Abstract

DNA methylation is an epigenetic modification that contributes to the transcriptional regulation occurring during normal development in the absence of changes to the DNA sequence itself. Methylation of cytosines within CpG dinucleotides is catalyzed by the DNA methyltransferase (DNMT) family comprised of DNMT1, -3A, and -3B. DNMT3A and -3B establish the DNA methylation pattern while DNMT1 is primarily responsible for propagation of this pattern following DNA replication. In cancer, DNA methylation is universally dysregulated leading to focal hypermethylation and subsequent transcriptional silencing of CpG island-associated gene promoters. Inhibition of DNA methylation by traditional nucleoside analogue DNA hypomethylating agents (HMAs), such as decitabine or azacitidine, has shown benefit for the treatment of hematologic malignancies including myelodysplastic syndrome, acute myeloid leukemia (AML), and chronic myelomonocytic leukemia. However, the clinical efficacy of these DNA-incorporating, covalent pan-DNMT inhibitors has been constrained by dose-limiting toxicities and poor pharmacokinetic properties. These limitations highlight a need for a DNMT inhibitor with improved pharmacological properties and a larger therapeutic index. Collaboration between the CRUK-Manchester Institute and GSK resulted in the successful development of a screening cascade which led to the discovery of reversible DNMT1-selective inhibitors. Further testing demonstrated that the inhibitors induce cellular reprogramming, robust loss of DNA methylation, transcriptional activation of many hypermethylated and silenced genes and inhibition of cancer cell growth across a panel of histologically distinct cell lines. Furthermore, the inhibitors achieved prolonged and durable tumour regression in AML xenograft models. The data demonstrate that these novel selective and reversible inhibitors of DNMT1 may provide benefit in the clinic over traditional DNA HMAs.