Abstract BS1-2: A new perspective on androgen receptor action in estrogen receptor-α positive breast cancer

Resistance to estrogen receptor alpha (ER) target therapies is the major cause of breast cancer death. Therapeutic engagement of steroid receptors that impinge on, but do not ablate, ER signalling is an emerging new treatment strategy. The AR is expressed in the majority of breast tumors and represents an exceptional therapeutic target, especially as a range of drugs including AR agonists, antagonists and selective AR modulators (SARMs) are available. Interest in targeting AR for treatment of breast cancer has escalated over the past decade. Despite clinical correlations and preclinical studies supporting a protective role for AR in breast cancer, especially in ER-positive disease, enthusiasm was largely directed toward antagonizing AR with anti-androgenic drugs used to treat men with prostate cancer, a disease definitively driven by oncogenic AR activity. While some pre-clinical studies supported use of an AR antagonist for ER-positive breast cancer, this strategy has had minimal success in clinical trials. Our most recent preclinical studies using a diverse range of in vivo breast cancer models (Hickey et al, Nature Medicine 2021) provides compelling evidence for (i) AR being a tumor suppressor in ER+ breast cancer, and (ii) an AR agonist, not an antagonist, treatment strategy being the optimal therapeutic approach.

Citation Format: W Tilley. A new perspective on androgen receptor action in estrogen receptor-α positive breast cancer. [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr BS1-2.

Abstract P6-20-04: Activation of AR inhibits growth of endocrine-resistant breast cancer

Introduction

Resistance to endocrine therapy is a major clinical problem in estrogen receptor positive (ER+) breast cancer. The androgen receptor (AR) is expressed in ˜90% of all ER+ breast cancers and high expression of AR is associated with a better patient outcome in this subtype. In agreement, AR activation in breast cancer cell line models reduces proliferation of cells via antagonism of ER signaling. However, uncertainty surrounding the role of AR in endocrine resistance is reflected in current clinical trials in which both AR agonists and antagonists are being investigated. In this study, we sought to investigate the optimal approach in targeting AR in endocrine-resistant breast cancer.

Methods

We evaluated the consequences of AR activation, using AR cognate ligand 5α-dihydrotestosterone (DHT) and selective AR modulator enobosarm, and AR antagonism using enzalutamide on in vitro and in vivo models of endocrine-resistance. The efficacy of these AR modulators were assessed in vitro using tamoxifen-resistant (TamR) and long-term estrogen derived (LTED) models of MCF7 cells, and in vivo using ESR1 mutant E2-dependent (HCI-005) and ESR1 wild-type E2-independent (Gar15-13) endocrine-resistant PDX models

Results

Treatment with DHT and enobosarm inhibited the growth of MCF7 TamR and LTED cells but enzalutamide had no effect. AR activation was associated with loss of ER in MCF7 TamR cells and loss of ER-regulated PR expression in MCF7 LTED which suggests that this growth suppression was mediated through the antagonism of ER signaling. Notably, an additive anti-proliferative effect was observed with the combination of enobosarm and CDK4/6 inhibitor palbocilib in the MCF7 TamR cells. A similar pattern was observed in vivo with DHT strongly inhibiting the proliferation of both PDX models. Enobosarm similarly suppressed the proliferation of HCI-005, and to a lesser extent in Gar15-13. The benefit of enobosarm in Gar15-13 was significant given that this model is fulvestrant-resistant. Antagonizing AR with enzalutamide had no effect on growth of Gar15-13 model, similar to our in vitro data. AR agonists reduced expression levels of ER and PR in HCI-005, and transcriptomic analysis of AR agonist-treated Gar15-13 identified significant negative enrichment of genes related to proliferation and estrogen response. These observations indicate that the growth-suppressive effects of AR activation in vivo were mediated through inhibiting ER signaling. We identified an AR gene signature, through RNA-seq analysis of DHT-treated Gar15-13 PDX, which is strongly associated with good outcome in the METABRIC dataset, supporting the hypothesis that an active canonical AR signaling is tumor suppressive in both endocrine-sensitive and -resistant disease contexts. Lastly, we present in vivo data demonstrating enhanced suppression of Ki-67 with the combination of enobosarm and palbociclib in the Gar15-13 PDX.

