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`Breast Cancer Research and Treatment
`
`Marc E. Lippman, MD.‘ (Editor~in—Chief), Gary C. Chamness, Ph.D.2/Robert L. Dickson, Ph.D.‘ (Editors),
`C. Kent Osborne, M.D.1/Gary M. Clark, Ph.D.2 (Associate Editors)
`‘Vincent I Lombardi Cancer Research Center; Georgetown University, Washington DC, USA
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`
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`|nnoPharma Exhibit 1058.0002
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`Breast Cancer Research and Treatment
`
`Marc E. Lippman, M.D. ' (Editor—in~Chiei), Gary C. Chamness, Ph.D. 3 / Robert L. Dickson, Ph.D. 1 (Editors),
`C. Kent Osborne. M.D. 3 / Gary M. Clark, Ph.D. 2 (Associate Editors)
`1 Vincent T. Lombardi Cancer Research Center, Georgetown Uniwzrst'!y, lVa.s'ltr'ngI0n DC, USA
`2 University of Texas Health Science Center at San Antonio. San Antonio. TX, USA
`
`Editorial ofiice 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; Kttren@world.std.com.
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`Germany)
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`Roger King (London, United Kingdom)
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`North Carolina)
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`|nnoPharma Exhibit 10580003
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`

`

`Breast Cancer Research and Treatment 25: l~9, 1993,
`© 1993 Kluwer Academic Publishers. Printed in the Netherlands.
`
`15th San Antonio Breast Cancer Symposium —— Plenary lecture
`
`The future of new pure antiestrogens in clinical breast cancer
`
`Alan E. Wakeling
`Biosczence I, ICI Pharmaceuticals, Alderley Park, Macclesfield, Cheshire SK10 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
`antxestrogens, 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
`Whlch may be of particular relevance to their therapeutic application in the treatment of breast cancer are
`d6SCl‘lbCd. 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
`more rapid, 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
`
`The nonsteroidal antiestrogen tamoxifen, (‘Nolva—
`deX’1,ICI 46,474), is established as the treatment
`Of choice for the endocrine therapy of advanced
`bffiast 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-
`mem Of primary breast cancer [2,3] and, more re-
`Gently, the initiation of trials to test its potential
`is at chemo-preventive agent in women at high
`risk of developing breast cancer [4,5]. The pro-
`P0rtion of patients with advanced breast cancer
`
`who respond to Nolvadex, and the average dura-
`tionlof 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,
`
`'Aj3n Wakeling, Bioscience I, ICI Pharmaceuticals, Alderley Park, Macclesfield,
`Addressfor oflprints and c0rrespoindenCéi,_.
`I
`I
`fllfishire SK10 4TG, United Kingdom
`Nolvadex’ is a Trade Mark, the property of Imperial Chemical Industries plc
`
`‘\EE;33.1%?-
`
`{Bl}.
`
`iii‘
`
`~,........;............¢........l.......«.....,..,,
`
`|nnoPharma Exhibit 1058.0004
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`

