Breast Cancer Research and Treatment 33: 19-26, 1994.
`© 1994 Kluwer Academic Publishers. Printed in the Netherlands.
`
`New agents in breast cancer —— minisymposium
`
`Aromatase inhibitor development for treatment of breast cancer
`
`Shigeru Masamural, Herman Adlercreutzz, Harold Harvey3, Allan Lipton3, Laurence M. Demers4, Richard
`J. Santenl, and Steven J. Santnerl
`2Department of Clinical
`1Department of Internal Medicine, Wayne State University, Detroit, MI;
`Chemistry, University of Helsinki, Helsinki, Finland; 3Department of Medicine and 4Departments of
`Pathology and Medicine, The Milton S. Hershey Medical Center, The Pennsylvania State University,
`Hershey, PA, USA
`
`Key words: breast cancer, aromatase, estradiol, hormonal therapy, CGS 20267
`
`Summary
`
`Inhibition of estrogen production provides effective therapy for patients with horrnone-dependent breast
`cancer. The source of estrogens in premenopausal women is predominantly the ovary, but after the
`menopause, estradiol
`is synthesized in peripheral
`tissues through the aromatization of androgens to
`estrogens. Uptake from plasma is the primary mechanism for maintenance of estradiol concentrations in
`breast cancer tissue in premenopausal women, whereas several steps may be operant in postmenopausal
`women. These include enzymatic synthesis of estradiol via sulfatase, aromatase, and 17B-hydroxysteroid
`dehydrogenase in the tumor itself. Aromatization of androgens secreted by the adrenal to estrogens in
`peripheral tissues and transport to the tumor via circulation in the plasma provides another means of
`maintaining breast tumor estradiol levels in postmenopausal women. These various sources contribute to
`the high tissue estrogen levels measured in breast tumor tissue.
`To effectively suppress tissue concentrations of estrogens and circulating estradiol in postmenopausal
`patients, various aromatase inhibitors have been developed recently. These include steroidal inhibitors such
`as 4-hydroxy—androstenedione as well as non-steroidal compounds with imidazole and triazole structures.
`The most potent of these, CGS 20267, is reported to suppress levels of active estrogens (i.e., estrone,
`estrone sulfatase, and estradiol) by more than 95%. This compound can suppress both serum and 24-hr
`urine estrogens to a greater extent than produced by the second generation inhibitor, CGS l6949A. CGS
`20267 is highly specific since it does not affect cortisol and aldosterone serum levels during ACTH
`stimulation tests nor sodium and potassium balance in 24-hr urine samples. These data suggest that CGS
`20267 can be expected to bring improved response rates in the treatment of metastatic hormone—dependent
`breast cancer without substantial side effects.
`
`Introduction
`
`pendent upon estradiol for cellular proliferation.
`Studies to elucidate the mechanism of estradiol
`
`A subpopulation of human breast cancers are de-
`
`stimulated growth have been ongoing for two
`
`Presented by R.J. Santen at the 16th Annual San Antonio Breast Cancer Symposium, San Antonio TX, November 4, 1993;
`Mini-symposium on New Agents in Breast Cancer (supported by an educational grant from Rhone-Poulenc Rorer).
`Address for correspondence and ofiprints: Richard J. Santen, M.D., Department of Internal Medicine, Wayne State University,
`Harper Hospital, 1 Webber 8, Detroit, MI 48201, USA; Tel: 313-745-8244; Fax: 313-993-0645.
`
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`
`20
`
`S Masamura et al
`
`Several hormonally related strategies
`decades.
`have been developed for treatment of human
`breast cancer which are based upon the principle
`that estrogens are mitogenic for these tumor cells.
`Initial methods involved surgical ablative ther-
`apies such as oophorectomy, adrenalectomy, and
`hypophysectomy.
`These procedures eliminate
`ovarian
`estrogen
`synthesis,
`adrenal
`steroid
`synthesis, and the stimulatory effects of the
`gonadotropins on estrogen production in the
`ovaries, respectively. The rates of response to
`these
`therapies
`range
`from 30-40% [1].