Conclusion

We have demonstrated that activating AR is an effective therapeutic approach in endocrine-resistant breast cancer, and the combination of an AR agonist with a CDK4/6 inhibitor warrants further investigation in this breast cancer subtype.

Citation Format: Chia KM, Milioli H, Portman N, Laven-Law G, Yong A, Swarbrick A, Caldon L, Tilley W, Hickey T, Lim E. Activation of AR inhibits growth of endocrine-resistant breast cancer [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P6-20-04.

Abstract OT1-01-03: The WinPro study: A window of opportunity study of endocrine therapy with and without prometrium in postmenopausal women with early stage hormone receptor-positive breast cancer

Background

There is bidirectional interplay between PR and ER in human breast cancers (Lim et al, Endo Rel Can 2016). There is evidence for a reprogramming of ER chromatin binding sites with 470 genes differentially regulated by dual treatment with estrogen plus progestogen compared to estrogen alone in breast cancer cell lines (Mohammed et al, Nature 2015). Functionally, there was an additive anti-cancer effect with the addition of natural progesterone to endocrine therapy in preclinical breast cancer models.

Trial Design

This is a phase II multi-site, randomised, open-label, three-arm, study in 200 postmenopausal women with early-stage ER+, PR+, HER2-negative breast cancer. Eligible patients will be randomised 1:1:1 to receive 14 days of intervention with either letrozole 2.5mg PO daily (arm 1), letrozole 2.5mg + prometrium 300mg PO daily (arm 2) or tamoxifen 20mg + prometrium 300mg PO daily (arm 3), between diagnosis of breast cancer and definite surgery.

Australian Clinical Trials Registry: ACTRN1261800092813

Eligibility Criteria

Inclusion Criteria

a) Histologically confirmed ER+ and PR+ breast cancers (≥10% positive staining cells)

b) HER2/CEP17 ratio of <2 and mean HER2 copy number <6 (ASCO CAP 2013 guidelines)

c) Tumour size ≥1cm on ultrasound and/or mammogram

d) Aged ≥18 years

Exclusion Criteria

a) Currently on hormone therapies (HRT and OCP)

b) Locally advanced/inoperable and inflammatory breast cancer

c) Clinical evidence of metastatic disease

d) Received other preoperative systemic therapies

e) Nut allergy (prometrium contains peanut oil)

f) Prior history of uterine cancer, deep vein thrombosis, pulmonary embolism or clotting disorder

g) Women who are pregnant/breast feeding

Specific Aims

a) Primary Endpoint

The geometric mean suppression of the centrally assessed proliferation marker Ki67, after two weeks of intervention, compared with baseline. This will be obtained by comparing the mean difference in Ki67 staining between pre and post-treated samples in each intervention arm.

b) Secondary Endpoint

Safety and tolerability of combination therapy (NCI-CTCAE v4.0)

c) Translational Endpoints

1. Define a gene set as a predictive biomarker for a reduction in Ki67

2. Evaluate changes in the apoptotic markers Bcl-2 and Caspase 3 in the tumors following intervention

3. Evaluate changes in ER, PR, AR, FoxA1, Cyclin D1 protein and mRNA expression in the tumors following intervention

Statistical Methods

The IMPACT study reported a geometric mean reduction in Ki67 after 2 weeks of preoperative tamoxifen of 59.5% and anastrazole of 76% (Dowsett et al, JNCI 2007). This allows estimation of power to detect differences between Arm 1 and either Arm 2 or Arm 3 with a p-value of 0.025. For the third possible comparison of Arm 2 vs Arm 3, there is no prior evidence, therefore this as a purely exploratory comparison. With a total trial recruitment of 200 and allowing 4% dropouts, this would give 80% power to detect an improvement in Ki67 suppression from 76% in the letrozole alone control arm to 92% in either experimental arm.

