Advances in targeting histone deacetylase for treatment of solid tumors.

Histone deacetylase (HDAC) serves as a critical molecular regulator in the pathobiology of various malignancies and have garnered attention as a viable target for therapeutic intervention. A variety of HDAC inhibitors (HDACis) have been developed to target HDACs. Many preclinical studies have conclusively demonstrated the antitumor effects of HDACis, whether used as monotherapy or in combination treatments. On this basis, researchers have conducted various clinical studies to evaluate the potential of selective and pan-HDACis in clinical settings. In our work, we extensively summarized and organized current clinical trials, providing a comprehensive overview of the current clinical advancements in targeting HDAC therapy. Furthermore, we engaged in discussions about several clinical trials that did not yield positive outcomes, analyzing the factors that led to their lack of anticipated therapeutic effectiveness. Apart from the experimental design factors, issues such as toxicological side effects, tumor heterogeneity, and unexpected off-target effects also contributed to these less-than-expected results. These challenges have naturally become significant barriers to the application of HDACis. Despite these challenges, we believe that advancements in HDACi research and improvements in combination therapies will pave the way or lead to a broad and hopeful future in the treatment of solid tumors.

Chiglitazar Preferentially Regulates Gene Expression via Configuration-Restricted Binding and Phosphorylation Inhibition of PPARγ.

Type 2 diabetes mellitus is often treated with insulin-sensitizing drugs called thiazolidinediones (TZD), which improve insulin resistance and glycemic control. Despite their effectiveness in treating diabetes, these drugs provide little protection from eminent cardiovascular disease associated with diabetes. Here we demonstrate how chiglitazar, a configuration-restricted non-TZD peroxisome proliferator-activated receptor (PPAR) pan agonist with moderate transcription activity, preferentially regulates ANGPTL4 and PDK4, which are involved in glucose and lipid metabolism. CDK5-mediated phosphorylation at serine 273 (S273) is a unique regulatory mechanism reserved for PPARγ, and this event is linked to insulin resistance in type 2 diabetes mellitus. Our data demonstrates that chiglitazar modulates gene expression differently from two TZDs, rosiglitazone and pioglitazone, via its configuration-restricted binding and phosphorylation inhibition of PPARγ. Chiglitazar induced significantly greater expression of ANGPTL4 and PDK4 than rosiglitazone and pioglitazone in different cell models. These increased expressions were dependent on the phosphorylation status of PPARγ at S273. Furthermore, ChIP and AlphaScreen assays showed that phosphorylation at S273 inhibited promoter binding and cofactor recruitment by PPARγ. Based on these results, activities from pan agonist chiglitazar can be an effective part of a long-term therapeutic strategy for treating type 2 diabetes in a more balanced action among its targeted organs.

CS2164, a novel multi-target inhibitor against tumor angiogenesis, mitosis and chronic inflammation with anti-tumor potency.

Although inhibitors targeting tumor angiogenic pathway have provided improvement for clinical treatment in patients with various solid tumors, the still very limited anti-cancer efficacy and acquired drug resistance demand new agents that may offer better clinical benefits. In the effort to find a small molecule potentially targeting several key pathways for tumor development, we designed, discovered and evaluated a novel multi-kinase inhibitor, CS2164. CS2164 inhibited the angiogenesis-related kinases (VEGFR2, VEGFR1, VEGFR3, PDGFRα and c-Kit), mitosis-related kinase Aurora B and chronic inflammation-related kinase CSF-1R in a high potency manner with the IC50 at a single-digit nanomolar range. Consequently, CS2164 displayed anti-angiogenic activities through suppression of VEGFR/PDGFR phosphorylation, inhibition of ligand-dependent cell proliferation and capillary tube formation, and prevention of vasculature formation in tumor tissues. CS2164 also showed induction of G2/M cell cycle arrest and suppression of cell proliferation in tumor tissues through the inhibition of Aurora B-mediated H3 phosphorylation. Furthermore, CS2164 demonstrated the inhibitory effect on CSF-1R phosphorylation that led to the suppression of ligand-stimulated monocyte-to-macrophage differentiation and reduced CSF-1R+ cells in tumor tissues. The in vivo animal efficacy studies revealed that CS2164 induced remarkable regression or complete inhibition of tumor growth at well-tolerated oral doses in several human tumor xenograft models. Collectively, these results indicate that CS2164 is a highly selective multi-kinase inhibitor with potent anti-tumor activities against tumor angiogenesis, mitosis and chronic inflammation, which may provide the rationale for further clinical assessment of CS2164 as a therapeutic agent in the treatment of cancer.