`

`Estrogens stimulate tumor growth by binding to
`estrogen receptors(ER) -in the cell nucleus. The
`estrogen—ER complex then dimerizes and binds to
`
`rspecific 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—receptor “complex 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 anticipated that pure antiestrogens should bind
`to;ER to form an ER-complex which either does
`not bind to ERE’s or, if DNA binding does occur,
`
`,
`
`2
`
`elAE Wakeling
`
`two of which are considered here. Firstly, what
`
`treatment(s) should be applied in patients re—w~
`tlapsing during or after Nolvadex treatment?
`Secondly, will pure antiestrogens provide more is
`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 willjjg.
`provide answers to these important questions.
`
`Rationale for pure antiestrogens
`
`In early animal studies it was shown that tamox°-“‘“
`A ifen antagonises the tropic actions of endogenous»,
`or exogenous estrogens but also, when adminis— ,,
`tered alone to immature (or ovariectomised) rats,
`
`
`
`is unable to promote transcription.
`
`Discovery of
`
`antiestrogens
`
`itself has tropic (estrogenic) effects .
`and mice,
`[6,7]. Thus, tamoxifen has the characteristicsiof
`an antiestrogen with partial agonist activity. In,
`animals and in man the balance between stimula-fl,
`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, firstly, _a medicinal chemistry
`protein measured as an indicator of estrogenic.
`activity [8,9]. Tamoxifen shares this property
`strategy to . identify novel ER ligands
`and,
`with chemically similar, triphenylethylene—derived
`secondly,
`robust and reliable biological
`test
`agents, described earlier and more recently [10].
`systems. The strategy chosen for initial chemistry
`is described elsewhere [12] andinvolved synthesis
`A consequence of this partial agonist activity is
`.
`that complete blockade of the action of estrogens,
`. ofg estradiolteanalogues » bearing C7-substiwenis
`which retain a high affinity ‘forER, an essential
`cannot be achieved with tamoxifen. Although it 1.
`is not known whether the partial agonist activity,"
`“feature recognized in our driigitarget profile [13]-I
`of tamoxifen in any way limits its clinical effi-~
`Facile and reproducible testing.-for both estrogen
`cacy, complete ablation of the estrogen,-mediated“
`.. figonist and antagonist activity
`vivo W35 PT°Vid'
`tumor growth is a desirable objective since iti
`, ed by measurement of uterotropic and ant1utero-
`might be anticipated to provide more rapid, more ’l
`I
`
`(“tropic effects in immature rats [14]. In this assay,
`complete, or
`longer-lasting tumor
`responses.
`tamoxifen alone maximallyhncreases the uterine
`Conceptually, this objective could be achieved by
`weight 2-fold, compared withi5—fold for estrad101-
`treatment with a pure antiestrogen.
`Correspondingly, coadministration of tamoxifen
`? The profile of activity of a pure antiestrogen is
`and estradiol demonstrates a maximum 60% iI1h1'
`s easily understood in the pharmacological sense;
`bition of the tropic action of estradiol.
`1“
`developments in understanding the molecular
`addition to this bioassay, the intrinsic p0t6I1CY of
`mode of action of estrogens and how this is
`new compounds could be monitored accurately ’”
`affected by tamoxifen, also facilitated a bio-
`vitro by receptor binding measurements [15] and
`chemical concept of how such agents might work.
`cell growth inhibition assays with . estrogen’
`
`
`
`bi
`
`
`
`|nnoPharma Exhibit 1058.0005
`
`