Accrual

Present: 5 (1 site open)

Target: 200 (8 sites total)

Contact Information

Elgene Lim, MBBS, FRACP, PhD. e.lim@garvan.com.au

Citation Format: Carson E, Segara D, Parker A, O'Toole S, Coates A, Mann B, Lindeman G, Tilley W, Lim E. The WinPro study: A window of opportunity study of endocrine therapy with and without prometrium in postmenopausal women with early stage hormone receptor-positive breast cancer [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr OT1-01-03.

Evaluation of Testosterone Supplementation during Anastrozole Therapy in a Breast Explant Model

Background: Aromatase inhibitors (AI) are currently used as first line adjuvant therapy for postmenopausal women with estrogen receptor (ER) positive breast cancer. Side effects of AI therapy, such as arthralgia, can cause significant patient discomfort leading to compliance issues. This may be exacerbated by low tissue testosterone (T), which is naturally lower post-menopause and may be decreased further following chemotherapy. T supplementation has emerged as a potential means to treat AI-associated arthralgia and has generated favourable results in a phase II clinical trial (NCT00497458). However, T replacement in breast cancer had been contraindicated until the advent of powerful 3rd generation AIs such as anastrozole. AIs are highly efficacious in blocking conversion of T to estrogen, thereby increasing the potential for 5α-reduction of T to its more active tissue form, 5α-dihydrotestosterone (DHT), which counterbalances estrogen induced proliferative effects in hormonally sensitive breast tumors1. Our objective was to test the effects of T supplementation during AI administration on tumor growth in a human breast explant system.Materials and Methods: Fresh breast tumor samples collected from 17 post-menopausal women were cut into 3 mm3 pieces, cultured for 24h on gelatine sponges submersed in culture media with 10% steroid depleted fetal calf serum and treated with vehicle (control), T (5nM) and/or AI (25ng/ml). Tissues were stained with antibodies for ER, progesterone receptor (PR), androgen receptor (AR), and Ki67, a marker of cell proliferation that has been used to predict the outcome of therapy with anastrozole2. Tissue sections were scanned using a high resolution image scanner (NanoZoomer) and the percent Ki67 positive cells was determined by counting at least 2000 cells per slide.Results: All tumor tissues were positive (>30%) for ER, AR and PR, with the exception of 1 tumor that lacked PR. As expected for primary tissues, percent Ki67 positivity (mean; range) in the control was highly variable (6.45; 1-43.2). Tissue responses to T (7.9; 0.1-46), AI (6.06; 1.4-35.3), and T+AI (4.97; 0.7-26.1) were not significantly different from control (Wilcoxon signed rank test). However, the combination of T+AI showed a trend towards reduced Ki67 positivity compared to AI alone (p=0.07). In two patients T significantly increased Ki67 positivity by 2-4 fold, and in both instances this stimulatory effect of T was reduced to or below control values by treatment with AI.Discussion: Our results suggest that T supplementation during adjuvant AI therapy does not compromise AI-mediated inhibition of breast tumor growth. Indeed, combined therapy with T and AI may further enhance tumor suppression through elevation of DHT levels in the breast. This finding supports the clinical potential of T supplementation in post-menopausal women on adjuvant AI therapy to prevent or relieve AI-associated side effects.1. Peters A et al Cancer Res (In Press)2. Dowsett M et al JNCI 2007

Citation Information: Cancer Res 2009;69(24 Suppl):Abstract nr 4089.

