Antiviral Properties of the LSD1 Inhibitor SP-2509

Lysine-specific demethylase 1 (LSD1) targets cellular proteins, including histone H3, p53, E2F, and Dnmt1, and is involved in the regulation of gene expression, DNA replication, the cell cycle, and the DNA damage response. LSD1 catalyzes demethylation of histone H3K9 associated with herpes simplex virus 1 (HSV-1) immediate early (IE) promoters and is necessary for IE gene expression, viral DNA replication, and reactivation from latency. We previously found that LSD1 associates with HSV-1 replication forks and replicating viral DNA, suggesting that it may play a direct role in viral replication or coupled processes. We investigated the effects of the LSD1 inhibitor SP-2509 on the HSV-1 life cycle. Unlike previously investigated LSD1 inhibitors tranylcypromine (TCP) and OG-L002, which covalently attach to the LSD1 cofactor flavin adenine dinucleotide (FAD) to inhibit demethylase activity, SP-2509 has previously been shown to inhibit LSD1 protein-protein interactions. We found that SP-2509 does not inhibit HSV-1 IE gene expression or transcription factor and RNA polymerase II (Pol II) association with viral DNA prior to the onset of replication. However, SP-2509 does inhibit viral DNA replication, late gene expression, and virus production. We used EdC labeling of nascent viral DNA to image aberrant viral replication compartments that form in the presence of SP-2509. Treatment resulted in the formation of small replication foci that colocalize with replication proteins but are defective for Pol II recruitment. Taken together, these data highlight a potential new role for LSD1 in the regulation of HSV-1 DNA replication and gene expression after the onset of DNA replication. IMPORTANCE Treatment of HSV-1-infected cells with SP-2509 blocked viral DNA replication, gene expression after the onset of DNA replication, and virus production. These data support a potential new role for LSD1 in the regulation of viral DNA replication and successive steps in the virus life cycle, and further highlight the promising potential to utilize LSD1 inhibition as an antiviral approach.