Piperacetazine directly binds to the PAX3::FOXO1 fusion protein and inhibits its transcriptional activity
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ABSTRACT: The tumor-specific chromosomal translocation product, PAX3::FOXO1, is an aberrant fusion protein that plays a key role for oncogenesis in the alveolar subtype of rhabdomyosarcoma (RMS). PAX3::FOXO1 represents a validated molecular target for alveolar RMS and successful inhibition of its oncogenic activity is likely to have significant clinical applications. Even though several PAX3::FOXO1 function-based screening studies have been successfully completed, a directly binding small molecule inhibitor of PAX3::FOXO1 has not been reported. Therefore, we screened small molecule libraries to identify compounds that were capable of directly binding to PAX3::FOXO1 protein using surface plasmon resonance technology. Compounds that directly bound to PAX3::FOXO1 were further evaluated in secondary transcriptional activation assays. We discovered that piperacetazine can directly bind to PAX3::FOXO1 protein and inhibit fusion protein-derived transcription in multiple alveolar RMS cell lines. Piperacetazine inhibited anchorage-independent growth of fusion positive alveolar RMS cells but not embryonal RMS cells. Based on our findings, piperacetazine is a molecular scaffold upon which derivatives could be developed as specific inhibitors of PAX3::FOXO1. These novel inhibitors could potentially be evaluated in future clinical trials for recurrent or metastatic alveolar RMS as novel targeted therapy options.
Project description:Chimeric transcription factors drive lineage-specific oncogenesis but are notoriously difficult to target. Alveolar rhabdomyosarcoma (RMS) is an aggressive childhood soft tissue sarcoma transformed by the pathognomonic PAX3–FOXO1 fusion protein, which governs a core regulatory circuitry transcription factor (CRC TF) network. Here we show that the histone lysine demethylase KDM4B is a therapeutic vulnerability for PAX3–FOXO1+ RMS. Genetic and pharmacologic inhibition of KDM4B significantly delays tumor growth by disrupting the expression of CRC TFs caused by epigenetic alterations of PAX3–FOXO1-governed super enhancers. Combining KDM4B inhibition with cytotoxic chemotherapy leads to significant tumor regression in preclinical PAX3–FOXO1+ RMS models. In summary, we have identified a targetable mechanism required for maintenance of PAX3-FOXO1-related CRC TF network, which may translate to a novel therapeutic approach for fusion-positive RMS.
Project description:Chimeric transcription factors drive lineage-specific oncogenesis but are notoriously difficult to target. Alveolar rhabdomyosarcoma (RMS) is an aggressive childhood soft tissue sarcoma transformed by the pathognomonic PAX3–FOXO1 fusion protein, which governs a core regulatory circuitry transcription factor (CRC TF) network. Here we show that the histone lysine demethylase KDM4B is a therapeutic vulnerability for PAX3–FOXO1+ RMS. Genetic and pharmacologic inhibition of KDM4B significantly delays tumor growth by disrupting the expression of CRC TFs caused by epigenetic alterations of PAX3–FOXO1-governed super enhancers. Combining KDM4B inhibition with cytotoxic chemotherapy leads to significant tumor regression in preclinical PAX3–FOXO1+ RMS models. In summary, we have identified a targetable mechanism required for maintenance of PAX3-FOXO1-related CRC TF network, which may translate to a novel therapeutic approach for fusion-positive RMS.
Project description:Chimeric transcription factors drive lineage-specific oncogenesis but are notoriously difficult to target. Alveolar rhabdomyosarcoma (RMS) is an aggressive childhood soft tissue sarcoma transformed by the pathognomonic PAX3–FOXO1 fusion protein, which governs a core regulatory circuitry transcription factor (CRC TF) network. Here we show that the histone lysine demethylase KDM4B is a therapeutic vulnerability for PAX3–FOXO1+ RMS. Genetic and pharmacologic inhibition of KDM4B significantly delays tumor growth by disrupting the expression of CRC TFs caused by epigenetic alterations of PAX3–FOXO1-governed super enhancers. Combining KDM4B inhibition with cytotoxic chemotherapy leads to significant tumor regression in preclinical PAX3–FOXO1+ RMS models. In summary, we have identified a targetable mechanism required for maintenance of PAX3-FOXO1-related CRC TF network, which may translate to a novel therapeutic approach for fusion-positive RMS.