`Adrenalectomy and hypophysectomy, because
`they involve major surgery, are infrequently
`employed currently, whereas oophorectomy con-
`tinues to be selected. Pharmacologic methods to
`alter the hormonal milieu eliminate the need for
`
`major surgery and have generally replaced sur-
`gical ablative therapies. Agents currently used
`are the antiestrogen tamoxifen,
`the progestins
`medroxyprogesterone
`acetate
`and megestrol
`acetate, gonadotropin releasing hormone analogs
`such as goserelin, and inhibitors of estrogen
`biosynthesis such as the aromatase inhibitors.
`Surprisingly,
`inhibition of aromatase, which
`blocks the conversion of androgens to estrogens,
`is effective therapy in patients with breast cancer
`even after they relapse from responses to anties-
`trogen or progestin (medroxyprogesterone acetate
`or megestrol acetate) therapy. Several second-
`and third-generation aromatase inhibitors are now
`available which are highly potent and associated
`with few side effects. Their role in the therapy of
`breast cancer will probably become increasingly
`important.
`In this review, the current status of
`aromatase inhibitors will be discussed.
`
`General role of aromatase
`
`Fat, liver, muscle, and hair follicles contain the
`
`aromatase enzyme which catalyzes the conversion
`of androgens to estrogens [2,3].
`In postmeno-
`pausal women,
`the major source of circulating
`estrogens is the peripheral conversion from andro-
`gens in fat tissue and in muscle [2]. Androstene-
`
`dione, the major precursor androgen, and testos-
`terone, a minor substrate, are secreted primarily
`from the adrenal glands and are converted in
`peripheral
`tissues
`to estrone
`and estradiol,
`respectively, through the catalytic action of the
`enzyme aromatase. The major aromatized pro-
`duct, estrone,
`is then enzymatically reduced to
`estradiol by the enzyme 17B-hydroxysteroid de-
`hydrogenase. These enzymatic activities result in
`measurable amounts of circulating estrogen in the
`range of 10-20 pg/ml in the plasma of postmeno-
`pausal women.
`Despite relatively low serum concentrations,
`the levels of estradiol in breast tumors of post-
`menopausal women are almost equivalent to those
`in premenopausal women [4]. The tumor tissue
`levels are much higher than the values predicted
`from calculations of serum concentrations and the
`
`affinity (Kd) of tissue receptors for estradiol. One
`of the explanations for maintenance of high tissue
`estradiol concentrations is the in situ synthesis of
`estradiol catalyzed by the various enzymatic activ-
`ities present in breast tumor tissue itself. These
`include sulfatase which catalyzes the conversion
`of estrone sulfate to estrone, aromatase which
`
`mediates androgen to estrogen conversation, and
`17$-hydroxysteroid dehydrogenase which allows
`formation of estradiol from estrone. The absolute
`
`levels of aromatase activity in human breast
`cancer tissues are low (5-100 pg/gm tissue/hr)
`when compared to those of sulfatase and 17B-
`hydroxysteroid dehydrogenase [5]. However, it is
`difficult to quantitate experimentally the amount
`of estradiol synthesized locally by each enzymatic
`pathway and the amount concentrated in tissue via
`uptake from plasma. Nonetheless, tissue enzymes
`such as sulfatase, 17B-hydroxysteroid dehydrogen-
`ase, and aromatase are likely to be involved in the
`production of at least some of the estrogen pre-
`sent in situ in tumor tissue. As another possible
`source of estrogens in breast
`tumors,
`lipoidal
`estradiol
`is reported to accumulate in estrogen
`receptor (ER) positive as well as ER negative
`breast cancer cells and can be hydrolyzed to free
`estradiol by esterase or lipase in tissues [6,7].
`Androstenedione is
`the major circulating
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`
`Type of
`inhibition
`
`Mechanism
`based
`
`Competitive
`
`Type of
`compound
`
`Steroid
`Steroid
`
`Steroid
`Steroid
`
`Steroid
`Steroid
`Steroid
`Steroid
`Steroid
`Non-steroid
`Non-steroid
`Imidazole
`Imidazole
`Imidazole
`
`1,4,6-androsta-triene-3,17-dione
`4-OH—androstenedione
`
`4-androstene-3,6, 17- trione
`Testolactone
`
`10B-propargylestr-4-ene-3,17-dione
`7ot(4 ’-amino)phenylthio-1,4-androstadiene-3,l7-dione
`1-methyl-androsta—1,4-diene-3,17-dione
`60¢-bromo-androstene-dione
`70t(4 ’-amino)phenylthio-4-androstene-3, l 7-dione
`Aminoglutethimide
`Pyridoglutethimide
`CGS l6949A
`R-767 13
`CGS 20267
`
`1.1x 1 0‘3 S'1
`4.5xl0'3S‘1
`
`4.03); 1 0'3S'1
`5.5x 1 O'4S'1
`
`1.1 1x 1 0f3S'1
`8.4x 1 0‘3 S‘1
`1.8x 1 O'4S'1
`
`3 .4nM
`18nM
`540nM
`1 100nM
`0. l9nM
`0.70nM
`—
`
`0.06uM°
`
`Table 1. Partial list of aromatase inhibitors [20].
