• Genetic or pharmacologic inhibition of MEK4 and MEK2 enhances prednisoloneinduced cell death in ALL models.• MAPK signaling cascades are activated at relapse compared to diagnosis in ALL samples and have enhanced response to MEK inhibition.The outcome for pediatric acute lymphoblastic leukemia (ALL) patients who relapse is dismal. A hallmark of relapsed disease is acquired resistance to multiple chemotherapeutic agents, particularly glucocorticoids. In this study, we performed a genome-scale short hairpin RNA screen to identify mediators of prednisolone sensitivity in ALL cell lines. The incorporation of these data with an integrated analysis of relapse-specific genetic and epigenetic changes allowed us to identify the mitogen-activated protein kinase (MAPK) pathway as a mediator of prednisolone resistance in pediatric ALL. We show that knockdown of the specific MAPK pathway members MEK2 and MEK4 increased sensitivity to prednisolone through distinct mechanisms. MEK4 knockdown increased sensitivity specifically to prednisolone by increasing the levels of the glucocorticoid receptor. MEK2 knockdown increased sensitivity to all chemotherapy agents tested by increasing the levels of p53. Furthermore, we demonstrate that inhibition of MEK1/2 with trametinib increased sensitivity of ALL cells and primary samples to chemotherapy in vitro and in vivo. To confirm a role for MAPK signaling in patients with relapsed ALL, we measured the activation of the MEK1/2 target ERK in matched diagnosis-relapse primary samples and observed increased phosphorylated ERK levels at relapse. Furthermore, relapse samples have an enhanced response to MEK inhibition compared to matched diagnosis samples in xenograft models. Together, our data indicate that inhibition of the MAPK pathway increases chemosensitivity to glucocorticoids and possibly other agents and that the MAPK pathway is an attractive target for prevention and/or treatment of relapsed disease. (Blood. 2015;126(19):2202-2212

Summary While childhood acute lymphoblastic leukemia (ALL) is now highly curable, the dismal prognosis for children who relapse warrants novel therapeutic approaches. Previously, using an integrated genomic analysis of matched diagnosis - relapse paired samples, we identified overactivation of the Wnt pathway as a possible mechanism of recurrence. To validate these findings and document whether Wnt inhibition may sensitize cells to chemotherapy, we analyzed the expression of Activated β-catenin (and its downstream target BIRC5) using multiparameter phosphoflow cytometry and tested the efficacy of a recently developed Wnt inhibitor, iCRT14, in ALL cell lines and patient samples. We observed increased activation of β-catenin at relapse in 6 /10 patients. Furthermore, treatment of leukemic cell lines with iCRT14 led to significant downregulation of Wnt target genes and combination with traditional chemotherapeutic drugs resulted in a synergistic decrease in viability as well as a significant increase in apoptotic cell death. Finally, pre-treatment of purified blasts from patients with relapsed leukemia with the Wnt inhibitor followed by exposure to prednisolone, restored chemosensitivity in these cells. Our results demonstrate that overactivation of the Wnt pathway may contribute to chemoresistance in relapsed childhood ALL and that Wnt-inhibition may be a promising therapeutic approach.

Background:Resistance to glucocorticoid agonists is a major challenge in the treatment of pediatric leukemia. Results: TBL1XR1 knockdown decreases glucocorticoid signaling and response in leukemia cells. Conclusion:Deletions in TBL1XR1 at relapse may drive resistance to glucocorticoid agonists. Significance: Identifying drivers of glucocorticoid resistance in leukemia may allow for the identification of novel therapies for the treatment of recurrent disease.

Menin inhibitors constitute a novel class of agents targeting the underlying biology of nucleophosmin (NPM1) mutant and KMT2A (formerly known as MLL1) rearranged (KMT2Ar) acute leukemias. KMT2Ar acute leukemias constitute 5% to 10% of acute leukemias, and NPM1 mutations are identified in 30% of newly diagnosed acute myeloid leukemias (AMLs). In preclinical AML models, small molecule inhibitors of the menin-KMT2A protein-protein interaction induce differentiation, downregulate critical gene expression programs, and confer a survival advantage in patient-derived xenograft models of NPM1 mutant and KMT2Ar AML. Multiple clinical trials evaluating oral menin inhibitors in acute leukemias are ongoing. Preliminary results in relapsed/refractory NPM1 mutant and KMT2Ar AML have shown on-target effects, tolerable toxicity, and promising clinical activity. This review details the current clinical experience of menin inhibitors in AML and discusses how these agents can be successfully integrated into future therapeutic approaches.

Objective Sleep disordered breathing (SDB) has not been well studied in urban adolescents with asthma in community settings. Nor has the association of SDB symptoms and asthma severity been studied. We characterized self-reported symptoms suggesting SDB and investigated the association of SDB symptoms, probable asthma, and asthma severity. Methods 9,565 adolescents from 21 inner-city high schools were screened for an asthma intervention study. Students reported on symptoms suggesting SDB using questions from the 2007 NHANES, if they were ever diagnosed with asthma, and on asthma symptoms. Using generalized linear mixed models with logit link with school as a random intercept and adjusting for age, gender, and race/ethnicity, we examined associations of SDB symptoms, and demographic characteristics, probable asthma, and asthma severity. Results 12% reported SDB symptoms. Older and biracial participants (compared to Caucasian) had higher odds of symptoms suggesting SDB (p<.001). Compared to those without probable asthma, adolescents with probable asthma had 2.63 greater odds of reporting SDB symptoms (p<.001). Among those with probable asthma, the odds of reporting SDB symptoms increased with asthma severity. When exploring daytime severity and severity due to night wakening separately, results were similar. All results remained significant when controlling for age, gender, and ethnicity. Conclusions In a large urban community cohort of predominately ethnic minority adolescents, self-reported SDB symptoms were associated with probable asthma and increased asthma severity. This study highlights the importance of SDB as a modifiable co-morbidity of asthma.