Estrogen action in human ovarian cancer

Critical

Reviews

in

ONCOLOGY/ HEMATOLOGY Critical

ELSEVIER

Reviews

in Oncology/Hematology

25 (1997)

1-9

Estrogen action in human ovarian cancer Gail M. Clintona,*, “Department

oj Biochemistry

and Molecular ‘Department

Biology,

Wenhui Huab

Oregon

Health Sciences IJniversity, OR 97201-3098, USA of Pharmacology, University of’ Washington, Accepted

L224,

3181 SW Sam Jackson

Seattle

WA,

Park

USA

20 June 1996

Contents I.

Introduction.

2.

Epidcmiological 2.1. Exposure 2.2. Biological

3.

Clinical

4.

Effects of estrogens and antiestrogens 4.1. Cell growth in vitro. 4.2. Growth in xenograft models

5.

Investigations of estrogen regulated gene products in ovarian 5.1. The progesterone receptor 5.2. Cathepsin D 5.3. C-myc early growth response gene 5.4. pNR-2/pS2 5.5 Fibulin-1 5.6. HER-2/neu. 5.7. Breast and ovarian cancer susceptibility gene, BRCAl

6.

Estrogen

7.

Summary.

2

results

of steroid

and antiestrogen

hormone

resistant

therapy

3

on growth

cell culture

of ovarian

carcinoma

carcinoma

References

~

Biographies

author

1040.8428;97i$32.00 Copyright PllS1040-X428(96)00216-8

8 1997 Elsevier

Science

Ireland

Ltd.

All rights

cells.

cells..

6

models

Reviewer

* Corresponding

2 2 2

Studies to exogenous estrogens and risk of ovarian cancer and molecular basis for epidemiological results.

reserved

Road,

Portland,

2

G.M.

Clinton,

W. Hua

i Critica!

Recielvs

m Oncology~Hematolog~~

25 (I 997) I- 9

1. Introduction

associated with infertile women who take antiestrogens, usually clomiphene, as ovulation stimulating medication

Ovarian cancer is the leading cause of death from gynecological tumors and is the fourth most frequent cause of death from cancer in women [ 11. Ovarian cancer is highly lethal mainly because of occult metastasis within the peritoneal cavity and the advanced stage at detection when curative therapy is ineffective. Approximately SO--9O”/o of adult ovarian cancers are derived from ovarian surface epithelium. The ovarian surface epithelial cells originate during fetal development from the coelomic epithelium, but in the mature ovary their dynamic morphology, including crypts and inclusion cysts, contrasts with the structural uniformity of the immediately adjacent peritoneal epithelium [2]. Current treatment of ovarian cancer consists of surgery, usually followed by cisplatin-based combination chemotherapy [3]. Unfortunately the survival rate of ovarian cancer patients is dismal with little improvement in the past few decades. Less than 20% of patients diagnosed with advanced cancer survive 5 years and most patients are advanced to stage III or IV at detection [4]. Research to understand the genetic and molecular basis of the disease may ultimately provide the greatest payoff in earlier detection and development of new treatment therapies [3]. Endocrine factors, particularly gonadotropins and estrogens, play an important role in ovarian cancer (see Ref. [5]). Although a subset of these cancers have estrogen receptors (ER) the clinical significance is uncertain since both a protective and facilitative role of estrogen in human ovarian cancer have been suggested. Definition of the role of estrogen has significance beyond academic interest since antiestrogen therapy can be an effective, nontoxic therapy as in breast cancer and estrogen responsive markers may provide valuable prognostic indicators. The role of hormones in ovarian cancer was extensively reviewed by Rao and Slotman in 1991 [5]. In the present review, new information on the role of estrogen in epithelial ovarian cancer will be considered with emphasis on in vitro cell culture models, and potential use of estrogen regulated protein products as markers for early detection and for hormone responsive disease.

[9,101.

