Co-targeting ASAH1 and the histone reader BRD1 potently suppresses TNBC growth through the transcriptional repressor BCL6

Triple-negative breast cancer (TNBC) is a highly aggressive breast cancer subtype with limited targeted therapeutic options, leading to higher mortality rates compared to other breast cancer subtypes. In our previous study, we identified that N-acyl sphingosine amidohydrolase 1 (ASAH1) is overexpressed in TNBC cells, and its genetic and pharmacological targeting suppresses TNBC growth and progression. In the current study, we performed a small-molecule screen using epigenetic inhibitors in combination with the ASAH1 inhibitor carmofur to identify potential epigenetic regulators that can be co-targeted to enhance the antitumor effect of carmofur. We identified the bromodomain containing protein 1 (BRD1) inhibitors (BAY-299, NI57 and OF1), which when combined with carmofur led to stronger inhibition of TNBC tumor growth in cell culture and in in vivo model compared to either single agent alone. Mechanistically, BAY-299 in combination with carmofur induced higher expression of the transcriptional repressor B-cell lymphoma 6 (BCL6), resulting in stronger inhibition of the anti-apoptotic gene, B-cell lymphoma 2 (BCL2) than either treatment alone. This consequently led to enhanced apoptosis in TNBC cells treated with both BAY-299 and carmofur. Collectively, these results identify a previously undocumented therapeutic combination of BRD1 inhibitors and ASAH1 inhibitor carmofur as a promising treatment strategy for TNBC.