Abstract P5-10-02: High expression of BAD, PUMA, BOK and TRADD mRNA is associated with higher overall survival in ER+ and PR+ breast cancer patients
Authors: Lindner AU , Lucantoni F , Vareslija D , Resler A , Gallagher WM , Hill A , Young L , Prehn JHM 
Published: February 2018

Background: Apoptosis signalling is controlled by a complex interaction of pro- and anti-apoptotic BCL2 proteins and its dysregulation is believed to be a major contributor to therapy responses and resistance in cancer. We previously demonstrated that inhibition of cell death in cancer cell is associated to poor outcome in colorectal cancer (Lindner et al., Cancer Res, 2012) and to lower cell death in triple negative breast cancer (TNBC) cells in vitro (Lucantoni et al., in review). In ER+ breast cancer, the anti-apoptotic protein BCL2 is commonly overexpressed, but its expression is associated with improved clinical outcome. The aim of this study was to assess whether system modelling of BCL2 protein interactions stratifies low- and high-risk breast cancer patients, and to determine the contribution of apoptosis signalling in different molecular subtypes of breast cancer.

Methods: Protein levels of BAK, BAX, BCL2 and BCL(X) were determined in fresh frozen, TNBC samples from the BREAST-PREDICT Irish Cancer Society Collaborative Research Centre cohort, using HeLa cells as standard in which absolute protein levels were previously determined. Clinical, protein level and gene expression datasets of 845 invasive breast carcinoma patients were accessed from The Cancer Genome Atlas project, and BCL2 protein profiles were calculated by linear regression based on the BREAST-PREDICT cohort. In both cohorts, profiles were used to calculate the stress dose required to induce mitochondrial apoptosis (η).

Results: In contrast to experiments with TNBC cells in which a high η indicated lower rates of cell death in vitro (Lucantoni et al., in review), we found that in breast cancer patients, η ≤ 0 was associated with lower overall survival (OS) compare to η &gt; 0 (HR 2.1, 95%CI 1.3-3.3, p &lt; 0.01). η &gt; 0 was associated with lower levels of cleaved caspase 7 compared to η ≤ 0 (ANOVA & Tukey post-hoc; p &lt; 0.1). Cleaved caspase 7 levels &gt; mean were associated with improved OS compared to levels ≤ mean (HR 0.4, 95%CI 0.3-0.7, p = 0.001). High values of η were significantly associated with lower proliferation in ER/PR+ cancer (ANOVA & Tukey post-hoc; p &lt; 0.01), but not in HER2+ or TNBC. Next we performed hierarchical cluster analysis (ConsensusClusterPlus; Monti et al, Machine Learning, 2003) with 61 additional mRNAs and proteins which are not implemented in our systems modelling approach. We found a subgroup with high BAD, PUMA, BOK and TRADD mRNA expression levels in ER/PR+ breast cancer patients, independently of the value of η. ER/PR+, but not HER2+ or TNBC, patients with an averaged expression of these 4 mRNA &gt; mean had significant higher OS compared with patients with an averaged expression ≤ mean (HR 0.4, 95%CI 0.2-0.9, p = 0.02).

Conclusions: Impairment of apoptosis assessed solely on the levels of BAK, BAX, BCL2 and BCLX(L) proteins were not sufficient as prognostic marker in breast cancer patients. However, our analysis suggest that patients with ER/PR+ cancer cells potentially 'primed' towards apoptosis - via the expression of pro-apoptotic BAD, PUMA, BOK and TRADD - had a more favourable clinical outcome compared to patients with cancer cells lacking this priming.

Citation Format: Lindner AU, Lucantoni F, Vareslija D, Resler A, Gallagher WM, Hill A, Young L, Prehn JHM. High expression of BAD, PUMA, BOK and TRADD mRNA is associated with higher overall survival in ER+ and PR+ breast cancer patients [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr P5-10-02.