<div>Abstract<p>No special-type breast cancer [NST; commonly known as invasive ductal carcinoma (IDC)] and invasive lobular carcinoma (ILC) are the two major histological subtypes of breast cancer with significant differences in clinicopathological and molecular characteristics. The defining pathognomonic feature of ILC is loss of cellular adhesion protein, E-cadherin (<i>CDH1</i>). We have previously shown that E-cadherin functions as a negative regulator of the IGF1R and propose that E-cadherin loss in ILC sensitizes cells to growth factor signaling that thus alters their sensitivity to growth factor–signaling inhibitors and their downstream activators. To investigate this potential therapeutic vulnerability, we generated CRISPR-mediated <i>CDH1</i> knockout (<i>CDH1</i> KO) IDC cell lines (MCF7, T47D, and ZR75.1) to uncover the mechanism by which loss of E-cadherin results in IGF pathway activation. <i>CDH1</i> KO cells demonstrated enhanced invasion and migration that was further elevated in response to IGF1, serum and collagen I. <i>CDH1</i> KO cells exhibited increased sensitivity to IGF resulting in elevated downstream signaling. Despite minimal differences in membranous IGF1R levels between wild-type (WT) and <i>CDH1</i> KO cells, significantly higher ligand–receptor interaction was observed in the <i>CDH1</i> KO cells, potentially conferring enhanced downstream signaling activation. Critically, increased sensitivity to IGF1R, PI3K, Akt, and MEK inhibitors was observed in <i>CDH1</i> KO cells and ILC patient-derived organoids.</p>Implications:<p>Overall, this suggests that these targets require further exploration in ILC treatment and that <i>CDH1</i> loss may be exploited as a biomarker of response for patient stratification.</p></div>
Abstract Invasive Ductal Carcinoma (IDC) and Invasive Lobular Carcinoma (ILC) are two major subtypes of breast cancer with significant differences in their histological and molecular underpinnings. ILC has a unique loss of E-cadherin (CDH1) which we have previously demonstrated as a negative regulator of the Insulin-like Growth Factor 1 receptor (IGF1R) through a comprehensive analysis of cell line models and tumor samples. We propose that loss of E-cadherin in ILC sensitizes cells to growth factor signaling and thus alters their sensitivity to growth factor signaling inhibitors. To investigate this, we used CRISPR to generate CDH1 knockout (KO) IDC cell lines (MCF7, T47D, ZR75.1) to uncover the mechanism by which E-cadherin loss activates the IGF pathway while also assessing its targetability. CDH1 KO cells exhibited anchorage independent growth in suspension culture and altered p120 catenin localization as observed in ILC tumors. Through in vitro studies, we show increased signaling sensitivity to IGF/insulin ligands and enhanced signaling duration in CDH1 KO cells. In addition, we observed a higher migratory potential of CDH1 KO cells compared to wild type (WT) cells, which was further enhanced as a chemotactic response to IGF1 or serum. Further, this phenotype could be reversed with an IGF1R inhibitor, BMS-754807. We additionally identified an increase in Collagen I haptotaxis in the CDH1 KO cells, which was also translated into a novel invasive phenotype towards serum in the T47D CDH1 KO cells. Despite no significant differences in membranous IGF1R levels between WT and CDH1 KO cells, higher ligand-receptor interaction was observed with CDH1 KO cells, demonstrating an increased ligand-receptor complex formation upon stimulation. Our results suggest that loss of CDH1 results in an increase in IGF1 receptor availability for ligand binding which in turn allows for an enhanced downstream signaling activation. Interestingly, a physical repression of E-cadherin on IGF1R could not be demonstrated, suggesting spatial changes on the membrane following E-cadherin loss may control ligand binding. Critically, increased sensitivity to IGF1R, PI3K, AKT and MEK inhibitors was observed in CDH1 KO cells suggesting that these targets should be further explored in ILC and that CDH1 loss may be exploited as a biomarker of response, or for patient stratification to inhibitors targeting these pathways. Citation Format: Ashuvinee Elangovan, Laura Savariau, Megan E. Yates, Jagmohan Hooda, Alison M. Nagle, Steffi Oesterreich, Jennifer M. Atkinson, Adrian V. Lee. Loss of E-cadherin induces IGF1R activation revealing a targetable pathway in invasive lobular breast carcinoma [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 2690.
Abstract The molecular events and transcriptional plasticity driving brain metastasis in clinically relevant breast tumor subtypes has not been determined. Here we comprehensively dissect genomic, transcriptomic and clinical data in patient-matched longitudinal tumor samples, and unravel distinct transcriptional programs enriched in brain metastasis. We report on subtype specific hub genes and functional processes, central to disease-affected networks in brain metastasis. Importantly, in luminal brain metastases we identify homologous recombination deficiency operative in transcriptomic and genomic data with recurrent breast mutational signatures A, F and K, associated with mismatch repair defects, TP53 mutations and homologous recombination deficiency (HRD) respectively. Utilizing PARP inhibition in patient-derived brain metastatic tumor explants we functionally validate HRD as a key vulnerability. Here, we demonstrate a functionally relevant HRD evident at genomic and transcriptomic levels pointing to genomic instability in breast cancer brain metastasis which is of potential translational significance.
Abstract Invasive lobular carcinoma (ILC) is a histological subtype of breast cancer with distinct molecular and clinical features from the more common subtype invasive ductal carcinoma (IDC). ILC cells exhibit anchorage-independent growth in ultra-low attachment (ULA) suspension cultures, which is largely attributed to the loss of E-cadherin. In addition to anoikis resistance, herein we show that human ILC cell lines exhibit enhanced cell proliferation in ULA cultures as compared to IDC cells. Proteomic comparison of ILC and IDC cell lines identified induction of PI3K/Akt and p90-RSK pathways specifically in ULA culture in ILC cells. Further transcriptional profiling uncovered unique upregulation of the inhibitors of differentiation family transcription factors ID1 and ID3 in ILC ULA culture, the knockdown of which diminished the anchorage-independent growth of ILC cell lines through cell cycle arrest. We find that ID1 and ID3 expression is higher in human ILC tumors as compared to IDC, correlated with worse prognosis uniquely in patients with ILC and associated with upregulation of angiogenesis and matrisome-related genes. Altogether, our comprehensive study of anchorage independence in human ILC cell lines provides mechanistic insights and clinical implications for metastatic dissemination of ILC and implicates ID1 and ID3 as novel drivers and therapeutic targets for lobular breast cancer.
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