`
`Aromatase inhibition for breast cancer therapy
`
`21
`
`Name of compound
`
`Ki“
`
`K intact”
`
`Imidazole
`
`Econazole
`
`3 Ki —- inhibitory constant
`b K inact — rate constant for inactivation of the enzyme (S=seconds)
`° IC50
`
`substrate for estrogens in the plasma of post-
`menopausal women and aromatase is the rate-
`limiting enzyme that regulates the conversion of
`androstenedione to estrone. Thus, the control of
`
`aromatase activity in tumors and in peripheral
`tissues can be a critical factor for regulation of
`postmenopausal breast cancer growth. Conse-
`quently, this enzyme provides a unique target for
`inhibition of tumor estradiol concentrations.
`
`Development of aromatase inhibitors
`
`The first aromatase inhibitor used in clinical
`
`studies was aminoglutethimide [8—lO]. The rates
`of objective (complete or partial) tumor regression
`with this agent were equal to those induced by
`surgical ablative therapies, antiestrogens, or high
`doses of progestin [11]. Aminoglutethimide was
`also active in a substantial number of patients
`with breast cancer who exhibited total resistance
`
`In spite of the clinical effec-
`to tamoxifen [12].
`tiveness and partial non-cross resistance with anti-
`estrogens, aminoglutethimide is not an ideal aro-
`
`matase inhibitor because of its non-specificity and
`side effects.
`
`To overcome these drawbacks, more potent
`and specific aromatase inhibitors have been under
`development. As a class, these inhibitors can be
`divided into those which are steroidal and com-
`
`pete for the active site of the enzyme, and non-
`steroidal compounds which structurally fit into or
`near the enzyme active site. Further, some inhibi-
`tors are altered by the aromatase enzyme to make
`sites available which bind covalently to and per-
`manently inactive the enzyme. Agents of this
`type are called mechanism-based or "suicide" in-
`hibitors.
`
`Pyridoglutethimide is one of the non-steroidal
`compounds developed through modification of the
`structure of aminoglutethimide to bring greater
`specificity and lesser side effects. While lacking
`the drawbacks of aminoglutethimide such as inhi-
`bition of cholesterol side-chain cleavage and
`sedative properties on the CNS [l3,l4], this com-
`pound is considerably less potent than its parent.
`Another non-steroidal competitive inhibitor, R-
`767l3,
`is also highly potent and specific as an
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`

`
`CVCVC Q’.
`C O O O O
`.;.:.;.;.
`o‘o'¢’o‘o
`C O C O Q
`c'o‘o’o‘o
`o:o:o:¢:o
`9 O C O
`° '0'.‘
`
`0’ '
`
`'
`'
`~
`‘:=:=:=:~.
`9 9 0 9
`
`:~:~:~:o:9 9 O 9 o
`. o o 0 O
`o.
`o‘$‘o‘¢’c
`. 0 0
`9:0
`50:00..99.9
`Estrone
`
`22
`
`S Masamura et al
`
`100 - AG 1000 mg/day
`
`/-\
`
`U) 75
`
`‘~4—.
`O
`4.»
`c 50
`8
`5
`!
`l
`
`,
`.
`—- 2 5
`‘D
`>
`Q)
`:1
`
` CGS 2 mg/day
`
`um-
`
`1 1:
`
`'3’I’Z’I°1
`o o o o -
`:¢:o:o:o:~
`’o’o‘o‘.0.
`0.9.0.»;
`53°34’:
`I Q ‘ C O
`-2~:~2'Z'f
`
`eggs)‘:
`Q Q Q .
