Abstract P3-11-07: Inhibition of FASN as a potential treatment of advanced endocrine therapy-resistant breast cancer
Authors: Balinda Henriette 
Published: March 2023

Abstract
INTRODUCTION: The past decade has seen significant advancement in increasing survival in estrogen receptor alpha (ERα) positive breast cancer. The use of selective estrogen receptor down-regulators and modulators (SERMs) (e.g. fulvestrant and tamoxifen), mTOR inhibitors (e.g. everolimus), aromatase inhibitors (AIs), and cyclin-dependent kinase inhibitors (e.g. palbociclib, ribociclib, and abemaciclib) have helped to extend overall survival of breast cancer patients. Unfortunately, resistance to endocrine therapy is a common occurrence and all patients will eventually succumb to their disease. Fatty acid synthase (FASN) is a key enzyme in lipid biosynthesis and is overexpressed in more aggressive and therapy-resistant tumors, including breast cancers. FASN inhibitor, TVB-2640, has been evaluated in multiple tumor cell lines and in a phase 1 clinical study, and showed partial responses in 5 patients and multiple patients with prolonged stable disease (≥16 weeks). METHODS: We generated tamoxifen- and fulvestrant-resistant MCF7 cells by long term exposure to tamoxifen (MCF7/TamR cells) and fulvestrant (MCF7/FR cells), and palbociclib-resistant (MCF7/RB1Crispr and ZR75/RB1Crispr) cells were generated through CRISPR/Cas9 knockout of the retinoblastoma (RB) gene. We assessed the impact of TVB-3166 inhibitor (and analog of TVB-2640 with slightly lower molecular weight for in vitro use) on proliferation, viability, cell cycle, and apoptosis in these cells. We evaluated the impact of TVB on proliferation and ERα expression in patient derived explants, and tumor growth in xenografts. RNA sequencing of tamoxifen- and fulvestrant-resistant cells was performed to investigate alterations in gene expression. Subcellular localization of ERα was assessed using subcellular fractionations. Palmitoylation and ubiquitination of ERα were assessed by immunoprecipitation. ERα and p-eIF2α protein levels were analyzed by western blotting after treatment with TVB with or without the addition of palmitate or BAPTA. RESULTS: TVB treatment leads to a marked inhibition of proliferation in tamoxifen-, fulvestrant- and palbociclib-resistant cells compared to the parental cells. RNA sequencing of explants of patients with ERα positive disease showed down regulation of ESR1 related genes and genes involved in invasiveness. RNA sequencing of fulvestrant-resistant cells showed that treatment with TVB results in down regulation of EMT and E2F target genes, cholesterol homeostasis genes and mTORC1 signaling. Additionally, TVB significantly inhibited tumor growth in mice and decreased proliferation of primary tumor explants compared to untreated controls. FASN inhibition significantly reduced ERα levels most prominently in endocrine resistant cells and altered its subcellular localization. Furthermore, we showed that the reduction of ERα expression upon TVB treatment is mediated through the induction of endoplasmic reticulum stress in tamoxifen-resistant cells. CONCLUSION: Our preclinical data provide evidence that FASN inhibition by TVB-3166 presents a promising therapeutic strategy for treatment of endocrine-resistant breast cancer. Further clinical development of FASN inhibitors for endocrine resistant breast cancer should be considered.
Citation Format: Henriette Balinda. Inhibition of FASN as a potential treatment of advanced endocrine therapy-resistant breast cancer [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P3-11-07.