166. MATERNAL OBESITY IS ASSOCIATED WITH AN INCREASED INCIDENCE OF PROSTATE ABNORMALITIES IN ADULT RAT OFFSPRING

The World Health Organization has stated that 75% of adults worldwide are overweight, and in Australia nearly 25% of men are obese. Obesity is associated with an increased risk of cardiovascular disease, type 2 diabetes and cancer, with 30 to 40% of the latter possibly preventable by maintaining a healthy weight (The International Association for the Study of Obesity). Prostate cancer is the most commonly diagnosed cancer in men and there is increasing evidence that obesity increases the risk of prostate cancer mortality. High birth weight, an indication of excess nutrition during foetal development, has been associated with an increased risk of childhood and adult obesity, and for cancer. Using an animal model, we investigated whether obese mothers are more likely to have obese sons who are at an increased risk of developing prostate abnormalities and thus prostate cancer, in adulthood. Female rats were fed with either a control diet (4g fat/kg) or high fat diet (100g fat/kg) from before mating and throughout pregnancy. Prostate tissues were collected from the male offspring at 90 days (post-puberty) and 180 days (young adult). Histological analysis of the day 90 prostates identified hyperplasia in 100% of the ventral lobes (VL) and 64% of the dorsolateral lobes (DLP) in offspring of the maternal high fat group compared to 0% in each respectively, in those of the maternal control diet group. The VL is the most hormone sensitive prostate lobe of the rat, while the DLP is considered the equivalent of the human peripheral zone, the region from which the majority of human prostate cancers arise. These results suggest for the first time that maternal high fat diet may induce prostate abnormalities in male offspring that may in turn, predispose to an increased risk of prostate cancer in later life.

415. Increased expression of an androgen receptor regulated gene, kit ligand, in polycystic ovaries

Polycystic ovaries (PCO) are induced by pathological or pharmacological female androgen excess, but the role of the androgen receptor (AR) in the pathogenesis of PCO is unknown. We therefore tested the hypothesis that PCO have increased expression of AR or kit ligand (KITL), a cytokine that was recently identified as a candidate AR-regulated gene in the ovary (1). Immunohistochemical analysis of AR and KITL expression was performed on archival paraffin-embedded sections of 8 morphologically normal and 8 polycystic ovaries from women under the age of 40 years. Stained sections were scanned with a NanoZoomer Digital Pathology System and immunoreactivity was qualitatively assessed using a 0-3+ scale, where 3+ represents the most intense staining. Electronic images of follicles at different stages of folliculogenesis were assessed by two independent observers who were blinded to the morphology of the source ovary. Each individual ovary contributed a minimum of 1 follicle per size class and a minimum of 10 follicles per size class were analysed. AR immunoreactivity was present in granulosa cells at all stages of folliculogenesis, in thecal cells of large antral follicles, and in the ovarian stroma. Staining intensity for AR did not differ between normal and polycystic ovaries. KITL expression, summarised in Table 1, was found to be significantly elevated in the oocytes of primordial and primary follicles and in the granulosa cells of follicles at all stages of folliculogenesis. These results show that AR expression is normal in PCO but expression of an AR-regulated gene is increased, potentially due to an excess of androgen hormone that is characteristic of women with PCO. Based on the roles of KITL established by murine studies, increased expression of KITL could explain many of the features of PCO including follicle excess, hyperthecosis and abnormal androgen secretion.

Rehabilitation of the burned upper extremity

With the advancement in medical technology and more effective life-sustaining measures, the rehabilitation therapist is faced with the immense task of effectively restoring functional ROM, strength, and mobility and producing a cosmetic result acceptable to the patient. Rehabilitation therapists have a very significant role to play in achieving these goals. The patients and their families come to rely very heavily on the therapists for advice, support, and information both in the acute phase of burn management and, potentially, for years to follow. A concerted team approach is necessary for a satisfactory functional outcome following burn injury.

Functional evaluation of the shoulder following latissimus dorsi muscle transfer

The dynamic muscle function of the shoulder in 26 patients (10 males, 16 females) who underwent a pedicled or free vascularized latissimus dorsi muscle transfer between 1985 and 1991 (mean follow-up, 4.4 yr) was studied. Instrumented muscle testing was performed on the Kinetic Communicator machine (Kin Com) and the Baltimore Therapeutic Equipment (BTE) work simulator. The female unilateral pedicle group (n = 13) showed a significant difference between operated and nonoperated shoulders for both peak torque (power) and work (endurance) measurements of shoulder adduction and extension on the Kin Com (mean ratios operated/nonoperated shoulders, 55% to 69%). They also showed significant differences for work performance on three of four BTE tests (mean ratios, 77% to 84%). The male free vascularized group (n = 10) similarly showed a significant deficit of both peak torque and work for shoulder extension and adduction on the Kin Com (mean ratios, 74% to 84%); however, they showed no deficit on the BTE tests. In conclusion, dynamic muscle tests demonstrate a deficit of muscle power and endurance of shoulder extension and adduction following latissimus dorsi muscle transfer.

