Mechanisms of medulloblastoma vulnerability and new targeted therapies

Buzzetti, M

Abstract

Medulloblastoma (MB) is the most common malignant paediatric brain tumour accounting for about 20% of all childhood brain cancers. Over the last decade, a consensus has been reached over the existence of 4 main molecular subtypes, known as WNT-activated MB, SHH-activated MB, group 3 MB and group 4 MB. Despite their extreme heterogeneity, medulloblastoma patients are still uniformly treated with a combination strategy that encompasses surgery, radiation therapy and chemotherapy. The standard of care has now reached a plateau failing to cure more than 50% of the diagnosed children resulting in debilitating long-term side effects; therefore, there is an urgent need for developing new targeted therapies.
The aim of this PhD research was focused on expanding the knowledge of MB biology and providing tailored therapeutic options to be used in the clinic:
Project 1. A well-defined feature of MB is the genetic alterations of the cell cycle machinery, which controls cell cycle progression and transcription. Therefore, pharmacologic intervention to inhibit the activity of specific cyclin-dependant kinases (CDK) is an attractive therapeutic approach to boost MB standard of care, reducing morbidities associated with specific treatments.
Herein, we identified the pan-CDKi, dinaciclib, as a promising and more effective alternative to palbociclib, a CDK4/6 inhibitor currently pursued in clinical studies. We present evidence supporting dinaciclib’s ability to inhibit MB proliferation, impair cancer stemness and induce apoptosis at considerably lower doses than palbociclib. Furthermore, sequencing data confirmed that dinaciclib is a potent apoptotic inducer, possibly through transcriptional shifts mediated by MYC downregulation and RNA polymerase II phosphorylation reduction.
Finally, we observed the in vitro pharmacological synergy when using dinaciclib with clinically used chemotherapeutic drugs and BH3 mimetics, an approach that may boost therapeutic efficacy and reduce treatment-related morbidities.
Project 2. Group 3 MB patients have the worst overall survival rates, with MYC amplification/overexpression being the strongest adverse prognostic factor. Furthermore, the repressive transcriptional complex formed by MYC and MIZ1 is required for the maintenance of the group 3 MB identity.
Considering the failure of MYC-targeted therapies and the importance of MYC/MIZ1 interaction, we hypothesised that targeting MIZ1 might represent a valid therapeutic strategy tailored to MYC-driven group 3 MB patients.
Here we proved that the knockdown of MIZ1 specifically inhibits proliferation of group 3 MB cells by reducing MYC expression and MYC-regulated microRNA networks. From computational predictions that identified miR-124-3p as a miRNA targeting MIZ1, we confirmed through luciferase assay in vitro that miR-124-3p binds to the 3’ untranslated region of MIZ1 and represses its protein levels. Over-expression of miR-124-3p impairs proliferation of group 3 cells, mimicking the effects obtained after MIZ1 silencing. Transcriptomic analysis identified essential genes and pathways controlled by miR-124-3p in group 3 MB, which predominantly clustered around different aspects of cell cycle and cell division regulation determining vulnerable pathways that could be therapeutically pursued and targeted in future studies.
Finally, we show that miR-124-3p synergises with currently used chemotherapeutic agents, further highlighting the potential of miR-124-3p for the treatment of group 3 patients.

Citation

Buzzetti, M. Mechanisms of medulloblastoma vulnerability and new targeted therapies. (Thesis). University of Salford

• Thesis Type: Thesis
• Deposit Date: Aug 7, 2020
• Publicly Available Date: Aug 7, 2020
• Award Date: Jan 1, 2020