Explain what effect histone deacetylase inhibitors would have on gene expression

Histone acetylation interferes with the interaction between DNA and the nucleosomes, leading to less compact, more transcriptionally active chromatin. Histone deacetylases remove acetyl groups, causing chromatin to become condensed and transcriptionally silenced. Histone deacetylase inhibitors (HDI) cause hyperacetylation of histones, which increases gene expression.

Many cancer cells show increased growth because they have decreased or lost expression of tumor suppressor genes. HDIs can inhibit the proliferation of tumor cells by reactivating transcription of cell cycle control genes and inducing cell cycle arrest, differentiation, and apoptosis of cancer cells. Since HDIs cause hyperacetylated histones to accumulate, this leads to transcriptional activation of some genes and repression of other genes.