A phase 1 dose-escalation study of the oral histone deacetylase inhibitor abexinostat in combination with standard hypofractionated radiotherapy in advanced solid tumors

The Bioequivalence of Abexinostat (CRA-024781) Tosylate Tablets (20 mg) in Chinese Healthy Subjects Under Fasting Conditions

This study aimed to investigate the pharmacokinetic parameters of single oral administration of postchange and prechange abexinostat (CRA-024781) tosylate tablets in Chinese healthy subjects under fasting conditions, and assess the bioequivalence (BE) of the 2 formulations (Test [T1] and Reference [T2]). This study was a randomized, open-label, 2-formulation, fasting administration, single-dose, 2-sequence, 2-cycle, crossover BE study. Thirty-six subjects were enrolled in the study and 33 subjects completed 2 cycles. The plasma concentrations were determined by liquid chromatography-tandem mass spectrometry. The 90% confidence intervals (CIs) for the Cmax, AUC0-t, and AUC0-∞ of CRA-024781 and its 2 major metabolites (PCI-27789 and PCI-27887, both metabolites are pharmacologically inactive on HDAC1) fell within the acceptable range of 80%-125%. The results suggest that the CRA-024781 test preparation (Test [T1]) is bioequivalent to the reference preparation (Reference [T2]) in healthy Chinese subjects under fasting conditions.

Differential gene expression-based connectivity mapping identified novel drug candidate and improved Temozolomide efficacy for Glioblastoma

BACKGROUND

Glioblastoma (GBM) has a devastating median survival of only one year. Treatment includes resection, radiation therapy, and temozolomide (TMZ); however, the latter increased median survival by only 2.5 months in the pivotal study. A desperate need remains to find an effective treatment.

METHODS

We used the Connectivity Map (CMap) bioinformatic tool to identify candidates for repurposing based on GBM's specific genetic profile. CMap identified histone deacetylase (HDAC) inhibitors as top candidates. In addition, Gene Expression Profiling Interactive Analysis (GEPIA) identified HDAC1 and HDAC2 as the most upregulated and HDAC11 as the most downregulated HDACs. We selected PCI-24781/abexinostat due to its specificity against HDAC1 and HDAC2, but not HDAC11, and blood-brain barrier permeability.

RESULTS

We tested PCI-24781 using in vitro human and mouse GBM syngeneic cell lines, an in vivo murine orthograft, and a genetically engineered mouse model for GBM (PEPG - PTENflox/+; EGFRvIII+; p16Flox/- & GFAP Cre +). PCI-24781 significantly inhibited tumor growth and downregulated DNA repair machinery (BRCA1, CHK1, RAD51, and O6-methylguanine-DNA- methyltransferase (MGMT)), increasing DNA double-strand breaks and causing apoptosis in the GBM cell lines, including an MGMT expressing cell line in vitro. Further, PCI-24781 decreased tumor burden in a PEPG GBM mouse model. Notably, TMZ + PCI increased survival in orthotopic murine models compared to TMZ + vorinostat, a pan-HDAC inhibitor that proved unsuccessful in clinical trials.

CONCLUSION

PCI-24781 is a novel GBM-signature specific HDAC inhibitor that works synergistically with TMZ to enhance TMZ efficacy and improve GBM survival. These promising MGMT-agnostic results warrant clinical evaluation.

Emerging epigenetic targets in rheumatoid arthritis

Rheumatoid arthritis is a complex disorder that is characterized by irreversible and progressive destructions of joints, but its exact etiology remains mainly unknown. The occurrence and the progression of the disease entirely depend on environmental and genetic factors. In recent years, various epigenetic changes involving DNA methylation, histone modification, miRNA, X-chromosome inactivation, bromodomain, sirtuin, and many others were identified that were found to be linked to the activation and the aggressive phenotype in rheumatoid arthritis. Epigenetics is found to be one of the root causes, which brings changes in the heritable phenotype and is not determined by changes in the DNA sequences and understanding these epigenetic mechanisms and the pathogenesis of the disease can help in understanding the disease and various other possible ways for its control and/or prevention. The various epigenetic modification occurring are reversible and can be modulated by drugs, diet, and environmental factors. This article focuses on various epigenetic factors involved in the pathogenesis of rheumatoid arthritis. Further, various epigenetic therapies that might be successful in inhibiting these epigenetic modifications are summarized. Several therapeutic agents alter the epigenetic modifications occurring in various diseases and many of the epigenetic therapies are under pre-clinical and clinical trial. However, exploring these epigenetic prognostic biomarkers would give a broader perspective and provide more ideas and knowledge regarding the process and pathways through which the diseases occur, and also combining various therapeutic agents would show more beneficial and synergistic effects.

