MAPK signaling cascades mediate distinct glucocorticoid resistance mechanisms in pediatric leukemia

Abstract

• 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

Progress and Prospects in Pediatric Leukemia

“…33 A number of relapse-specific alterations have been shown to confer resistance to single agents (e.g., glucocorticoid resistance: TBLXR1 deletions and CREBBP mutations; 6 MP and 6 TG resistance-NT5C2 and PRPS1 mutations) or pan-resistance to all agents (e.g., Wnt and MAP kinase pathway activation Ϯ Ras mutations). [34][35][36] Genomics has also helped identify host characteristics, like single nucleotide polymorphisms in the host that affect the pharmacokinetics and associated side effects of multiple drugs such as methotrexate, vincristine, glucocorticoids, and asparaginase. 8 Relapse can occur in the bone marrow and/or in extramedullary sites (CNS or testes).…”

Genetic drivers of vulnerability and resistance in relapsed acute lymphoblastic leukemia

“…Moreover, given that the therapeutic studies described above were performed in T-ALL models, evaluation of these findings in the context of B-ALL will also be important. Finally, RAS mutations have also previously been linked to prednisolone resistance (15) as well, and the MEK inhibitor trametinib was shown in at least one study to be synergistic with prednisolone (12,16).…”

“…Moreover, given that the therapeutic studies described above were performed in T-ALL models, evaluation of these findings in the context of B-ALL will also be important. Finally, RAS mutations have also previously been linked to prednisolone resistance (15) as well, and the MEK inhibitor trametinib was shown in at least one study to be synergistic with prednisolone (12,16).Given these findings and the data here revealing collaborative cytotoxic effects of MTX and MEK inhibition, combining MEK inhibitors with conventional therapies may be important to evaluate clinically in the treatment of RAS-mutant ALL.The insights from this study and prior literature on the genomic analysis of relapsed ALL further highlights that, in most cases, relapse in ALL represents evolution from an ancestral clone present as a subclone at diagnosis. Furthermore, it is clear that relapses in pediatric ALL are not associated with marked increases in genomic alterations.…”

Therapies on the horizon for childhood acute lymphoblastic leukemia

“…Specific alterations are associated with pan-resistance to all conventional agents or may be associated with resistance to a single class (22). For example activation of both the Wnt and mitogen activated protein kinase pathways (MAPK) is commonly observed at relapse and is associated with resistance to all agents used in therapy (23, 24). Ras mutations in part drive MAPK activation and targeted agents are available that are attractive candidates for novel therapy (24, 25).…”