Novel experimental targeted therapy of neuroblastoma

• Neuroblastoma, a malignancy of the sympathetic nervous system, is the most common solid extracranial tumor of infancy and is responsible for around 15% of the cancer-related deaths in children. For the entire group the survival has increased over the last decades, but despite today's intense muti-modal therapy the survival of high-risk neuroblastomas lies just around 50%. Therefore, novel treatment options are urgently needed and awaited. The development of novel cancer therapies has geared up with more and more agents entering trials and become clinically available, but this has predominately been directed towards the adult oncology area. Hopefully, legal directives will act as a 'carrot and a stick' on companies to take more interest in the pediatric area. There are concerns, with all rights, about how much efficacy a novel drug should need to show before it can be justified to move into the clinic. Preclinical animal models of cancer have established their role in the evaluation of these agents. But there is everlasting uncertainty about how truly they represent all or parts of a particular disease, and if in vivo efficacy is predictive of clinical value. This thesis describes the investigation of six novel targeted therapies, evaluated in vitro and in vivo in neuroblastoma. Anti-angiogenic antibody-therapy with bevacizumab (Avastin®) showed efficacy in vivo in three neuroblastoma xenograft models. Primary material from neuroblastoma was shown to express activated Akt and mTOR. Inhibition of the mTOR signalling pathway with rapamycin (Rapamune®) or its novel analogue CCI-779 (Torisel®) showed promising potential in vitro and in vivo, where the most interesting finding was that MYCN-amplified or over expressing cells were more sensitive. Upon treatment in vitro and in vivo we observed a down regulation of MYCN and cyclin D1 protein. Inhibition of the upstream signalling pathway with the PDK1 inhibitor OSU03012 or the dual PI3K/mTOR inhibitor PI103 did also show promising effects in vitro and in vivo. The major finding was that inhibition upstream of mTOR seemed most effective in MYCN-amplified or over expressing cells. As observed previously, treatment was associated with a down regulation of MYCN and cyclin D1 proteins. Targeting the MYCN protein with the Myc-Max disruptor 10058-F4 had effect in vitro. There were modest effects of 10058-F4 in vivo on a MYCN-amplified xenograft model, whereas in vivo in the transgenic MYCN-driven model of neuroblastoma, 10058-F4 showed some interesting potential. In summary, this thesis suggests that targeting angiogenesis in neuroblastoma appear as an interesting strategy. Primary neuroblastoma seems to be over expressing key proteins in the PI3K/Akt/mTOR pathway and targeting these with inhibitors seems to have efficacy, especially in the context of a MYCN-amplification or over expression. Also, interfering with the MYCN protein appears as an interesting approach. Some of these compounds are currently easing their way into the pediatric oncology area and hopefully in the future they, and the results generated in this thesis, will aid in improving the survival of children with neuroblastoma.

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