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Page 804 Tucker et al. Cancer Drug Resist 2019;2:803-12 I http://dx.doi.org/10.20517/cdr.2019.09

proposed, based upon age greater than 5 years, high serum lactate dehydrogenase and the involvement of
at least one metastatic site, to enable clinicians to pick out these patients at diagnosis for early referral to
[1]
novel therapeutic trials . However, there is also increasingly robust pre-clinical and clinical evidence of
molecular subgroups which predict poor outcome, not least the ultra-high-risk patient cohort exhibiting
[2,3]
both amplification of MYCN and kinase domain mutations of anaplastic lymphoma kinase (ALK) .
Herein we discuss the consequences of MYCN amplification and expression of the ALK tyrosine kinase
both individually and concomitantly, and highlight the small molecule strategies under investigation to
target these aberrations.

NOVEL THERAPEUTIC APPROACHES FOR MYCN-AMPLIFIED NEUROBLASTOMA
Amplification of MYCN is a defining feature of high-risk neuroblastoma, which when present at diagnosis,
[4]
predicts a five-year overall survival of only 50% . Tumors with amplification of MYCN are also more likely
to exhibit unfavorable histology, diploidy, 1p deletion and 17q gain, all of which are associated with poor
prognosis. Multi-modality high-risk treatment regimens for these children are contributing to improved
outcomes, but it is hoped that clinical implementation of novel targeted therapeutics will have a greater
impact for this group of patients. Various strategies to therapeutically down-regulate the activity of MYCN
have been the subject of multiple preclinical studies, but few of these have progressed to tangible clinical
[5]
trials . The development of MYCN-targeted drugs has been hindered by the complexity and variability
of primary MYC structure in solution. As a result, despite being an attractive therapeutic target, there are
no clinically available drugs that directly target MYCN. However, many promising approaches to target
MYCN indirectly and its transcriptional output have been developed. These mainly act by blocking MYCN
stability, using transcriptional inhibitors or targeting synthetic lethal interactions.

The MYC-family of oncoproteins are stabilized by altered phosphorylation at the conserved T58 and S62
[6]
residues . Signaling via the PI3K/Akt pathway in neuroblastoma regulates the phosphorylation of MYCN
through GSK3b and mTOR, which makes this pathway a suitable candidate for pharmacological inhibition
in order to indirectly target MYCN stability. Preferential sensitivity to inhibitors of PI3K/mTOR, including
NVP-BEZ235, were prominently identified in a chemical-genetic screen of isogenic neuroblastoma cells
[7]
with genetically modified MYCN stabilization versus wild-type MYCN expression . NVP-BEZ235 went
on to demonstrate growth inhibition of neuroblastoma cells via suppression of MYCN both in vitro and
in vivo. Whilst NVP-BEZ235 is not a clinical candidate compound, the PI3K/mTOR inhibitor SF1126, was
taken into pediatric trials for relapsed or refractory neuroblastoma (NCT02337309) (see Table 1 for full
summary of targeted inhibitors in clinical studies for neuroblastoma). Recruitment to this study did not
meet expectations, but it was the first pediatric study to feature the biomarkers PI3K/AKT/mTOR which
[8]
can be measured from disseminated tumor cells or platelet-rich plasma . The more potent TORC1/TORC2
inhibitor, AZD2014, has also been added to the European Proof-of-Concept therapeutic Stratification Trial
of Molecular Anomalies in Relapsed or Refractory Tumors (ESMART, NCT02813135). This trial aims to
provide targeted therapy options for pediatric patients with molecular anomalies in their tumors which are
not actionable via any other open study for children in Europe.

The control of MYCN expression has been further clarified in recent years. During the cell cycle MYCN
stability is directly controlled by Aurora-A which competes with the E3 ligase FBXW7 to prevent the
proteosomal degradation of MYCN [9-12] . Interestingly, Aurora-A is expressed at an elevated level in
[12]
MYCN-amplified neuroblastoma . We and others have reported that allosteric Aurora-A inhibitors
(such as Alisertib and CD532) can dissociate the interaction between Aurora-A and MYCN, resulting
in degradation of MYCN and reduced transcriptional output of MYCN [10,11] . Following this, two Aurora
inhibitors have been clinically evaluated in pediatrics; AT9283 (EudraCT2008-005542-23), an Aurora-A/
B inhibitor and Alisertib (NCT02444884, NCT01154816, NCT01601535, NCT01601535), a specific Aurora-A