Faculty Bibliography

In the field of oncology, a growing emphasis is now being placed on individualizing treatment in a way that maximizes chance for cure while minimizing unwanted side effects. In childhood acute lymphoblastic leukemia (ALL), several well-established clinical and biologic prognostic variables have traditionally been used to risk stratify therapy for individual patients. While this approach has been very successful, many relapses still occur unpredictably in patients characterized as having favorable features of their disease at diagnosis. Furthermore, it is likely that other children are overtreated. Therefore, current initiatives in childhood leukemia have focused on identifying new prognostic markers to refine treatment decision-making. Recent advances, which include the sequencing of the human genome, and technical developments in high-throughput genomics and proteomics, have facilitated these efforts. This review will chart the evolution of individualized therapy for ALL, the most common malignancy of children.

Childhood acute lymphoblastic leukemia is one of the most curable of all human cancers, but new approaches are urgently needed for children who relapse and to avoid severe side effects of curative therapy. Work from the laboratories of Rob Pieters and William Evans, including a paper in this issue of Cancer Cell, has led to the identification of genes whose expression correlates with drug crossresistance and long term outcome. The goal is now to integrate these and other findings using gene expression technology into the care of children with the most common pediatric malignancy

BACKGROUND: Autoregulation of the myc gene family is a negative feedback mechanism known to occur at high levels of Myc expression. Loss of this mechanism and associated Myc overexpression has been observed in human tumors, thereby contributing to tumorigenesis. The childhood tumor neuroblastoma is characterized by N-myc amplification in aggressive and highly proliferative tumors that occur in a subset of patients. The precise molecular mechanism of autoregulation is unknown, and previous observations indicated that N-myc autoregulation was intact only in single-copy neuroblastoma cell lines. METHODS: Transient reporter assays and trichostatin A (TSA) experiments were performed to evaluate several candidate genes, including Mxi1, c-myc promoter binding protein 1 (MBP-1), Miz, and histone deacetylase 2 (HDAC2), for their involvement in N-myc autoregulation. Mxi1 and HDAC2 were examined further for their expression levels and effects on endogenous N-myc levels. Finally, their recruitments to the N-myc promoter were investigated by chromatin immunoprecipitation (ChIP). RESULTS: The autoregulatory circuit was operative, even in amplified cell lines. Mxi1 consistently showed a modest effect in down-regulating N-myc in transient reporter assays. Overexpression of the c-myc, Mxi1, and mHDAC2 genes resulted in a threefold to fourfold decrease in endogenous N-myc levels. Mxi1 and HDAC2 were up-regulated by N-Myc in an myc-inducible cell line and in N-myc-expressing cell lines. In addition, down-regulation of the N-myc promoter was relieved in the presence of TSA. Increased association of HDAC2 with the autoregulatory region within the N-myc promoter by ChIP was observed upon down-regulation of endogenous N-myc. CONCLUSIONS: The autoregulatory circuit was intact in both amplified and single-copy neuroblastoma cell lines. Furthermore, myc gene autoregulation occurred through histone deacetylation

BACKGROUND: Amplification of the N-myc oncogene is associated with adverse outcomes in the common childhood tumor, neuroblastoma. Because the transforming properties of Myc are related to its ability to modulate gene expression, the authors used cDNA microarrays to identify potential Myc target genes. METHODS: Expression levels of 4608 genes were analyzed in a series of neuroblastoma cell lines. Identical analyses were performed in a panel of medulloblastoma cell lines to identify c-Myc targets and to determine the extent to which N-Myc targets and c-Myc targets were shared. Comparisons were made between cell lines with high levels versus low levels of Myc protein expression. RESULTS: Array analyses yielded 121 genes with increased expression levels (>or= 1.65-fold) and 9 genes with decreased expression levels in N-Myc-expressing versus nonexpressing cell lines. Many of these were newly identified targets of biologic interest. Fifty percent of the N-Myc targets (60 of 121) were mutual c-Myc targets. A significant correlation between the level of N-myc and selected target gene expression was demonstrated independently in 27 neuroblastoma tumor samples and in an N-myc-inducible cell line system. CONCLUSIONS: A number of diverse pathways are modulated by N-Myc in neuroblastoma. Although, overall, there was significant correlation between myc and target transcript expression among cohorts of tumors, great variability in levels of target expression was seen among individual tumor samples, and this biologic heterogeneity in the levels of target gene expression may offer insight into differences in the clinical behavior of neuroblastoma and may prove to be of prognostic significance in the future