Non-toxic dose chidamide synergistically enhances platinum-induced DNA damage responses and apoptosis in Non-Small-Cell lung cancer cells.

Combination of low doses of histone deacetylases inhibitors and chemotherapy drugs is considered as one of the most promising strategies to increase the anticancer efficacy. Chidamide is a novel benzamide chemical class of HDAC inhibitor that selectively inhibited HDAC1, 2, 3 and 10. We sought to determine whether chidamide may enhance platinum-induced cytotoxicity in NSCLC cells. In this study, the combination of chidamide with carboplatin showed a good synergism on growth inhibition with the mean combination index value as 0.712 and 0.639 in A549 and NCI-H157 cells, respectively. The used concentration of chidamide was non-toxic on cells by itself as low as 0.3µM. All of our experiments were comparisons between combination regimen and single carboplatin regimen in A549 and NCI-H157 cell lines. Phosphorylated histone H2A.X (γH2A.X), a hall marker of DNA damage response, was dramatically increased by the combination treatment. Cell cycle analysis by flow cytometry and phosphorylation level analysis of histone H3 (Ser10) by western blotting showed that combination treatment significantly increased the percentage of G2/M phase of cells. Mitochondrial membrane potential and cleaved-PARP1 level analysis indicate that chidamide synergistically enhances carboplatin-induced apoptosis. Additionally, synergistic effects of chidamide were found when it was combined with two other platinum drugs (cisplatin and oxaliplatin). The results suggest that Chidamide in combination with platinum drugs may be a novel therapeutic option for NSCLC.

Chidamide (CS055/HBI-8000): a new histone deacetylase inhibitor of the benzamide class with antitumor activity and the ability to enhance immune cell-mediated tumor cell cytotoxicity.

PURPOSE: Chidamide (CS055/HBI-8000) is a new histone deacetylase (HDAC) inhibitor of the benzamide class currently under clinical development in cancer indications. This study reports the in vitro and in vivo antitumor characteristics of the compound. METHODS: Selectivity and potency of chidamide in inhibition of HDAC isotypes were analyzed by using a panel of human recombinant HDAC proteins. Tumor cell lines either in culture or inoculated in nude mice were used for the evaluation of the compound's antitumor activity. To investigate the immune cell-mediated antitumor effect, isolated peripheral blood mononuclear cells from healthy donors were treated with chidamide, and cytotoxicity and expression of relevant surface proteins were analyzed. Microarray gene expression studies were performed on peripheral white blood cells from two T-cell lymphoma patients treated with chidamide. RESULTS: Chidamide was found to be a low nanomolar inhibitor of HDAC1, 2, 3, and 10, the HDAC isotypes well documented to be associated with the malignant phenotype. Significant and broad spectrum in vitro and in vivo antitumor activity, including a wide therapeutic index, was observed. Chidamide was also shown to enhance the cytotoxic effect of human peripheral mononuclear cells ex vivo on K562 target cells, accompanied by the upregulation of proteins involved in NK cell functions. Furthermore, the expression of a number of genes involved in immune cell-mediated antitumor activity was observed to be upregulated in peripheral white blood cells from two T-cell lymphoma patients who responded to chidamide administration. CONCLUSIONS: The results presented in this study provide evidence that chidamide has potential applicability for the treatment of a variety of tumor types, either as a single agent or in combination therapies.