Preclinical Pharmacokinetics Study of R- and S-Enantiomers of the Histone Deacetylase Inhibitor, AR-42 (NSC 731438), in Rodents

Exploring viral mimicry combined with epigenetics and tumor immunity: new perspectives in cancer therapy

Viral mimicry refers to an active antiviral response triggered by the activation of endogenous retroviruses (ERVs), usually manifested by the formation of double-stranded RNA (dsRNA) and activation of the cellular interferon response, which activates the immune system and produces anti-tumor effects. Epigenetic studies have shown that epigenetic modifications (e.g. DNA methylation, histone modifications, etc.) play a crucial role in tumorigenesis, progression, and treatment resistance. Particularly, alterations in DNA methylation may be closely associated with the suppression of ERVs expression, and treatment by demethylation may restore ERVs activity and thus strengthen the tumor immune response. Therefore, we propose that viral mimicry can induce immune responses in the tumor microenvironment by activating the expression of ERVs, and that epigenetic alterations may play a key regulatory role in this process. In this paper, we review the intersection of viral mimicry, epigenetics and tumor immunotherapy, and explore the possible interactions and synergistic effects among the three, aiming to provide a new theoretical basis and potential strategies for cancer immunotherapy.

Exploring the role of histone deacetylase and histone deacetylase inhibitors in the context of multiple myeloma: mechanisms, therapeutic implications, and future perspectives

Histone deacetylase inhibitors (HDACis) are a significant category of pharmaceuticals that have developed in the past two decades to treat multiple myeloma. Four drugs in this category have received approval from the U.S. Food and Drug Administration (FDA) for use: Panobinonstat (though canceled by the FDA in 2022), Vorinostat, Belinostat and Romidepsin. The efficacy of this group of drugs is attributed to the disruption of many processes involved in tumor growth through the inhibition of histone deacetylase, and this mode of action leads to significant anti-multiple myeloma (MM) activity. In MM, inhibition of histone deacetylase has many downstream consequences, including suppression of NF-κB signaling and HSP90, upregulation of cell cycle regulators (p21, p53), and downregulation of antiapoptotic proteins including Bcl-2. Furthermore, HDACis have a variety of direct and indirect oxidative effects on cellular DNA. HDAC inhibitors enhance normal immune function, thereby decreasing the proliferation of malignant plasma cells and promoting autophagy. The various biological effects of inhibiting histone deacetylase have a combined or additional impact when used alongside other chemotherapeutic and targeted drugs for multiple myeloma. This helps to decrease resistance to treatment. Combination treatment regimens that include HDACis have become an essential part of the therapy for multiple myeloma. These regimens incorporate drugs from other important classes of anti-myeloma agents, such as immunomodulatory drugs (IMiDs), conventional chemotherapy, monoclonal antibodies, and proteasome inhibitors. This review provides a comprehensive evaluation of the clinical efficacy and safety data pertaining to the currently approved histone deacetylase inhibitors, as well as an explanation of the crucial function of histone deacetylase in multiple myeloma and the characteristics of the different histone deacetylase inhibitors. Moreover, it provides a concise overview of the most recent developments in the use of histone deacetylase inhibitors for treating multiple myeloma, as well as potential future uses in treatment.

Population Pharmacokinetic Analysis from First-in-Human Data for HDAC Inhibitor, REC-2282 (AR-42), in Patients with Solid Tumors and Hematologic Malignancies: A Case Study for Evaluating Flat vs. Body Size Normalized Dosing

Background and Objectives

REC-2282 is a novel histone deacetylase inhibitor that has shown antitumor activity in in vitro and in vivo models of malignancy.  The aims of this study were to characterize the population pharmacokinetics of REC-2282 (AR-42) from the first-in-human (NCT01129193) and phase I acute myeloid leukemia trials (NCT01798901) and to evaluate potential sources of variability. Additionally, we sought to understand alternate body size descriptors as sources of inter-individual variability (IIV), which was significant for dose-normalized maximum observed concentration and area under the concentration-time curve (AUC).

Methods

Datasets from two clinical trials were combined, and population pharmacokinetic analysis was performed using NONMEM and R softwares; patient demographics were tested as covariates.

Results

A successful population pharmacokinetic model was constructed. The pharmacokinetics of REC-2282 were best described by a two-compartment model with one transit compartment for absorption, first-order elimination and a proportional error model. Fat-free mass (FFM) was retained as a single covariate on clearance (CL), though it explained < 3% of the observed variability on CL. Tumor type and formulation were retained as covariates on lag time, and a majority of variability, attributed to absorption, remained unexplained. Computed tomography (CT)-derived lean body weight estimates were lower than estimated lean body weight and fat-free mass measures in most patients. Analysis of dose-normalized AUC vs. body size descriptors suggests flat dosing is most appropriate for REC-2282.

Conclusions

FFM was identified as a significant covariate on CL; however, it explained only a very small portion of the IIV; major factors contributing significantly to REC-2282 pharmacokinetic variability remain unidentified.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13318-021-00722-z.

