CRLF2 rearrangement in Ph-like acute lymphoblastic leukemia predicts relative glucocorticoid resistance that is overcome with MEK or Akt inhibition.

Philadelphia chromosome-like (Ph-like) acute lymphoblastic leukemia (ALL) is a genetically heterogeneous subtype of B-cell ALL characterized by chromosomal rearrangements and mutations that result in aberrant cytokine receptor and kinase signaling. In particular, chromosomal rearrangements resulting in the overexpression of cytokine receptor-like factor 2 (CRLF2) occur in 50% of Ph-like ALL cases. CRLF2 overexpression is associated with particularly poor clinical outcomes, though the molecular basis for this is currently unknown. Glucocorticoids (GCs) are integral to the treatment of ALL and GC resistance at diagnosis is an important negative prognostic factor. Given the importance of GCs in ALL therapy and the poor outcomes for patients with CRLF2 overexpression, we hypothesized that the aberrant signal transduction associated with CRLF2 overexpression might mediate intrinsic GC insensitivity. To test this hypothesis, we exposed Ph-like ALL cells from patient-derived xenografts to GCs and found that CRLF2 rearranged (CRLF2R) leukemias uniformly demonstrated reduced GC sensitivity in vitro. Furthermore, targeted inhibition of signal transduction with the MEK inhibitor trametinib and the Akt inhibitor MK2206, but not the JAK inhibitor ruxolitinib, was sufficient to augment GC sensitivity. These data suggest that suboptimal GC responses may in part underlie the poor clinical outcomes for patients with CRLF2 overexpression and provide rationale for combination therapy involving GCs and signal transduction inhibitors as a means of enhancing GC efficacy

Targeted inhibitors and antibody immunotherapies: Novel therapies for paediatric leukaemia and lymphoma

Despite improved outcomes achieved in the last decades for children with newly diagnosed leukaemia and lymphoma, treatment of patients with refractory/relapsed disease remains a challenge. The cure rate is still unsatisfactory and often achieved at the cost of significant morbidity. Exploring treatment with novel agents should offer less toxic therapeutic options, without compromising efficacy. Bispecific and antibody-drug conjugates targeting CD19 and CD22 (blinatumomab and inotuzumab ozogamicin) play an important role in the treatment of relapsed and refractory B-cell precursor acute lymphoblastic leukaemia (BCP-ALL); antibodies targeting CD123 and CD38 are also under investigation for acute myeloid leukaemia (AML) and T-ALL, respectively. Targeted therapy with small molecules is of primary importance for specific genetic subtypes, such as BCR-ABL-positive ALL, FLT3-ITD AML and anaplastic lymphoma kinase (ALK)-positive anaplastic large cell lymphoma. KMT2A-directed targeted therapy with menin inhibitors holds promise to be of relevance in KMT2A-rearranged leukaemias, known to have dismal prognosis. Target inhibition in cellular pathways such as BCL-2, RAS, MEK, Bruton's tyrosine kinase, JAK-STAT or CDK4/CDK6 inhibition may be suitable for different diseases with common mutated pathways. Nevertheless, development and approval of new agents for paediatric cancers lags behind adult therapeutic options. New regulations were implemented to accelerate drug development for children. Considering the number of oncology medicinal products available for adults and the rarity of paediatric cancers, prioritisation based on scientific evidence and medical need, as well as international collaboration, is critical. Herein, we review the current status of drug development for children with leukaemia and lymphoma, excluding cellular therapy despite its well-known significance

Novel roles for cyclin -dependent kinases in checkpoint pathway function and prevention of DNA damage

Cyclin-dependent kinases (Cdks) promote cellular proliferation, are often deregulated in human cancers, and are targets of ongoing cancer chemotherapy trials. To better understand Cdk functions in cell cycle regulation, we have investigated the consequences of Cdk inhibition in human cells. We demonstrate that Cdk activity is required to maintain function of the Chk1 pathway, a key component of the response to DNA damage and stalled replication. Chk1 expression was markedly reduced in primary fibroblasts and U2OS osteogenic sarcoma cells by treatment with small molecule Cdk inhibitors or induction of a dominant negative mutant of Cdk2. The findings of decreased Chk1 activity and accumulation of Cdc25A, a protein targeted for degradation by Chk1, confirmed that Chk1 function was impaired. Strikingly, Cdk inhibition triggered a DNA damage response, characterized by the accumulation of activated forms of ATM and Chk2 as well as nuclear foci containing phosphorylated substrates of ATM/ATR, including historic H2AX (γH2AX). Moreover, both Cdk and Chk1 inhibitors enhanced the cytotoxicity of etoposide, a DNA-damaging agent. Time course experiments demonstrated that the bulk of ATM activation, mediated by Cdk inhibitors, followed Chk1 down-regulation. Ectopic expression of Chk1 significantly diminished the induction of γH2AX foci by Cdk inhibitors, indicating that Chk1 down-regulation was necessary to elicit the full phenotype. Conversely, Chk1 RNAi combined with partial inhibition of DNA replication was sufficient to evoke a DNA damage response, while Chk1 down-regulation alone was not, suggesting that replication defects also contributed to the induction of DNA damage. Accordingly, Cdk inhibition disrupted the normal dynamics of the replication complex, as evidenced by increased mid S phase chromatin association of MCM2 and MCM7, members of the putative replicative helicase. These results define a pathway through which Cdk inhibition can mediate DNA damage and potentially enhance the efficacy of extant cancer chemotherapies

Novel roles for cyclin -dependent kinases in checkpoint pathway function and prevention of DNA damage

