RESUMO
Rhabdomyosarcoma (RMS) is a highly aggressive pediatric cancer with features of skeletal muscle differentiation. More than 80% of the high-risk patients ultimately fail to respond to chemotherapy treatment, leading to limited therapeutic options and dismal prognostic rates. The lack of response and subsequent tumor recurrence is driven in part by stem cell-like cells, the tumor subpopulation that is enriched after treatment, and characterized by expression of the AXL receptor tyrosine kinase (AXL). AXL mediates survival, migration, and therapy resistance in several cancer types; however, its function in RMS remains unclear. In this study, we investigated the role of AXL in RMS tumorigenesis, migration, and chemotherapy response, and whether targeting of AXL with small-molecule inhibitors could potentiate the efficacy of chemotherapy. We show that AXL is expressed in a heterogeneous manner in patient-derived xenografts (PDX), primary cultures and cell line models of RMS, consistent with its stem cell-state selectivity. By generating a CRISPR/Cas9 AXL knock-out and overexpressing models, we show that AXL contributes to the migratory phenotype of RMS, but not to chemotherapy resistance. Instead, pharmacologic blockade with the AXL inhibitors bemcentinib (BGB324), cabozantinib and NPS-1034 rapidly killed RMS cells in an AXL-independent manner and augmented the efficacy of the chemotherapeutics vincristine and cyclophosphamide. In vivo administration of the combination of bemcentinib and vincristine exerted strong antitumoral activity in a rapidly progressing PDX mouse model, significantly reducing tumor burden compared with single-agent treatment. Collectively, our data identify bemcentinib as a promising drug to improve chemotherapy efficacy in patients with RMS.
Assuntos
Receptor Tirosina Quinase Axl , Benzocicloeptenos , Proteínas Proto-Oncogênicas , Receptores Proteína Tirosina Quinases , Rabdomiossarcoma , Humanos , Rabdomiossarcoma/tratamento farmacológico , Rabdomiossarcoma/patologia , Rabdomiossarcoma/genética , Receptores Proteína Tirosina Quinases/antagonistas & inibidores , Receptores Proteína Tirosina Quinases/metabolismo , Animais , Camundongos , Proteínas Proto-Oncogênicas/antagonistas & inibidores , Proteínas Proto-Oncogênicas/metabolismo , Proteínas Proto-Oncogênicas/genética , Benzocicloeptenos/farmacologia , Ensaios Antitumorais Modelo de Xenoenxerto , Linhagem Celular Tumoral , Criança , Proliferação de Células/efeitos dos fármacos , Proteínas de Fusão Oncogênica/genética , Proteínas de Fusão Oncogênica/metabolismo , Movimento Celular/efeitos dos fármacos , Inibidores de Proteínas Quinases/farmacologia , TriazóisRESUMO
Activation of oncogenic gene expression from long-range enhancers is initiated by the assembly of DNA-binding transcription factors (TF), leading to recruitment of co-activators such as CBP/p300 to modify the local genomic context and facilitate RNA-Polymerase 2 (Pol2) binding. Yet, most TF-to-coactivator recruitment relationships remain unmapped. Here, studying the oncogenic fusion TF PAX3-FOXO1 (P3F) from alveolar rhabdomyosarcoma (aRMS), we show that a single cysteine in the activation domain (AD) of P3F is important for a small alpha helical coil that recruits CBP/p300 to chromatin. P3F driven transcription requires both this single cysteine and CBP/p300. Mutants of the cysteine reduce aRMS cell proliferation and induce cellular differentiation. Furthermore, we discover a profound dependence on CBP/p300 for clustering of Pol2 loops that connect P3F to its target genes. In the absence of CBP/p300, Pol2 long range enhancer loops collapse, Pol2 accumulates in CpG islands and fails to exit the gene body. These results reveal a potential novel axis for therapeutic interference with P3F in aRMS and clarify the molecular relationship of P3F and CBP/p300 in sustaining active Pol2 clusters essential for oncogenic transcription.