Inflammation and organ failure strongly reduce midazolam clearance, a surrogate marker of CYP3A-mediated drug metabolism, in critically ill children. Hence, critically ill patients receiving CYP3A substrate drugs may be at risk of increased drug levels and associated toxicity.

Our findings suggest that locally elevated leptin levels may promote neointima formation, independent of obesity and systemic hyperleptinemia, but also underline the importance of perivascular inflammation in mediating the increased cardiovascular risk in obesity.

Still 20% of pediatric acute lymphoblastic leukemia (ALL) patients relapse on or after current treatment strategies. Treatment failure is associated with resistance to prednisolone. We aimed to find new druggable targets that modulate prednisolone resistance. We generated microarray gene expression profiles of 256 pediatric ALL patient samples and identified a 3.4-fold increase in epithelial membrane protein 1 (EMP1) expression in in vitro prednisolone-resistant compared with -sensitive patients (P=0.003). EMP1 silencing in six precursor-B ALL (BCP-ALL) and T-ALL cell lines induced apoptosis and cell-cycle arrest leading to 84.1±4.5% reduction in survival compared with non-silencing control transduced cells (non-silencing control short hairpin, shNSC) (P=0.014). Moreover, EMP1 silencing sensitized to prednisolone up to 18.8-fold (P<0.001). EMP1 silencing also abrogated migration and adhesion to mesenchymal stromal cells (MSCs) by 78.3±9.0 and 29.3±4.1% compared with shNSC (P<0.05). We discovered that EMP1 contributes to MSC-mediated prednisolone resistance. Pathway analysis indicated that EMP1 signals through the Src kinase family. EMP1-high BCP-ALL patients showed a poorer 5-year event-free survival compared with EMP1-low patients (77±2 vs. 89±2%, P=0.003). Multivariate analysis taking along white blood cell count, age, prednisolone resistance and subtype identified EMP1 as an independent predictor for poor outcome in BCP-ALL (P=0.004, hazard ratio: 2.36 (1.31-4.25). This study provides preclinical evidence that EMP1 is an interesting candidate for drug development to optimize treatment of BCP-ALL.

RAS pathway mutations have been linked to relapse and chemotherapy resistance in pediatric B-cell precursor acute lymphoblastic leukemia (BCP-ALL). However, comprehensive data on the frequency and prognostic value of subclonal mutations in well-defined subgroups using highly sensitive and quantitative methods are lacking. Targeted deep sequencing of 13 RAS pathway genes was performed in 461 pediatric BCP-ALL cases at initial diagnosis and in 19 diagnosis-relapse pairs. Mutations were present in 44.2% of patients, with 24.1% carrying a clonal mutation. Mutation frequencies were highest in high hyperdiploid, infant t(4;11)-rearranged, BCR-ABL1-like and B-other cases (50–70%), whereas mutations were less frequent in ETV6-RUNX1-rearranged, and rare in TCF3-PBX1- and BCR-ABL1-rearranged cases (27–4%). RAS pathway-mutated cells were more resistant to prednisolone and vincristine ex vivo. Clonal, but not subclonal, mutations were linked to unfavorable outcome in standard- and high-risk-treated patients. At relapse, most RAS pathway mutations were clonal (9 of 10). RAS mutant cells were sensitive to the MEK inhibitor trametinib ex vivo, and trametinib sensitized resistant cells to prednisolone. We conclude that RAS pathway mutations are frequent, and that clonal, but not subclonal, mutations are associated with unfavorable risk parameters in newly diagnosed pediatric BCP-ALL. These mutations may designate patients eligible for MEK inhibitor treatment.

