Patient-derived xenograft mouse models to investigate tropism to the central nervous system and retina of primary and secondary central nervous system lymphoma.

AIMS: How and why lymphoma cells home to the central nervous system and vitreoretinal compartment in primary diffuse large B-cell lymphoma of the central nervous system remain unknown. Our aim was to create an in vivo model to study lymphoma cell tropism to the central nervous system. METHODS: We established a patient-derived central nervous system lymphoma xenograft mouse model and characterised xenografts derived from four primary and four secondary central nervous system lymphoma patients using immunohistochemistry, flow cytometry and nucleic acid sequencing technology. In reimplantation experiments, we analysed dissemination patterns of orthotopic and heterotopic xenografts and performed RNA sequencing of different involved organs to detect differences at the transcriptome level. RESULTS: We found that xenografted primary central nervous system lymphoma cells home to the central nervous system and eye after intrasplenic transplantation, mimicking central nervous system and primary vitreoretinal lymphoma pathology, respectively. Transcriptomic analysis revealed distinct signatures for lymphoma cells in the brain in comparison to the spleen as well as a small overlap of commonly regulated genes in both primary and secondary central nervous system lymphoma. CONCLUSION: This in vivo tumour model preserves key features of primary and secondary central nervous system lymphoma and can be used to explore critical pathways for the central nervous system and retinal tropism with the goal to find new targets for novel therapeutic approaches.

CXCR4, CXCR5 and CD44 May Be Involved in Homing of Lymphoma Cells into the Eye in a Patient Derived Xenograft Homing Mouse Model for Primary Vitreoretinal Lymphoma.

Background: Primary vitreoretinal lymphoma (PVRL), a rare malignancy of the eye, is strongly related to primary central nervous system lymphoma (PCNSL). We hypothesized that lymphoma cells disseminate to the CNS and eye tissue via distinct homing receptors. The objective of this study was to test expression of CXCR4, CXCR5, CXCR7 and CD44 homing receptors on CD20 positive B-lymphoma cells on enucleated eyes using a PCNSL xenograft mouse model. Methods: We used indirect immunofluorescence double staining for CD20/CXCR4, CD20/CXCR5, CD20/CXCR7 and CD20/CD44 on enucleated eyes of a PCNSL xenograft mouse model with PVRL phenotype (PCNSL group) in comparison to a secondary CNS lymphoma xenograft mouse model (SCNSL group). Lymphoma infiltration was evaluated with an immunoreactive score (IRS). Results: 11/13 paired eyes of the PCNSL but none of the SCNSL group were infiltrated by CD20-positive cells. Particularly the choroid and to a lesser extent the retina of the PCNSL group were infiltrated by CD20+/CXCR4+, CD20+/CXCR5+, few CD20+/CD44+ but no CD20+/CXCR7+ cells. Expression of CXCR4 (p = 0.0205), CXCR5 (p = 0.0004) and CD44 (p < 0.0001) was significantly increased in the PCNSL compared to the SCNSL group. Conclusions: CD20+ PCNSL lymphoma cells infiltrating the eye co-express distinct homing receptors such as CXCR4 and CXCR5 in a PVRL homing mouse model. These receptors may be involved in PVRL homing into the eye.

Induction of Acquired Resistance towards EGFR Inhibitor Gefitinib in a Patient-Derived Xenograft Model of Non-Small Cell Lung Cancer and Subsequent Molecular Characterization.

In up to 30% of non-small cell lung cancer (NSCLC) patients, the oncogenic driver of tumor growth is a constitutively activated epidermal growth factor receptor (EGFR). Although these patients gain great benefit from treatment with EGFR tyrosine kinase inhibitors, the development of resistance is inevitable. To model the emergence of drug resistance, an EGFR-driven, patient-derived xenograft (PDX) NSCLC model was treated continuously with Gefitinib in vivo. Over a period of more than three months, three separate clones developed and were subsequently analyzed: Whole exome sequencing and reverse phase protein arrays (RPPAs) were performed to identify the mechanism of resistance. In total, 13 genes were identified, which were mutated in all three resistant lines. Amongst them the mutations in NOMO2, ARHGEF5 and SMTNL2 were predicted as deleterious. The 53 mutated genes specific for at least two of the resistant lines were mainly involved in cell cycle activities or the Fanconi anemia pathway. On a protein level, total EGFR, total Axl, phospho-NFκB, and phospho-Stat1 were upregulated. Stat1, Stat3, MEK1/2, and NFκB displayed enhanced activation in the resistant clones determined by the phosphorylated vs. total protein ratio. In summary, we developed an NSCLC PDX line modelling possible escape mechanism under EGFR treatment. We identified three genes that have not been described before to be involved in an acquired EGFR resistance. Further functional studies are needed to decipher the underlying pathway regulation.

Epigenetic upregulation of lncRNAs at 13q14.3 in leukemia is linked to the In Cis downregulation of a gene cluster that targets NF-kB.