`..O‘C.O‘1
`D O U C O
`035%‘:
`~:-:»:o:»:
`’:=:I:=:=‘
`o o
`‘
`
`
`
`Estrone
`Estrone
`|_i_ Sulfate ____J L__ Urine __‘
`Plasma
`
`Estrodiol
`
`Estrodiol
`
`Figure 1. Estrogen levels in plasma and urine (mean i SE), expressed as percent suppression from basal values (before
`treatment).
`In this study, postmenopausal breast cancer women are treated either with 1000 mg aminoglutethimide (AG) and
`40 mg cortisol for 2-12 weeks or with 2 mg CGS 16949A. The numbers over the bars represent the number of patients
`analyzed.
`(**, P<0.01; ***, P<0.001; by paired comparison of basal and treatment values.)
`
`aromatase inhibitor. R-76713 has the potency to
`suppress circulating estradiol
`to undetectable
`levels in normal men and to achieve 64% inhibi-
`
`tion in premenopausal women [15,16]. While the
`racemic form was initially studied,
`the stereo-
`isomer R83842 is more potent and is currently
`under clinical study [17].
`4-hydroxyandrostenedione is one of the mech-
`anism—based ("suicide") class of inhibitors. This
`
`compound effectively suppresses estrogen syn-
`thesis while associated with no estrogenic, anti-
`estrogenic, or antiandrogenic properties
`[18].
`Metabolism to 4-hydroxytestosterone renders it
`slightly androgenic but this does not appear to be
`associated with clinical sequelae. A large clinical
`trial conducted by Hoffken et al. [19] utilized 500
`mg of 4-hydroxyandrostenedione administered in-
`tramuscularly every two weeks for six weeks, and
`then 250 mg every two weeks thereafter. This
`compound reduced plasma estradiol of postmeno-
`pausal patients from 10-11 pg/ml to 4 pg/ml for
`up to 7 months. 24% of women experienced an
`
`objective tumor responses while 11% noted minor
`side effects such as hot flashes or constipation.
`Other studies reported sterile abscesses due to the
`intramuscular injection required for administration
`of this compound [14]. However, this effect is
`apparently reduced by improved. formulation.
`While oral administration of this agent might be
`considered preferable, this route is limited by the
`marked first—pass effect on metabolism in the liver
`and rapid production of glucuronidated deriva-
`tives.
`
`Other non-steroidal aromatase inhibitors are
`
`being developed as well. CGS 16949A(fadrazo1e
`hydrochloride) and CGS 20267 represent two of
`these agents (Table 1) [13]. Our studies demon-
`strated that fadrazole is 500-fold more potent than
`aminoglutethimide, but not completely specific for
`aromatase (Figure 1). Fadrazole hydrochloride
`also blocks cortisol and aldosterone synthesis
`through inhibiting 11[3—hydroxylase activity and
`corticosterone methyl oxidase [21]. While basal
`levels of circulating cortisol and aldosterone are
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`

`
`Aromatase inhibition for breast cancer therapy
`
`23
`
`and other estrogens were measured by the method
`of Fotsis and Adlercreutz [24]. A total of 13
`
`postmenopausal breast cancer patients received
`CGS 20267 for 6 weeks in initial doses of 0.1-2.5
`
`mg/day followed over a 6-week period by an
`increasing amount of the compound to 0.25-5
`mg/day.
`Since
`there were no statistically
`significant differences in levels of suppression
`
`
`
`.
`
`O
`
`10
`5
`Weeks of therapy
`
`15
`
`..
`CGS 20257
`
`‘ ces 20267
`
`Estradiol
`
`not significantly influenced, ACTH-stimulated
`cortisol and aldosterone responses are blunted,
`even when low doses (i.e., 1.8, 2.0, and 4.0
`
`mg/day) of fadrazole hydrochloride are used.
`Blockade of llB—hydroxylation by CGS l6949A
`also increases levels of precursor steroids such as
`170:-hydroxyprogesterone and androstenedione in
`some patients.