2. Epidemiological 2.1. Expomre ovarian canw

Studies

to exogenous estrogens and risk

qf

Epidemiological studies provide important clues to the causes of human disease. Estrogens, taken as oral contraceptives by women of reproductive age, have consistently been found to lower the risk of ovarian cancer [6-81. On the other hand, an increased risk of ovarian cancer is

The risk of noncontraceptive use of estrogens on ovarian cancer has also been investigated. A recent study, conducted on 240 000 postmenopausal women, indicated an increased risk of ovarian cancer of 40% for 6 ~ 10 years and 70% for greater than 10 years of estrogen replacement therapy [l 11.The strength of this study was the large number of subjects and consideration of the duration of oral contraceptive use. While some past studies also suggested increased risk [12- 151 there is disagreement on the association of hormone replacement therapy with frequency of ovarian cancer [16]. Because the risk associated with use of estrogen replacement therapy was small [I l] and because of conflicting reports [16], additional studies will be required to resolve how exogenous estrogens affect cancer risk in postmenopausal women. 2.2. Biological results

and molecular basis for t~pidenziological

Protection against ovarian cancer with use of oral contraceptives and enhanced risk associated with use of fertility drugs is consistent with either of two hypotheses. The first, which has widespread acceptance, is that “incessant ovulations” promotes tumorigenesis [ 171. Modulation of the frequency of ovulations by oral contraceptives and fertility drugs then best explains the risks associated with their use. A second hypothesis is that direct stimulation of the ovary by pituitary gonadotropins contributes to ovarian carcinogenesis [13,18]. Consistent with the second is that endogenous levels of gonadotropins are diminished by use of oral contraceptives and elevated by use of fertility drugs, which increase risk. However, direct administration of human chorionic gonadotropin, for treatment of infertility, was not associated with increased ovarian cancer risk in one study [lo]. In addition: estrogen replacement therapy, while decreasing endogenous gonadotropins, was reported to enhance the risk of ovarian cancer [ll--151. A two step hypothesis encompassing “incessant ovulation” and “estrogen mediated proliferation” [ 191 is congruous with much of the evidence. At ovulation, follicle rupture is followed by proliferation of surface epithelial cells which normally stops when the rupture is repaired. Repetitive or incessant ovulation accompanied by epithelial proliferation increases the probability of genetic abnormalities leading to genetic instability [20] and selection of cells with allele loss and inactive tumor suppressor genes [21]. The premalignant and malignant cells with estrogen receptors are then hypothesized to proliferate in response to estrogen. Proliferation of ovarian carcinoma cells in response to estrogen has been directly demonstrated in several cultured ovarian carcinoma cells that have estrogen receptor [22-301.

G.M.

Clinton,

W. Hua / Critical

Review

In summary, for women of reproductive age, the risk of ovarian cancer associated with use of exogenous estrogens or antiestrogens appears to be dominated by their effects on frequency of ovulations. However in postmenopausal women, the predominant effect of exogenous estrogen may be to increase risk as a consequence of stimulation of cell proliferation.

3. Clinical results of steroid hornione therapy

Therapy with the antiestrogen, tamoxifen, is an effective and nontoxic treatment of estrogen receptor positive (ER+) breast cancer patients, although tamoxifen resistance, either present at the onset or acquired during hormonal therapy, is a significant clinical problem [31,32]. The following suggests the potential of antiestrogen hormonal therapy for treatment of ovarian cancer: ER is present in a subset of ovarian cancers [5,33,34]; ovarian cancer risk may be increased with duration of estrogen replacement therapy suggesting a facilitative role for estrogen [l 11; estrogen stimulates proliferation of ER + ovarian carcinoma cells in culture [22-301; expression of similar growth regulatory genes is induced by estrogen in breast and ovarian carcinoma cells in culture [27,28,30,35,36]. Clinical response of ovarian cancer patients to tamoxifen therapy has been disappointing, however, with about 15% response rate (see Ref. [37] for review). More recent studies reported an 18% [38] and a 17% response [39] although the numbers tested were small. There are several explanations for the poor response of ovarian cancer to steroid hormone therapy in comparison to breast cancer: (a) ovarian cancers that express ER, a requirement for hormone responsiveness, may be lower than breast cancer and less than the original estimates of 60% [5]. Immunohistochemical studies of cancer epithelial cells indicate that about 38% of ovarian cancers are positive for ER [33,34]. Kommoss et al. [33,34] suggest that biochemical assays have given inflated values due to contamination of epithelial cancer cells with stroma. (b) The role of estrogen in ovarian cancer may be complex with a facilitative role mainly expressed in postmenopausal women as discussed above. (c) Clinical studies of tamoxifen therapy may not accurately represent effectiveness since they were conducted on small numbers of patients as a last resort after failure of other therapeutic approaches [5,37-391. Metastatic, late stage ovarian cancers that resist chemotherapy have possibly developed cross resistance to multiple growth regulators. (d) Estrogens and antiestrogens may be produced and/or metabolized differently in ovarian epithelial cancer cells. For example, production of endogenous steroids observed in some ovarian cancer cells [35,40] would be expected to interfere with the action of tamoxifen. (e) The antago-