Non-coding RNAs are much more common than previously thought. However, for the vast majority of non-coding RNAs, the cellular function remains enigmatic. The two long non-coding RNA (lncRNA) genes DLEU1 and DLEU2 map to a critical region at chromosomal band 13q14.3 that is recurrently deleted in solid tumors and hematopoietic malignancies like chronic lymphocytic leukemia (CLL). While no point mutations have been found in the protein coding candidate genes at 13q14.3, they are deregulated in malignant cells, suggesting an epigenetic tumor suppressor mechanism. We therefore characterized the epigenetic makeup of 13q14.3 in CLL cells and found histone modifications by chromatin-immunoprecipitation (ChIP) that are associated with activated transcription and significant DNA-demethylation at the transcriptional start sites of DLEU1 and DLEU2 using 5 different semi-quantitative and quantitative methods (aPRIMES, BioCOBRA, MCIp, MassARRAY, and bisulfite sequencing). These epigenetic aberrations were correlated with transcriptional deregulation of the neighboring candidate tumor suppressor genes, suggesting a coregulation in cis of this gene cluster. We found that the 13q14.3 genes in addition to their previously known functions regulate NF-kB activity, which we could show after overexpression, siRNA-mediated knockdown, and dominant-negative mutant genes by using Western blots with previously undescribed antibodies, by a customized ELISA as well as by reporter assays. In addition, we performed an unbiased screen of 810 human miRNAs and identified the miR-15/16 family of genes at 13q14.3 as the strongest inducers of NF-kB activity. In summary, the tumor suppressor mechanism at 13q14.3 is a cluster of genes controlled by two lncRNA genes that are regulated by DNA-methylation and histone modifications and whose members all regulate NF-kB. Therefore, the tumor suppressor mechanism in 13q14.3 underlines the role both of epigenetic aberrations and of lncRNA genes in human tumorigenesis and is an example of colocalization of a functionally related gene cluster.

Chronic lymphocytic leukemia and 13q14: miRs and more.

Loss of a critical region in 13q14.3 [del(13q)] is the most common genomic aberration in chronic lymphocytic leukemia (CLL), occurring in more than 50% of patients (Stilgenbauer et al., Oncogene 1998;16:1891 - 1897, Dohner et al., N Engl J Med 2000;343:1910 - 1916). Despite extensive investigations, no point mutations have been found in the remaining allele that would inactivate one of the candidate tumor suppressor genes and explain the pathomechanism postulated for this region. However, the genes in the region are significantly down-regulated in CLL cells, more than would be expected by gene dosage, and recently a complex epigenetic regulatory mechanism was identified for 13q14.3 in non-malignant cells that involves asynchronous replication timing and monoallelic expression of candidate tumor suppressor genes. Here, we propose a model of a multigenic pathomechanism in 13q14.3, where several tumor suppressor genes, including the miRNA genes miR-16-1 and miR-15a, are co-regulated by the two long non-coding RNA genes DLEU1 and DLEU2 that span the critical region. Furthermore, we propose these co-regulated genes to be involved in the same molecular pathways, thereby also forming a functional gene cluster. Elucidating the molecular and cellular function of the 13q14.3 candidate genes will shed light on the underlying pathomechanism of CLL.

Off-target effects of siRNA specific for GFP.

BACKGROUND: Gene knock down by RNAi is a highly effective approach to silence gene expression in experimental as well as therapeutic settings. However, this widely used methodology entails serious pitfalls, especially concerning specificity of the RNAi molecules. RESULTS: We tested the most widely used control siRNA directed against GFP for off-target effects and found that it deregulates in addition to GFP a set of endogenous target genes. The off-target effects were dependent on the amount of GFP siRNA transfected and were detected in a variety of cell lines. Since the respective siRNA molecule specific for GFP is widely used as negative control for RNAi experiments, we studied the complete set of off-target genes of this molecule by genome-wide expression profiling. The detected modulated mRNAs had target sequences homologous to the siRNA as small as 8 basepairs in size. However, we found no restriction of sequence homology to 3'UTR of target genes. CONCLUSION: We can show that even siRNAs without a physiological target have sequence-specific off-target effects in mammalian cells. Furthermore, our analysis defines the off-target genes affected by the siRNA that is commonly used as negative control and directed against GFP. Since off-target effects can hardly be avoided, the best strategy is to identify false positives and exclude them from the results. To this end, we provide the set of false positive genes deregulated by the commonly used GFP siRNA as a reference resource for future siRNA experiments.

Allelic silencing at the tumor-suppressor locus 13q14.3 suggests an epigenetic tumor-suppressor mechanism.

Genomic material from chromosome band 13q14.3 distal to the retinoblastoma locus is recurrently lost in a variety of human neoplasms, indicating an as-yet-unidentified tumor-suppressor mechanism. No pathogenic mutations have been found in the minimally deleted region until now. However, in B cell chronic lymphocytic leukemia tumors with loss of one copy of the critical region, respective candidate tumor-suppressor genes are down-regulated by a factor >2, which would be expected by a normal gene-dosage effect. This finding points to an epigenetic pathomechanism. We find that the two copies of the critical region replicate asynchronously, suggesting differential chromatin packaging of the two copies of 13q14.3. Although we also detect monoallelic silencing of genes localized in the critical region, monoallelic expression originates from either the maternal or paternal copy, excluding an imprinting mechanism. DNA methylation analyses revealed one CpG island of the region to be methylated. DNA demethylation of this CpG island and global histone hyperacetylation induced biallelic expression, whereas replication timing was not affected. We propose that differential replication timing represents an early epigenetic mark that distinguishes the two copies of 13q14.3, resulting in differential chromatin packaging and monoallelic expression. Accordingly, deletion of the single active copy of 13q14.3 results in significant down-regulation of the candidate genes and loss of function, providing a model for the interaction of genetic lesions and epigenetic silencing at 13q14.3 in B cell chronic lymphocytic leukemia.