The DNA Methyltransferase Inhibitor RG108 is Converted to Activator Following Conjugation with Short Peptides

We report serendipitous findings within a wider effort to design and characterize novel derivatives of the DNA methyltransferase inhibitor RG108 (N-phthalyl- l -tryptophan) consisting of peptides N-terminally linked to the carboxyl group of RG108. Derivatives were originally designed to be internalized by specific cell types and subsequently cleaved by intracellular proteases to produce minimally derivatized RG108 that retain DNA methyltransferase inhibitor activity. Unexpectedly, predicted RG108 derivatives resulting from proteolytic cleavage— i.e. RG108 linked to the short peptides KQVY or GGGKQVY (collectively referred to as RG108p)—activated DNA methyltransferase in a cell-free assay and in cultured human THP-1 monocytes. THP-1 DNA hypermethylation was detectable at submicromolar RG108p concentration, with no significant cellular toxicity. In turn, unlinked peptides were inactive. Available THP-1 monocyte transcriptome data indicate that RG108p target the human DNA methyltransferase DNMT1. Docking modelling suggests that RG108p may act by relaxing allosteric autoinhibition of human DNMT1. To our knowledge, this is the first example of switch from DNA methyltransferase inhibitor to activator. RG108p are potential tools to correct human conditions associated with predominant DNA hypomethylation, including ageing.