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Combination ofÃ‚Â ribociclibÃ‚Â andÃ‚Â gemcitabineÃ‚Â forÃ‚Â theÃ‚Â treatment ofÃ‚Â medulloblastoma

ABSTRACT: Group 3 (G3) medulloblastoma (MB) is one of the deadliest forms of the disease for which novel treatment is desperately needed. Here we evaluate ribociclib, a highly selective CDK4/6 inhibitor, with gemcitabine in mouse and human G3 MBs. Ribociclib CNS penetration was assessed by in vivo microdialysis and by immunohistochemistry and gene expression studies. Survival studies to determine the efficacy of ribociclib and gemcitabine combination were performed on mice orthotopically implanted with luciferase labelled mouse and human G3 MB. Pharmacokinetic-pharmacodynamic outcomes and univariable survival models were analyzed to estimate survival. Gene activity inference using NetBID and tumor differentiation analysis investigated the effects of the combination after short and long-term treatments. Tumors from mice treated with oral ribociclib displayed inhibited RB phosphorylation, downregulated E2F target genes, and decreased proliferation. Treatment of mice with the combination of ribociclib and gemcitabine was well tolerated, slowed tumor progression and metastatic spread, and increased survival. Molecular analysis of treated versus untreated tumors showed a significant decrease in the activity and expression of genes involved in cell cycle progression and DNA damage response, and an increase in activity and expression of genes implicated in neuronal identity and neuronal differentiation. Ribociclib is CNS-penetrant. When administered/combined with gemcitabine in orthotopic G3 MB models resulted in improved survival. Our findings, with both mouse and human patient-derived-orthotopic xenograft models, suggest that this combination therapy has promise for children with G3 MB and may represent an effective treatment strategy for other CNS malignancies.

PROVIDER: EGAS00001006001 | EGA |

REPOSITORIES: EGA

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Project description:Pediatric medulloblastoma (MB) is the most common solid malignant brain neoplasm, with group 3 (G3) MB representing the most aggressive subgroup associated with a poor prognosis and a remarkable ability to resist upfront multimodal therapy. Despite a low mutational burden of disease and MYC amplification identified as a independent factor associated with poor survivorship, efforts to target the MYC has met with limited therapeutic success. Consequently alternative mediators associated with the aggressive phenotype of G3 MB continues as a common goal within the MB community. Here we show how the neural stem cell determinant Musashi 1 (MSI1) is a central and vital moderator of G3 MB in both a MYC amplified mouse model of G3 MB and patient derived xenografts (PDX). Specifically, we modified the MYC amplified and p53 mutated (MP) mouse model of G3 MB to generate Msi1 conditional knockout mice (Msi1flox/flox), which led to the observation that MSI1 is required for tumor initiation of MP tumors. To identify the translational potential of these findings, we employed shRNA against Msi1 in multiple PDX lines, observing a striking deficit in multiple key stem cell features including self-renewal, proliferation, and failure to progress through the cell cycle. Notably, Msi1 inhibition resulted in a failure of tumor initiation, translating to a significantly prolonged survival, reaffirming the essential role for MSI1 in G3 MB. To determine how MSI1 symphonizes the anarchic post-transcriptional landscape of G3MB, we differentially analyzed the MSI1 binding sites in normal neural stem cells and G3 MB and subsequently compared the MSI1-binding transcriptome, and proteome following Msi1 inhibition. Comparative analysis suggested an integral role for post-transcriptional regulators, such as MSI1 and its binding prey mRNA, as a therapeutic target. Here we propose the neural RNA binding protein MSI1, as a master regulator, hijacked from its normal neural developmental function, orchestrating the aberrant translational landscape of G3 MB.

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Combination ofÃ‚Â ribociclibÃ‚Â andÃ‚Â gemcitabineÃ‚Â forÃ‚Â theÃ‚Â treatment ofÃ‚Â medulloblastoma

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