Background: Polyamines are highly regulated essential cations that are elevated in rapidly proliferating tissues including cancers. The polyamine biosynthetic gene and MYC/N target ornithine decarboxylase (ODC1) has previously been identified as a therapeutic target for neuroblastoma. Studies in preclinical models targeting multiple steps in the pathway enhances therapeutic efficacy (Haber ANR 2012) and an international phase I clinical trial for refractory neuroblastoma will open shortly, using the ODC1 inhibitor, α-difluoromethylornithine (DFMO), and the SAT1 inducer, celecoxib. Here we examine the prognostic impact of all the polyamine pathway genes in a large cohort of neuroblastoma tumours and investigate their regulation by MYCN.
Methods: Gene-expression profiles of 650 primary untreated neuroblastomas were analysed for all polyamine pathway genes and related to clinical outcome. Activation or repression of the genes by MYCN was determined by chromatin immunoprecipitation (ChIP) studies and polyamine gene promoters were cloned into luciferase reporter vectors and tested as a function of MYCN expression.
Results: Expression of all polyamine pathway genes was highly prognostic of outcome in neuroblastoma, with high levels of each biosynthetic gene and low levels of each catabolic gene predicting poor outcome. In the MYCN amplified cohort of tumours, there was increased expression of each biosynthetic gene and decreased expression of each catabolic gene compared to the non-amplified cohort. ChIP and luciferase activity assays confirmed that MYCN binds each biosynthetic gene at the E-box site, activating transcription, whilst each catabolic gene was transcriptionally repressed by MYCN, which binds in proximity to the transcription start site by interacting with the Sp1 protein.
Conclusions: The results provide a remarkable demonstration of an oncogene coordinately regulating the expression of every gene in a metabolic pathway in order to drive cell proliferation. The findings highlight the importance of polyamines in neuroblastoma and identify additional target enzymes for potential therapeutic intervention.