Project description:Malignant rhabdoid tumors (MRT) are highly aggressive pediatric cancers that respond poorly to current therapies. We screened several MRT cell lines each with large-scale RNAi, CRISPR-Cas9, and small-molecule libraries to identify potential drug targets specific for these cancers. We discovered MDM2 and MDM4, the canonical negative regulators of p53, as significant vulnerabilities. Using two compounds currently in clinical development, idasanutlin and ATSP-7041, we show that MRT cells are more sensitive than other p53 wild-type cancer cell lines to MDM2 and dual MDM2/4 inhibition in vitro. These compounds cause significant upregulation of the p53 pathway in MRT cells, and sensitivity is ablated by CRISPR-Cas9-mediated inactivation of TP53. We show that loss of SMARCB1, a subunit of the SWI/SNF (BAF) complex mutated in nearly all MRT, sensitizes cells to MDM2 and MDM2/4 inhibition by enhancing p53-mediated apoptosis. Both MDM2 and MDM2/4 inhibition slowed MRT xenograft growth in vivo, with a five-day idasanutlin pulse causing marked regression of all xenografts including durable complete responses in 50% of mice. Together, these studies identify a genetic connection between mutations in the SWI/SNF chromatin-remodeling complex and the tumor suppressor gene p53, and provide preclinical evidence to support the targeting of MDM2 and MDM4 in this often-fatal pediatric cancer.
Project description:Malignant rhabdoid tumors (MRT) are highly aggressive pediatric cancers that respond poorly to current therapies. In this study, we screened several MRT cell lines with large-scale RNAi, CRISPR-Cas9, and small-molecule libraries to identify potential drug targets specific for these cancers. We discovered MDM2 and MDM4, the canonical negative regulators of p53, as significant vulnerabilities. Using two compounds currently in clinical development, idasanutlin (MDM2-specific) and ATSP-7041 (MDM2/4-dual), we show that MRT cells were more sensitive than other p53 wild-type cancer cell lines to inhibition of MDM2 alone as well as dual inhibition of MDM2/4. These compounds caused significant upregulation of the p53 pathway in MRT cells, and sensitivity was ablated by CRISPR-Cas9-mediated inactivation of TP53. We show that loss of SMARCB1, a subunit of the SWI/SNF (BAF) complex mutated in nearly all MRTs, sensitized cells to MDM2 and MDM2/4 inhibition by enhancing p53-mediated apoptosis. Both MDM2 and MDM2/4 inhibition slowed MRT xenograft growth in vivo, with a 5-day idasanutlin pulse causing marked regression of all xenografts, including durable complete responses in 50% of mice. Together, these studies identify a genetic connection between mutations in the SWI/SNF chromatin-remodeling complex and the tumor suppressor gene TP53 and provide preclinical evidence to support the targeting of MDM2 and MDM4 in this often-fatal pediatric cancer. SIGNIFICANCE: This study identifies two targets, MDM2 and MDM4, as vulnerabilities in a deadly pediatric cancer and provides preclinical evidence that compounds inhibiting these proteins have therapeutic potential.
Project description:Malignant rhabdoid tumors (MRT) represent one of the most aggressive childhood malignancies. No effective treatment options are available, and prognosis is therefore dismal. Previous studies have demonstrated that tumor organoids capture the heterogeneity of patient tumors and can be used to predict patient therapy response. Here, we perform drug screening on patient-derived normal and tumor organoids to identify MRT-specific therapeutic vulnerabilities. We identify neddylation inhibitor MLN4924 as a potential therapeutic agent. Mechanistically, we find increased neddylation in MRT organoids and tissues and show that MLN4924 induces a cytotoxic response via upregulation of the unfolded protein response. Lastly, we demonstrate in vivo efficacy in an MRT PDX mouse model, in which single agent MLN4924 treatment significantly extends survival. Our study demonstrates that organoids can be used to find drugs selectively targeting tumor cells while leaving healthy cells unharmed and proposes neddylation inhibition as therapeutic strategy in MRT.
Project description:We have generated DNA methylation profiles for patient-derived malignant rhabdoid tumor organoids and re-expressed SMARCB1 to assess SMARCB1-dependent changes in DNA methylation
Project description:We hypothesized that prolonged treatment of malignant rhabdoid tumor cells with low-dose HDACi will drive cellular differentiation. We assessed changes in gene expression following 21 days treatment with the HDACi, Panobinostat, versus a DMSO vehcile control in three human MRT cell lines. Total RNA obtained from three human malignant rhabdoid tumor cell lines (G401, SJSC, STM91-01) cultured for 21 days in the presence of low-dose Panobinostat was compared to 21-day treated DMSO control cells. All treatments and cell lines were performed in triplicate.
Project description:To uncover the molecular mechanisms by which CD146+ malignant rhabdoid tumor cells exhibited higher tumorigenic potential, microarray analysis was carried out to compare gene expression profiles between CD146+ and CD146− cells isolated from three cell lines
Project description:The aim of this experiment has been to investigate the transcriptional profile of HCT116 cells treated with Peptide-3 (Pep3) compared to untreated (NT), treated with solvent (DMSO) or with a mutated peptide (Pep3M) cells. Peptide-3 is a dodecapeptide able to interact with MDM2 at the levels of the interaction region of the MDM4 and MDM2 proteins, thereby interfering with the coopeartivy function of the proteins in the regulation of p53. This peptide is indeed able to specifically activate p53 and to cause apoptotis in different cancer cell lines and tumor growth inhibition in xenograft models.
Project description:Microsatellite instability high (MSI-H) tumors are malignant tumors that, despite harboring a high mutational burden, often have intact TP53. One of the most frequent mutations in MSI-H tumors is a frameshift mutation in RPL22, a ribosomal protein. Here, we identified RPL22 as a modulator of MDM4 splicing through an alternative splicing switch in exon 6. RPL22 loss increased MDM4 exon 6 inclusion, cell proliferation, and augmented resistance to the MDM inhibitor Nutlin-3A. RPL22 represses expression of its paralog, RPL22L1, by mediating the splicing of a cryptic exon corresponding to a truncated transcript. Therefore, RPL22 loss is a driver of oncogenic MDM4 induction and key to a common splicing circuit in MSI-H tumors that may inform therapeutic targeting of the MDM4-p53 axis and oncogenic RPL22L1 induction.