Anticancer Therapy with HDAC Inhibitors: Mechanism-Based Combination Strategies and Future Perspectives

The increasing knowledge of molecular drivers of tumorigenesis has fueled targeted cancer therapies based on specific inhibitors. Beyond "classic" oncogene inhibitors, epigenetic therapy is an emerging field. Epigenetic alterations can occur at any time during cancer progression, altering the structure of the chromatin, the accessibility for transcription factors and thus the transcription of genes. They rely on post-translational histone modifications, particularly the acetylation of histone lysine residues, and are determined by the inverse action of histone acetyltransferases (HATs) and histone deacetylases (HDACs). Importantly, HDACs are often aberrantly overexpressed, predominantly leading to the transcriptional repression of tumor suppressor genes. Thus, histone deacetylase inhibitors (HDACis) are powerful drugs, with some already approved for certain hematological cancers. Albeit HDACis show activity in solid tumors as well, further refinement and the development of novel drugs are needed. This review describes the capability of HDACis to influence various pathways and, based on this knowledge, gives a comprehensive overview of various preclinical and clinical studies on solid tumors. A particular focus is placed on strategies for achieving higher efficacy by combination therapies, including phosphoinositide 3-kinase (PI3K)-EGFR inhibitors and hormone- or immunotherapy. This also includes new bifunctional inhibitors as well as novel approaches for HDAC degradation via PROteolysis-TArgeting Chimeras (PROTACs).

Small Molecules Targeting HATs, HDACs, and BRDs in Cancer Therapy

Evidence for research over the past decade shows that epigenetic regulation mechanisms run through the development and prognosis of tumors. Therefore, small molecular compounds targeting epigenetic regulation have become a research hotspot in the development of cancer therapeutic drugs. According to the obvious abnormality of histone acetylation when tumors occur, it suggests that histone acetylation modification plays an important role in the process of tumorigenesis. Currently, as a new potential anti-cancer therapeutic drugs, many active small molecules that target histone acetylation regulatory enzymes or proteins such as histone deacetylases (HDACs), histone acetyltransferase (HATs) and bromodomains (BRDs) have been developed to restore abnormal histone acetylation levels to normal. In this review, we will focus on summarizing the changes of histone acetylation levels during tumorigenesis, as well as the possible pharmacological mechanisms of small molecules that target histone acetylation in cancer treatment.

Identification of Combinations of Protein Kinase C Activators and Histone Deacetylase Inhibitors That Potently Reactivate Latent HIV

Combination antiretroviral therapy (cART) is successful in maintaining undetectable levels of HIV in the blood; however, the persistence of latent HIV reservoirs has become the major barrier for a HIV cure. Substantial efforts are underway in finding the best latency-reversing agents (LRAs) to purge the latent viruses from the reservoirs. We hypothesize that identifying the right combination of LRAs will be the key to accomplishing that goal. In this study, we evaluated the effect of combinations of three protein kinase C activators (prostratin, (-)-indolactam V, and TPPB) with four histone deacetylase inhibitors (AR-42, PCI-24781, givinostat, and belinostat) on reversing HIV latency in different cell lines including in a primary CD4+ T-cell model. Combinations including indolactam and TPPB with AR-42 and PCI produced a strong synergistic effect in reactivating latent virus as indicated by higher p24 production and envelope gp120 expression. Furthermore, treatment with TPPB and indolactam greatly downregulated the cellular receptor CD4. Indolactam/AR-42 combination emerged from this study as the best combination that showed a strong synergistic effect in reactivating latent virus. Although AR-42 alone did not downregulate CD4 expression, indolactam/AR-42 showed the most efficient downregulation. Our results suggest that indolactam/AR-42 is the most effective combination, showing a strong synergistic effect in reversing HIV latency combined with the most efficient CD4 downregulation.

The application of the improved 3D rat testicular cells co-culture model on the in vitro toxicity research of HZ1006

The aims of the present research are to further validate the application of the improved three-dimensional (3 D) rat testicular cell co-culture model to evaluate the effects of various reprotoxic chemicals on the function of the main somatic cells, as well as on spermatogonial cell differentiation and even spermatogenesis, and to investigate the specific toxicant mechanisms in testes treated with HZ1006, a hydroxamate-based a hydroxamate-based histone deacetylase inhibitor (HDACI). Based on the characteristics of HZ1006, the appropriate exposure duration (8, 16, or 24 days), dosage (0, 3.125, 6.25, 12.5, or 25 μM) and toxic endpoints suitable for detection were selected in the experiments. The results showed inhibition of cell proliferation, reduced testosterone levels, and decreased spermatogonial cell meiosis-specific gene expression, as well as decreased protein levels of androgen receptor (AR) and decreased expression of the AR target gene PSA, accompanied by inhibition of Hdac6 expression after HZ1006 exposure in the 3 D rat testicular cell co-culture model. These findings indicate that the improved 3 D rat testicular cell co-culture model we have established has the potential to become a new testicular toxicity test system that can be used to test toxic characteristics and mechanisms of new compounds and has good application prospects, although more research on the model is required.