Identification of a targetable JAK-STAT enriched androgen receptor and androgen receptor splice variant positive triple-negative breast cancer subtype

Triple-negative breast cancer (TNBC) is an aggressive subtype with no targeted therapeutics. The luminal androgen receptor (LAR) subtype constitutes 15% of TNBC and is enriched for androgen receptor (AR) and AR target genes. Here, we show that a cohort of TNBC not only expresses AR at a much higher rate (∼80%) but also expresses AR splice variants (AR-SVs) (∼20%), further subclassifying LAR-TNBC. Higher AR and AR-SV expression and corresponding aggressive phenotypes are observed predominantly in specimens obtained from African American women. LAR TNBC specimens are enriched for interferon, Janus kinase (JAK)-signal activator and transducer (STAT), and androgen signaling pathways, which are exclusive to AR-expressing epithelial cancer cells. AR- and AR-SV-expressing TNBC cell proliferation and xenograft and patient-tumor explant growth are inhibited by AR N-terminal domain-binding selective AR degrader or by a JAK inhibitor. Biochemical analysis suggests that STAT1 is an AR coactivator. Collectively, our work identifies pharmacologically targetable TNBC subtypes and identifies growth-promoting interaction between AR and JAK-STAT signaling.

Abstract 1777: Androgen receptor (AR) agonists inhibit AR- and estrogen-receptor-positive breast cancer

Introduction: Breast cancer is the most common cancer diagnosed in women. About 13% of women will develop invasive breast carcinoma in their lifetime and it is estimated that about 280,000 new cases will be diagnosed in 2021. Seventy-percent of diagnosed breast cancers are estrogen receptor (ER)-positive and about 90% of the ER-positive breast cancers are androgen receptor (AR)-positive. We have previously shown that AR agonists inhibit ER-positive breast cancer growth by sequestering the pioneer-transcription factor FOXA1 from ER-cistrome. Tissue-selective AR modulators (SARMs) such as enobosarm are in clinical trials to treat ER-positive breast cancers. Since resistance is a major impediment to sutained treatment, it is important to identify new therapeutic strategies and their mechanisms of resistance. Here, we evaluated the possible mechanisms of resistance to AR agonists in ER-positive breast cancer.

Description: ER-positive breast cancer cell line xenografts and patient-derived xenografts (PDX) were used as experimental models. Once tumors grew to ~100-300 mm3, mice were randomized and treated orally with vehicle or enobosarm (30 mg/kg/day). Animals were sacrificed after 4 weeks when the tumors responded to treatment and after 10 weeks once resistance developed to treatment. Tumor volumes were measured twice weekly and tumors were collected at sacrifice for further analyses. RNA-seq and ChIP-seq were performed on tumor tissues.

Summary: AR agonists, enobosarm and dihydrotestosterone (DHT), inhibited the proliferation of ER-positive breast cancer cells ZR-75-1 and T47D. Transcriptome analysis revealed that AR agonists activate AR in ER-positive breast cancer cells and inhibit ER-target gene signature. AR agonists inhibited the growth of breast cancer cell line xenograft T47D and breast cancer PDXs HCI-7 that express wildtype ER, and HCI-13 and WHIM-23, two models that express Y537S mutant ER. Treatment of WHIM-23 and T47D xenograft for over ten weeks resulted in resistance and regrowth. AR agonist-sensitive and -resistant tumors were analyzed using RNA-seq, ChIP-seq, and ATAC-seq to understand the mechanism of resistance development. The results indicate that the prolonged activation of AR will result in resistance. These mechanisms of resistance can be utilized as possible therapeutic targets.

Conclusion: These results suggest that the AR is a promising therapeutic target in the treatment of ER-positive breast cancer. However, resistance development is possible with AR agonists and the mechanism provides suggestions for future combination therapies.

Disclosure: This work was supported by an NCI grant (CA229164 and CA229164S1 to RN) and by a DOD grant (W81XWH2110055 to RN).

Citation Format: Sarah Asemota, Suriyan Ponnusamy, Thirumagal Thiyagarajan, Ramesh Narayanan. Androgen receptor (AR) agonists inhibit AR- and estrogen-receptor-positive breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1777.

Abstract 1235: Selective androgen receptor degraders for the treatment of androgen receptor-positive, triple-negative breast cancer

Introduction: Triple-negative breast cancer (TNBC) is an aggressive breast cancer with shorter overall survival compared to other breast cancer types. One of the six molecularly-classified TNBC subtypes is the luminal androgen receptor subtype (LAR), which overexpresses androgen receptor (AR) and is dependent on AR for its growth. About 10-20% of TNBCs belong to the LAR subtype. Competitive AR antagonists, enzalutamide and bicalutamide, were effective in preclinical models of LAR TNBC and in clinical trials. This led us to hypothesize that potent selective AR degraders (SARDs), due to their ability to inhibit and degrade the AR, could provide a novel therapeutic approach for the treatment of LAR subtype of TNBC.