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3

nist activity of tamoxifen might be weak in ovarian epithelial cancer cells. The extent to which tamoxifen acts as an agonist or antagonist on ER is tissue specific [41-431 and has not been extensively investigated in ovarian cancer cells. While further investigations are required to better define the effectiveness of tamoxifen and other antiestrogens on ovarian cancer cell growth in vitro and in vivo, identification of a subgroup of patients likely to respond to antiestrogen therapy would be an important advance in ovarian cancer treatment.

4. Effects of estrogens and antiestrogens ovarian carcinoma cell lines 4.1. Cell growth

on growth

of

in vitro

Several ovarian carcinoma cell lines have been established and are of critical importance in determining the role of hormones in ovarian cancer. Estrogen responsive cell lines developed from metastatic breast tumors have supplied information that has had direct clinical application. Antiestrogens that inhibit cultured cell growth are currently used or are in clinical trials for hormonal therapy [44-461. Estrogen regulated gene products identified in cell lines have been used as prognostic markers for breast cancer [47,48]. There is ample evidence that estrogen stimulates proliferation of cells that contain sufficient levels of ER (in excess of 10 fmol/mg protein) [22--301. A summary of cell lines, their origin, and their growth response to estrogen and antiestrogens is included in Table 1. 4.2. Grobvth in xenograft

models

There have been few studies so far on the effects of estrogens in vivo on xenografts of ovarian carcinoma cells in nude mice. Growth of the implanted PE04 cell line, was reduced in ovariectomized animals consistent with a mitogenic effect of estrogen [54]. However, in this same study, when ovariectomized or intact mice were given exogenous estrogens, unexpectedly, the PE04 xenograft growth was inhibited while the breast carcinoma cells, used as a positive control, were stimulated by estrogen as expected. The possibility that these ovarian carcinoma cells may be more sensitive to growth inhibition by the artificially elevated levels of estrogen achieved by exogenous administration needs to be further evaluated. The effects of antiestrogens, on the other hand, were clear and consistent with an antagonistic action on ER. Growth of xenografts of PE04 cells was inhibited by tamoxifen [29,54] and by the pure antiestrogen ICI 182,780 [54]. In another study, xenografts of an ovarian carcinoma explant, OXA-5, had inhibited growth in ovariectomized ani-

4

G.M.

Table 1 Ovarian carcinoma -~ Cell

line

cell lines with

Clinton,

estrogen

W. Hua / Critical

Reviews

in Oncology/Hematology

25 (1997)

receptors

Origin

Xenografts

Solid metastasis of primary papillary adenocarcinoma [28]

ND“

ND

PE04

Peritoneal ascites, mutinous adenocarcinoma [50]

Tumorigenic [54]; inhibited by: ovariectomy [54], E, [54], tamoxifen [29], ICI 182,780 [29]

112 fmol/mg [22,241

PEOI

Peritoneal ferentiated

ascites, [50]

poorly

ND

96 fmol/mg

PE06

Peritoneal

ascites

[50]

ND

132 fmol/mg

Peritoneal ferentiated, carcinoma

ascites, poorly difpapillary adeno[5 1]

SKOV3

Peritoneal ascites adenocarcinema [52]

[49]

receptor

BR

dif-

Tumorigenic

Estrogen

Stage III primary, poorly ferentiated adenocarcinoma [491

OVCAR-3

dif-

in nude mice

BG-1

NIH:

23 fmol/mg

proteina

protein

protein

28 fmol/mg ER mRNA’

protein [35]

Tumorigenic

[53]

ER mRNA protein’

[36]; ER

5. Investigations of estrogen regulated gene products ovarian carcinoma cells

in

The function of the estrogen receptor as a transcriptional regulator has led to the suggestion that estrogen stimulates proliferation in target tissues by induction of growth regulatory genes [55]. Assays of these gene products in clinical specimens can then be used to predict hormone responsiveness and prognosis. Several estrogen responsive gene products, discussed in more detail below, are regulated by estrogen in ER+ ovarian carcinoma cells lines and some of their protein products have been detected in ovarian cancer tissue (Table 2). receptor (PR)

Production of PR is under the control of estrogen in normal steroid target tissues and in breast carcinoma cells [56]. PR is also regulated by estrogen in some

[49]

protein

[51]

mals and stimulated growth in animals that were administered exogenous estrogen in agreement with a proliferative effect [25].

