Clinical significance of NTRK family gene expression in neuroblastomas.

BACKGROUND: Neuroblastomas (NBs) are characterized by clinical heterogeneity, from spontaneous regression to relentless progression. The pattern of NTRK family gene expression contributes to these disparate behaviors. TrkA/NTRK1 is expressed in favorable NBs that regress or differentiate, whereas TrkB/NTRK2 and its ligand brain-derived neurotrophic factor (BDNF) are co-expressed in unfavorable NBs, representing an autocrine survival pathway. We determined the significance of NTRK family gene expression in a large, representative set of primary NBs. PATIENTS AND METHODS: We analyzed the expression of the following genes in 814 NBs using quantitative real-time reverse transcriptase polymerase chain reaction (RT-PCR): NTRK1, NTRK2, NTRK3, P75/NGFR, nerve growth factor (NGF), BDNF, IGFR1, and EGFR. Expression (high vs. low) was dichotomized by median expression value and compared to clinical and biological variables as well as outcome. RESULTS: High NTRK1 expression was strongly correlated with favorable age, stage, MYCN status, histology, ploidy, risk group, and outcome (P < 0.0001 for all). However, it did not add significantly to the panel of prognostic variables currently used for cooperative group trials. NTRK2 expression was associated with risk factors but not with outcome. High NGF expression was also associated with most risk factors and weakly with unfavorable outcome. CONCLUSIONS: High expression of NTRK1 is strongly associated with favorable risk factors and outcome in a large, representative population of NB patients. It did not add significantly to the current risk prediction algorithm, but it may contribute to future expression classifiers. Indeed, prospective assessment of NTRK1 and NTRK2 expression will identify tumors that would be candidates for NTRK-targeted therapy, either alone or in combination with conventional agents.

Trk receptor expression and inhibition in neuroblastomas.

Neuroblastoma, the most common and deadly solid tumor in children, exhibits heterogeneous clinical behavior, from spontaneous regression to relentless progression. Current evidence suggests that the TRK family of neurotrophin receptors plays a critical role in these diverse behaviors. Neuroblastomas expressing TrkA are biologically favorable and prone to spontaneous regression or differentiation, depending on the absence or presence of its ligand (NGF) in the microenvironment. In contrast, TrkB-expressing tumors frequently have MYCN amplification and are very aggressive and often fatal tumors. These tumors also express the TrkB ligand (BDNF), resulting in an autocrine or paracrine survival pathway. Exposure to BDNF promotes survival, drug resistance, and angiogenesis of TrkB-expressing tumors. Here we review the role of Trks in normal development, the different functions of Trk isoforms, and the major Trk signaling pathways. We also review the roles these receptors play in the heterogeneous biological and clinical behavior of neuroblastomas, and the activation of Trk receptors in other cancers. Finally we address the progress that has been made in developing targeted therapy with Trk-selective inhibitors to treat neuroblastomas and other tumors with activated Trk expression.

Mechanisms of CHD5 Inactivation in neuroblastomas.

PURPOSE: Neuroblastomas (NBs) have genomic, biological, and clinical heterogeneity. High-risk NBs are characterized by several genomic changes, including MYCN amplification and 1p36 deletion. We identified the chromatin-remodeling gene CHD5 as a tumor suppressor gene that maps to 1p36.31. Low or absent CHD5 expression is associated with a 1p36 deletion and an unfavorable outcome, but the mechanisms of CHD5 inactivation in NBs are unknown. EXPERIMENTAL DESIGN: We examined (i) the CHD5 sequence in 188 high-risk NBs investigated through the TARGET initiative, (ii) the methylation status of the CHD5 promoter in 108 NBs with or without 1p36 deletion and/or MYCN amplification, and (iii) mRNA expression of CHD5 and MYCN in 814 representative NBs using TaqMan low-density array microfluidic cards. RESULTS: We found no examples of somatically acquired CHD5 mutations, even in cases with 1p36 deletion, indicating that homozygous genomic inactivation is rare. Methylation of the CHD5 promoter was common in the high-risk tumors, and it was generally associated with both 1p deletion and MYCN amplification. High CHD5 expression was a powerful predictor of favorable outcome, and it showed prognostic value even in multivariable analysis after adjusting for MYCN amplification, 1p36 deletion, and/or 11q deletion. CONCLUSIONS: We conclude that (i) somatically acquired CHD5 mutations are rare in primary NBs, so inactivation probably occurs by deletion and epigenetic silencing; (ii) CHD5 expression and promoter methylation are associated with MYCN amplification, suggesting a possible interaction between these 2 genes; and (iii) high CHD5 expression is strongly correlated with favorable clinical/biological features and outcome.

