Abstract PO4-13-10: The anti-metastatic role of BMP4 through cholesterol biosynthesis inhibition and consequent interaction with statin benefit in breast cancer
Authors: Chi Lap Hing , Redfern Andrew , Burrows Allan , Roslan Suraya , Oh Leone , Spalding Lisa , Anderson Robin 
Published: May 2024

Abstract
We have previously identified a role for bone morphogenic protein 4 (BMP4) in reducing distant relapse risk after early breast cancer (BrCa) (1). We therefore set out to identify mechanisms underlying the protective effect of BMP4, looking to translate this finding for patient benefit.
A highly metastatic variant of the triple negative MDA-MB-231 human BrCa line (231-HM-turboGFP) was transduced with BMP4, leading to sustained BMP4 secretion. These modified tumours were established in NSG mice, resected at a given size and turboGFP-positive cancer cells were recovered from primary tumours for RNA sequencing analysis. Gene set enrichment analysis (GSEA) was completed to identify signalling pathways that were significantly modulated by BMP4. The four most significantly downregulated gene sets were associated with cholesterol synthesis, with the overwhelming majority of genes in this pathway being downregulated. BMP4 downregulation of 3-hydroxy-3-methylglutaryl-CoA synthase 1 (HMGCS1, involved in cholesterol biosynthesis) was confirmed at the protein level by western blotting on whole tumour lysates. Forced expression of BMP4 also led to a significant reduction in the levels of free and total cholesterol. In a confirmatory analysis of the METABRIC human BrCa dataset, the expression of cholesterol biosynthesis-related genes inversely correlated with the expression of BMP4. Further, for the majority of these genes, expression was elevated in high-grade breast tumours, and predicted worse overall survival of patients. Finally, we tested the effect of a lipophilic statin, lovastatin, on the growth and metastasis of 231-HM-turboGFP tumours. Treatment did not affect the growth of primary tumours but significantly less metastases were observed in the lungs of treated mice, at least partially replicating the anti-metastatic effect of BMP4.
Having identified inhibition of cholesterol biosynthesis as a potential mechanism of protective BMP4 action we then asked if BMP4 status interacted with any protective effect of co-administered statins. We therefore returned to the cohort initially employed to demonstrate BMP4 benefit (1) and looked at the interaction between BMP4 protein levels and statin usage with regards to recurrence. BMP4 protein and statin usage data were available on a cohort of 417 patients with early BrCa. Statin use compared to none led to a reduced risk of distant relapse (8 v 22%, 0.0029) at 15 years. BMP4 led to borderline reduction in distant relapse (16 v 24%, p=0.052). In BMP4 negative tumours, statin protected against any relapse (p=0.0025) whereas in BMP4 positive disease no significant risk reduction was not significant (p=0.074). Absence of BMP4 expression may be a biomarker of both higher relapse risk and statin benefit in early BrCa.
1. Eckhardt et al, Cancer Res. 2020;80(6):1304-1315
Citation Format: Lap Hing Chi, Andrew Redfern, Allan Burrows, Suraya Roslan, Leone Oh, Lisa Spalding, Robin Anderson. The anti-metastatic role of BMP4 through cholesterol biosynthesis inhibition and consequent interaction with statin benefit in breast cancer [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO4-13-10.