Gavinostat is an orally bioavailable hydroxymate inhibitor of histone deacetylase (HDAC) with potential anti-inflammatory, anti-angiogenic, and antineoplastic activities. Gavinostat inhibits class I and class II HDACs, resulting in an accumulation of highly acetylated histones, followed by the induction of chromatin remodeling and an altered pattern of gene expression. At low, nonapoptotic concentrations, this agent inhibits the production of pro-inflammatory cytokines such as tumor necrosis factor- (TNF-), interleukin-1 (IL-1), IL-6 and interferon-gamma. It is currently in phase 2 trials for Myeloproliferative disorders, Polycythaemia vera and Phase III for Duchenne muscular dystrophy announced. In clinical trials of givinostat as a salvage therapy for advanced Hodgkin's lymphoma, the most common adverse reactions were fatigue, mild diarrhea or abdominal pain, moderate thrombocytopenia, and mild leukopenia.

Belinostat is a hydroxamate-type histone deacetylase inhibitor indicated for the treatment of relapsed or refractory peripheal T-cell lymphoma. The compound received orphan drug designation for the treatment of malignant thymomas. Acting on a histone deacetylase Belinostat causes the accumulation of acetylated histones and other proteins, inducing cell cycle arrest and/or apoptosis of some transformed cells. Belinostat targets HDAC enzymes, thereby inhibiting tumor cell proliferation, inducing apoptosis, promoting cellular differentiation, and inhibiting angiogenesis. This agent may sensitize drug-resistant tumor cells to other antineoplastic agents, possibly through a mechanism involving the down-regulation of thymidylate synthase. PXD101 has been shown in preclinical studies to have the potential to treat a wide range of solid and hematologic malignancies either as a monotherapy or in combination with other active agents, and both an oral and intravenous formulation of the drug are being evaluated in clinical trials.

Vorinostat (rINN) or suberoylanilide hydroxamic acid (SAHA), is a drug currently under investigation for the treatment of cutaneous T cell lymphoma (CTCL). Vorinostat inhibits the enzymatic activity of histone deacetylases HDAC1, HDAC2 and HDAC3 (Class I) and HDAC6 (Class II) at nanomolar concentrations (IC50< 86 nM). These enzymes catalyze the removal of acetyl groups from the lysine residues of histones proteins. In some cancer cells, there is an overexpression of HDACs, or an aberrant recruitment of HDACs to oncogenic transcription factors causing hypoacetylation of core nucleosomal histones. By inhibiting histone deacetylase, vorinostat causes the accumulation of acetylated histones and induces cell cycle arrest and/or apoptosis of some transformed cells. The mechanism of the antineoplastic effect of vorinostat has not been fully characterized. Vorinostat is used for the treatment of cutaneous manifestations in patients with cutaneous T-cell lymphoma who have progressive, persistent or recurrent disease on or following two systemic therapies. Vorinostat is marketed under the name Zolinza by Merck for the treatment of cutaneous manifestations in patients with cutaneous T cell lymphoma (CTCL) when the disease persists, gets worse, or comes back during or after two systemic therapies.

Dacinostat (also known as LAQ824), is a hydroxamate histone deacetylase inhibitor with potential anticancer activity. Dacinostat inhibits histone deacetylase enzymatic activities in vitro and transcriptionally activated the p21 promoter in reporter gene assays. Tumor cells treated with Dacinostat caused acetylation of HSP90 and degradation of its cargo oncoproteins. Flow cytometry studies revealed that both tumor cell lines and normal diploid fibroblasts arrested in the G2/M phase of the cell cycle after Dacinostat treatment. However, an increased sub-G1 population at 48 h (reminiscent of apoptotic cells) was only observed in the cancer cell lines treated with Dacinostat. Dacinostat exhibited antitumor effects in a xenograft animal models. In phase I trials, Dacinostat was well tolerated at doses that induced accumulation of histone acetylation, with higher doses inducing changes consistent with HSP90 inhibition. In another phase 1 in patients with advanced solid tumors, grade 3 or 4 toxicities were observed. Dacinostat had been in phase II clinical trials by Novartis for the treatment of solid tumors but further studies were discontinued.

