How Epigenetic Therapy Beats Adverse Genetics in Monosomy Karyotype AML

The study by Greve and colleagues, in this issue of Cancer Research, provides new molecular insights into the intriguing clinical activity of DNA hypomethylating agents (HMA) in patients with acute myeloid leukemia (AML) with monosomal karyotypes. Patients with AML with adverse monosomal karyotypes are known to benefit from HMAs, but not cytarabine, a cytidine analog without HMA activity, but the specific molecular mechanisms remain poorly understood. The authors investigated the mechanistic effects of HMAs on gene reactivation in AML in the context of the most common monosomal karyotypes, genetic deletion of chromosome 7q and 5q. They identified genes with tumor-suppressive properties, an endogenous retrovirus cooperatively repressed by DNA hypermethylation, and increased genetic losses on hemizygous chromosomal regions versus normal biallelic regions in AML cell models. Treatment with HMAs preferentially induced expression of these hemizygous genes to levels similar to those of genes in a biallelic state. In addition to CpG hypomethylation, decitabine treatment resulted in histone acetylation and an open chromatin configuration specifically at hemizygous loci. By using primary blood blasts isolated from patients with AML receiving decitabine and AML patient-derived xenograft models established from patients with either monosomal karyotypes or normal cytogenetics, Greve and colleagues both validated their findings in primary patient samples and demonstrated superior antileukemic activity of decitabine compared with chemotherapy with cytarabine. These mechanistic insights into how epigenetic therapy beats adverse genetics in monosomy karyotype AML will open new therapeutic opportunities for a difficult-to-treat patient group. See related article by Greve et al., p. 834