`We have recently directed our attention toward
`CGS 20267, an even more potent and specific
`aromatase inhibitor. CGS 20267 (letrozole) is a
`
`compound of the benzonitrile class which is
`approximately 1,000- to 10,000-fold more potent
`than aminoglutethimide and approximately 8-fold
`more potent than fadrazole hydrochloride. We
`initially studied 8 postmenopausal patients with
`advanced breast cancer who received 0.1 mg/day
`of CGS 20267 for 6 weeks, followed by 0.25
`mg/day for an additional 6 weeks. Greater than
`90% suppression of estradiol, estrone, and estrone
`sulfate were achieved over a 2-week period and
`the patients reached over 97% suppression by 6
`weeks of therapy with the dose of 0.1 mg/ml
`(Figure 2)
`[22].
`Since very low levels of
`circulating estrogens are present in these patients,
`standard radioimmunoassays are not sufficiently
`sensitive
`for
`the
`assessment of
`aromatase
`
`inhibition under these circumstances [23]. For
`this reason, in our studies estradiol was measured
`
`with a highly sensitive assay combining a high
`specific
`activity trace with a high affinity
`antiserum obtained from Baker Clinical Assays
`(Germany). This radioimmunoassay provides a
`sensitivity of 0.1 pg/ml with a direct non—chro-
`matographic method involving diethyl ether ex-
`traction of plasma [22]. The radioimmunoassay
`utilized for estrone measurements is also sensitive
`
`enough to detect levels as low as l pg/ml. To
`further
`substantiate
`the degree of estrogen
`suppression achieved with CGS 20267, we also
`utilized a highly sensitive technique involving gas
`liquid chromatography-mass spectrometry (GLC/
`MS) analysis of 24—hr urine specimens. Before
`and 12 weeks after treatment with three different
`
`doses of CGS 20267, 24—hr urines were collected
`
`and estrone, estradiol, estriol, catecholestrogens,
`
`10
`
`E 8
`E:
`3 6
`‘5
`E 4
`
`E 2
`
`O
`
`30
`
`E
`B 20
`E:
`
`2’
`g 10
`U3
`U1
`
`0
`
`E so
`3
`Q) 60
`‘:3
`"E": 40
`(I)
`(D
`
`8 2o
`*3
`L“
`
`o
`
`O
`
`10
`5
`Weeks of therapy
`
`15
`
` O
`
`10
`5
`Weeks of therapy
`
`1 5
`
`CGS 20267
`
`Estrone sulfate
`
`2. Effects of CGS 20267 on plasma estradiol,
`Figure
`estrone, and estrone sulfate in 8 patients at doses of 0.1
`mg/day (first 6 weeks) and 0.25 mg/day (second 6 weeks)
`over 12 weeks of therapy. Results represent mean i SD.
`Data reproduced from ref. [22].
`
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`
`24
`
`S Masamura et al
`
`Table 2. Effects of CGS 20267 on 24-h urinary excretion of estrogens.
`
`Catechol estrogens
`
`Estriol“
`
`Total
`
`2-hydroxy-
`estrone
`6.50:i:2.38
`
`4-hydroxy-
`estrone
`1.36:l:0.51
`
`2-hydroxy-
`estradiol
`l.27i0.39
`
`2-methoxy-
`estrone
`1.78:t0.49
`
`Total catechol
`estrogens
`10.9l:t3.68
`
`7.64i2.68
`
`unnarya b
`estmgens ’
`37.02i9.55
`
`0.62:i:0.10
`
`0.06i0.02
`
`0.90i0.27
`
`02310.05
`
`1.81i0.36
`
`0.47i0.09
`
`4.10i0.59
`
`90
`
`96
`
`39
`
`87
`
`83
`
`94
`
`89
`
`Before
`treatment°’d’°
`
`d f
`After
`treatment°’ '
`
`% inhibition
`
`3 Since enzymatic hydrolysis was used to free conjugated steroids for estrone, estradiol, and estriol, the results reflect quantities
`of conjugated steroids, but are expressed as nanomoles of free steroid excreted per 24 h.
`1’ Numerical total of all estrogens measured, including catechol estrogens, estrone, estradiol, estriol, 17-epiestriol, 16-epiestriol,
`16ot—hydroxy-estrone, 15cc-hydroxy-estrone, 160-hydroxy-estrone, and 16-keto-estradiol.
`° Mean iSE, nmol/24h.
`d Postmenopausal breast cancer patients (n=13).
`" Blood taken before administration of CGS 20267.
