NEW Project 2: Targeting Heat Shock Protein 90 Client Proteins in Triple Negative Breast Cancer
Suzanne Conzen, MD (basic science) Olufunmilayo Olopade, MBBS (clinical)
Rita Nanda, MD (clinical)
Although a significant proportion of triple negative breast cancer (TNBC) is chemotherapy-resistant, there are a few promising molecular targets currently being studied to overcome and/or bypass this resistance. One of the targets we have explored is glucocorticoid receptor (GR) signaling. In our first cycle of breast cancer SPORE funding, based in part on pilot developmental research funding, our laboratory successfully collaborated with the clinical research group to launch a Phase 1 trial using the GR antagonist mifepristone in TNBC. GR activation has been shown to decrease chemotherapy-induced apoptosis in several TNBC models.
Moreover, a meta-analysis of early-stage TNBC showed that the highest levels of tumor GR expression are associated with an increased risk of relapse. Our laboratory has also shown that GR-mediated inhibition of apoptosis in breast epithelial cells requires transcriptional regulation of direct GR target genes including SGK1. The tyrosine kinase activities of JAK1 and 2 have also been shown to promote breast cancer tumorigenesis and chemoresistance and SGK1 and JAK1,2 are overexpressed in a subset of TNBC patients with the highest risk of relapse. Interestingly, additional studies have shown that there is crosstalk between GR and JAK/Signal transducer and activator of transcription (STAT) signaling, suggesting the importance of the cell survival pathways mediated by these proteins.
Several important proteins associated with high expression TNBC recurrence and chemotherapy-resistance require Hsp90 to function: these include the GR, serum/ glucocorticoid-regulated kinase 1 (SGK1) and the Janus kinase (JAK) 1 and 2 proteins. Here we propose to use the novel approach of targeting Heat Shock protein 90 (Hsp90) to reverse chemotherapy-resistance through targeting GR as well as through targeting additional pro-survival pathways.
We hypothesize that inactivating the Hsp90 client proteins GR/SGK1 (Aim 1) and JAK (Aim 2) will increase TNBC chemotherapy sensitivity and tumor responsiveness.
Aim 1. To determine whether inactivation of the GR/SGK1 pathway mediates Hsp90-inhibitor-induced TNBC tumor cell death. In vitro experiments using live cell imaging of GR-expressing or -depleted tumor cells to measure apoptosis following Hsp90 inhibitor treatment will be performed with or without chemotherapy. The same approach will be used to study SGK1 function. These experiments will be performed in vivo using mouse xenografts.
Aim 2. To determine whether inactivation of the JAK/STAT pathway mediates Hsp90-inhibitor-induced TNBC tumor cell death. Parallel in vitro and in vivo experiments to those outlined in Aim 1 will be performed to determine whether the Hsp90 client proteins JAK1 and JAK2 are also inactivated by Hsp90 inhibition and whether the subsequent inactivation of the JAK/STAT pathway leads to increased chemo-sensitivity in TNBC.
Aim 3. To determine whether GR/SGK1 and/or JAK/STAT3 expression in TNBC is decreased following neoadjuvant treatment with an Hsp90 inhibitor. Tumor GR/SGK1 and JAK/STAT expression levels before and after two weeks of ganetespib (Hsp90 inhibitor) monotherapy will be measured. Following ganetespib and the second study biopsy, all patients (n=30) will receive weekly pre-operative ganetespib/paclitaxel for 12 weeks followed by dose-dense doxorubicin and cyclophosphamide for 4 cycles. Tumor GR/SGK1 and JAK/STAT activity will be determined at definitive resection (lumpectomy or mastectomy).
Impact on breast cancer outcome
Approximately 45,000 women per year are diagnosed with TNBC (1, 2). The impact of improving the treatment and cure of TNBC by targeting the chemotherapy-resistant TNBC subset will be significant. Because TNBC is a heterogeneous group of cancers, understanding how GR- and JAK/STAT-expressing tumors may be differentially sensitive and whether their treatment may be improved by the addition of Hsp90 inhibitors is predicted to have a significant impact on women with TNBC.