Histone deacetylase inhibitors require caspase activity to induce apoptosis in lung and prostate carcinoma cells.

Histone deacetylase inhibitors (HDIs) are a promising new class of antineoplastic agents with the capacity to induce growth arrest and/or apoptosis of cancer cells. However, their precise mechanism of action is uncertain; particularly, the role of caspases in the apoptotic response to HDIs is controversial. Here, we show that the HDIs explored, suberoylanilide hydroxamic acid, sodium butyrate and trichostatin A, activated caspase-3 in A549 and PC-3 carcinoma cells. Additionally, the poly-caspase inhibitor z-VAD-fmk prevented HDI-induced apoptosis, as judged by determining mitochondrial membrane potential and by quantifying internucleosomal DNA fragmentation. Importantly, z-VAD-fmk also significantly inhibited HDI-elicited cell death, as assessed by measuring propidium iodide uptake. As an accessory finding, with the inhibition of caspases, a HDI-induced G2-M arrest became evident. Taken together, these results provide evidence that HDIs require activated caspases to induce apoptosis of carcinoma cells.