Mocetinostat is an rationally designed, orally available, Class 1-selective, small molecule, 2-aminobenzamide HDAC inhibitor with potential antineoplastic activity. Mocetinostat binds to and inhibits Class 1 isoforms of HDAC, specifically HDAC 1, 2 and 3, which may result in epigenetic changes in tumor cells and so tumor cell death; although the exact mechanism has yet to be defined, tumor cell death may occur through the induction of apoptosis, differentiation, cell cycle arrest, inhibition of DNA repair, upregulation of tumor suppressors, down regulation of growth factors, oxidative stress, and autophagy, among others. It is undergoing clinical trials for treatment of various cancers including bladder cancer, diffuse large B cell lymphoma, follicular lymphoma, myelodysplastic syndromes, non-small cell lung cancer. Fatigue, weight loss or anorexia were most common treatment-related adverse events.

4SC-202 is an epigenetic oncology compound with a unique therapeutic profile, which was developed by biotechnology company: 4SC. 4SC-202 works as a selective inhibitor of LSD1 (lysine-specific demethylase 1) and HDAC (histone deacetylase) 1, 2 and 3. 4SC-202 also strengthens the endogenous immune response to cancer tissue. This compound demonstrated successfully completed Phase I of the clinical study, where it was proved safe and well tolerated in patients with advanced hematologic cancer. In addition, 4SC-202 shows substantial anti-tumor activity in a broad range of cancer cell lines including hepatocellular carcinoma, Urothelial Carcinoma Cell Lines and colorectal cancer.

CUDC-907 is a small molecule inhibitor of histone deacetylase and PI3 kinase developed by Curis. It is investigated in clinical trials for the treatment of relapsed or refractory lymphomas, thyroid cancer, multiple myeloma, breast cancer and other malignancies.

HDAC-IN-2 (also known as citarinostat or ACY-241) was developed as a selective histone deacetylase (HDAC) 6 inhibitor with potential antineoplastic activity. Inhibition of HDAC leads to the inhibition of tumor oncogene transcription, and the selective transcription of tumor suppressor genes, which inhibit tumor cell division and induce tumor cell apoptosis. HDAC-IN-2 participates in phase 1b clinical trial in patients with multiple myeloma to determine the maximum tolerated dose (MTD) and evaluate the safety and preliminary antitumor activity. Besides, HDAC-IN-2 in combination with paclitaxel participates in phase Ib in patients with advanced solid tumors. In addition, HDAC-IN-2 in combination with nivolumab participates in phase I in patients with unresectable non-small cell lung cancer to determine the safety, tolerability, dose-limiting toxicities (DLTs), and maximum tolerated dose (MTD) of the drug.

Abexinostat (PCI-24781) is a novel, second-generation phenyl hydroxamic acid–based, orally bioavailable HDAC inhibitor that has previously been shown to have activity in vitro and in vivo against a broad array of cancers, including hematopoietic malignancies and bone and soft-tissue sarcomas. Abexinostat is a pan-HDAC inhibitor mostly targeting HDAC1 with Ki of 7 nM, modest potent to HDACs 2, 3, 6, and 10 and greater than 40-fold selectivity against HDAC8. Abexinostat exhibits potent antitumor activity against a variety of tumor cell lines with GI50 ranging from 0.15 uM to 3.09 uM. PCI-24781 also has an antiproliferative effect on HUVEC endothelial cells with GI50 of 0.43 uM. Abexinostat treatment causes dose-dependent accumulation of both acetylated histones and acetylated tubulin in HCT116 or DLD-1 cells, induces expression of p21, and leads to PARP cleavage and accumulation of the γH2AX. It has also shown good tolerability and activity in Phase I and II clinical trials against lymphoma, as well as against solid tumors in Phase-I trials. Additionally, it acts as a potent radiosensitizing agent and is synergistic with cytotoxic chemotherapy, such as doxorubicin in preclinical models.