In vitro growth response to estrogens and antiestrogens Stimulated by E, b; inhibited by tamoxifen’ [23,26,25

Stimulated

Tumorigenic

a Determined by estrogen binding assays; b E, = 17 a-estradiol; ’ indicates inhibition of E, stimulated detected by Northern blot analysis; f ER protein detected by Western blot analysis.

5.1. The progesterone

l-9

growth;

by E, [28]

Stimulated by E, [22,24,30,54]; inhibited by: tamoxifen [22,24,29], ICI 164,384 [29], ICI 182,780 P91 [24]

Stimulated by E, PO]; inhibited by: tamoxifen [29], ICI 164,384 [29], ICI 182,780 [29]

[24] [51];

Stimulated

by E, [30]

Stimulated by E, [35]; no effect of E, [22]

No effect of E,, tamoxifen, ICI 164,384 [36] d ND,

not determined;

e ER mRNA

[22,30,57] but not all [22,36] estrogen responsive ovarian carcinoma cell lines. Therefore, expression of PR is not always coupled to estrogen responsive growth, but its presence suggests functional ER and may be of value for predicting responsiveness to antiestrogen therapy. PR has also been detected in about half of ovarian cancer clinical samples examined by biochemical methods [5] and about 31% estimated by immunohistochemical analysis [33,34]. Importantly, the presence of PR is a positive prognostic indicator in ovarian cancer most likely because it is associated with a higher degree of differentiation (see Ref. [5]). 5.2. Cathepsin D

This lysosomal protease, secreted from breast carcinoma cells, and believed to be involved in metastasis [41], has been found to be controlled by estrogen in ER+ ovarian carcinoma cell lines [27,36]. Induction of secreted cathepsin D by estrogen correlates with growth regulation in PE04 and BGl ovarian carcinoma cells [27,36] while cathepsin D is constitutively produced in an ER+ ovarian carcinoma cell line, SKOV3, that is resistant to growth regulation by estrogens and anti-

G.M.

Clinton,

W. Hua 1 Critical

Revie:ss

estrogens [36]. Constitutive production of cathepsin D by estrogen independent cells [36] and by some ER negative cells [48] suggests that this protease will not be useful for predicting the hormone responsiveness of ovarian cancer. Cathepsin D has also been detected in cytosols of ovarian tumors and initial studies indicate that it does not correlate with ER and PR presence but is at higher levels in omental metastases than in corresponding primary tumors [58,59]. 5.3. c-myc early growth

response gene

Expression of this nuclear proto-oncogene is rapidly and transiently induced by a variety of mitogens including estrogen in breast carcinoma cells [60,61]. c-myc mRNA levels are also stimulated by estrogen and correlate with growth stimulation of CAOV-3 [35] and PE04 [36] ovarian carcinoma cells, while estrogen induction of c-myc in SKOV3 cells is uncoupled from proliferaTable 2 Estrogen

responsive

Product Cathepsin

Progesterone Receptor

D

gene products

in ovarian

c-myc

BGI PE04 SKOV3

Yes [proteinla Yes [protein] No [protein]

BGI NTH:OVCAR-3 PE04

Yes [protein] [49] Yes [protein] [22,57] Yes [protein] [30]; undetectedb [protein] [22] Yes [protein] [30] Undetected [protein, mRNA]

by EZ [27] [36] [36]

NIH:OVCAR-3 PEOl PE04 PE06

Yes [mRNA] [35] Undetected [protein] Undetected [protein] Undetected [protein]

NIH:OVCAR-3 PE04

Yes [mRNA] Yes [mRNA] Yes [mRNA]

[35] [36] [36]

Yes [mRNA] Yes [mRNA]

[36] [36]

Yes [protein] Yes [protein] Yes [protein]

[72] [72] [72]

SKOV3

l-9

5

tive response [36]. Amplification of the c-myc gene [62,63] and expression of the c-myc protein product [64,65] has been found in a fraction of ovarian cancers where elevated levels likely indicate gene dose rather than estrogen responsiveness. 5.4. pNR-2/pS2

