Wang, Sarah

Invasive lobular breast carcinoma (ILC), the most common special histological subtype of breast cancer, is characterized by nearly universal expression of estrogen receptor alpha (ER) and unique sites of metastases, neither of which is fully recapitulated by genetically engineered mouse models. Using reporter-labeled ILC mouse xenografts, herein we used mammary fat pad, tail vein and intracardiac orthotopic growth to analyze spontaneous and experimental metastasis and gene expression. We observed ER-positive primary tumors with single-file histology and collagen deposition, and spontaneous metastasis from the mammary fat pad to bones, ovaries, and brain including the leptomeninges, thereby closely mirroring the growth and metastatic spread of human ILC. Brain metastases showed strong ER staining, confirmed by sequencing analyses which identified estrogen signaling as top activated pathway, and the lesions exhibited robust response to endocrine therapy. In summary, we report endocrine responsive mammary fat pad, tail vein and intracardiac xenografts that faithfully demonstrate unique ILC features and can serve as invaluable pre-clinical translational platforms for validating candidate ILC genetic drivers and testing novel therapeutics.

Abstract Invasive lobular carcinoma (ILC) accounts for 10-15% of all breast cancers, making it the most common special histological subtype of breast cancer. Initially, ILC is associated with a better response to adjuvant hormonal therapy compared to invasive ductal breast cancer (IDC). However, patients with ILC often experience a worse long-term outcome. Over 90% of ILCs are estrogen receptor positive (ER+) and do not express functional E-cadherin (CDH1). There are limited studies aimed at improved understanding of the tumor microenvironment (TME) in ILC. Therefore, we set out to generate and characterize a syngeneic mouse cell line model that mimics the genetic loss of CDH1 seen in ILC. We created an ER+ ILC-like mammary cancer model using the syngeneic SSM3 cell line, derived from an ER+ mouse mammary tumor in STAT1-deficient mice. To mimic the hallmark feature of ILC, we used CRISPR-Cas9 to knock out Cdh1. In vitro assays were performed to evaluate the effects of Cdh1 knockout (KO) in both 2D and 3D environments, focusing on cell proliferation and estrogen sensitivity. These experiments demonstrated increased growth of Cdh1 KO SSM3 cells in both 2D and 3D environments, together with altered cell morphology and increased sensitivity to estrogen.For in vivo characterization, we focused on tumor growth and metastasis. SSM3 Scr and Cdh1 KO cells were injected into the mammary fat pad of mice. Initial findings revealed increased tumor growth in mice injected with SSM3 Cdh1 KO cells, while metastasis studies are ongoing. RNA-seq analysis of both SSM3 cells grown in vitro, and in vivo tumor tissues is ongoing and will help to identify distinctive gene expression changes in the Cdh1 KO model. We will also analyze changes in the TME, such as immune cells, ECM and fibroblasts. In summary, we have successfully generated an ER+ syngeneic ILC model, and we expect that growing the cells in vitro and in vivo represents a valuable tool for studying ILC and holds promise for advancing the development of targeted immunotherapies and endocrine therapies for this breast cancer subtype. Citation Format: Insa Thale, Dixcy J. John Mary, Sarah Wang, Lora Rigatti, Jagmohan Hooda, Peter Lucas, George C. Tseng, Adrian V. Lee, Steffi Oesterreich. In vitro and in vivo characterization of Cdh1 CRISPR knockout in syngeneic ER+ SSM3 mouse mammary tumor cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 3925.

Abstract Background: Most patients with advanced OC relapse after initial standard platinum-based chemotherapy, and eventually the disease becomes platinum-resistant. Niraparib (ZEJULA®) was the first selective poly(ADP-ribose) polymerase inhibitor (PARPi) approved in the United States and Europe for maintenance treatment in patients with recurrent OC regardless of BRCA mutation status. Preclinical evidence suggests that niraparib activates the stimulator of interferon genes pathway to increase immune cell infiltration and synergizes with anti-PD-1 therapy. Additionally, hypoxia induces contextual synthetic lethality by impairing homologous recombination, and therefore induction of hypoxia by inhibition of angiogenesis could lead to synergy with PARPi. In the TOPACIO/KEYNOTE-162 trial, niraparib in combination with pembrolizumab has shown efficacy in recurrent, platinum-resistant OC. Niraparib in combination with the anti-angiogenic agent bevacizumab is under study for the treatment of recurrent platinum-sensitive OC (AVANOVA trial) and advanced OC following response on frontline platinum-based chemotherapy (OVARIO trial). TSR-042 is an anti-PD-1 humanized monoclonal antibody that has shown clinical activity as monotherapy in early phase trials. Cohort A of the OPAL trial will evaluate the novel triple combination of the PARPi niraparib, angiogenesis inhibitor bevacizumab, and PD-1 inhibitor TSR-042 in patients with platinum-resistant OC who are naïve to PARPi therapy. Methods: Eligible patients will have high-grade recurrent epithelial ovarian, fallopian tube, or primary peritoneal cancer of the ovary and progressed ≤6 months from completion of ≥4 cycles of platinum-based chemotherapy. Additional key eligibility criteria include 1-2 prior lines of anticancer therapy for OC, no prior therapy with an anti-PD-1 or anti-PD-L1 antibody, and no prior therapy for OC with a PARPi. Patients will receive a combination regimen of 500 mg TSR-042 on day 1 of each 3-week cycle for 4 cycles, then 1000 mg on day 1 of every other cycle beginning on cycle 5 until progression or toxicity, 15 mg/kg bevacizumab on day 1 of each 3-week cycle for up to 15 months, and niraparib 300 mg or 200 mg (for patients <77 kg or platelet count <150,000/µL at screening) daily until disease progression or toxicity. The primary endpoint is to evaluate treatment efficacy by confirmed objective response rate per investigator-assessed RECIST v1.1 criteria. Secondary objectives are evaluation of progression-free survival, overall survival, duration of response, and disease control rate. Exploratory objectives are to identify potential biomarkers of tumor response, including BRCA status and homologous recombination repair gene status and to evaluate the evolution of the molecular profile of the tumor and tumor microenvironment in response to treatment. Clinical trial identification: NCT03574779 Citation Format: Joyce Liu, Camille Gunderson, Andrea Wahner Hendrickson, Elena Ratner, Elisabeth Diver, John Moroney, Rebecca C. Arend, Melinda Louie-Gao, Sarah Wang, Katarina Luptakova, Gottfried E. Konecny. An open-label Phase II study of combination of TSR-042, bevacizumab, and niraparib in patients with platinum-resistant ovarian cancer (OC): Cohort A of the OPAL trial [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr CT157.