Targeting Menin in T-lineage Acute Lymphoblastic Leukemia.

T-lineage acute lymphoblastic leukemia (T-ALL) lacks effective targeted therapies, with poor outcomes in relapsed/refractory (R/R) disease. HOXAhigh T-ALL is biologically aggressive and often resistant to standard therapy. Menin inhibitors, recently approved for KMT2A-rearranged leukemias, may be effective in T-ALL, but biomarkers of response remain undefined. This study aims to evaluate the efficacy of menin inhibition in T-ALL and identify molecular predictors of sensitivity. We tested menin inhibitors (ziftomenib, revumenib, and VTP50469) in 14 primary T-ALL samples and 8 cell lines, representing HOXAhigh and HOXAlow genotypes. In vitro sensitivity assays, xenograft mouse models, transcriptomics, proteomics, and phosphoproteomics were used to characterize drug response. MEF2C modulation experiments and combination studies with cyclin-dependent kinase (CDK) 1/2 and ERK1/2 inhibitors were performed in vitro and in vivo. Menin inhibitors suppressed leukemic growth in a subset of HOXAhigh and HOXAlow primary human T-ALL samples. Similarly, ziftomenib was effective in reducing tumor burden in xenografts without major toxicity. Upon treatment, we observed downregulation of canonical menin targets (HOXA, MEIS1, and MEF2C) and upregulation of T-cell differentiation programs. Phosphoproteomic studies identified MEF2C S222 phosphorylation-mediated by CDK1/2 and ERK1/2-as a predictor of ziftomenib sensitivity in T-ALL. MEF2C overexpression promoted proliferation and ziftomenib resistance, whereas its knockdown impaired growth. Ziftomenib synergized with CDK1/2 and ERK1/2 inhibitors in vitro and improved survival in xenografted mice. In conclusion, a subset of T-ALL, defined by high p-MEF2C S222, is sensitive to menin inhibition. Combining ziftomenib with CDK or ERK inhibition offers synergistic efficacy, supporting biomarker-driven clinical trials of this strategy in R/R T-ALL.