Targeting Transcriptional CDKs in Medulloblastoma

Safari, Nazila

Abstract

Medulloblastoma (MB) is the most common malignant tumour of the brain in children. Current treatments include surgery, radiotherapy and chemotherapy. Although the five-year survival rate is over 70%, the treatment is exceptionally aggressive, leaving severe and long-lasting side effects on patients. Cyclin-dependent kinases (CDKs) are a family of proteins that regulate important cellular processes including cell cycle and transcription. Overexpression of CDKs has been reported in many types of cancer, hence, targeting CDKs to inhibit cancer cell proliferation has been aimed by several studies and the use of cyclin-dependent kinase inhibitors in the treatment of various types of cancer is growing rapidly.
Here in this work, we investigated the effectiveness of newly developed transcriptional CDK inhibitors (tCDKs) on four medulloblastoma cell lines including HD-MB03 (from Group 3 medulloblastoma), and ONS76, UW228, DAOY (from SHH subgroup). Results of the efficacy study of these chemical inhibitors on MB cell proliferation indicated the highest anti-proliferative effects of two transcriptional CDK inhibitors, namely THZ1 and THZ531, which inhibit CDK7 and CDK12/13, respectively. The Group 3 subtype medulloblastoma exhibited the highest sensitivity to THZ1 and THZ531 inhibitors. It was also found that the inhibitory effects of the above-mentioned inhibitors were through the induction of apoptosis. In addition, treatment of medulloblastoma cell lines with THZ1 or THZ531 in combination with chemotherapeutic agents including vincristine, cisplatin and cyclophosphamide suggested synergistic effects which enhanced cytotoxicity when compared to the single drug treatments (Combination Index < 1).
With the hypothesis that the growth of medulloblastoma cells could be dependent on CDK7, 12 and 13, the study was further focused on the expression of these CDKs at both protein and mRNA levels in cell lines treated with these inhibitors. In general, results demonstrated no significant (p-value > 0.05) variations in the expression of CDK7, 12 and 13 at mRNA and protein levels. However, treatment with these inhibitors resulted in a significant (p-value ≤ 0.05) decrease in the phosphorylation of RNA polymerase II at Ser2 and Ser5 carboxy-terminal domain (CTD).
Additionally, the investigation of the role of CDK7 in HD-MB03 cell proliferation through knocking down the CDK7 gene showed a significant (p-value ≤ 0.05) decrease of proliferative cells suggestive of the essential role of CDK7 in the proliferation of these cells.
In general, it was found that the Group 3 medulloblastoma cell line, which exhibited more promising results, could potentially serve as the optimal target for the studied transcriptional inhibitors. The findings of this study can provide an in-depth understanding of the biology of medulloblastoma and help identify less toxic and more efficient treatment strategies based on tumour-specific subtypes.

• Thesis Type: Thesis
• Deposit Date: Jun 20, 2024
• Publicly Available Date: Jun 29, 2026
• Award Date: Jun 28, 2024