Xenografted small cell undifferentiated cancer of prostate: possible common origin with prostatic adenocarcinoma

The first xenograft line of small cell undifferentiated carcinoma of the prostate (UCRU-PR-2) has been established and characterized. The donor tumor and the xenograft share the common morphological and ultrastructural features of small cell undifferentiated carcinoma (including neurosecretory granules) but also elaborate epithelial membrane antigen and carcinoembryonic antigen, in addition to neurone-specific enolase. The line expresses a diploid DNA complement. Androgen and estrogen receptors are not expressed, although prostatic acid phosphatase is present in sera from tumor-bearing mice in low levels. From these studies, we postulate a possible common stem cell origin for adenocarcinoma and small cell undifferentiated carcinoma of the prostate; further studies of a cell line derived from this tumor may clarify the issue.

Effectiveness of ivermectin in the treatment of equine Parascaris equorum and Oxyuris equi infections

Fifteen horses harboring naturally acquired, patent Parascaris equorum and Oxyuris equi infections were equally allotted to 3 treatment groups given (1) injectable vehicle; (2) injectable ivermectin at the dose rate of 200 microgram/kg of body weight; and (3) injectable ivermectin at the rate of 300 microgram/kg. All treatments were given IM in the neck. All animals were killed 14 days after treatment and examined for the targeted nematodes. Regardless of dose rate, ivermectin proved 100% effective in the removal of adult O equi and P equorum infections. Levels of immature P equorum were decreased by 98.5% in both ivermectin-treated groups. Oxyuris equi 4th-stage larval injections were decreased by 95.7% and 99.9% by the 200 and 300 microgram/kg ivermectin treatments, respectively. Adverse reactions to the injections of drug were not seen.

Antiparasitic effectiveness of ivermectin in the horse

By way of a controlled trial, the anthelmintic efficacies of the injectable and paste formulations of ivermectin were evaluated in the horse. Treatment was given at the rate of 200 microgram/kg of body weight. Regardless of formulation, 100% removals were demonstrated for Strongylus vulgaris (intestinal), S edentatus, 2nd and 3rd instars of Gastrophilus nasalis and G intestinalis, "small strongyles," Triodontophorus serratus and T tenuicollis. Adult Cylicocyclus insigne populations were eliminated at the rates of 99.9% and 96.3% by the injectable and paste formulations, respectively. Levels of 4th-stage Cylicocyclus spp larvae, as detected in the luminal contents of the colon, were reduced by 88.3% and 33.2% by the injectable and paste formulations, respectively. There were no adverse tissue or behavioral reactions induced by either preparation of ivermectin.

Anthelmintic activities of ivermectin against gastrointestinal nematodes of cattle

The anthelmintic efficacy of ivermectin, a combined solution of the B1a and B1b fractions of avermectin, was assessed in a controlled trial. Twenty-four yearling calves experiencing naturally acquired, clinical gastrointestinal helminthiasis were evenly divided on the basis of weight into two 12-animal groups. The medicated group was given (subcutaneously) ivermectin at the dose rate of 200 microgram/kg of body weight. The control animals were given the vehicle alone, at an equivalent rate. All animals were killed 14 days later. At necropsy of the calves, gastrointestinal helminth arithmetic means were 178,626 and 575 for the control and the treated groups, respectively, an overall reduction of 99.7%. Nematodes which were present at substantial levels were Ostertagia ostertagi, O lyrata, Trichostrongylus axei, Cooperia punctate, C oncophora, C mcmasteri, and Oesophagostomum radiatum. Anthelmintic activity of ivermectin was excellent regardless of nematode species, sex, or stage of development.