This gene encodes a secreted protein, is under control of estrogen in ER+ breast carcinoma cells, and its presence is positively correlated with ER in tumors [66,67]. High levels of the pS2 protein in breast cancer predicts favorable prognosis and responsiveness to endocrine therapy [68]. Of five ovarian carcinoma cell lines examined by Langdon et al [30] pS2 was not found to be regulated by estrogen even in those cells that had PR induced and their growth regulated. The PS2 protein has been found in a subset of ovarian tumors [69971]. It is not known whether pS2 correlates with presence of ER and with estrogen responsiveness as in breast cancer. 5.5. fibdin- 1

Regulated

[361 PS2

25 (1997)

cancer

Cell line

PE06 SKOV3

in Oncology/Hematology

[30] [30] [30]

Recently, the extracellular matrix (ECM) protein, fibulin 1, has been found to be induced by estrogen in three ovarian carcinoma cell lines [72]. While the function of this protein is unknown, its association with other ECM components including fibronectin, laminin, and nidogen [73,74] suggests a role in cell morphology, adhesion, and motility. Despite the ubiquitous distribution of fibulin-1 in connective tissue and in blood, interestingly it is not generally found in epithelial cells and is not in several types of cancer cells [75]. Additional investigations stimulated by the discovery that fibulin-1 production in ovarian carcinoma cells is induced by estrogen should reveal its role in invasion and metastasis and may be of value in development of new treatment strategies based on controlling the spread of ovarian cancer in the peritoneal cavity. 5.6. HER-2/neu

c-fos

PE04

SKOV3 Fibulin-I

BG- I PE:04

SKOV3 HER-2/neu

PE:04

SKOV3

No [protein]’ No [overexpressed

protein]

[361 a Brackets designate the level of expression, protein or mRNA, that was investigated in each study. ’ Undetected means that the product was not detected in the study. In these cases, it is difficult to conclude whether estrogen regulation occurred, or not. ’ Hua, WH and Clinton, GM, unpublished observations.

This proto-oncogene, which encodes a receptor-like tyrosine kinase, is overexpressed in about 20% of ovarian cancers [76-811 and has been associated with cancer progression and poor prognosis in breast as well as in ovarian cancers [76,81], although there is disagreement [76]. In contrast to other growth regulatory genes that are induced by estrogen, the HER-2,neu protooncogene is down-regulated by estrogen in responsive breast carcinoma cell lines [82-841. Although there are many parallels in growth regulatory genes regulated by estrogen in breast and ovarian cancer, we discovered that estrogen does not down-regulate the HER-2/neu product in two ovarian carcinoma cell lines including

6

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W. Hua / Critical

Reviews

the antiestrogen resistant SKOV3 cells, which overexpress HER-2/neu [36], nor the estrogen responsive PE04 cells (Hua and Clinton, unpublished observations). Stuclies of other ER+ ovarian carcinoma cells are needed to test the possibility that regulation of HER-2/neu by estrogen does not occur in ovarian epithelial cancer cells. Alternatively, a step in cancer progression may be the loss of estrogen-mediated down-regulation of HER-2jneu leading to its overexpression. Overexpression of HER-2/neu may saturate mitogenic pathways resulting in antiestrogen resistance. Indeed recent studies suggest that ectopic expression of HER-2/neu in breast carcinoma cells can confer antiestrogen resistance [85,86]. A relationship between level of HER-2/neu expression and response to antiestrogen therapy has been observed for breast cancer [87]. These studies conducted on breast cancers suggest the value of further investigations regarding the possible value of HER-2/neu expression levels in predicting responsiveness of ovarian cancers to endocrine therapy. 5.7. Breast and Ouariun cancer susceptibility BRCAl

gene,

The Brcal gene which confers susceptibility to breast and ovarian cancer [88] points towards understanding the development and progression of some ovarian cancers. This gene, which appears to function as a tumor suppressor gene, has also been found to be mutated in sporadic ovarian cancer but similar mutations have not yet been found in sporadic breast cancer [89-911. The finding that carriers of mutant alleles of Brcal are susceptible to cancers of hormone responsive tissue, has raised interest in the possible hormone regulation of expression of this gene [92]. Recent studies in mice suggest that Brcal expression is not regulated by estrogen alone, but a combination of estrogen and progesterone stimulate expression in mammary glands of ovariectomized females [93]. In this same study, expression of Brcal in the ovary was mainly follicular and was not detected in the surface epithelial cells where most cancers originate. It will be important to determine whether expression in surface epithelial cells of the ovary may be regulated by estrogen and progesterone as found in breast tissue, and whether levels may be modulated during different times of the estrous cycle particularly when the surface epithelium is undergoing repair following ovulation.

