Developing Lysine Methyltransferase SETD8 Selective Inhibitors for Treating Multiple Myeloma

PROJECT SUMMARY Multiple Myeloma (MM) is an incurable plasma cell malignancy and is the second most common hematologic malignancy. SETD8 (also known as SET8, PR-Set7, or KMT5A) is the lysine methyltransferase that is responsible for monomethylation of histone H4 lysine 20 (H4K20me), an important histone methylation mark. SETD8 also monomethylates non-histone substrates such as the tumor suppressor p53 and replication factor PCNA, causing suppression of p53-dependent transcriptional activation in cancer cells and promoting cancer cell proliferation. Consistent with this, SETD8 is overexpressed in numerous cancers. In particular, we recently reported that SETD8 is overexpressed in relapsed primary MM and high SETD8 expression is associated with poor prognosis. Importantly, SETD8 knockdown (KD) effectively suppressed the proliferation of SETD8-high MM cells, but not SETD8-low MM cells and normal cells. Moreover, primary malignant plasma cells are particularly addicted to the methyltransferase activity of SETD8. We therefore hypothesized that pharmacological inhibition of SETD8 could be a novel and effective therapeutic strategy for the treatment of MM. In our preliminary studies, we discovered UNC0379 (the first SETD8 selective inhibitor), MS453 (the first SETD8 selective covalent inhibitor), and MS2928 (the most potent and selective SETD8 inhibitor to date). Inhibition of SETD8 by UNC0379 reduced H4K20me, induced cell-cycle defects and apoptosis, and suppressed the growth of MM cell lines and primary MM cells without significant toxicity in non-myeloma cells. Furthermore, MS2928 reduced H4K20me more effectively than UNC0379 and effectively inhibited the growth of SETD8-high MM cells, but not SETD8-low MM cells and normal cells, thereby phenocopying the effect of SETD8 KD. Importantly, MS2928 was bioavailable in mouse pharmacokinetic studies and significantly inhibited tumor growth in vivo in two MM cell line xenograft mouse models without apparent toxicity. Encouraged by these promising preliminary results, we propose to optimize our SETD8 inhibitors into in vivo chemical probes and evaluate SETD8 selective inhibitors in MM cellular and mouse models to further test and validate our therapeutic hypothesis. The optimized SETD8 inhibitors to be generated in this project will also be invaluable chemical tools for assessing the therapeutic potential of SETD8 inhibition in other SETD8-overexpressing cancers, and can be further optimized into drug candidates in the future and ultimately translated in the clinic for cancer patients.