`f Blood taken after 12 week administration of cos 20267.
`
`Table 3. Effects of CGS 16949A on 24-h urinary excretion of estrogens.
`
`2-hydroxy-
`estrone
`
`4-hydroxy-
`estrone
`
`Catechol estrogens
`2-hydroxy-
`estradiol
`
`2-methoxy- Total catechol
`estrone
`estrogens
`
`Estriola
`
`Total
`“rinarya b
`estrogens '
`
`4.90j:1.23
`
`0.4li0.06
`
`1.50i0.26
`
`1.37i0.31
`
`8.17il.83
`
`5.53:l:0.77
`
`27.2i3.5
`
`1.40:t0.28
`
`02210.07
`
`0.32i0.04
`
`038120.12
`
`2.3li0.46
`
`2.19i0.37
`
`8.84i1.47
`
`Normal
`women°’d
`
`CGS 16949A-
`treated women”
`
`% inhibition
`
`71
`
`50
`
`79
`
`72
`
`72
`
`60
`
`67
`
`3 Since enzymatic hydrolysis was used to free conjugated steroids for estrone, eslradiol, and estriol, the results reflect quantities
`of conjugated steroids, but are expressed as nanomoles of free steroid excreted per 24 h.
`b Numerical total of all estrogens measured, including catechol estrogens, estrone, estradiol, estriol, 17—epiestriol, 16-epiestriol,
`16ot-hydroxy-estrone, 15a-hydroxy-estrone, 16B—hydroxy-estrone, and 16-keto-estradiol.
`° Mean iSE, nmol/24h.
`d Normal postmenopausal women, aged 48-64 yr (n=l0, mean 57).
`5 All treated women (n=9) had metastatic breast carcinoma previously treated with hormonal agents. They continued to take
`4mg CGS 16949A 4-8 weeks after the dose escalation phase of the study (0.3-16mg).
`(Reproduced from Ref. [25].)
`
`between these three dosage groups, the data from
`the 13 patients were pooled and analyzed. As
`shown in Table 2, the sums of the excretion of
`
`free and conjugated estrogens decreased to 10-
`20% of basal
`levels during therapy, and total
`urinary estrogens fell
`to levels reflecting 89%
`inhibition.
`
`The plasma radioimmunoassay and urinary
`GLC/MS data in patients receiving CGS 20267
`
`suggested that this compound is a highly potent
`aromatase inhibitor. While different
`radio-
`
`immunoassays were used, the degree of suppres-
`sion with CGS 20267 appeared greater than that
`observed previously in patients receiving CGS
`16949A (fadrazole hydrochloride)
`[25].
`For
`example, our data from studies using CGS
`16949A revealed 58-71% inhibition of serum
`
`estrone, 68-73% for estrone sulfate, 23-33% for
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`

`
`estradiol, 74-79% for 24—hr urinary estrone, and
`52-66% for 24—hr urinary estradiol. This degree
`of suppression was substantially less than that
`(i.e., >95% suppression) observed in patients
`receiving CGS 20267. Measurement of total
`urinary estrogens with GLC/MS provided more
`direct means of comparing these two aromatase
`inhibitors since identical methodology was used to
`assess estrogen suppression in patients receiving
`either compound. Total urinary estrogen levels
`were suppressed by 67% with CGS 16949A and
`by 89% with CGS 20267 (Table 2,3).
`With respect to specificity, CGS 20267 did not
`block cortisol or aldosterone production. Sodium
`and potassium balance in 24—hr urine specimens
`was
`unaffected.
`Cortisol
`and
`aldosterone
`
`measured in serum during ACTH stimulation tests
`responded similarly under control conditions and
`during drug administration [22]. As more than
`95% suppression of estrogens can be achieved
`with CGS 20267, we expect that tumor regression
`can be expected in clinical studies of antitumor
`efficacy. Phase II trials are currently ongoing to
`determine the precise percentages of patients with
`tumor regression in response to this agent.
`side
`CGS 20267 produced only nominal
`effects
`in the 23 patients
`treated at The
`Pennsylvania State University trial. Hot flashes
`were observed in 10 patients, hair thinning in 3,
`nausea in 4, diarrhea in 2, and dyspepsia in 2.
`All toxicity was ECOG Grade 1 and not substan-
`tial. Hot flashes have been observed with all
`aromatase inhibitors.