AZ64 inhibits TrkB and enhances the efficacy of chemotherapy and local radiation in neuroblastoma xenografts.

Neuroblastoma is a common pediatric tumor characterized by clinical heterogeneity. Because it is derived from sympathetic neuroblasts, the NTRK family of neurotrophin receptors plays an integral role in neuroblastoma cell survival, growth, and differentiation. Indeed, high expression of NTRK1 is associated with favorable clinical features and outcome, whereas expression of NTRK2 and its ligand, brain-derived neurotrophic factor (BDNF), are associated with unfavorable features and outcome. AZ64 (Astra Zeneca) is a potent and selective inhibitor of the NTRK tyrosine kinases that blocks phosphorylation at nanomolar concentrations. To determine the preclinical activity of AZ64, we performed intervention trials in a xenograft model with NTRK2-overexpressing neuroblastomas. AZ64 alone significantly inhibited tumor growth compared to vehicle-treated animals (p = 0.0006 for tumor size). Furthermore, the combination of AZ64 with conventional chemotherapeutic agents, irinotecan and temozolomide (irino-temo), showed significantly enhanced anti-tumor efficacy compared to irino-temo alone [(p < 0.0001 for tumor size, p < 0.0005 for event-free survival (EFS)]. We also assessed the combination of AZ64 and local radiation therapy (RT) on a neuroblastoma hindlimb xenograft model, and the efficacy of local RT was significantly increased when animals were treated simultaneously with AZ64 (p < 0.0001 for tumor size, p = 0.0006 for EFS). We conclude that AZ64 can inhibit growth of NTRK-expressing neuroblastomas both in vitro and in vivo. More importantly, it can significantly enhance the efficacy of conventional chemotherapy as well as local RT, presumably by inhibition of the NTRK2/BDNF autocrine survival pathway.

The effect of P75 on Trk receptors in neuroblastomas.

Neuroblastomas (NBs) with favorable outcome usually express TrkA, whereas unfavorable NBs frequently express TrkB and its cognate ligand BDNF. P75 (p75(LNTR), NGFR, TNFRSF16) binds NGF-related neurotrophins with low affinity and usually is coexpressed with Trk receptors in NBs. Here, we investigated the importance of p75 coexpression with Trk receptors in NBs. We transfected p75 into two Trk-null NB cell lines, SH-SY5Y and NLF that were also engineered to stably express TrkA or TrkB. Cell numbers were compared between single (Trk alone) and double (Trk+p75) transfectants, and proliferation was assessed by flow cytometry. P75 coexpression had little effect on cell growth in Trk NB cells in the absence of ligand, but it increased sensitivity and greatly enhanced the effect of cognate ligand. Exogenous NGF induced greater phosphorylation of TrkA and AKT. This was associated with increased cell number in TrkA/p75 cells compared to TrkA cells (p<0.01), which was due to increased proliferation in TrkA/p75 cells (p<0.05), followed by differentiation. Exogenous BDNF also increased cell number in TrkB/p75 compared to TrkB cells (p<0.01), due to an increase in proliferation, but without differentiation. Coexpression of p75 also increased specificity of Trk-expressing cells to ligand. NT3-induced phosphorylation of TrkA and AKT was reduced in TrkA/p75 cells. NT3-induced phosphorylation of TrkB (as well as AKT and MAPK) was also reduced with p75 coexpression. Our results suggest that p75 plays an important role in enhancing both the sensitivity of Trk receptors to low levels of ligand, as well as increasing the specificity of Trks to their cognate ligands. It also enhances ligand-induced differentiation in TrkA/p75 but not TrkB/p75 cells.