Description: Western blots, cell line proliferation assays, and gene expression analyses were performed to evaluate novel small molecule SARDs. LAR TNBC cell lines and patient-derived xenografts (PDX) were utilized for in vivo evaluation of the SARDs. Once tumors grew to ~100-300 mm3, mice were randomized and treated orally for four weeks with vehicle, SARD UT-34, SARD UT-105, enzalutamide, or bicalutamide. Tumor volumes were measured twice weekly and tumors were collected at sacrifice for further analyses.

Summary: SARDs bind to the N-terminus of the AR and have been characterized in preclinical advanced prostate cancer models. In this study, the SARDs were evaluated in preclinical models of LAR TNBC. Western blot for AR in LAR MDA-MB-453 cells demonstrated degradation of the AR protein by SARDs at low micromolar concentrations. Gene expression studies showed a complete inhibition of androgen-induced AR target gene transcription by the SARDs. Androgen-induced proliferation of MDA-MB-453 cells was inhibited by SARDs. MDA-MB-453 cells implanted subcutaneously in NOD SCID Gamma female mice grew robustly to 100-300 mm3 in 15-20 days. Treatment of tumor-bearing animals with the SARDs completely inhibited or regressed the tumors.

Conclusion: These results support the findings that AR is the driver of MDA-MB-453 cell and tumor growth. SARDs with their unique mechanism of action may provide a new therapeutic option to women affected by the LAR subtype of TNBC.

Disclosure: This work was partially supported by Oncternal Therapeutics and by an NCI supplement award to R01 (CA229164S1 to author RN). The SARD program has been licensed to Oncternal Therapeutics, Inc. by the University of Tennessee Research Foundation. Author RN is a consultant to Oncternal Therapeutics.

Citation Format: Sarah Asemota, Kirsten Young Young, Suriyan Ponnusamy, Thirumagal Thiyagarajan, Dong-Jin Hwang, Yali He, James B. Breitmeyer, Gunnar F. Kaufmann, Duane D. Miller, Ramesh Narayanan. Selective androgen receptor degraders for the treatment of androgen receptor-positive, triple-negative breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1235.

Immune checkpoint blockade reprograms systemic immune landscape and tumor microenvironment in obesity-associated breast cancer

Immune checkpoint blockade (ICB) has improved outcomes in some cancers. A major limitation of ICB is that most patients fail to respond, which is partly attributable to immunosuppression. Obesity appears to improve immune checkpoint therapies in some cancers, but impacts on breast cancer (BC) remain unknown. In lean and obese mice, tumor progression and immune reprogramming were quantified in BC tumors treated with anti-programmed death-1 (PD-1) or control. Obesity augments tumor incidence and progression. Anti-PD-1 induces regression in lean mice and potently abrogates progression in obese mice. BC primes systemic immunity to be highly responsive to obesity, leading to greater immunosuppression, which may explain greater anti-PD-1 efficacy. Anti-PD-1 significantly reinvigorates antitumor immunity despite persistent obesity. Laminin subunit beta-2 (Lamb2), downregulated by anti-PD-1, significantly predicts patient survival. Lastly, a microbial signature associated with anti-PD-1 efficacy is identified. Thus, anti-PD-1 is highly efficacious in obese mice by reinvigorating durable antitumor immunity. VIDEO ABSTRACT.

Integrin-Linked Kinase Is a Novel Therapeutic Target in Ovarian Cancer

OBJECTIVE

The objective of this study is to identify and validate novel therapeutic target(s) in ovarian cancer.

BACKGROUND

Development of targeted therapeutics in ovarian cancer has been limited by molecular heterogeneity. Although gene expression datasets are available, most of them lack appropriate pair-matched controls to define the alterations that result in the transformation of normal ovarian cells to cancerous cells.

METHODS

We used microarray to compare the gene expression of treatment-naïve ovarian cancer tissue samples to pair-matched normal adjacent ovarian tissue from 24 patients. Ingenuity Pathway Analysis (IPA) was used to identify target pathways for further analysis. Integrin-linked kinase (ILK) expression in SKOV3 and OV90 cells was determined using Western blot. ILK was knocked down using CRISPR/Cas9 constructs. Subcutaneous xenograft study to determine the effect of ILK knockdown on tumor growth was performed in NOD SCID gamma mice.

