A combination of trastuzumab and BAG-1 inhibition synergistically targets HER2 positive breast cancer cells

Abstract

Treatment of HER2+ breast cancer with trastuzumab is effective and combination anti-HER2 therapies have demonstrated benefit over monotherapy in the neoadjuvant and metastatic settings. This study investigated the therapeutic potential of targeting the BAG-1 protein co-chaperone in trastuzumab-responsive or -resistant cells. In the METABRIC dataset, BAG-1 mRNA was significantly elevated in HER2+ breast tumors and predicted overall survival in a multivariate analysis (HR = 0.81; p = 0.022). In a breast cell line panel, BAG-1 protein was increased in HER2+ cells and was required for optimal growth as shown by siRNA knockdown. Overexpression of BAG-1S in HER2+ SKBR3 cells blocked growth inhibition by trastuzumab, whereas overexpression of a mutant BAG-1S protein (BAG-1S H3AB), defective in binding HSC70, potentiated the effect of trastuzumab. Injection of a Tet-On SKBR3 clone, induced to overexpress myc-BAG-1S into the mammary fat pads of immunocompromised mice, resulted in 2-fold larger tumors compared to uninduced controls. Induction of myc-BAG-1S expression in two Tet-On SKBR3 clones attenuated growth inhibition by trastuzumab in vitro. Targeting endogenous BAG-1 by siRNA enhanced growth inhibition of SKBR3 and BT474 cells by trastuzumab, while BAG-1 protein-protein interaction inhibitor (Thio-S or Thio-2) plus trastuzumab combination treatment synergistically attenuated growth. In BT474 cells this reduced protein synthesis, caused G1/S cell cycle arrest and targeted the ERK and AKT signaling pathways. In a SKBR3 subpopulation with acquired resistance to trastuzumab BAG-1 targeting remained effective and either Thio-2 or BAG-1 siRNA reduced growth more compared to trastuzumab-responsive parental cells. In summary, targeting BAG-1 function in combination with anti-HER2 therapy might prove beneficial.

BAG-1 as a biomarker in early breast cancer prognosis: a systematic review with meta-analyses

“…Sixteen studies utilised cohorts of 100 or more patients ( Tang et al , 1999 ; Turner et al , 2001 ; Townsend et al , 2002 ; Cutress et al , 2003 ; O’Driscoll et al , 2003 ; Sirvent et al , 2004 ; Tang et al , 2004 ; Yun et al , 2005 ; Lin et al , 2008 ; Nadler et al , 2008 ; Millar et al , 2009 ; Afentakis et al , 2013 ; Wang et al , 2014 ; Dowsett et al , 2015 ; Davidson et al , 2016 ; Papadakis et al , 2016 ) and 2 studies ( Yang et al , 2008 ; Athanassiadou et al , 2009 ) recruited <100 patients. With the exception of one prospective immunocytochemical study ( Athanassiadou et al , 2009 ), and two retrospective analyses of a prospective clinical trial ( Afentakis et al , 2013 ; Dowsett et al , 2015 ), the studies associating BAG-1 expression with clinicopathological variables involve retrospective analysis of patient survival data ( Table 2a and b ).…”

“…Two studies reported analysis of mRNA expression from published data sets: Millar et al (2009) from two studies ( van de Vijver et al , 2002 ; Naderi et al , 2007 ) and Papadakis et al (2016) from a third ( Curtis et al , 2012 ). Of the 18 studies, all clearly stated inclusion and/or exclusion criteria.…”

“…Two studies ( O’Driscoll et al , 2003 ; Dowsett et al , 2015 ) used RT-PCR to examine BAG-1 mRNA expression, whereas 15 studies examined BAG-1 protein expression by immunohistochemical staining ( Tang et al , 1999 , 2004 ; Turner et al , 2001 ; Townsend et al , 2002 ; Cutress et al , 2003 ; O’Driscoll et al , 2003 ; Sirvent et al , 2004 ; Yun et al , 2005 ; Lin et al , 2008 ; Yang et al , 2008 ; Athanassiadou et al , 2009 ; Millar et al , 2009 ; Afentakis et al , 2013 ; Wang et al , 2014 ; Davidson et al , 2016 ). Full-face sections from formalin-fixed paraffin-embedded (FFPE) tumours were used in 11 studies ( Tang et al , 1999 ; Turner et al , 2001 ; Townsend et al , 2002 ; Cutress et al , 2003 ; O’Driscoll et al , 2003 ; Sirvent et al , 2004 ; Tang et al , 2004 ; Yun et al , 2005 ; Athanassiadou et al , 2009 ; Dowsett et al , 2015 ; Papadakis et al , 2016 ), whereas 7 studies utilised FFPE tissue microarrays ( Lin et al , 2008 ; Nadler et al , 2008 ; Yang et al , 2008 ; Millar et al , 2009 ; Afentakis et al , 2013 ; Wang et al , 2014 ; Davidson et al , 2016 ). To address the issue of tumour heterogeneity involved with the use of tissue microarrays, two studies included in their analyses at least 2 cores taken from different sites from within the same breast tumour ( Nadler et al , 2008 ; Millar et al , 2009 ).…”

Downregulation of BAG‑1 in T47D cells promotes resistance to tamoxifen via activation of the PI3K/Akt/mTOR signaling pathway

“…Bcl-2-associated athanogene 1 (BAG-1) is a multifunctional protein that interacts with a wide range of molecules and subsequently affects various cellular functions (5)(6)(7)(8)(9)(10). BAG-1 protects cells from apoptosis otherwise induced by treatment with cytotoxic drugs, growth factor withdrawal, radiation and stress (11)(12)(13)(14)(15). BAG-1 is expressed in three main isoforms, which differ in their translation initiation starting positions (16,17).…”

Comment on ‘BAG-1 as a biomarker in early breast cancer prognosis: a systematic review with meta-analyses'

“…Papadakis et al 2 state ‘In general, data were too heterogeneous, and outcome measures were too varied to perform meta-analyses for the majority of studies. Meta-analyses of mRNA expression from the two data sets analysed in Millar et al 7 and the data set analysed in Papadakis et al 11 including a total of 2422 patients produced an HR of 0.55 (95% CI: 0.36–0.85) favouring improved BCSS with high expression of BAG-1 (Figure 2a in Papadakis et al 2 ).’ The first sentence implies that a sensible meta-analysis is not possible, an unfortunate situation seen in many systematic reviews of prognostic biomarkers. Nevertheless, Papadakis et al 2 conducted three meta-analyses summarising two or three studies.…”