Project description:Chimeric transcription factors drive lineage-specific oncogenesis but are notoriously difficult to target. Alveolar rhabdomyosarcoma (RMS) is an aggressive childhood soft tissue sarcoma transformed by the pathognomonic PAX3–FOXO1 fusion protein, which governs a core regulatory circuitry transcription factor (CRC TF) network. Here we show that the histone lysine demethylase KDM4B is a therapeutic vulnerability for PAX3–FOXO1+ RMS. Genetic and pharmacologic inhibition of KDM4B significantly delays tumor growth by disrupting the expression of CRC TFs caused by epigenetic alterations of PAX3–FOXO1-governed super enhancers. Combining KDM4B inhibition with cytotoxic chemotherapy leads to significant tumor regression in preclinical PAX3–FOXO1+ RMS models. In summary, we have identified a targetable mechanism required for maintenance of PAX3-FOXO1-related CRC TF network, which may translate to a novel therapeutic approach for fusion-positive RMS.
Project description:Chimeric transcription factors drive lineage-specific oncogenesis but are notoriously difficult to target. Alveolar rhabdomyosarcoma (RMS) is an aggressive childhood soft tissue sarcoma transformed by the pathognomonic PAX3–FOXO1 fusion protein, which governs a core regulatory circuitry transcription factor (CRC TF) network. Here we show that the histone lysine demethylase KDM4B is a therapeutic vulnerability for PAX3–FOXO1+ RMS. Genetic and pharmacologic inhibition of KDM4B significantly delays tumor growth by disrupting the expression of CRC TFs caused by epigenetic alterations of PAX3–FOXO1-governed super enhancers. Combining KDM4B inhibition with cytotoxic chemotherapy leads to significant tumor regression in preclinical PAX3–FOXO1+ RMS models. In summary, we have identified a targetable mechanism required for maintenance of PAX3-FOXO1-related CRC TF network, which may translate to a novel therapeutic approach for fusion-positive RMS.
Project description:Fusion-positive alveolar rhabdomyosarcoma (FP-RMS) is an aggressive pediatric sarcoma driven primarily by the PAX3-FOXO1 fusion oncogene, for which therapies targeting PAX3-FOXO1 are lacking. We screened 62,643 compounds using an engineered cell line that monitors PAX3-FOXO1 transcriptional activity identifying a hitherto uncharacterized compound, PFI-63. RNA-seq, ATAC-seq, and docking analyses implicated histone lysine demethylases (KDMs) as its targets. Enzymatic assays confirmed the inhibition of multiple KDMs with highest selectivity for KDM3B. Structural similarity search of PFI-63 identified PFI-90 with improved solubility and potency. Biophysical binding of PFI-90 to KDM3B was demonstrated using NMR and SPR. PFI-90 suppressed the growth of FP-RMS in vitro and in vivo through downregulating PAX3-FOXO1 activity, and combined knockdown of KDM3B and KDM1A phenocopied PFI-90 effects. Thus, we report novel KDM inhibitors with highest specificity for KDM3B. Its potent suppression of PAX3-FOXO1 activity can be exploited as a new therapeutic approach for FP-RMS and other transcriptionally driven cancers.
Project description:Rhabdomyosarcoma (RMS), a malignancy of impaired myogenic differentiation, is the most common soft tissue pediatric cancer. PAX3-FOXO1 oncofusions drive the majority of the clinically more aggressive fusion-positive rhabdomyosarcoma (FP-RMS). Recent studies have established an epigenetic basis for PAX3-FOXO1-driven oncogenic processes. However, details of PAX3-FOXO1 epigenetic mechanisms, including interactions with, and dependence on, other chromatin and transcription factors, are incompletely understood. We previously identified a novel disease-promoting epigenetic axis in RMS, involving the histone demethylase KDM3A and the ETS1 transcription factor, and demonstrated that this epigenetic axis interfaces with PAX3-FOXO1 both phenotypically and transcriptomically, including co-regulation of biological processes and genes important to FP-RMS progression. In this study, we demonstrate that KDM3A and ETS1 colocalize with PAX3-FOXO1 to enhancers of important disease-promoting genes in FP-RMS, including FGF8, IL4R, and MEST, as well as PODXL, which we define herein as a new FP-RMS-promoting gene. We show that ETS1, which is induced by both PAX3-FOXO1 and KDM3A, exists in complex with PAX3-FOXO1, and augments PAX3-FOXO1 chromatin occupancy. We further show that the PAX3-FOXO1/ETS1 complex can be disrupted by the clinically relevant small molecule inhibitor YK-4-279. YK-4-279 displaces PAX3-FOXO1 from chromatin and interferes with PAX3-FOXO1-dependent gene regulation, resulting in potent inhibition of growth and invasive properties in FP-RMS, along with downregulation of FGF8, IL4R, MEST and PODXL expression. We additionally show that, in some FP-RMS, KDM3A also increases PAX3-FOXO1 levels. Together, our studies illuminate mechanisms of action of the KDM3A/ETS1 regulatory module, and reveal novel targetable mechanisms of PAX3-FOXO1 chromatin complex regulation, in FP-RMS.
