<scp>NF</scp> ‐ <scp>κB</scp> Is a Potential Therapeutic Target for Histone Deacetylase Inhibitor‐Resistant Cutaneous T‐Cell Lymphoma

Histone deacetylase inhibitors, such as vorinostat, show promise as treatment for T-cell lymphomas including cutaneous T-cell lymphoma. However, the emergence of resistance ultimately leads to disease relapse. To elucidate the underlying mechanisms and identify potential countermeasures, we established histone deacetylase inhibitor-resistant cutaneous T-cell lymphoma cell lines by prolonged exposure to vorinostat. We then comprehensively profiled gene expression in these cell lines by using microarrays and in silico analytical approaches. We identified 83 genes that were significantly upregulated in the resistant cell lines. Subsequent enrichment analyses using ChIP-Atlas and Enrichr revealed that these genes are regulated by particular transcription factors, including RELA/p65, GATA3, and EP300, of which RELA (p65) exhibited the highest composite score. RELA is a key subunit of the NF-κB complex, which is involved in inflammation, cell survival, and proliferation. We demonstrated marked upregulation and nuclear enrichment of p65 and pronounced NF-κB pathway activation in the histone deacetylase inhibitor-resistant cells. The mechanism involved acetylation-mediated inhibition of p65 ubiquitination, which resulted in protein stabilization and enhanced transcriptional activity. Histone deacetylase inhibitor-resistant cell lines displayed heightened sensitivity to inhibition of the NF-κB pathway by bortezomib and dimethyl fumarate. These findings implicate aberrant NF-κB activation as a central driver of the emergence of histone deacetylase inhibitor resistance in cutaneous T-cell lymphoma. Ultimately, our results provide a strong rationale for exploring NF-κB inhibition as a therapeutic strategy to restore or enhance the efficacy of histone deacetylase inhibitor-based therapies, overcome histone deacetylase inhibitor resistance, and improve outcomes for patients with cutaneous T-cell lymphoma.