Suberoylanilide hydroxamic acid as a potential therapeutic agent for humanbreast cancer treatment

Background: Suberoylanilide hydroxamic acid (sAHA) is a prototype of the ne wly developed, second-generation, hybrid polar compounds. It is a novel his tone deacetylase inhibitor with high potency for inducing cell differentiat ion of cultured murine erythroleukemia cells. Studies with SAHA have primar ily been performed with hematopoietic tumor cells. Here we extent these stu dies with SAHA to human breast cancer cell lines in an attempt to find bett er therapeutic agents for breast cancer treatment. Materials and Methods: Human breast cancer cell lines, MCF7, MDA-MB-231, an d MDA-MB-435, as well as normal cells, including the normal breast epitheli al cell line MCF-10A, and fibroblasts, were treated with sAHA. Cells assaye d for cell survival by using trypan blue exclusion assay, colony formation assay, and cell cycle and apoptosis analysis. The effects of sAHA on cell c ycle and apoptosis regulatory proteins were examined by Western blots analy sis. The identification of additional target genes was carried out by diffe rential display (DD) and reverse transcription-polymerase chain reaction (R T-PCR). Results: SAHA inhibited clonogenic growth of MCF7, MDA-MB-231, and MDA-MB-4 35 breast cancer cells. These cells were more sensitive to SAHA-mediated cy totoxic effects than normal breast epithelial cells and fibroblasts. The cy totoxic effects of sAHA on breast cancer cells were manifested by G1 and G2 /M cell cycle arrest and eventual apoptosis. The pan-caspase inhibitor, Z-V AD.fmk, blocked SAHA-induced cell death, DNA laddering, and cleavage of pol y(ADP-ribose) polymerase, indicating the involvement of caspases in SAHA-me diated apoptosis. In addition, SAHA modulated cell cycle and apoptosis regu latory proteins. For example, cyclin-dependent kinase (CDK) inhibitors p21W AF1/Cip1 and p27Kip1 were induced, and retinoblastoma protein pRb was hypop hosphorylated. Moreover, SAHA induced several genes associated with differe ntiation and/ or growth inhibition. These genes encode gelsolin, isopenteny l-diphosphate delta isomerase (IDI1), and 1,25-dihydroxyvitamin D-3 up-regu lated protein 1 (VDUP1), the last two of which were identified by DD. Induc tion of these genes may contribute to SAHA-mediated pro-differentiating and antiproliferative effects. Conclusions: SAHA induced growth inhibition, cell cycle arrest, and eventua l apoptosis in human breast cancer cells, possibly by modulating cell cycle and apoptosis regulatory proteins, such as CDK inhibitors p21 and p27, pRb , and other differentiation and/or growth inhibition-associated genes, incl uding gelsolin, IDI1 and VDUP1. This, together with the low toxicity in nor mal cells, suggests that SAHA might have therapeutic potential for the trea tment of human breast cancers.