Project description:Rhabdomyosarcoma (RMS), a malignancy of impaired myogenic differentiation, is the most common soft tissue pediatric cancer. PAX3-FOXO1 oncofusions drive the majority of the clinically more aggressive fusion-positive rhabdomyosarcoma (FP-RMS). Recent studies have established an epigenetic basis for PAX3-FOXO1-driven oncogenic processes. However, details of PAX3-FOXO1 epigenetic mechanisms, including interactions with, and dependence on, other chromatin and transcription factors, are incompletely understood. We previously identified a novel disease-promoting epigenetic axis in RMS, involving the histone demethylase KDM3A and the ETS1 transcription factor, and demonstrated that this epigenetic axis interfaces with PAX3-FOXO1 both phenotypically and transcriptomically, including co-regulation of biological processes and genes important to FP-RMS progression. In this study, we demonstrate that KDM3A and ETS1 colocalize with PAX3-FOXO1 to enhancers of important disease-promoting genes in FP-RMS, including FGF8, IL4R, and MEST, as well as PODXL, which we define herein as a new FP-RMS-promoting gene. We show that ETS1, which is induced by both PAX3-FOXO1 and KDM3A, exists in complex with PAX3-FOXO1, and augments PAX3-FOXO1 chromatin occupancy. We further show that the PAX3-FOXO1/ETS1 complex can be disrupted by the clinically relevant small molecule inhibitor YK-4-279. YK-4-279 displaces PAX3-FOXO1 from chromatin and interferes with PAX3-FOXO1-dependent gene regulation, resulting in potent inhibition of growth and invasive properties in FP-RMS, along with downregulation of FGF8, IL4R, MEST and PODXL expression. We additionally show that, in some FP-RMS, KDM3A also increases PAX3-FOXO1 levels. Together, our studies illuminate mechanisms of action of the KDM3A/ETS1 regulatory module, and reveal novel targetable mechanisms of PAX3-FOXO1 chromatin complex regulation, in FP-RMS.
Project description:PAX3-FOXO1 is a fusion transcription factor that is the main driver of tumorigenesis leading to the development of alveolar rhabdomyosarcoma (aRMS). Since aRMS cells are addicted to PAX3-FOXO1 activity, the fusion protein also represents a major target for therapeutic interference, which is however challenging as transcription factors usually cannot be inhibited directly by small molecules. Hence, characterization of the biology of PAX3-FOXO1 might lead to the discovery of new possibilities for an indirect inhibition of its activity. Here, our goal was to characterize the proteomic neighborhood of PAX3-FOXO1 and to find candidates potentially affecting its activity and tumor cell viability. Towards this aim, we expressed BirA fused versions of PAX3-FOXO1 (N- and C-terminal) in HEK293T cells under presence of biotin. In the control setup, we expressed the BirA enzyme alone. After Streptavidin purification of biotinylated proteins, we performed mass spectrometry and quantified relative abundances compared to control conditions. This enabled us to determine PAX3-FOXO1 proximal proteins, which we investigated further in orthogonal endogenous systems.
Project description:Recurrent chromosomal rearrangements found in rhabdomyosarcoma (RMS) produce the PAX3-FOXO1 fusion protein, which is an oncogenic driver and a dependency in this disease. One important function of PAX3-FOXO1 is to arrest myogenic differentiation, which is linked to the ability of RMS cells to gain an unlimited proliferation potential. Here, we developed a phenotypic screening strategy for identifying factors that collaborate with PAX3-FOXO1 to block myo-differentiation in RMS. Unlike most genes evaluated in our screen, we found that loss of any of the three subunits of the Nuclear Factor Y (NF-Y) complex leads to a myo-differentiation phenotype that resembles the effect of inactivating PAX3-FOXO1. While the transcriptomes of NF-Y- and PAX3-FOXO1-deficient RMS cells bear remarkable similarity to one another, we found that these two transcription factors occupy non-overlapping sites along the genome: NF-Y preferentially occupies promoters, whereas PAX3-FOXO1 primarily binds to distal enhancers. By integrating multiple functional approaches, we map the PAX3 promoter as the point of intersection between these two regulators. We show that NF-Y occupies CCAAT motifs present upstream of PAX3 to function as a transcriptional activator of PAX3-FOXO1 expression in RMS. These findings reveal a critical upstream role of NF-Y in the oncogenic PAX3-FOXO1 pathway, highlighting how a broadly essential transcription factor can perform tumor-specific roles in governing cellular state.