`

`Clinical potential of pure antiestriogensi
`
`3
`
`action of ICI 164,384ihave_ shownrthatl-it binds
`ER with fa substantially higher’? affinity than
`tamoxifen (~10-ifold), but, unlike tamoxifen,fails
`1 to activate transcription of estrogen-responsive
`genes (see [18] for review).
`It is not yet clear
`whether the blockade of ZER‘-si’gnaling« by ICI
`164,384 is due (to a2failurefiofa«the.;.re<:eptor
`complex to diinerizearid bindito ERE1[19] or to
`
`an inactivation of the transcriptional activation
`function of the DNA-bound ireceptorcomplex
`[20]. Both mechanisms. mayfcontribute to the
`expression of “pure 7?; antagonistrgactivitys} 0, ICI
`164,384 treatment leads itorarapid reduction of
`cell and tissue] ER concentration — [21',22]; an effect
`which is likelyitofseverely, attenuate thegcapacity
`of estrogen—responsivefjcells
`respond to" the
`»I
`natural hormone.
`Complete ablationfiof esrfégéfi amaby ICI]
`164,384 in viva] _r.equiredihigh7‘doses‘v of drug.{23]
`, and, for this reason, ICI1.‘16_4,384’did ,notmerit
`serious consideration
`iajdruggycandidatew. ‘_il\_IIore
`.8 potent compounds] vyerefisought which retained the
`8. advantageous‘ pharmag9lOgiQal:;profile 01‘_fICI
`, 164,384, compared with the tamoxifen‘-like partial
`"L agonists. A new compound,.ICI»l82,780,79t+[9-
`(4,4,5,5,5épentalfluoropentylsulfiny1)nony1]4.
`estra—1,3,5(10)—trieIie:3,17[3gdiol (Figure*1),r:was
`selected for intensive study [24].];::lClf182;780.
`differs from ICI 164,384 tattoo“/15¢y‘* features of»
`the 70t side-chain]; thej; gamoiety ‘of
`164,384 was replaced by a sulfinyl 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 S—fold more
`potent in inhibiting the [growth .ofiMCF-7 cells
`[24].
`In the rateuterotropic/antiuterotropic test,
`ICI 182,780 is 10-fold more potent
`than ICI
`
`164,384 [24].
`
`
`
`,
`
`|nnoPharma Exhibit 1058.0006
`
`1
`
`’
`
`sensitive human breast cancer (MCF-7) cells [:16].
`Synthesis of novel 7ot-alkylamide analogues of
`estradiol provided the first examples of com-
`pounds devoid of estrogenic activity but capable,
`when administered. together with estradiol, trof
`blockingvcompletely the uterotropic effect of the
`natural hormone in rodents [12,17]. Structure4
`
`.
`
`1]
`
`1
`
`1
`
`e
`
`e
`
`activity analysis revealed the importance of the
`position,<length, and flexibility of the C7 side-
`chain in determining pure antagonist activity [12].
`For example; it..was shown that receptor binding
`and biological activity residesalmost exclusively
`in the 705 rather than’the 713. isomers. Pure ranti-
`estrogens were found amongst compounds with an
`overall chain length of 16-18 -atorns,.ancl tertiary.
`rather than secondary amides are preferred» he
`most potent pure antagonist amongst the alkylj
`amides was N-n-butyl—N-methyl~ll—(»3,¥17B-di¥
`hydroxyest1a— 1 ,3,5(10)-trien-70t—yl)undecanamide,
`ICI 164,384 (Figure 1). Studies of the modeof
`
`OH
`
`
`
`
`
`
`
`
`”’t<;H;>.i;;¢i<?.t,#.<
`
`
`
`
`
`/3’/(CH 2)9S0(CH2)3QF2CF3
`lCl 132,780
`, Figure 1. Structures of pure antiestrogens J 8
`
`

`

`4
`
`AE Wakeling
`
`Comparative pharmacology of tamoxifen and
`pure antiestrogens
`
`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 estradio1,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 viva.
`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 rovariectomy, ‘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
`
`-
`
`studies of antiestrogen effects in intact
`
`rats.
`
`Firstly, pure antiestrogen treatment did not affect
`
`gonadotropin concentrations or the body weight of
`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 ICI
`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 ha‘/6
`also been expressed that its uterotropic action 11133’
`increase the incidence of endometrial cancer [23]?
`such concerns would be eliminated by treatment
`
`_
`with pure antiestrogens.
`One predicted undesirable action of pure antl-
`estrogens in therapeutic use may be a tendencl/rt”
`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, ovar1eC-
`tomy significantly reduced bone density (Table 1)‘
`This suggests that there are differentials in the
`sensitivity of peripheral estrogen target Organs to
`
`
`
`
`
`
`
`.....,\,....._..c.....,._.......,.......y....,._..~4--_.w.._....c._......_..._.,,,-....~M.._..,.~,.-._.._......w._,.,_-...._..'-m-——-
`
`
`
`
`
`
`
`|nnoPharma Exhibit 1058.000?
`
`