Background Despite significant improvements in the outcome of children with B-cell precursor acute lymphoblastic leukemia (BCP-ALL), therapeutic strategies for high risk and relapsed patients are limited and cause severe side effects. Reliable risk assessment and new therapeutic targets with high specificity are therefore warranted. The RAS pathway is the most frequently mutated pathway in cancer, and the RAF-MEK-ERK kinase axis is crucial for mediating the oncogenic effects of RAS. We and others have previously shown that in pediatric BCP-ALL, RAS pathway mutations can be retrospectively linked to relapse and chemotherapy resistance. However, data on the frequency of (sub-)clonal mutations at diagnosis and hence information about the prognostic relevance at initial diagnosis is lacking. Aim Guide therapy adaptation in pediatric BCP-ALL by evaluating the prognostic relevance of RAS pathway mutations and investigating the sensitivity to MEK inhibition. Methods We performed targeted next-generation sequencing of mutational hotspots in 13 RAS pathway genes to determine the frequency and clonality of RAS pathway mutations in a large, clinically and biologically characterized cohort of BCP-ALL patients. Initial diagnosis samples of 461 patients and 19 matched diagnosis-relapse sets were included. Mutations were considered clonal at ≥25% variant allele frequency, and high coverage allowed detection of subclones with down to 1% variant allele frequency. Clinical outcome was evaluated in 244 patients treated according to a contemporary, minimal residual disease (MRD)-based protocol (DCOG ALL10). The evolution of RAS pathway mutations was studied in 19 matched sets from diagnosis and relapse. Ex vivo sensitivity of RAS pathway mutated cells towards chemotherapeutic agents and trametinib was evaluated in an MTT-based cytotoxicity assay. Results Variants in RAS pathway genes were observed in 44% of initial diagnosis pediatric BCP-ALL cases, mostly affecting NRAS, KRAS, PTPN11, and FLT3. Clonal and subclonal mutations were found in 24% and 20% of patients, respectively. The mutation frequency was highest in high hyperdiploid, infant t(4;11)-positive, BCR-ABL1-like, and B-other cases (50-70%), whereas mutations were rare in ETV6-RUNX1-positive (27%), TCF3-PBX1-positive (8%) and BCR-ABL1-positive cases (4%). In matched diagnosis-relapse sets, clonal mutations at diagnosis were preserved at relapse, whereas the kinetics of subclones was variable. Interestingly, most RAS pathway mutations at relapse were clonal and exclusive. Cells carrying RAS pathway mutations, especially KRAS G13 mutations, were more often ex vivo resistant to prednisolone and vincristine. No association was found with ex vivo response to daunorubicine, L-asparaginase, 6-mercaptopurine, and 6-thioguanine. Mutant primary leukemic cells were ex vivo sensitive to the MEK-inhibitor trametinib. In addition, trametinib could enhance the cytotoxic effect of prednisolone ex vivo. In DCOG-ALL10 and COALL-97/-03 patients with clonal but not subclonal mutations, MRD levels tended to be more often high compared to wildtype cases (31% vs. 19%, p=0.057), while other risk factors (age, gender, white blood cell count, CNS, prednisone response) where not different. Event-free survival was lower in the standard risk and high risk arms of the DCOG ALL10 protocol (69% vs. 96%, p=0.027 and 56% vs. 100%, p=0.015, respectively). Conclusions Collectively, analysis of 461 diagnostic BCP-ALL patient samples identified RAS pathway mutations in 44% of patients, and one out of four carried a clonal mutation. MRD was the only risk factor associated with clonal RAS pathway mutations. MRD is essential to treatment stratification in many contemporary protocols, such as the DCOG ALL10 protocol, where only patients with negative MRD after induction courses are treated with a reduced regimen (standard risk arm). Given their unfavorable event-free survival, therapy should be adapted for mutated patients in future protocols. Since treatment intensification is not feasible for high risk or relapsed cases, addition of MEK inhibitors may be of benefit especially because they enhance the cytotoxicity of prednisolone. RAS pathway mutation status may therefore serve as biomarker to select patients for MEK-inhibitor treatment in new treatment protocols for children with BCP-ALL. Disclosures No relevant conflicts of interest to declare.