`It is not clear whether the
`
`Aromatase inhibition for breast cancer therapy
`
`25
`
`side effects suggest that this compound may have
`great therapeutic benefit.
`Its current role will
`probably be in patients
`relapsing following
`adjuvant therapy with tamoxifen. The mechan-
`isms whereby aromatase inhibitors are active
`following antiestrogen therapy are,
`as yet,
`incompletely understood. A working hypothesis
`is that tumor cells deprived of estrogen develop
`enhanced sensitivity to
`estradiol.
`If
`this
`hypothesis is proven in ongoing studies, aro-
`matase inhibitors which can completely inhibit
`estrogen biosynthesis would provide additional
`benefit
`to patients whose tumor cells have
`enhanced sensitivity to estradiol. Further studies
`are required to assess the actual clinical advan-
`tages of CGS 20267 and to test the concept of
`complete estrogen inhibition. Phase II studies to
`assess these aspects are currently ongoing.
`
`References
`
`2.
`
`1. Henderson IC, Canellos GP: Cancer of the breast: The
`past decade. N Engl J Med 302: 17-30; 78-90, 1980.
`Siiteri PK, MacDonald PC: Role of extraglandular
`estrogen in human endocrinology.
`In: Geiger SR.
`Astwood EB, Greep R0 (eds) Handbook of Physi-
`ology. American Physiology Society, Baltimore, MD,
`1973, Vol 2, pt 1, pp 615-629.
`Santen RJ, Boucher AE, Santner SJ, Henderson IC,
`Harvey H, Lipton A:
`Inhibition of aromatase as
`treatment of breast carcinoma in ‘postmenopausal
`women. J Lab Clin Med 109:278-289, 1987.
`Thijssen JHH, Van Landeghem AAJ, Poortman J: Up-
`take and concentration of steroid hormones in mam-
`
`3.
`
`4.
`
`overall side effects would be greater than that
`observed in patients receiving a placebo.
`
`5.
`
`Overview
`
`A third-generation aromatase inhibitor, CGS
`20267, produced a
`reduction of circulating
`estrogens to undetectable levels which appeared to
`reflect at least a 95% reduction. No significant
`side effects were reported by patients receiving
`this compound.
`The substantial reduction of
`circulating estrogens with CGS 20267 and lack of
`
`mary tissues. Ann NY Acad Sci 464:106-116, 1986.
`Santen RJ, Leszczynski D, Tilson-Mallet N, Feil PD,
`Wright C, Manni A, Santner SJ: Enzymatic control of
`estrogen production in human breast cancer: relative
`significance of aromatase versus sulfatase pathways.
`In: Angeli A, Bradlow HL, Dogliotti L (eds)
`Endocrinology of
`the Breast: Basic and Clinical
`Aspects. NY Acad Sci, New York, Vol 464, 1986, pp
`126-137.
`
`6. Hochberg RB, Pahuja SL, Zielinski JE, Lamer JM:
`Steroidal fatty acid.
`J Steroid Biochem Molec Biol
`40:577-585, 1991.
`7. Adams JB, Vrahimis R, Young CE: Metabolism of
`lipoidal
`derivatives
`of
`estradiol-1713
`in
`human
`mammary cancer tissue and cell
`lines.
`J Steroid
`
`Astrazeneca Ex. 2025 p. 7
`
`

`
`26
`
`S Masamura et al
`
`11.
`
`Biochem Molec Biol 39: 751-758, 1991.
`Cash R, Brough AJ, Cohen MNP, Satoh PS: Amino-
`glutethimide (Elipten-CIBA) as an inhibitor of adrenal
`steroidogenesis. Mechanism of action and therapeutic
`trial. J Clin Endocr Metab 27:1239-1248, 1967.
`Santen RJ, Lipton A, Kendall J: Successful medical
`adrenalectomy with aminoglutethimide: role of altered
`drug metabolism.
`J Am Med Assoc 230:1661-1665,
`1974.
`
`Griffith CT, Hall TC, Saba Z, Barlow JJ, Nevinny HB:
`Preliminary trial of aminoglutethimide in breast cancer.
`Cancer 32:31-37, 1973.
`Henderson IC: Endocrine therapy in metastatic breast
`cancer.
