Abstract 1429: Characterization of trametinib combined with venetoclax in acute myeloid leukemia (AML) treatment

Acute myeloid leukemia (AML) is a type of hematologic malignancy with rapid progression and high genetic heterogeneity. Activating RAS pathway mutations are found in approximately 10 - 25% of AML patients and have been implicated to targeted drug resistance and disease relapse suggesting a potential benefit of MAPK pathway inhibitors in AML therapy. In patients with RAS-mutated myeloid malignancies, an inhibitor targeting MEK1/2, trametinib, demonstrated benefit in a phase 1/2 clinical study. Effective combinations of trametinib with other drugs has remained elusive. To identify potential combinatorial strategies, we generated AML cell lines resistant to MEKi. Whole exome sequencing revealed MEK1 variants in these cells. Drug sensitivity assays performed on parental AML cells and cells harboring wild type and the MEK1 variants validated their ability to confer trametinib resistance. BCL2 inhibitors, including venetoclax, were able to re-sensitize the resistant cells to trametinib, suggesting potential efficacy of combining trametinib with venetoclax. Indeed, this drug combination revealed synergistic efficacy in AML cell lines with diverse genetic backgrounds and in the resistant cells.To further investigate combination of trametinib and venetoclax in AML, we examined ~200 primary AML patient specimens using an ex vivo drug sensitivity assay, whole exome, and RNA sequencing data. We confirmed the enhanced efficacy of this combination relative to single agents. Patient samples resistant to trametinib showed increased sensitivity to venetoclax. Since, hyper-activation of MAPK signaling has been correlated with venetoclax resistance, we analyzed venetoclax resistant specimens and observed increased sensitivity to MEK and ERK inhibitors. We also observed correlation of MEK1 but not MEK2 RNA levels with trametinib sensitivity and negative correlation of MEK1 RNA levels with that of BCL2. AML samples with FLT3-ITD, NPM1, WT1, FLT3, CEBPA, DNMT3A, IDH1, IDH2, SRSF2, and TP53 mutations exhibited increased sensitivity to the combination. Samples with NRAS, KRAS, and PTPN11; although, highly sensitive to trametinib, did not benefit from this combination. Consistent with previous studies, we observed that venetoclax sensitivity was correlated with higher blast percentage. We also observed correlation of higher percentage of bone marrow blast and sensitivity to the combination. Moreover, while monocytic leukemias (AML-M4/M5) showed reduced sensitivity to venetoclax, they were sensitive to trametinib and showed increased expression of MEK1. Furthermore, we demonstrated that while venetoclax treatment increased protein levels of MCL1 in MOLM13 AML cells, combining trametinib with venetoclax reduced MCL1 levels. In summary, we demonstrate efficacy of trametinib and venetoclax combination in AML and propose mechanisms underlying the synergistic relationship of this drug combination. Citation Format: Alisa Damnernsawad, Christopher A. Eide, Sofia Beer, Haijiao Zhang, Daniel Bottomly, Stephen E. Kurtz, Jeffrey W. Tyner. Characterization of trametinib combined with venetoclax in acute myeloid leukemia (AML) treatment [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1429.