Research ArticleCancer therapy

Developmental phosphoproteomics identifies the kinase CK2 as a driver of Hedgehog signaling and a therapeutic target in medulloblastoma

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Sci. Signal.  11 Sep 2018:
Vol. 11, Issue 547, eaau5147
DOI: 10.1126/scisignal.aau5147

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A targeted, resilient treatment for medulloblastoma

Medulloblastoma is an aggressive type of brain tumor that most often arises in children and lacks targeted therapeutic options. The subtypes driven by activity in the sonic hedgehog (SHH) pathway are particularly resistant to current drugs, such as those known as SMO inhibitors, which target this pathway. Purzner et al. used phosphoproteomics to track the development of mouse cells that give rise to medulloblastoma and identified the kinase CK2 as a likely target. CK2 inhibitors blocked the growth of SMO inhibitor–resistant, SHH-type human and mouse medulloblastoma cells and markedly extended the survival of tumor-bearing mice, in which the drug was well tolerated. One of the compounds also blocked the growth of tumors that had mutant CK2, suggesting that it is less susceptible to a common mode of drug resistance. A clinical trial is under way to test this inhibitor in pediatric patients.

Abstract

A major limitation of targeted cancer therapy is the rapid emergence of drug resistance, which often arises through mutations at or downstream of the drug target or through intrinsic resistance of subpopulations of tumor cells. Medulloblastoma (MB), the most common pediatric brain tumor, is no exception, and MBs that are driven by sonic hedgehog (SHH) signaling are particularly aggressive and drug-resistant. To find new drug targets and therapeutics for MB that may be less susceptible to common resistance mechanisms, we used a developmental phosphoproteomics approach in murine granule neuron precursors (GNPs), the developmental cell of origin of MB. The protein kinase CK2 emerged as a driver of hundreds of phosphorylation events during the proliferative, MB-like stage of GNP growth, including the phosphorylation of three of the eight proteins commonly amplified in MB. CK2 was critical to the stabilization and activity of the transcription factor GLI2, a late downstream effector in SHH signaling. CK2 inhibitors decreased the viability of primary SHH-type MB patient cells in culture and blocked the growth of murine MB tumors that were resistant to currently available Hh inhibitors, thereby extending the survival of tumor-bearing mice. Because of structural interactions, one CK2 inhibitor (CX-4945) inhibited both wild-type and mutant CK2, indicating that this drug may avoid at least one common mode of acquired resistance. These findings suggest that CK2 inhibitors may be effective for treating patients with MB and show how phosphoproteomics may be used to gain insight into developmental biology and pathology.

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