Malawsky, D. | bioRxiv Science

bioRxiv2022

PRC2 disruption in cerebellar progenitors produces cerebellar hypoplasia and aberrant myoid differentiation without blocking medulloblastoma growth

We show that the Polycomb Repressive Complex 2 (PRC2) maintains neural identity in Sonic Hedgehog (SHH)-driven cerebellar granule neuron progenitors (CGNPs) and SHH-driven medulloblastoma, a cancer of CGNPs. Proliferating CGNPs and medulloblastoma cells pass the neural fate commitment to their progeny through epigenetic mechanisms. The PRC2 mediates epigenetic regulation through histone methylation, and PRC2 inhibitors have been proposed for medulloblastoma therapy. We investigated PRC2 function in CGNPs and medulloblastoma by conditionally deleting PRC2 components Eed or Ezh2 in CGNPs and analyzing cerebellar growth, cellular gene expression (scRNA-seq), and tumorigenesis in medulloblastoma-prone Smo-mutant mice. Eed-deleted CGNPs showed reduced growth, with decreased proliferation, increased apoptosis and inappropriate myoid differentiation. Ezh2-deleted CGNPs also showed myoid differentiation without reduced growth. Eed-deleted and Ezh2-deleted medulloblastomas similarly demonstrated myoid differentiation, but progressed more rapidly than PRC2-intact controls. The PRC2 thus maintained neural fate in CGNPs and medulloblastoma, but PRC2 disruption did not block SHH medulloblastoma progression.

neuroscience↗

bioRxiv2021

Nanoparticle-delivered palbociclib enable CDK4/6 inhibitor therapy while combination with mTORC1 inhibitor sapanisertib induces long term benefits in SHH medulloblastoma.

CDK4/6 inhibitors hold promise for brain tumor treatment, but efficacy has been limited by recurrence in both preclinical models and clinical trials. To address recurrence, we tested a nanoparticle formulation of the CDK4/6 inhibitor palbociclib (POx-palbo) in mice genetically-engineered to develop SHH-driven medulloblastoma. We then analyzed medulloblastomas in mice receiving palbociclib treatment, and compared the efficacy of combining palbociclib with specific inhibitors suggested by our analysis. POx-Palbo showed reduced toxicity compared to conventional palbociclib, was tolerable in parenteral administration, improved CNS pharmacokinetics, and extended survival of mice with medulloblastoma. Recurrence, however, remained problematic as fractions of tumor cells proliferated during therapy. ScRNA-seq identified a gene expression pattern unique to proliferating medulloblastoma cells in POx-Palbo-treated mice, marked by up-regulation of the glutamate transporter Slc1a2 and down-regulation of diverse ribosomal genes. Reduced mTORC1 signaling, suggested by ribosomal suppression in POx-Palbo-treated tumors was confirmed by decreased 4EBP1 phosphorylation (p4EBP1). Further reducing mTORC1 activity by combining POx-Palbo with the mTORC1 inhibitor sapanisertib produced mutually enhancing effects, with increased suppression of both pRB and p4EBP1, and prolonged mouse survival compared to either agent alone. In contrast, targeting cell cycle progression by combining POx-Palbo with the SHH-pathway inhibitor vismodegib, or with the replication-targeting agents gemcitabine or etoposide, failed to enhance efficacy. Our data show the potential of nanoparticle formulation and scRNA-seq analysis of resistance to improve brain tumor treatment, and identify POx-palbo plus sapanisertib as effective combinatorial therapy for SHH medulloblastoma. This combination may be appropriate for testing in patients with recurrence, who need new options.

cancer biology↗