Blockade of MYCN in neuroblastoma
Neuroblastoma is the third most common pediatric cancer. Amplification of MYCN is a strong independent predictor of poor patient outcome. MYCN represents an attractive target for therapy, as it is serves as a genetic marker for subset of high-risk neuroblastoma and it is expressed at relatively low levels in normal tissues. The ability to inhibit MYCN in patients however, presents a formidable challenge. Many proteins active in cancer (kinases) act by adding a phosphate to a target, thereby altering the activity of the modified target. A second class of molecules active in cancer are transcription factors, proteins that bind DNA and turn on the expression of genes critical to the continued survival of cancer cells. Although many drugs have been developed that block kinase function, there is little precedent for development of orally available small molecules that selectively target transcription factors. Our proposal leverages the observation that the stability of MYCN protein, a transcription factor, is markedly impacted by phosphorylation, and that MYCN can be destabilized and degraded using small molecules that drive its phosphorylation. Since identifying this class of inhibitors, we have more fully characterized both the efficacy and toxicity of these drug-like molecules against neuroblastoma tumors in cell culture, and in animal models. We have previously generated and characterized a mouse model of neuroblastoma driven by MYCN, which shares many features with high-risk childhood neuroblastoma. In mice with neuroblastoma, daily treatment with PW12, a tool compound PI3K inhibitor that blocked MYCN (but also interfered with other cell functions) was effective, but was associated with significant toxicity. In our initial ALSF application, we obtained the Novartis drug NVP-BEZ235 that worked through the same mechanism, with fewer off-target effects. In work supported by ALSF and now in revision, we showed that NVP-BEZ235 improved survival in mice with neuroblastoma. Tumors relapsed after discontinuing therapy however, consistent with a drug that could block cells from growing, but was not actually killing cancer cells. In this application, we explore combination therapy approaches, using drugs rather than drug-like compounds, to finesse cell death in neuroblastoma. Successful completion of this application will determine whether this combination of drugs induces apoptosis in genetically engineered and in xenografted mouse models of neuroblastoma, resulting in durable remissions preclinically; and provides a preclinical rationale to test this combination of agents in children with neuroblastoma.