Anti-ovarian cancer effects of histone deacetylase inhibitors and calpain inhibitor

Ovarian cancer is the leading cause of death among gynecologic malignancies. The risk of developing ovarian cancer in a woman’s lifetime is 1 to 2 in 100. This high rate of development and death from the tumorigenesis is a result of its asymptomatic manifestation. Ovarian cancer is usually found in its advanced stage; therefore the survival rate is lower than for other types of cancers. The most common type of ovarian cancer, serous epithelial ovarian cancer, arises from the surface epithelium of the ovary and less frequent from the fallopian tubes or uterus. The treatment of surgery is limited by the fact that most ovarian cancers are detected after they have metastasized. Chemotherapy is often difficult because of the lack of sufficient target specific drugs. Typically, platinum in combination with other drugs is provided as the standard treatment. These combinations exhibit higher toxicity, are often not target specific, and frequently despite treatment, the tumor relapses. Current studies suggest epigenetics plays a significant role in carcinogenesis by the silencing of tumor suppressor genes (TSG). Histone modifications and the methylation of specific cytosine phosphate guanosine (CpG) residues in the upstream region of genes silence the TSG. Many clinical trials are in progress to develop combination therapies utilizing histone deacetylase inhibitors (HDACi), and DNA methyl transferase I (DNMTI) inhibitors, in combination with other cytotoxic agents. HDACi are known to be effective against different types of leukemia’s, such as Cutaneous T-cell Lymphoma; however, they are not as effective against solid tumors when used as a single agent. Our laboratory was one of the first to demonstrate that HDACi, in addition to its known property to increase histone acetylation, additionally decrease CpG island methylation in the upstream region of TSG. This demethylation causes re-expression of TSG. Our laboratory hypothesizes that re-expression of TSG sensitize cancer cells to other cytotoxic drugs. In an effort to develop improved therapy for ovarian cancer, we employed a combination therapy, which includes epigenetic drugs, HDACi, in combination with calpain protease inhibitor, calpeptin. Calpain is a ubiquitous protease usually activated in cardiovascular diseases and cancer cells. The present study discerns that combination of HDACi and calpeptin produce more than additive growth inhibition of diverse ovarian cancer cells. HDACi re-expressed TSG. Additionally, the observed growth inhibition of ovarian cancer cells was caused by cell-cycle arrest, induction of apoptosis, followed by autophagy. The phosphorylation of growth promoting signaling protein, Mitogen Activated Protein Kinase 1 (ERK), was inhibited. In addition, the inhibitors also partially inhibited phosphorylation of anti-apoptotic protein V-ask Murine Thyomoma Viral Oncogene Homolog 1 (Akt). Collectively, the outcome of this study suggests that epigenetic drugs (HDACi) sensitize the diverse ovarian cancer cell lines by re-expression of TSG, followed by cell death, when treated in combination with calpain inhibitor, calpeptin