unc-0638 and Neoplasms

Increasing studies show that methylation of histone lysine residues is implicated in the development and progression of varying disease states such as schizophrenia, diabetes, and multiple human cancers. Targeting the specific enzymes responsible for these processes has fueled global investigation into the understanding and correction of epigenetic pathology. This review aims to assemble a timely account of the current progress against chromatin-modifying histone lysine methyltransferases (KMTs) and demethylases (KDMs) to inform ongoing and future efforts into this promising field. In particular, we report on their role in tumor growth and progression and the development of small molecules that modulate these enzymes.

Topics: Animals; Epigenomics; Histone Demethylases; Histone-Lysine N-Methyltransferase; Histones; Humans; Lysine; Methylation; Neoplasms

Cancer cells often exhibit altered epigenetic signatures that can misregulate genes involved in processes such as transcription, proliferation, apoptosis and DNA repair. As regulation of chromatin structure is crucial for DNA repair processes, and both DNA repair and epigenetic controls are deregulated in many cancers, we speculated that simultaneously targeting both might provide new opportunities for cancer therapy. Here, we describe a focused screen that profiled small-molecule inhibitors targeting epigenetic regulators in combination with DNA double-strand break (DSB) inducing agents. We identify UNC0638, a catalytic inhibitor of histone lysine N-methyl-transferase G9a, as hypersensitising tumour cells to low doses of DSB-inducing agents without affecting the growth of the non-tumorigenic cells tested. Similar effects are also observed with another, structurally distinct, G9a inhibitor A-366. We also show that small-molecule inhibition of G9a or siRNA-mediated G9a depletion induces tumour cell death under low DNA damage conditions by impairing DSB repair in a p53 independent manner. Furthermore, we establish that G9a promotes DNA non-homologous end-joining in response to DSB-inducing genotoxic stress. This study thus highlights the potential for using G9a inhibitors as anti-cancer therapeutic agents in combination with DSB-inducing chemotherapeutic drugs such as etoposide.

Topics: Antibiotics, Antineoplastic; Antineoplastic Combined Chemotherapy Protocols; Apoptosis; Cell Proliferation; DNA Breaks, Double-Stranded; DNA End-Joining Repair; Dose-Response Relationship, Drug; Enzyme Inhibitors; Etoposide; HCT116 Cells; Histocompatibility Antigens; Histone-Lysine N-Methyltransferase; Humans; Neoplasms; Phleomycins; Quinazolines; RNA Interference; Signal Transduction; Time Factors; Topoisomerase II Inhibitors; Transfection; Tumor Suppressor Protein p53

BRCA1 and 53BP1 antagonistically regulate homology-directed repair (HDR) and non-homologous end-joining (NHEJ) of DNA double-strand breaks (DSB). The histone deacetylase (HDAC) inhibitor trichostatin A directly inhibits the retention of 53BP1 at DSB sites by acetylating histone H4 (H4ac), which interferes with 53BP1 binding to dimethylated histone H4 Lys20 (H4K20me2). Conversely, we recently found that the retention of the BRCA1/BARD1 complex is also affected by another methylated histone residue, H3K9me2, which can be suppressed by the histone lysine methyltransferase (HKMT) inhibitor UNC0638. Here, we investigate the effects of the class I HDAC inhibitors MS-275 and FK228 compared to UNC0638 on histone modifications and the DNA damage response. In addition to H4ac, the HDAC inhibitors induce H3K9ac and inhibit H3K9me2 at doses that do not affect the expression levels of DNA repair genes. By contrast, UNC0638 selectively inhibits H3K9me2 without affecting the levels of H3K9ac, H3K56ac or H4ac. Reflecting their effects on histone modifications, the HDAC inhibitors inhibit ionizing radiation-induced foci (IRIF) formation of BRCA1 and BARD1 as well as 53BP1 and RIF1, whereas UNC0638 suppresses IRIF formation of BRCA1 and BARD1 but not 53BP1 and RIF1. Although HDAC inhibitors suppressed HDR, they did not cooperate with the poly(ADP-ribose) polymerase inhibitor olaparib to block cancer cell growth, possibly due to simultaneous suppression of NHEJ pathway components. Collectively, these results suggest the mechanism by that HDAC inhibitors inhibit both the HDR and NHEJ pathways, whereas HKMT inhibitor inhibits only the HDR pathway; this finding may affect the chemosensitizing effects of the inhibitors.

Topics: Blotting, Western; BRCA1 Protein; DNA Breaks, Double-Stranded; DNA End-Joining Repair; DNA Repair; HeLa Cells; Histone Deacetylase Inhibitors; Humans; Intracellular Signaling Peptides and Proteins; Microscopy, Fluorescence; Neoplasms; Quinazolines; Reverse Transcriptase Polymerase Chain Reaction; Tumor Suppressor p53-Binding Protein 1