JAK2 abnormalities may serve as target for precision medicines in pediatric B-cell precursor acute lymphoblastic leukemia (BCP-ALL). In the current study we performed a screening for JAK2 mutations and translocations, analyzed the clinical outcome and studied the efficacy of two JAK inhibitors in primary BCP-ALL cells. Importantly, we identify a number of limitations of JAK inhibitor therapy.JAK2 mutations mainly occurred in the poor prognostic subtypes BCR-ABL1-like and non- BCR-ABL1-like B-other (negative for sentinel cytogenetic lesions). JAK2 translocations were restricted to BCR-ABL1-like cases. Momelotinib and ruxolitinib were cytotoxic in both JAK2 translocated and JAK2 mutated cells, although efficacy in JAK2 mutated cells highly depended on cytokine receptor activation by TSLP. However, our data also suggest that the effect of JAK inhibition may be compromised by mutations in alternative survival pathways and microenvironment-induced resistance. Furthermore, inhibitors induced accumulation of phosphorylated JAK2Y1007, which resulted in a profound re-activation of JAK2 signaling upon release of the inhibitors. This preclinical evidence implies that further optimization and evaluation of JAK inhibitor treatment is necessary prior to its clinical integration in pediatric BCP-ALL.

Key Points• XLF belongs to the NHEJ ligation complex and has a dual role in DNA doublestrand break repair and V(D)J recombination.• XLF is involved in Nnucleotide addition, and thereby contributes to junctional diversity of the antigen receptors.Repair of DNA double-strand breaks (DSBs) by the nonhomologous end-joining pathway (NHEJ) is important not only for repair of spontaneous breaks but also for breaks induced in developing lymphocytes during V(D)J (variable [V], diversity [D], and joining [J] genes) recombination of their antigen receptor loci to create a diverse repertoire. Mutations in the NHEJ factor XLF result in extreme sensitivity for ionizing radiation, microcephaly, and growth retardation comparable to mutations in LIG4 and XRCC4, which together form the NHEJ ligation complex. However, the effect on the immune system is variable (mild to severe immunodeficiency) and less prominent than that seen in deficiencies of NHEJ factors ARTEMIS and DNA-dependent protein kinase catalytic subunit, with defects in the hairpin opening step, which is crucial and unique for V(D)J recombination. Therefore, we aimed to study the role of XLF during V(D)J recombination. We obtained clinical data from 9 XLF-deficient patients and performed immune phenotyping and antigen receptor repertoire analysis of immunoglobulin (Ig) and T-cell receptor (TR) rearrangements, using next-generation sequencing in 6 patients. The results were compared with XRCC4 and LIG4 deficiency. Both Ig and TR rearrangements showed a significant decrease in the number of nontemplated (N) nucleotides inserted by terminal deoxynucleotidyl transferase, which resulted in a decrease of 2 to 3 amino acids in the CDR3. Such a reduction in the number of N-nucleotides has a great effect on the junctional diversity, and thereby on the total diversity of the Ig and TR repertoire. This shows that XLF has an important role during V(D)J recombination in creating diversity of the repertoire by stimulating N-nucleotide insertion. (Blood. 2016;128(5):650-659)

The FGF receptor signaling pathway is recurrently involved in the leukemogenic processes. Oncogenic fusions of FGFR1 with various fusion partners were described in myeloid proliferative neoplasms, and overexpression and mutations of FGFR3 are common in multiple myeloma. In addition, fibroblast growth factors are abundant in the bone marrow, and they were shown to enhance the survival of acute myeloid leukemia cells. Here we investigate the effect of FGFR stimulation on pediatric BCP-ALL cells in vitro, and search for mutations with deep targeted next-generation sequencing of mutational hotspots in FGFR1, FGFR2, and FGFR3. In 481 primary BCP-ALL cases, 28 samples from 19 unique relapsed BCP-ALL cases, and twelve BCP-ALL cell lines we found that mutations are rare (4/481 = 0.8%, 0/28 and 0/12) and do not affect codons which are frequently mutated in other malignancies. However, recombinant ligand FGF2 reduced the response to prednisolone in several BCP-ALL cell lines in vitro. We therefore conclude that FGFR signaling can contribute to prednisolone resistance in BCP-ALL cells, but that activating mutations in this receptor tyrosine kinase family are very rare.