Post-translational modifications (PTMs) of histone proteins allow for the reversible regulation of acquired and heritable gene expression, without altering the primary DNA sequence. Such epigenetic alterations, in addition to gene mutations, are responsible for the initiation of many diseases and consequent pathogenesis, especially cancer. Disruptor of telomeric silencing 1-like protein, or DOT1L, is a histone lysine methyltransferase (HKMT) enzyme that catalyses the mono-, di- and tri-methylation of histone 3 lysine 79 (H3K79). Due to its importance in normal physiology, alterations in the expression or activity of DOT1L can lead to an array of pathological conditions and diseases.
The most extensively studied example implicating DOT1L in disease is in MLL-rearranged leukaemia. Here the enzyme is ectopically recruited to the MLL-rearranged gene and results in H3K79 hypermethylation. Many functional inhibitors of DOT1L have been synthesised as potential therapeutics, however these require long treatment periods before a favourable clinical outcome can be observed. To this end, we decided to explore a different pathway by designing and synthesising PROTAC reagents for DOT1L. These will result in the complete removal of the enzyme from cells instead of functional inhibition and can therefore prove advantageous.
A total of 11 potential degrader molecules were successfully prepared following long and complex syntheses. Their activity was determined by growth assays and Western Blot analysis using MCF-7 cells. Unfortunately, the results obtained did not provide strong evidence of a PROTAC mechanism of action, though some degree of DOT1L degradation was observed with two compounds suggesting that the enzyme is amenable to degradation.
This project has provided a valuable foundation for future work surrounding induced DOT1L degradation as a new therapeutic strategy for leukaemia, however more testing and optimisation are required before this can be further translated.