RESULTS

Significant upregulation of the ILK pathway was identified in 22 of the 24 cancer specimens, identifying it as a potential player that could contribute to the transformation of normal ovarian cells to cancerous cells. Knockdown of ILK in SKOV3 cells resulted in decreased cell proliferation and tumor growth, and inhibition of downstream kinase, AKT (protein kinase B). These results were further validated using an ILK-1 chemical inhibitor, compound 22.

CONCLUSION

Our initial findings validate ILK as a potential therapeutic target for molecular inhibition in ovarian cancer, which warrants further investigation.

Abstract 5044: Integrin-linked kinase gene knockdown results in decreased growth of ovarian cancer xenograft models

Integrin-linked kinase (ILK) is overexpressed in ovarian cancer cells. In the present study, we sought to assess the effect of ILK silencing on ovarian cancer cell proliferation using shRNA. Our lab previously demonstrated that phosphorylation of ILK acts as a proliferative signal in a variety of ovarian cancer cell lines. Cytotoxicity of ILK knockdown using shRNA was analyzed in vitro using SKOV3 cell lines. Transfected cells were incubated in Incucyte®, which allowed for simultaneous assessment of viable cells at the end of the incubation period using CellTiter glo assay. Knockdown of ILK using shRNA significantly inhibited the proliferation of SKOV3 cells. SKOV3 cells were then infected with lentivirus expressing ILK shRNA to obtain stable knockdown of ILK, which was confirmed with Western blot. Both parental and ILK shRNA infected cells were injected subcutaneously in NOD SCID Gamma immunocompromised mice. Tumor growth was assessed by sequential tumor measurements and final weights. Xenograft data indicated significantly decreased tumor volume over multiple time points in the transfected cells (p <0.0001) (Figure 1). Average final volume for the ILK-shRNA group (n = 15) and control group (n = 13) was 660mm3 (SD = 366.7, range 271 - 1667 mm3) and 1165 mm3 (SD = 668.7, range 506 - 2664 mm3), respectively. Similarly, average tumor weight was less for the ILK-shRNA group (404.4mg [range 226.1 - 801mg]) relative to control (584.3mg [range 293.2 - 1033.4mg]). Our findings demonstrate that knockdown of ILK in ovarian cancer cell lines results in decreased cell proliferation, as well as decreased tumor growth in xenograft models. This supports the role for further investigation into ILK as a potential therapeutic target in ovarian cancer.

Days From Tumor Implantation1214161921232628313438VectorAverage Tumor Volume (mm^3)142.4151.6203274.7379.3482.1671.4741.2845.11083.81164.6Standard Error26.983.430.835.759.682112.3110.7133.9172.2185.5ILK-shRNAAverage Tumor Volume (mm^3)45.9107.282.4113150.9177263.4345.2397.3568.8659.9Standard Error6.39.99.915.225.822.841.558.455.19994.7

Citation Format: Tiffany Redfern, Benjamin Wilson, Michael Ulm, Adam ElNaggar, Suriyan Ponnusamy, Yinan Wang, Sarah Asemota, Ramesh Narayanan. Integrin-linked kinase gene knockdown results in decreased growth of ovarian cancer xenograft models [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 5044.

Androgen Receptor Is a Non-canonical Inhibitor of Wild-Type and Mutant Estrogen Receptors in Hormone Receptor-Positive Breast Cancers

Sustained treatment of estrogen receptor (ER)-positive breast cancer with ER-targeting drugs results in ER mutations and refractory unresponsive cancers. Androgen receptor (AR), which is expressed in 80%–95% of ER-positive breast cancers, could serve as an alternate therapeutic target. Although AR agonists were used in the past to treat breast cancer, their use is currently infrequent due to virilizing side effects. Discovery of tissue-selective AR modulators (SARMs) has renewed interest in using AR agonists to treat breast cancer. Using translational models, we show that AR agonist and SARM, but not antagonist, inhibit the proliferation and growth of ER-positive breast cancer cells, patient-derived tissues, and patient-derived xenografts (PDX). Ligand-activated AR inhibits wild-type and mutant ER activity by reprogramming the ER and FOXA1 cistrome and rendering tumor growth inhibition. These findings suggest that ligand-activated AR may function as a non-canonical inhibitor of ER and that AR agonists may offer a safe and effective treatment for ER-positive breast cancer.

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Androgen receptor (AR) agonists inhibit estrogen receptor (ER)-positive breast cancer

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Activating AR reprograms ER and FOXA1 cistrome, resulting in ER inhibition

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AR agonist alters the phosphoproteome signature consistent with growth inhibition