`

`Clinical potential of pure ‘antiestrogens
`
`5
`
`Table I. Effects of ICI 182,780 infladult female rats
`
`Plasma LH .-
`Z
`Treatment
`Uterine weight
`Body weight gain
`L’
`7 B05; dmsity T
`
`(mg)
`A
`«~
`(g)
`*
`;
`(ng/ml)
`*
`~
`1
`4 (g/ml) .;
`
`*
`
`Intact Control
`OVX control
`
`ICI 182,780
`(mg/kg/d X 28)
`
`0.1
`0.3
`1.0
`
`3.0
`
`302 i 36,?
`70 i l’:.<~'
`
`60 : 4
`114 i 6
`
`g
`
`T
`
`I
`
`if
`
`0.2” Q
`
`»
`
`T
`
`’
`
`T
`
`T
`
`i
`
`t
`
`£01008 if
`ii
`
`if
`
`.
`
`..
`
`.
`
`4
`
`.
`
`208 1 17
`174 i 16"u:.i
`94 : 9 :2
`
`4;
`
`=<::
`-;-::;;:.::
`
`68 : 4
`67 : 4
`70 1 4
`
`1.2 : 0.1”
`t
`i 71.3 : 0."1"I;
`s
`_ 2.8 i 0;3‘i”*
`
`“ 11528‘: 0.005 “
`1‘.52s 0: 0.008
`”1.532 350.005.
`
`‘
`
`.:
`
`103:|”_2.§s:a.
`
`4,:-~;;;s> 7li6
`
`'
`
`'- 2.4i0.6”I
`
`1.5330: 0.005.
`
`.0
`
`/ ..
`0
`
`if
`
`
`
`
`
`~-«.v.~.«~.«,,.._\sJaZ»~4/<“‘~~\.,.
`
`antiestrogens as well as central versuslperipheral
`differences, and cautions against premature judge‘-
`ment of likely pharmacological actions of ‘these
`agents in man.
`
`Breast cancer cells
`
`_
`
`Functional disablement of the ER’ isignalliiig
`°aP30ity by pure antiestrogens produces effects on
`human breast cancer cells which havemprofounid
`therapeutic implications. A comparison ‘of the
`P0tency and efficacy of tamoxifen, ICI 164;384;
`and ICI 182,780 as inhibitors of the growth, of
`°Stf0gen—responsive MCF-7 human breastcturnorfy
`derived cells, showed that the pure antiestrogens pl
`are “P to two orders of magnitude moreTfpotenti,iiii
`“fleeting in pan their higher affinitygfoiiri. g3R%,
`[23,24].
`More significantly, analysis
`I. the ;
`growth dynamics of the cultured cells showed
`that, although both classes of agent share the
`abi1itY,to block cell division in the G1 phase or
`the cell cycle [29], both ICI 164,384 and ICI
`_182»780 were much more effective than tamoxifen
`"1 reducing the proportion of cellswhich remain
`able to synthesize DNA after prolonged exposure
`[24,30]. The proportion of cells which continued
`*0 synthesize DNA in a two day period at the end
`of five days exposure to the antiestrogensuwas 4
`Feducedfrom 82% in control cultures to 37% by
`tamoxifen, but to onlyi7% by ICI 182,780 [24].
`
`T
`
`This difference may be due to the partial agonist
`activityof tamoxifen which
`amplified by inter?
`action with mitogenic signals provided by growth
`factors,'*‘an1effect«which is absénteinithe case of
`the pure antiestrogens [30]."~T”7
`=“
`7 If the greaterefficacy of ipure‘”versus partial
`agonist antiestrogens against huinan breast cancer
`cell growth’ described it above translates to the
`clinical s‘ctting;"cne;ntight anticipate significant
`benefits in therate and extent of tumor remission
`following pureviantiestrogen therapy . compared
`with other »}",'anties¢trogenic"
`therapiesli L
`It» is
`particularlygimportanitt to recognize ‘that i if if the
`synergistic growth stimulatory interaction between
`estradiol and insulin-like growth factors demon»
`strated
`vitro’ii[16,30,3l] occursin patients there if
`may be a massive difference gin.ef”ficacyibetween
`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. C
`T The major cause of death from breast cancer *
`is metastatic. disease rather. than uncontrolled
`proliferation of the primary tumor.
`in Metastatic
`spread depends on the capacity ofthe tumor cells
`to cross the basement membrane and invade into
`surrounding tissue. . Experimental studies with
`breast tumor-derived cell lines have shown that
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`6
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`AE Wakeling
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`s
`
`1
`
`invasive capacity and proliferative potential are
`It
`is
`therefore
`independently variable [32].
`important to know whether antiestrogens affect
