Modulation of splicing catalysis for therapeutic targeting of leukemias with spliceosomal mutations

Mutations in spliceosomal genes are commonly found in patients with myelodysplastic syndromes (MDS) and acute myeloid leukemia (AML)(1–3). These mutations occur at highly recurrent amino acid residues and perturb normal splice site and exon recognition(4–6). Spliceosomal mutations are always heterozygous and rarely co-occur with one another, suggesting that cells may only tolerate a partial deviation from normal splicing activity. To test this hypothesis, we engineered mice that express the SRSF2P95H mutation, which commonly occurs in MDS and AML, in an inducible hemizygous manner in hematopoietic cells. These mice developed lethal bone marrow failure, demonstrating that Srsf2-mutant cells depend on the wildtype Srsf2 allele for survival. In the context of leukemia, treatment with the spliceosome inhibitor E7107(7,8) resulted in significant reductions in leukemic burden specifically in isogenic mouse leukemias and patient-derived xenograft (PDX) AMLs carrying spliceosomal mutations. While in vivo E7107 exposure resulted in widespread intron retention and cassette exon skipping regardless of Srsf2 genotype, the magnitude of splicing inhibition following E7107 treatment was greater in Srsf2-mutant versus wildtype leukemias, consistent with its differential effect on survival in these two genotypes. Collectively, these data provide genetic and pharmacologic evidence that leukemias with spliceosomal mutations are preferentially susceptible to additional splicing perturbations in vivo compared with wildtype counterparts. Modulation of spliceosome function may provide a novel therapeutic avenue in genetically defined subsets of MDS and AML patients.