Integrating copy number data of 64 iAMP21 BCP-ALL patients narrows the common region of amplification to 1.57 Mb

Background and purposeIntrachromosomal amplification of chromosome 21 (iAMP21) is a rare subtype of B-cell precursor acute lymphoblastic leukaemia (BCP-ALL). It is unknown how iAMP21 contributes to leukaemia. The currently known commonly amplified region is 5.1 Mb.MethodsWe aimed to narrow down the common region of amplification by using high resolution techniques. Array comparative genomic hybridization (aCGH) was used to determine copy number aberrations, Affymetrix U133 Plus2 expression arrays were used to determine gene expression. Genome-wide expression correlations were evaluated using Globaltest.ResultsWe narrowed down the common region of amplification by combining copy number data from 12 iAMP21 cases with 52 cases from literature. The combined common region of amplification was 1.57 Mb, located from 36.07 to 37.64 Mb (GRCh38). This region is located telomeric from, but not including, RUNX1, which is the locus commonly used to diagnose iAMP21. This narrow region, which falls inside the Down Syndrome critical region, includes 13 genes of which the expression of eight genes was significantly upregulated compared with 143 non-iAMP21 B-other cases. Among these, transcriptional repressor RIPPLY3 (also known as DSCR6) was the highest overexpressed gene (fold change = 4.2, FDR DiscussionThe more precise definition of the common region of amplification could be beneficial in the diagnosis of iAMP21 based on copy number analysis from DNA sequencing or arrays as well as stimulate functional research into the role of the included genes in iAMP21 biology.</p

A novel mutation in the miR-128b gene reduces miRNA processing and leads to glucocorticoid resistance of MLL-AF4 Acute Lymphocytic Leukemia cells

MLL-AF4 Acute Lymphocytic Leukemia has a poor prognosis, and the mechanisms by which these leukemias develop are not understood despite intensive research based on well-known concepts and methods. MicroRNAs (miRNAs) are a new class of small noncoding RNAs that post-transcriptionally regulate expression of target mRNA transcripts. We recently reported that ectopic expression of miR-128b together with miR-221, two of the miRNAs downregulated in MLL-AF4 ALL, restores glucocorticoid resistance through downregulation of the MLL-AF4 chimeric fusion proteins MLL-AF4 and AF4-MLL that are generated by chromosomal translocation t(4;11). Here we report the identification of new mutations in miR-128b in RS4;11 cells, derived from MLL-AF4 ALL patient. One novel mutation significantly reduces the processing of miR-128b. Finally, this base change occurs in a primary MLL-AF4 ALL sample as an acquired mutation. These results demonstrate that the novel mutation in miR-128b in MLL-AF4 ALL alters the processing of miR-128b and that the resultant downregulation of mature miR-128b contributes to glucocorticoid resistance through the failure to downregulate the fusion oncogenes.National Institutes of Health (U.S.) (NIH Grant R01 DK068348)Netherlands Organization for Scientific ResearchDutch Cancer SocietyJapan Society for the Promotion of Scienc

Targeted treatment options for paediatric B-cell precursor acute lymphoblastic leukaemia patients with constitutional or somatic chromosome 21 alterations

Background: Chromosome 21 is affected in ∼60% of paediatric B-cell precursor acute lymphoblastic leukaemia (BCP-ALL) patients and includes somatic and constitutional gains, intrachromosomal amplification of chromosome 21 (iAMP21), and the translocation t(12;21) resulting in the ETV6::RUNX1 gene fusion. Methods: Since these numeric and structural chromosome 21 alterations are not targetable, we studied the type and frequency of yet-proven targetable events co-occurring with chromosome 21 alterations.Results: Among 307 primary paediatric BCP-ALL cases, JAK/STAT pathway lesions were most frequent in patients with constitutional gain of chromosome 21 (Down syndrome ALL; 35/71, 49%) and iAMP21 (9/22, 41%). RAS pathway lesions were most frequent in high hyperdiploidy (62/108, 57%) and FLT3 lesions were most frequent in iAMP21 (7/22, 32%). Virtually all cases expressed CD19 and CD22 at the cell surface. Positivity for CD20 surface expression ranged from 67% in iAMP21 (8/12) to 20% in ETV6::RUNX1 (26/129). Conclusion: Activated JAK/STAT, RAS or FLT3 signalling, and CD marker surface expression may provide targetable treatment options for the majority of chromosome 21-altered BCP-ALL cases.</p

Tyrosine kinase inhibitor resistance in de novo BCR::ABL1–positive BCP-ALL beyond kinase domain mutations

A better understanding of ABL1 kinase domain mutation–independent causes of tyrosine kinase inhibitor (TKI) resistance is needed for BCR::ABL1–positive B-cell precursor acute lymphoblastic leukemia (BCP-ALL). Although TKIs have dramatically improved outcomes, a subset of patients still experiences relapsed or refractory disease. We aimed to identify potential biomarkers of intrinsic TKI resistance at diagnosis in samples from 32 pediatric and 19 adult patients with BCR::ABL1–positive BCP-ALL. Reduced ex vivo imatinib sensitivity was observed in cells derived from newly diagnosed patients who relapsed after combined TKI and chemotherapy treatment compared with cells derived from patients who remained in continuous complete remission. We observed that ex vivo imatinib resistance was inversely correlated with the amount of (phosphorylated) BCR::ABL1/ABL1 protein present in samples that were taken at diagnosis without prior TKI exposure. This suggests an intrinsic cause of TKI resistance that is independent of functional BCR::ABL1 signaling. Simultaneous deletions of IKZF1 and CDKN2A/B and/or PAX5 (IKZF1plus), as well as deletions of PAX5 alone, were related to ex vivo imatinib resistance. In addition, somatic lesions involving ZEB2, SETD2, SH2B3, and CRLF2 were associated with reduced ex vivo imatinib sensitivity. Our data suggest that the poor prognostic value of IKZF1(plus) deletions is linked to intrinsic mechanisms of TKI resistance other than ABL1 kinase domain mutations in newly diagnosed pediatric and adult BCR::ABL1–positive BCP-ALL.</p