`In: Harris JR, Hellman S, Henderson IC,
`Kinne DW (eds) Breast Diseases, Lippincott, Phila-
`delphia, 1987, pp 398-428.
`Santen RJ: Clinical use of aromatase inhibitors in
`human breast carcinoma.
`J Steroid Biochem Molec
`Biol 40:247-253, 1991.
`Banting L, Nicholls PJ, Shaw MA, Smith HJ: Recent
`developments in aromatase inhibition as a potential
`treatment for oestrogen-dependent breast cancer. Prog
`Med Chem 26:253-298, 1989.
`Coombes RC, Stein RC: Aromatase inhibitors in
`human breast cancer. Proc Royal Soc 95B:283, 1989.
`Wouters W, De Coster R, Krekels M, van Den J,
`Beerens D, Haelterman C, Raeymaekers A, Freyne E,
`Van Gelger J, Venet M, Janssen PAJ: R76713, a new
`specific non-steroidal aromatase inhibitor.
`J Steroid
`Biochem 322781-788, 1989.
`Wouters W, De Coster R, Tuman RW, Bowden CR,
`Bruynseels J, Vanderpas H, Van Rooy P, Amery WK,
`Janssen PAJ:
`Aromatase inhibition by R76713:
`Experimental and clinical pharmacology.
`J Steroid
`Biochem 32:427-430, 1989.
`Willemsens G, Vanden Bossche H, Roels I, Bellens D,
`Le Jeune L, Coene MC, Janssen PAJ: R76713 and
`enantiomers: selective inhibitors of the p450—dependent
`estrogen synthesis. Biochem Pharmacol 40: 1707-1718,
`1990.
`
`Inhibition of peripheral
`Brodie AMH, Longcope C:
`aromatization by aromatase inhibitors, 4-hydroxy- and
`4-acetoxyandrostene-3,17-dione. Endocrinology 106:
`19-21, 1980.
`Hofflcen K, Jonat W, Possinger K, Kolbel M, Kunz
`TH, Wagner H, Becher R, Callies R, Friederich P,
`Willmanns W, Maass H, Schmidt CG: Aromatase
`inhibition with 4-hydroxyandrostenedione
`in the
`treatment of postmenopausal patients with advanced
`breast cancer: A phase II study.
`J Clin Oncol 8: 75-
`880, 1990.
`Santen RJ: Clinical use of aromatase inhibitors in
`
`20.
`
`breast carcinoma. In: Holland JF, Frei III E, Bast RC
`Jr, Kufe DW, Morton DL, Weichselbaum RR (eds)
`Cancer Medicine.
`Lea & Febiger, Philadelphia,
`London, 1993, vol 1, pp 865-876.
`. Santen RJ, Demers LM, Lynch J, Harvey H, Lipton A,
`Mulagha M, Hanagan J, Garber JE, Henderson IC,
`Navari RM, Miller AA:
`Specificity of low dose
`fadrozole hydrochloride (CGS 16949A) as an aro-
`matase inhibitor.
`J Clin Endocr Metab 73:99-106,
`1991.
`
`22.
`
`23.
`
`24.
`
`25.
`
`Demers LM, Lipton A, Harvey HA, Kambic KB,
`Grossberg H, Brady C, Santen RJ: The efficacy of
`CGS 20267 in suppressing estrogen biosynthesis in
`patients with advanced stage breast cancer. J Steroid
`Biochem Molec Biol 44:687-691, 1993.
`Albertson B, Santner SJ, Santulli M, Aiello D, Page C,
`Demers L, Harvey H, Lipton A, Sanders S, Santen RJ:
`Role of assay sensitivity in the assessment of aro-
`matase inhibition.
`(In preparation.)
`Fotsis T, Adlercreutz H: The multicomponent analysis
`of estrogens in urine by ion exchange chromatography
`and GC-MS. I. Quantitation of estrogens after initial
`hydrolysis of conjugates.
`J Steroid Biochem 28:203-
`213, 1987.
`Santen RJ, Demers LM, Adlercreutz H, Harvey H,
`Santner S, Sanders S, Lipton A: Inhibition of aro-
`matase with CGS 16949A in postmenopausal women.
`J Clin Endocr Metab 68:99-106, 1989.
`
`Astrazeneca Ex. 2025 p. 8