Cyclin-dependent kinases (Cdks) promote cellular proliferation, are often deregulated in human cancers, and are targets of ongoing cancer chemotherapy trials. To better understand Cdk functions in cell cycle regulation, we have investigated the consequences of Cdk inhibition in human cells. We demonstrate that Cdk activity is required to maintain function of the Chk1 pathway, a key component of the response to DNA damage and stalled replication. Chk1 expression was markedly reduced in primary fibroblasts and U2OS osteogenic sarcoma cells by treatment with small molecule Cdk inhibitors or induction of a dominant negative mutant of Cdk2. The findings of decreased Chk1 activity and accumulation of Cdc25A, a protein targeted for degradation by Chk1, confirmed that Chk1 function was impaired. Strikingly, Cdk inhibition triggered a DNA damage response, characterized by the accumulation of activated forms of ATM and Chk2 as well as nuclear foci containing phosphorylated substrates of ATM/ATR, including historic H2AX (γH2AX). Moreover, both Cdk and Chk1 inhibitors enhanced the cytotoxicity of etoposide, a DNA-damaging agent. Time course experiments demonstrated that the bulk of ATM activation, mediated by Cdk inhibitors, followed Chk1 down-regulation. Ectopic expression of Chk1 significantly diminished the induction of γH2AX foci by Cdk inhibitors, indicating that Chk1 down-regulation was necessary to elicit the full phenotype. Conversely, Chk1 RNAi combined with partial inhibition of DNA replication was sufficient to evoke a DNA damage response, while Chk1 down-regulation alone was not, suggesting that replication defects also contributed to the induction of DNA damage. Accordingly, Cdk inhibition disrupted the normal dynamics of the replication complex, as evidenced by increased mid S phase chromatin association of MCM2 and MCM7, members of the putative replicative helicase. These results define a pathway through which Cdk inhibition can mediate DNA damage and potentially enhance the efficacy of extant cancer chemotherapies

Chimeric Antigen Receptor T-Cell Therapy Clinical Results in Pediatric and Young Adult B-ALL

Abstract. Chimeric antigen receptor (CAR)-modified T-cell therapy has revolutionized the care of patients with relapsed and refractory B-cell acute lymphoblastic leukemia (B-ALL). Results from clinical trials across multiple institutions report remarkable remission rates with CD19-directed CAR-modified T-cell therapy. These remissions are also proving to be durable in many patients with a relapse-free survival (RFS) of approximately 50% to 60% at 1 year across several trials and institutions in this population that has been historically very difficult to treat. In addition, new products are being developed to enhance upon the original CAR T-cell products, which include a humanized CAR, allogeneic CARs, and both CD22 and biallelic CD19 and CD22 constructs. Toxicity after CAR-modified T-cell therapy is characterized by cytokine release syndrome (CRS) and neurotoxicity in the acute post-infusion period and B-cell aplasia as a long-term consequence of treatment. This review will summarize the published data thus far on the use of CAR-modified T-cell therapy in pediatric B-ALL and outline the various CAR products now being developed for this population. Delivery of this therapy and the decision to pursue hematopoietic stem cell transplant (HSCT) after treatment will be discussed

CRLF2 rearrangement in Ph-like acute lymphoblastic leukemia predicts relative glucocorticoid resistance that is overcome with MEK or Akt inhibition.

Philadelphia chromosome-like (Ph-like) acute lymphoblastic leukemia (ALL) is a genetically heterogeneous subtype of B-cell ALL characterized by chromosomal rearrangements and mutations that result in aberrant cytokine receptor and kinase signaling. In particular, chromosomal rearrangements resulting in the overexpression of cytokine receptor-like factor 2 (CRLF2) occur in 50% of Ph-like ALL cases. CRLF2 overexpression is associated with particularly poor clinical outcomes, though the molecular basis for this is currently unknown. Glucocorticoids (GCs) are integral to the treatment of ALL and GC resistance at diagnosis is an important negative prognostic factor. Given the importance of GCs in ALL therapy and the poor outcomes for patients with CRLF2 overexpression, we hypothesized that the aberrant signal transduction associated with CRLF2 overexpression might mediate intrinsic GC insensitivity. To test this hypothesis, we exposed Ph-like ALL cells from patient-derived xenografts to GCs and found that CRLF2 rearranged (CRLF2R) leukemias uniformly demonstrated reduced GC sensitivity in vitro. Furthermore, targeted inhibition of signal transduction with the MEK inhibitor trametinib and the Akt inhibitor MK2206, but not the JAK inhibitor ruxolitinib, was sufficient to augment GC sensitivity. These data suggest that suboptimal GC responses may in part underlie the poor clinical outcomes for patients with CRLF2 overexpression and provide rationale for combination therapy involving GCs and signal transduction inhibitors as a means of enhancing GC efficacy

INSPIRED Symposium Part 2: Prevention and Management of Relapse Following CAR T-cell therapy for B-ALL

While CD19-directed chimeric antigen receptor (CAR) T cell therapy for relapsed/refractory B-cell acute lymphoblastic leukemia (B-ALL) has been transformative in in inducing and sustaining remission, relapse rates remain unacceptably high, with about 50% of children and young adults experiencing relapse within the first-year post-infusion. Emerging strategies to extend the durability of remission involve the use of prognostic biomarkers to identify those at high risk of relapse or incorporate strategies aimed to enhancing functional CAR T cell persistence. Nonetheless, with antigen loss/downregulation or evolution to lineage switch as major mechanisms of relapse, optimizing single antigen targeting alone is insufficient. With a focus on relapse prevention strategies, including post-infusion surveillance and treatment approaches being explored to optimize post-CAR management (e.g., combinatorial antigen targeting strategies, pre-emptive hematopoietic cell transplantation), we review the current state of the art in the prevention and management of post CAR T cell relapse. We highlight the advancements made within the field as well as identify gaps in the literature to guide future research in optimizing the prevention and management of post-CAR T cell relapses in children and young adults with B-ALL