Neuroblastoma, a rapidly growing yet treatment responsive cancer, is the third most common cancer of children and the most common solid tumor in infants. Unfortunately, neuroblastoma that has lost p53 function often has a highly treatment-resistant phenotype leading to tragic outcomes. In the context of neuroblastoma, the functions of p53 and MYCN (which is amplified in ~25% of neuroblastomas) are integrally linked because they are mutually transcriptionally regulated, and because they together regulate the catalytic activity of RNA polymerases. Didymin is a citrus-derived natural compound that kills p53 wild-type as well as drug-resistant p53-mutant neuroblastoma cells in culture. In addition, orally administered didymin causes regression of neuroblastoma xenografts in mouse models, without toxicity to non-malignant cells, neural tissues, or neural stem cells. RKIP is a Raf-inhibitory protein that regulates MYCN activation, is transcriptionally upregulated by didymin, and appears to play a key role in the anti-neuroblastoma actions of didymin. In this review, we discuss how didymin overcomes drug-resistance in p53-mutant neuroblastoma through RKIP-mediated inhibition of MYCN and its effects on GRK2, PKCs, Let-7 micro-RNA, and clathrin-dependent endocytosis by Raf-dependent and -independent mechanisms. In addition, we will discuss studies supporting potential clinical impact and translation of didymin as a low cost, safe, and effective oral agent that could change the current treatment paradigm for refractory neuroblastoma.

The CUB and sushi multiple domains 1 (CSMD1) gene harbors signals provided by clusters of nearby SNPs with 10-2 > p > 10-8 associations in genome wide association (GWAS) studies of addiction-related phenotypes. A CSMD1 intron 3 SNP displays p < 10-8 association with schizophrenia and more modest associations with individual differences in performance on tests of cognitive abilities. CSDM1 encodes a cell adhesion molecule likely to influence development, connections and plasticity of brain circuits in which it is expressed. We tested association between CSMD1 genotypes and expression of its mRNA in postmortem human brains (n = 181). Expression of CSMD1 mRNA in human postmortem cerebral cortical samples differs 15–25%, in individuals with different alleles of simple sequence length and SNP polymorphisms located in the gene’s third/fifth introns, providing nominal though not Bonferroni-corrected significance. These data support mice with altered CSMD1 expression as models for common human CSMD1 allelic variation. We tested baseline and/or cocaine-evoked addiction, emotion, motor and memory-related behaviors in +/- and -/- csmd1 knockout mice on mixed and on C57-backcrossed genetic backgrounds. Initial csmd1 knockout mice on mixed genetic backgrounds displayed a variety of coat colors and sizable individual differences in responses during behavioral testing. Backcrossed mice displayed uniform black coat colors. Cocaine conditioned place preference testing revealed significant influences of genotype (p = 0.02). Homozygote knockouts displayed poorer performance on aspects of the Morris water maze task. They displayed increased locomotion in some, though not all, environments. The combined data thus support roles for common level-of-expression CSMD1 variation in a drug reward phenotype relevant to addiction and in cognitive differences that might be relevant to schizophrenia. Mouse model results can complement data from human association findings of modest magnitude that identify likely polygenic influences.

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Refractory and relapsed neuroblastoma (NB) present with significant challenges in clinical management. Though primary NBs largely with wild-type p53 respond well to interventions, dysfunctional signaling in the p53 pathways in a MYCN oncogene driven background is found in a number of children with NB. The p53-mutant NB is largely unresponsive to available therapies and p53-independent targeted therapeutics represents a vital need in pediatric oncology. We analyzed the findings on mercapturic acid pathway (MAP) transporter RLIP76, which has broad and critical effects on multiple pathways as essential for carcinogenesis, oxidative stress and drug-resistance, is over-expressed in NB. RLIP76 inhibition by antibodies or depletion by antisense causes apoptosis and sensitization to chemo-radiotherapy in many cancers. In addition, recent studies indicate that the interactions between p53, MYCN, and WNT regulate apoptosis resistance and protein ubiquitination. RLIP76 and p53 interact with each other and colocalize in NB cells. Targeted depletion/inhibition of RLIP76 causes apoptosis and tumor regression in NB irrespective of p53 status. In the present review, we discuss the mechanisms and the role of RLIP76 in oxidative stress, drug-resistance and clathrin-dependent endocytosis (CDE), and analyze the molecular basis for the role of RLIP76 targeted approaches in the context principal drivers of NB pathogenesis, progression and drug-resistance. The evidence from RLIP76 studies in other cancers, when taken in the context of our recent RLIP76 focused mechanistic studies in NB, provides strong basis for further characterization and development of RLIP76 targeted therapies for NB.

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