Spiruchostatin A and B, novel histone deacetylase inhibitors, induce apoptosis through reactive oxygen species-mitochondria pathway in human lymphoma U937 cells

Spiruchostatin A (SP-A) and spiruchostatin B (SP-B) are the potent histone deacetylase inhibitors (HDACi), that has the potential for chemotherapy of leukemia but the exact mechanism of these compounds remains unclear. In the present study, the role of reactive oxygen species (ROS) production and the mechanism involved in the apoptosis was investigated in human lymphoma U937 cell. When the U937 cells were treated with SP-A and SP-B for 24 h at different concentrations, evidence of apoptotic features, including increase in DNA fragmentation and changes in nuclear morphology, were obtained. SP-B showed maximum potency to induce apoptosis, while SP-A was less potent. Apoptosis was also determined by increase in the fraction of sub-G1 cells and Annexin V-FITC staining cells. SP-A and SP-B induced apoptosis was accompanied by significant increase in the formation of intracellular reactive oxygen species (ROS). Pre-treatment with N-acetyl-l-cysteine (NAC), significantly inhibited the SP-A and SP-B mediated apoptosis, suggesting a vital role of ROS involved in the lethality of both agents. Moreover, SP-A and SP-B treatment resulted in the loss of mitochondrial membrane potential (MMP), and Fas, caspase-8 and caspase-3 activation. In addition Bid activation and the release of cytochrome-c to the cytosol was also observed. In this study, we suggest that a marked induction of intracellular ROS mediated mitochondrial pathway and the Fas plays a role in the SP-A and SP-B induced apoptosis. Taken together, our data provides further insights of the mechanism of action of SP-A and SP-B and their potential application as novel chemotherapeutic agents.