RESUMO
BACKGROUND: RSPO ligands, activators of the Wnt/ß-catenin pathway, are overexpressed in different cancers. The objective of this study was to investigate the role of RSPOs in breast cancer (BC). METHODS: Expression of RSPO and markers of various cancer pathways were measured in breast tumours and cell lines by qRT-PCR. The effect of RSPO on the Wnt/ß-catenin pathway activity was determined by luciferase assay, western blotting, and qRT-PCR. The effect of RSPO2 inhibition on proliferation was determined by using RSPO2 siRNAs. The effect of IWR-1, an inhibitor of the Wnt/ß-catenin pathway, was examined on the growth of an RSPO2-positive patient-derived xenograft (PDX) model of metaplastic triple-negative BC. RESULTS: We detected RSPO2 and RSPO4 overexpression levels in BC, particularly in triple-negative BC (TNBC), metaplastic BC, and triple-negative cell lines. Various mechanisms could account for this overexpression: presence of fusion transcripts involving RSPO, and amplification or hypomethylation of RSPO genes. Patients with RSPO2-overexpressing tumours have a poorer metastasis-free survival (P=3.6 × 10-4). RSPO2 and RSPO4 stimulate Wnt/ß-catenin pathway activity. Inhibition of RSPO expression in a TN cell line inhibits cell growth, and IWR-1 significantly inhibits the growth of an RSPO2-overexpressing PDX. CONCLUSIONS: RSPO overexpression could therefore be a new prognostic biomarker and therapeutic target for TNBC.
Assuntos
Carcinoma Ductal de Mama/genética , Carcinoma Ductal de Mama/secundário , Expressão Gênica , RNA Mensageiro/análise , Neoplasias de Mama Triplo Negativas/genética , Neoplasias de Mama Triplo Negativas/patologia , Animais , Antineoplásicos/uso terapêutico , Carcinoma Ductal de Mama/química , Carcinoma Ductal de Mama/tratamento farmacológico , Proliferação de Células , Meios de Cultivo Condicionados/farmacologia , Feminino , Expressão Gênica/efeitos dos fármacos , Células HEK293 , Humanos , Imidas/uso terapêutico , Peptídeos e Proteínas de Sinalização Intercelular/análise , Peptídeos e Proteínas de Sinalização Intercelular/genética , Peptídeos e Proteínas de Sinalização Intercelular/metabolismo , Metaplasia/genética , Metaplasia/patologia , Camundongos Nus , Transplante de Neoplasias , Quinolinas/uso terapêutico , RNA Interferente Pequeno/genética , Receptores Acoplados a Proteínas G/genética , Proteína de Ligação a TATA-Box/genética , Trombospondinas/genética , Trombospondinas/metabolismo , Neoplasias de Mama Triplo Negativas/química , Neoplasias de Mama Triplo Negativas/tratamento farmacológico , Via de Sinalização Wnt , Proteína Wnt3A/metabolismoRESUMO
BACKGROUND: Metaplastic breast cancer (MBC) is a rare form of breast cancer characterized by an aggressive clinical presentation, with a poor response to standard chemotherapy. MBCs are typically triple-negative breast cancers (TNBCs), frequently with alterations to genes of the PI3K-AKT-mTOR and RTK-MAPK signaling pathways. The objective of this study was to determine the response to PI3K and MAPK pathway inhibitors in patient-derived xenografts (PDXs) of MBCs with targetable alterations. METHODS: We compared survival between triple-negative MBCs and other histological subtypes, in a clinical cohort of 323 TNBC patients. PDX models were established from primary breast tumors classified as MBC. PI3K-AKT-mTOR and RTK-MAPK pathway alterations were detected by targeted next-generation sequencing (NGS) and analyses of copy number alterations. Activation of the PI3K-AKT-mTOR and RTK-MAPK signaling pathways was analyzed with reverse-phase protein arrays (RPPA). PDXs carrying an activating mutation of PIK3CA and genomic changes to the RTK-MAPK signaling pathways were treated with a combination consisting of a PI3K inhibitor and a MEK inhibitor. RESULTS: In our clinical cohort, the patients with MBC had a worse prognosis than those with other histological subtypes. We established nine metaplastic TNBC PDXs. Three had a pathogenic mutation of PIK3CA and additional alterations to genes associated with RTK-MAPK signaling. The MBC PDXs expressed typical EMT and stem cell genes and were of the mesenchymal or mesenchymal stem-like TNBC subtypes. On histological analysis, MBC PDXs presented squamous or chondroid differentiation. RPPA analysis showed activation of the PI3K-AKT-mTOR and RTK-MAPK signaling pathways. In vivo, the combination of PI3K and MAPK inhibitors displayed marked antitumor activity in PDXs carrying genomic alterations of PIK3CA, AKT1, BRAF, and FGFR4. CONCLUSION: The treatment of metaplastic breast cancer PDXs by activation of the PI3K-AKT-mTOR and RTK-MAPK pathways at the genomic and protein levels with a combination of PI3K and MEK inhibitors resulted in tumor regression in mutated models and may therefore be of interest for therapeutic purposes.