Abstract 2310: Targeting transcription-associated CDKs is an effective way to combat glioblastoma and medulloblastoma with minimal effect on primary neurons

Abstract

Abstract Glioblastoma multiforme (GBM) is the most prevalent and malignant brain tumor in adults. Currently there are no effective therapies to manage the disease efficiently. Medulloblastoma is the most common type of pediatric tumor and accounts for approximately 15% of all pediatric brain tumors. We aimed to determine if targeting the transcription-associated cyclin-dependent kinases, cdk7 and cdk9, using specific inhibitors, could interfere with the growth and metastatic properties of glioblastoma and medulloblastoma cell lines. We tested the effectiveness of Flavopiridol, a known inhibitor of cdk4, cdk6, pTEFb and cdk9; THZ1, a cdk7 inhibitor; and SNS032, which is known to inhibit cdk2, cdk7 and cdk9, on U87 and SNB19 glioblastoma, H4 neuroglioma and Daoy medullobastoma cells. Treatment with these pharmacological agents showed very strong cytotoxic effects on these cancer cells as measured by MTT (3-(4, 5-dimethylthiazol-2yl)-2, 5-diphenyl tetrazolium bromide) assay. Among these agents the cdk7 inhibitor was most effective and showed efficacy at nanomolar concentrations. Additionally, the inhibitors interfered with the cancer cell migration, as measured by wound healing assay, and anchorage independent growth, as measured by soft agar colony formation. In stark contrast, the inhibitors had no cytotoxic effects on primary neurons. Mechanistically, western blot analysis showed that the tumor cells treated with the inhibitors had reduced levels of Pol II C-terminal domain phosphorylation, indicative of its inhibition and suppression of transcription. Furthermore, inhibitor treatment resulted in a significant reduction in p70S6 kinase phosphorylation, suggesting that in addition to the transcriptional machinery, the translational machinery is also affected upon treatment with the aforementioned cdk inhibitors. Immunostaining analysis of the cells showed a marked reduction in the levels of P-Pol II and P-p70S6 kinase upon inhibitor treatment, confirming that the cdk inhibitors indeed interfere with both transcription and translation. These inhibitors appear to be working in a p53-dependent fashion. These novel findings shed light on potential mechanisms that can be targeted to combat both glioblastoma and medulloblastoma effectively. More specifically, our studies imply that cdk7 and cdk9 inhibitors may serve as potential therapies for effective management of brain tumor. Citation Format: Isha Bhutada, Srikumar Chellappan, Jaya Padmanabhan. Targeting transcription-associated CDKs is an effective way to combat glioblastoma and medulloblastoma with minimal effect on primary neurons [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 2310.