Genome-wide profiling of p53-regulated enhancer RNAs uncovers a subset of enhancers controlled by a lncRNA

p53 binds enhancers to regulate key target genes. Here, we globally mapped p53-regulated enhancers by looking at enhancer RNA (eRNA) production. Intriguingly, while many p53-induced enhancers contained p53-binding sites, most did not. As long non-coding RNAs(lncRNAs) are prominent regulators of chromatin dynamics, we hypothesized that p53-induced lncRNAs contribute to the activation of enhancers by p53. Among p53-induced lncRNAs, we identified LED and demonstrate that its suppression attenuates p53 function. Chromatin-binding and eRNA expression analyses show that LED associates with and activates strong enhancers. One prominent target of LED was located at an enhancer region within CDKN1A gene, a potent p53-responsive cell cycle inhibitor. LED knockdown reduces CDKN1A enhancer induction and activity, and cell cycle arrest following p53 activation. Finally, promoter-associated hypermethylation analysis shows silencing of LED in human tumours. Thus, our study identifies a new layer of complexity in the p53 pathway and suggests its dysregulation in cancer

Chromosomal instability in aneuploid acute lymphoblastic leukemia associates with disease progression

Chromosomal instability (CIN) lies at the core of cancer development leading to aneuploidy, chromosomal copy-number heterogeneity (chr-CNH) and ultimately, unfavorable clinical outcomes. Despite its ubiquity in cancer, the presence of CIN in childhood B-cell acute lymphoblastic leukemia (cB-ALL), the most frequent pediatric cancer showing high frequencies of aneuploidy, remains unknown. Here, we elucidate the presence of CIN in aneuploid cB-ALL subtypes using single-cell whole-genome sequencing of primary cB-ALL samples and by generating and functionally characterizing patient-derived xenograft models (cB-ALL-PDX). We report higher rates of CIN across aneuploid than in euploid cB-ALL that strongly correlate with intraclonal chr-CNH and overall survival in mice. This association was further supported by in silico mathematical modeling. Moreover, mass-spectrometry analyses of cB-ALL-PDX revealed a "CIN signature" enriched in mitotic-spindle regulatory pathways, which was confirmed by RNA-sequencing of a large cohort of cB-ALL samples. The link between the presence of CIN in aneuploid cB-ALL and disease progression opens new possibilities for patient stratification and offers a promising new avenue as a therapeutic target in cB-ALL treatment.</p

Oncogenic and immunological targets for matched therapy of pediatric blood cancer patients: Dutch iTHER study experience

Over the past 10 years, institutional and national molecular tumor boards have been implemented for relapsed or refractory pediatric cancer to prioritize targeted drugs for individualized treatment based on actionable oncogenic lesions, including the Dutch iTHER platform. Hematological malignancies form a minority in precision medicine studies. Here, we report on 56 iTHER leukemia/lymphoma patients for which we considered cell surface markers and oncogenic aberrations as actionable events, supplemented with ex vivo drug sensitivity for six patients. Prior to iTHER registration, 34% of the patients had received allogeneic hematopoietic cell transplantation (HCT) and 18% CAR-T therapy. For 51 patients (91%), a sample with sufficient tumor percentage (≥20%) required for comprehensive diagnostic testing was obtained. Up to 10 oncogenic actionable events were prioritized in 49/51 patients, and immunotherapy targets were identified in all profiled patients. Targeted treatment(s) based on the iTHER advice was given to 24 of 51 patients (47%), including immunotherapy in 17 patients, a targeted drug matching an oncogenic aberration in 12 patients, and a drug based on ex vivo drug sensitivity in one patient, resulting in objective responses and a bridge to HCT in the majority of the patients. In conclusion, comprehensive profiling of relapsed/refractory hematological malignancies showed multiple oncogenic and immunotherapy targets for a precision medicine approach, which requires multidisciplinary expertise to prioritize the best treatment options for this rare, heavily pretreated pediatric population

Gene Expression Profiles Associated with Pediatric Relapsed AML

Development of relapse remains a problem for further improvements in the survival of pediatric AML patients. While virtually all patients show a good response to initial treatment, more patients respond poorly when treated at relapse. The cellular characteristics of leukemic blast cells that allow survival of initial treatment, relapse development and subsequent resistance to salvage treatment remain largely elusive. Therefore, we studied if leukemic blasts at relapse biologically resemble their initial diagnosis counterparts. We performed microarray gene expression profiling on paired initial and relapse samples of 23 pediatric AML patients. In 11 out of 23 patients, gene expression profiles of initial and corresponding relapse samples end up in different clusters in unsupervised analysis, indicating altered gene expression profiles. In addition, shifts in type I/II mutational status were found in 5 of these 11 patients, while shifts were found in 3 of the remaining 12 patients. Although differentially expressed genes varied between patients, they were commonly related to hematopoietic differentiation, encompassed genes involved in chromatin remodeling and showed associations with similar transcription factors. The top five were CEBPA, GFI1, SATB1, KLF2 and TBP. In conclusion, the leukemic blasts at relapse are biologically different from their diagnosis counterparts. These differences may be exploited for further development of novel treatment strategies