Efficacy of the Allosteric MEK Inhibitor Trametinib in Relapsed and Refractory Juvenile Myelomonocytic Leukemia: a Report from the Children's Oncology Group

Abstract

Juvenile myelomonocytic leukemia (JMML) is a hematologic malignancy of young children caused by mutations that increase Ras signaling output. Hematopoietic stem cell transplantation (HSCT) is a potentially curative treatment, but patients with relapsed or refractory (advanced) disease have dismal outcomes. This phase II trial evaluated the safety and efficacy of trametinib, an oral MEK1/2 inhibitor, in patients with advanced JMML. Ten infants and children were enrolled, and the objective response rate was 50%. Four patients with refractory disease proceeded to HSCT after receiving trametinib. Three additional patients completed all 12 cycles permitted on study and continue to receive off-protocol trametinib without HSCT. The remaining three patients had progressive disease with two demonstrating molecular evolution by the end of cycle 2. Transcriptomic and proteomic analyses provided novel insights into the mechanisms of response and resistance to trametinib in JMML. ClinicalTrials.gov Identifier: NCT03190915. Significance: Trametinib was safe and effective in young children with relapsed or refractory JMML, a lethal disease with poor survival rates. Seven of 10 patients completed the maximum 12 cycles of therapy or used trametinib as a bridge to HSCT and are alive with a median follow-up of 24 months. See related commentary by Ben-Crentsil and Padron, p. 1574.

Figure 1.. Responses in relapsed/refractory JMML patients treated with trametinib.

Swimmer plot demonstrating individual outcomes over time. Each row represents one patient. Outcomes are color-coded based on response as follows: Complete clinical response (CR; green); partial clinical response (PR; blue); stable disease (SD; yellow); and progressive disease (PD; red). Data regarding driver mutation, number of mutations at relapse, methylation status at relapse and prior therapy are to the left of the Swimmer plot. Data regarding use of post-ADVL1521 HSCT, use of post-ADVL1521 of trametinib and vital status are displayed to the right of the Swimmer plot. AZA: azacitidine FLA: fludarabine and cytarabine HSCT: hematopoietic stem cell transplant N/A: not available RUX: ruxolitinib

Figure 2.. Integrated analysis of proteomic and RNAseq data highlighting mechanisms of response and resistance.

(A) The sum log₂ fold change in multiplexed inhibitor bead (MIB) binding from panel A for the top 20 kinases with decreased MIB binding (matched patient post-treatment versus pre-treatment with trametinib) are shown. (B) All patient samples collected pre- and post- trametinib treatment (n=6) were analyzed by MIB/MS kinome profiling and the normalized log₂ label free quantification (LFQ) intensities (MIB binding) for identified kinases were assessed for significance using an unpaired t-test. The mean log₂ difference in MIB binding, post- versus pre-treatment, and -log10 P for each kinase is plotted. The dashed line indicates a p value of ≤0.05. MEK1 and MEK2 kinases are indicated in red. (C) Integration of the log₂ fold changes in transcript expression and MIB binding reveal SRC family genes to be among the most downregulated with respect to both RNAseq and MIB binding. MAP2K1 and MAPK2 were downregulated with respect to MIB binding but were nearly unchanged with respect to RNASeq. Cell cycle genes were among the most upregulated with respect to both RNASeq and MIB binding. UPN: universal patient number.

Figure 3.. Single cell RNASeq identifies distinct changes in cell types after exposure to trametinib.

(A) Two-dimensional uniform manifold approximation and projection visualization (UMAP), annotated with cell type classifications from seven longitudinal patient pairs (B) Bar plot comparing pre/post trametinib treatment cell type percentages. Error bars denote standard error of the mean. Percentages are adjusted as total cell count for each cellular type, divided by the total cells (C) Tabulated percentage of cells between pre/post-treated for each cell type. Populations that showed significant differences from pretreatment values are indicated with an asterisk. Independent t-tests were performed on the square root transformed of each percentage, p-values < 0.05. False discovery rate (FDR) correction was applied to adjust for multiple comparisons, with an FDR threshold of < 0.20. C_Monocytes: classical monocytes; NKT: natural killer T-cells; mDCs: myeloid dendritic cells; MLP: multipotent lymphoid progenitors; pDCs: plasmacytoid dendritic cells; HSC: hematopoietic stem cells: GMP: granulocyte-monocyte progenitors.