`the phenotypic expression of invasive behavior by
`breast
`tumor cells.
`This question has been
`3 examined in comparative studies of the effects of
`6 estradiol and several antiestrogens on the capacity
`of MCF-7 cells to cross a re-constituted basement
`
`6
`
`3 ‘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
`_ pantiestrogen might be particularly beneficial in
`4
`limiting tumor spread.
`
`3 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
`f [cancer cells grown either in vitra or in vivo as
`xenografts in nude mice, and exposed continuous-
`ly to growth inhibitory concentrations of tam-
`oxifen.
`In vitro,
`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 by tamoxifen, rather than the
`selective outgrowthpof cells which are unaffected
`bytamoxifen [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 estrogenicprather
`
`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 31055
`tumors which develop "resistance" to tamoxiffin
`are not resistant in the sense generally understood
`in cancer therapeutics, was shown in two W8Y5~
`Firstly, re-transplantation studies showed that such
`tumors would grow only if the host was treated
`with either tamoxifen or estradiol and, secondl}’s
`that
`the growth of these tamoxifen "resistant"
`tumors is attenuated by the pure antiestrogen ICI
`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 ma)’ be e
`explained-by metabolic adaptation of the tumor-
`This mechanism, provides an altemativfi “lathe
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`hypothesis examined above, that subpopulations
`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 antiestrogen treatment in such
`a Patients.
`It could be argued that simple with-
`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
`. lmprove response rates.
`.
`Treatment choice for patients who relapse
`during. or at some time after, adjuvant Nolvadex
`thfifapy for primary breast cancer, is a subject of
`Increasing importance. Based on the experimental ,
`e precedents discussed above,
`there is a sound
`. rationale for treating patients who relapse during
`adjuvant Nolvadex therapy with ‘pure antiestro- 4
`gens. The number of patients in this category is
`
`Clinical potential of pure antiestrogen:
`
`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
`
`The relatively low oral bioavailability of ICI
`182,780 [24] necessitated development of a1tema-
`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 inibreast cancer patients
`was assessed by measuring the duration of anti-
`estrogenic action of oil depots of ICI 182,780 in
`monkeys (Macaca nemestrina) 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].
`e Animal toxicology and human volunteer stud-’
`ies have recently been successfully completed as
`a prelude to therapeutic studies with the oil depot
`formulation of ICI 182,780 in patients. An initial
`therapeutic trialhas begun inpatients with ad-
`vanced breast cancer who have relapsed during,
`Nolvadex treatment.
`
`
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`v-xx:s«_-sat-A..«~.;.-.)4V7-.44..
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`8
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`AE Wakeling
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`Conclusions
`
`Extensive studies of the biological properties of a
`
`new class of steroidal antiestrogens, the 70t-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
`
`Antioestrogens in the
`Jackson M:
`1. Litherland S,
`management of hormone-dependent breast cancer.
`Cancer Treat Revs 15:183-194. 1987
`2. Smith I: Adjuvant tamoxifen for early breast cancer.
`BrJ Cancer 57:52?-528, 1987 i_
`3. EBCTCG: Systemic treatment of early breast cancer by
`hormonal, cytotoxic, or immune therapy. Lancet 339:
`1-15, 1992
`