6. Estrogen and antiestrogen resistant cell culture models Because a large proportion of ER + ovarian cancers appear to be antiestrogen resistant, evidenced by the poor response of patients to tamoxifen therapy, eluci-

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dation of mechanisms underlying resistance may directly impact the treatment and understanding of this disease. Antiestrogen resistant cell culture models provide the opportunity to assesseffectiveness of alternative ER targeted compounds for growth inhibition and to identify markers that may help in choosing the most effective forms of therapy [94-961. The type of antiestrogen resistance most commonly observed in ovarian cancer is “innate resistance” rather than “acquired resistance” which occurs in breast cancer patients that have undergone hormonal therapy. Recently we began investigations on the SKOV3 cell line as a model for “innate resistance” of ovarian cancer [36]. These cells are stably resistant to proliferative effects of estrogen and are cross-resistant to growth inhibition by OH-tamoxifen and the pure antiestrogen ICI 164,384. Yet, they express ER that is normal in its transcriptional activation function. With the goal of identifying markers that may help to predict the hormone responsiveness of ovarian cancer patients, we examined the regulation of several estrogen responsive gene products in the SKOV3 model cell line compared to mitogenically responsive cell lines. Surprisingly, estrogen stimulated mRNA levels of c-rn-vc and c-fos early growth responseproto-oncogenes, which are normally tightly connected to proliferative response. In addition, secretion of fibulin-1, was stimulated by estrogen suggesting a nonproliferative function of this extracellular matrix protein in SKOV3 cells. However, the progesterone receptor was not induced and cathepsin D and HER-2/neu were constitutively overexpressed and nonresponsive to estradiol treatment. Our preliminary assessmentof this antiestrogen resistant cell line is that the mitogenic pathway may be saturated by overexpression of HER-2/neu thereby eliminating proliferative responseto estrogen and antiestrogens. Moreover, these studies suggestthat progesterone receptor presencemay predict responsivenesswhereas overexpression of HER2/neu may predict nonresponsivenessof ovarian cancer to endocrine therapy. It is important to investigate other examples of antiestrogen resistant ovarian cancer to evaluate whether they are commonly cross-resistant to different classesof antiestrogens and to define classes of markers that may predict antiestrogen resistance.

7. Summary Evidence is accumulating for a facilitative role for estrogen in ovarian cancer. Although response to antiestrogen therapy has been poor, there is a distinct subset of patients that respond. Strategies for treatment of ovarian cancer would be improved by identification of patients likely to respond to hormonal therapy. Cell culture models that are responsive or resistant to estrogen and antiestrogen may be of value in finding mark-

G.M.

Clinton,

W. Hua

I Critical

Reviews

ers that predict responsiveness to hormonal therapy. Several model cell lines have been generated that express ER and proliferate in response to estrogen in vitro. Further studies are needed to better characterize the response of these ER positive cells lines to estrogen in vivo in mouse xenograft models. Expression of many of the same genes are regulated by estrogen in breast and in ovarian cancer cell lines. One exception may be the HER-2/neu oncogene product, which is down-regulated by estrogen in responsive breast carcinoma cells but not in two ovarian carcinoma cell lines. Initial analyses of several estrogen responsive and one resistant cell model suggests the potential value of progesterone receptor presence and low levels of HER-2/neu expression for predicting responsiveness to hormonal therapy. Additional cell models need to be investigated to determine the frequency with which these markers are associated with antiestrogen resistance.

Reviewer

This paper was reviewed by WR Miller, Professor of Experimental Oncology, Department of Clinical Oncology, The University of Edinburgh, Western General Hospital, Edinburgh, UK.

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W. Hua I Criticul

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G.M.

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Biographies Gail M. Clinton received her Ph.D. from the University of California at San Diego. She did a postdoctoral fellowship at Harvard Medical School and is currently an associate professor at Oregon Health Sciences University in Portland. Wenhui Huu received her Ph.D. from Oregon Health Sciences University and is currently a postdoctoral fellow at the University of Washington in Seattle.