Abstract A010: Development and characterization of novel models of lobular breast cancer metastases
Authors: Sottnik Joseph L. , Sikora Matthew J. 
Published: November 2024

Abstract
Invasive lobular carcinoma (ILC) is the most common special histological subtype of breast cancer, after No Special Type (NST, ductal carcinoma/IDC), and affects 10-15% of all breast cancer patients. ILC is characterized by E-cadherin loss, Estrogen Receptor (ER) positivity, and a distinct single file invasive growth pattern associated with a unique pattern of metastasis. ILC metastasizes to common breast cancer sites like bone and lung, but ILC also spreads to gynecologic tissues, the peritoneum, gastrointestinal tract and central nervous system - with enrichment for orbital and leptomeningeal metastases. In vitro and in vivo models of ILC metastasis have not been extensively developed. Models of spontaneous metastasis from ER+ breast cancer overall are critically limited; ER+ ILC metastases models present only micro-metastatic disease with extremely long latency (&gt;9 months). Together these issues limit research on the unique nature of metastatic ILC. We leveraged mammary intraductal (MIND) xenografting with two ER+ ILC cell lines (MM134 and 44PE) and confirmed prior reports that these lines spontaneously metastasize to bone, brain, ovary, uterus, lung, and adrenal glands with up to 100% incidence. Importantly, we find that supplementation with low dose estradiol (E2) in drinking water rapidly advances metastatic progression, but not primary tumor growth. Using ex vivo bioluminescence imaging (BLI), we find BLI+ lesions are detectable as early as 90 days. At 150 days post-challenge, 100% of mice have BLI+ metastases at multiple sites. Beyond 22 weeks, 100% of mice present with symptomatic and ultimately lethal CNS metastases. BLI+ macro-metastatic lesions were isolated and expanded ex vivo as organotrophic cell line variants. Analysis of RNA-seq data is ongoing to evaluate 1) common factors enriched in metastatic ILC, and 2) organotrophic factors and pathways enriched in specific metastatic sites. In patients with ILC, bone metastases are typically the first site of metastatic development, occur at a higher incidence versus NST, and are associated with increased morbidity. Bone metastases from ILC patients are more osteogenic compared to the characteristically osteolytic lesions of NST. To examine how ILC cells may promote osteoblastic responses, we prepared ILC and NST conditioned media (CM) and applied it to differentiating osteoblasts (OB). We observed increased OB differentiation and increased mineral deposition with ILC CM compared to NST CM, supporting that ILC cell lines have a distinct impact on the bone microenvironment which may manifest in vivo yet be defined in vitro. Collectively, our observations support that ER+ ILC cell lines can recapitulate key features of clinical disease progression, including spontaneous metastasis mimicking clinical phenotypes. We are leveraging these models to better understand the ILC metastatic cascade and adaptation to unique metastatic niches, and to identify shared and unique attributes of ILC metastases that can be exploited for advancing therapeutics.
Citation Format: Joseph L. Sottnik, Matthew J. Sikora. Development and characterization of novel models of lobular breast cancer metastases [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Tumor-body Interactions: The Roles of Micro- and Macroenvironment in Cancer; 2024 Nov 17-20; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2024;84(22_Suppl):Abstract nr A010.