MYCN, proliferative heterogeneity and treatment response in neuroblastoma

The amplification of the MYCN oncogene, occurring in 20% of neuroblastomas, a tumor of early childhood, is associated with drug-resistant relapse and poor prognosis. High MYCN expression has paradoxical effects in most cells: it promotes cell cycle progression and sensitizes to cell death. This work aims to characterize, at population and single-cell level, the mechanisms through which amplified MYCN allows tumor regrowth after chemotherapy in neuroblastoma. In MYCN-regulatable neuroblastoma cell line models, MYCN shortens the lengths of cell cycle phases, preferentially in G1, and increases the proportion of cycling cells under exponential growth. Upon DNA-damage induced by the chemotherapeutic agent, doxorubicin (DOX), MYCN delays activation of cell cycle checkpoints and boosts the proportion of transiting cells. During and after chemotherapy MYCN favors cell death and suppresses cellular senescence, shifting p53 downstream effects from cell cycle arrest to apoptosis. However, MYCN also drives clonal regrowth of a small fraction of surviving resister cells after DNA-damage. These resister cells exhibit nearly identical molecular and phenotypic profiles as cells before treatment. Live-cell imaging reveals that resister cells arise exclusively from the G1-phase-arrested subpopulation and rapidly repair DNA-damage-induced double-strand breaks (DSBs). The suppression of DNA repair via ATM inhibition during chemotherapy results in reduction of G1 phase arrest and prevents DNA DSB repair, completely eradicating resister cells. Taken together, these data show that non-genetic tumor heterogeneity and a key oncogenic lesion, MYCN, synergize to resume cellular proliferation after DNA damage and probably cause chemotherapy resistance. This work indicates that improved first-line therapies could specifically target resister cells and help avoid cellular regrowth

Characterization of Temozolomide Resistance Using a Novel Acquired Resistance Model in Glioblastoma Cell Lines

Temozolomide (TMZ) is the first line of standard therapy in glioblastoma (GBM). However, relapse occurs due to TMZ resistance. We attempted to establish an acquired TMZ resistance model that recapitulates the TMZ resistance phenotype and the relevant gene signature. Two GBM cell lines received two cycles of TMZ (150 µM) treatment for 72 h each. Regrown cells (RG2) were defined as TMZ resistant cells. MTT assay revealed significantly less susceptibility and sustained growth of RG2 compared with parental cells after TMZ challenge. TMZ-induced DNA damage significantly decreased in 53BP1-foci reporter transduced-RG2 cells compared with parental cells, associated with downregulation of MSH2 and MSH6. Flow cytometry revealed reduced G2/M arrest, increased EdU incorporation and suppressed apoptosis in RG2 cells after TMZ treatment. Colony formation and neurosphere assay demonstrated enhanced clonogenicity and neurosphere formation capacity in RG2 cells, accompanied by upregulation of stem markers. Collectively, we established an acute TMZ resistance model that recapitulated key features of TMZ resistance involving impaired mismatch repair, redistribution of cell cycle phases, increased DNA replication, reduced apoptosis and enhanced self-renewal. Therefore, this model may serve as a promising research tool for studying mechanisms of TMZ resistance and for defining therapeutic approaches to GBM in the future

Kalirin-RAC controls nucleokinetic migration in ADRN-type neuroblastoma

The migrational propensity of neuroblastoma is affected by cell identity, but the mechanisms behind the divergence remain unknown. Using RNAi and time-lapse imaging, we show that ADRN-type NB cells exhibit RAC1- and kalirin-dependent nucleokinetic (NUC) migration that relies on several integral components of neuronal migration. Inhibition of NUC migration by RAC1 and kalirin-GEF1 inhibitors occurs without hampering cell proliferation and ADRN identity. Using three clinically relevant expression dichotomies, we reveal that most of up-regulated mRNAs in RAC1- and kalirin-GEF1-suppressed ADRN-type NB cells are associated with low-risk characteristics. The computational analysis shows that, in a context of overall gene set poverty, the upregulomes in RAC1- and kalirin-GEF1-suppressed ADRN-type cells are a batch of AU-rich element-containing mRNAs, which suggests a link between NUC migration and mRNA stability. Gene set enrichment analysis-based search for vulnerabilities reveals prospective weak points in RAC1- and kalirin-GEF1-suppressed ADRN-type NB cells, including activities of H3K27- and DNA methyltransferases. Altogether, these data support the introduction of NUC inhibitors into cancer treatment research

Eye Tumors in Childhood as First Sign of Tumor Predisposition Syndromes: Insights from an Observational Study Conducted in Germany and Austria

Simple Summary Eye tumors in children are very rare. In Europe, these eye tumors are nearly always diagnosed early and cure rates are high. However, eye tumors in childhood often occur as the first sign of a genetic tumor predisposition syndrome. This study collected data of children with malignant eye tumors diagnosed in five years in Germany and Austria to learn about the association of eye tumors in childhood with tumor predisposition syndrome. The study recruited 300 children with malignant eye tumors in childhood. In the here-presented cohort, more than 40% of eye tumors were associated with rare tumor predisposition syndromes. For this reason, all children with eye tumors and their families should receive genetic counseling for a tumor predisposition syndrome. Children with a genetic predisposition to cancer should receive a tailored surveillance, including detailed history, physical examination and, if indicated, imaging to screen for other cancers later in life. Retinoblastoma and other eye tumors in childhood are rare diseases. Many eye tumors are the first signs of a genetic tumor predisposition syndrome and the affected children carry a higher risk of developing other cancers later in life. Clinical and genetic data of all children with eye tumors diagnosed between 2013-2018 in Germany and Austria were collected in a multicenter prospective observational study. In five years, 300 children were recruited into the study: 287 with retinoblastoma, 7 uveal melanoma, 3 ciliary body medulloepithelioma, 2 retinal astrocytoma, 1 meningioma of the optic nerve extending into the eye. Heritable retinoblastoma was diagnosed in 44% of children with retinoblastoma. One child with meningioma of the optic nerve extending into the eye was diagnosed with neurofibromatosis 2. No pathogenic constitutional variant in DICER1 was detected in a child with medulloepithelioma while two children did not receive genetic analysis. Because of the known association with tumor predisposition syndromes, genetic counseling should be offered to all children with eye tumors. Children with a genetic predisposition to cancer should receive a tailored surveillance including detailed history, physical examinations and, if indicated, imaging to screen for other cancer. Early detection of cancers may reduce mortality