity could be sustained for long periods with a
`single injection. The potential
`therapeutic utility
`of such oil-depot
`formulations was demonstrated
`by a sustained antitumor action following single
`s.c.
`injections
`in nude mice transplanted with
`human breast
`tumors [24]. The likely dose and
`frequency of treatment
`in breast cancer patients
`was assessed by measuring the duration of anti-
`estrogenic action of oil depots of ICI 182,780 in
`(Macaca nemestrina)
`monkeys
`using magnetic
`resonance
`imaging
`(MRI) of
`the uterus
`[27].
`These studies showed that a single injection of
`4mg of
`ICI 182,780/kg
`at 4-weekly
`intervals
`provided
`increasingly
`effective
`blockade
`of
`estrogen-induced
`uterine
`proliferation, without
`significant accumulation of the drug monitored by
`analysis of plasma drug concentration [27].
`stud-
`Animal
`toxicology and human volunteer
`ies have recently been successfully completed as
`a prelude to therapeutic studies with the oil depot
`formulation of ICI 182,780in patients. An initial
`therapeutic
`trial has begun in patients with ad-
`vanced breast cancer who have relapsed during
`Nolvadex treatment.
`
`that subpopulations
`above,
`hypothesis examined
`of tumor cells with differential
`sensitivities
`to
`tamoxifen may coexist
`in the tumor. Preliminary
`data indicate that similar metabolic changes may
`occur in patients relapsing on Nolvadex treatment
`[42,43].
`It can be predicted
`that pure
`anti-
`estrogens would block the mitogenic
`effects .of
`estrogenic tamoxifen metabolites
`as effectively as
`they do that of tamoxifen
`itself. Whether
`such
`metabolic adaptations
`could occur during long-
`term pure antiestrogen
`treatment
`is not known,
`but this seems unlikely
`to occur by the same
`mechanism(s) because the pure antiestrogens
`are
`quite different
`in structure from tamoxifen.
`These experimental
`data discussed above may
`have important
`clinical
`implications.
`Clearly,
`since pure antiestrogens
`are devoid of estrogenic
`activity, their therapeutic use would avoid at least
`one of the underlying reasons for the development
`of tamoxifen
`resistance,
`and implies
`that
`the
`average duration of response
`to treatment might
`be greater
`for
`a pure
`antiestrogen
`than
`for
`tamoxifen. Although
`it
`is not clear what pro-
`portion of breast
`tumors relapse during Nolvadex
`therapy because
`they
`become
`dependent
`for
`growth on tamoxifen
`rather
`than
`classically
`resistant,
`there is a sound pharmacological
`basis
`for evaluating pure anti estrogen treatment
`in such
`It could be argued that simple with-
`patients.
`drawal of tamoxifen might
`also lead to tumor
`remission,
`and there
`is clinical
`evidence
`that
`supports
`this
`assertion
`[44].
`However,
`since
`tamoxifen can remain in tissues
`for very long
`periods
`after
`drug withdrawal
`[45],
`additive
`treatment with a pure antiestrogen might
`further
`improve response rates.
`Treatment
`choice
`for patients who relapse
`dUring, or at some time after, adjuvant Nolvadex
`therapy for primary breast cancer,
`is a subject of
`increasing importance. Based on the experimental
`precedents
`discussed
`above,
`there
`is a sound
`rationale for treating patients who relapse during
`adjuvant Nolvadex
`therapy with pure antiestro-
`gens. The number of patients
`in this category is
`
`II I II, I
`
`MYLAN PHARMS. INC. EXHIBIT 1028 PAGE 10
`
`

`
`8
`
`AE Wakeling
`
`Conclusions
`
`Extensive studies of the biological properties of a
`new class of steroidal antiestrogens,
`the 7a-sub-
`stituted estradiol
`analogs
`exemplified
`by ICI
`164,384 and ICI 182,780, have shown that these
`agents are pure antagonists. Mode of action
`studies are consistent with competitive
`inhibition
`of estrogen action through ER,
`leading to com-
`plete blockade of estrogen-induced
`transcription.
`By comparison with partial agonist antiestrogens
`like tamoxifen, pure antiestrogens
`achieve more
`complete regression of estrogen-dependent
`tissues
`in vivo. Model studies with human breast cancer
`cells in vitro and in vivo predict
`that these agents
`have the potential
`to be more effective therapeut-
`ically than currently
`available
`treatments
`for
`breast cancer.
`In particular, a proportion of breast
`tumors which recur during tamoxifen
`therapy,
`may remain sensitive to the antitumor action of a
`pure antiestrogen.
`
`References
`
`in the
`cancer.
`
`Antioestrogens
`1. Litherland S, Jackson M:
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`Cancer Treat Revs 15:183-194, 1987
`2. Smith I: Adjuvant tamoxifen for early breast cancer.
`Br J Cancer 57:527-528, 1987
`3. EBCTCG: Systemic treatment of early breast cancer by
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`4. Powles TI, Tillyer CR, Jones AL, Ashley SE, Treleaven
`J, Davey JB, McKinna JA: Prevention of breast cancer
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`5. Nayfield SG, Karp IE, Ford LG, Dorr FA, Kramer BS:
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`6. Harper MJK, Walpole AL:
`Contrasting endocrine
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`substituted triphenyl ethylenes. Nature 212:87,1966
`7. Harper MJK, Walpole AL: A new derivative of tri-
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`J Reprod Fert 13:101-199, 1967
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`8. Furr BJA, Jordan VC: The pharmacology and clinical
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