Nonredundant, isoform-specific roles of HDAC1 in glioma stem cells

Glioblastoma (GBM) is characterized by an aberrant yet druggable epigenetic landscape. One major family of epigenetic regulators, the histone deacetylases (HDACs), are considered promising therapeutic targets for GBM due to their repressive influences on transcription. Although HDACs share redundant functions and common substrates, the unique isoform-specific roles of different HDACs in GBM remain unclear. In neural stem cells, HDAC2 is the indispensable deacetylase to ensure normal brain development and survival in the absence of HDAC1. Surprisingly, we find that HDAC1 is the essential class I deacetylase in glioma stem cells, and its loss is not compensated for by HDAC2. Using cell-based and biochemical assays, transcriptomic analyses, and patient-derived xenograft models, we find that knockdown of HDAC1 alone has profound effects on the glioma stem cell phenotype in a p53-dependent manner. We demonstrate marked suppression in tumor growth upon targeting of HDAC1 and identify compensatory pathways that provide insights into combination therapies for GBM. Our study highlights the importance of HDAC1 in GBM and the need to develop isoform-specific drugs.

Histone deacetylase inhibitor AR-42 and achiral analogues kill malaria parasites in vitro and in mice

Malaria is caused by infection with Plasmodium parasites and results in significant health and economic impacts. Malaria eradication is hampered by parasite resistance to current drugs and the lack of a widely effective vaccine. Compounds that target epigenetic regulatory proteins, such as histone deacetylases (HDACs), may lead to new therapeutic agents with a different mechanism of action, thereby avoiding resistance mechanisms to current antimalarial drugs. The anticancer HDAC inhibitor AR-42, as its racemate (rac-AR-42), and 36 analogues were investigated for in vitro activity against P. falciparum. Rac-AR-42 and selected compounds were assessed for cytotoxicity against human cells, histone hyperacetylation, human HDAC1 inhibition and oral activity in a murine malaria model. Rac-AR-42 was tested for ex vivo asexual and in vitro exoerythrocytic stage activity against P. berghei murine malaria parasites. Rac-AR-42 and 13 achiral analogues were potent inhibitors of asexual intraerythrocytic stage P. falciparum 3D7 growth in vitro (IC₅₀ 5–50 nM), with four of these compounds having >50-fold selectivity for P. falciparum versus human cells (selectivity index 56–118). Rac-AR-42 induced in situ hyperacetylation of P. falciparum histone H4, consistent with PfHDAC(s) inhibition. Furthermore, rac-AR-42 potently inhibited P. berghei infected erythrocyte growth ex vivo (IC₅₀ 40 nM) and P. berghei exoerythrocytic forms in hepatocytes (IC₅₀ 1 nM). Oral administration of rac-AR-42 and two achiral analogues inhibited P. berghei growth in mice, with rac-AR-42 (50 mg/kg/day single dose for four days) curing all infections. These findings demonstrate curative properties for HDAC inhibitors in the oral treatment of experimental mouse malaria.

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HDAC inhibitors rac-AR-42 and 13 analogues inhibit P. falciparum growth in vitro.

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Rac-AR-42 inhibits P. berghei exoerythrocytic forms in hepatocytes (IC₅₀ 1 nM).

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Rac-AR-42 causes in situ hyperacetylation of P. falciparum histone H4.

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Rac-AR-42 cures P. berghei infected mice with oral dosing.

A phase 1 trial of the histone deacetylase inhibitor AR-42 in patients with neurofibromatosis type 2-associated tumors and advanced solid malignancies

PURPOSE

Given clinical activity of AR-42, an oral histone deacetylase inhibitor, in hematologic malignancies and preclinical activity in solid tumors, this phase 1 trial investigated the safety and tolerability of AR-42 in patients with advanced solid tumors, including neurofibromatosis type 2-associated meningiomas and schwannomas (NF2). The primary objective was to define the maximum tolerated dose (MTD) and dose-limiting toxicities (DLTs). Secondary objectives included determining pharmacokinetics and clinical activity.

METHODS

This phase I trial was an open-label, single-center, dose-escalation study of single-agent AR-42 in primary central nervous system and advanced solid tumors. The study followed a 3 + 3 design with an expansion cohort at the MTD.

RESULTS

Seventeen patients were enrolled with NF2 (n = 5), urothelial carcinoma (n = 3), breast cancer (n = 2), non-NF2-related meningioma (n = 2), carcinoma of unknown primary (n = 2), small cell lung cancer (n = 1), Sertoli cell carcinoma (n = 1), and uveal melanoma (n = 1). The recommended phase II dose is 60 mg three times weekly, for 3 weeks of a 28-day cycle. DLTs included grade 3 thrombocytopenia and grade 4 psychosis. The most common treatment-related adverse events were cytopenias, fatigue, and nausea. The best response was stable disease in 53% of patients (95% CI 26.6-78.7). Median progression-free survival (PFS) was 3.6 months (95% CI 1.2-9.1). Among evaluable patients with NF2 or meningioma (n = 5), median PFS was 9.1 months (95% CI 1.9-not reached).

CONCLUSION

Single-agent AR-42 is safe and well tolerated. Further studies may consider AR-42 in a larger cohort of patients with NF2 or in combination with other agents in advanced solid tumors.

TRIAL REGISTRATION

NCT01129193, registered 5/24/2010.

Overcoming resistance to anabolic SARM therapy in experimental cancer cachexia with an HDAC inhibitor

No approved therapy exists for cancer-associated cachexia. The colon-26 mouse model of cancer cachexia mimics recent late-stage clinical failures of anabolic anti-cachexia therapy and was unresponsive to anabolic doses of diverse androgens, including the selective androgen receptor modulator (SARM) GTx-024. The histone deacetylase inhibitor (HDACi) AR-42 exhibited anti-cachectic activity in this model. We explored combined SARM/AR-42 therapy as an improved anti-cachectic treatment paradigm. A reduced dose of AR-42 provided limited anti-cachectic benefits, but, in combination with GTx-024, significantly improved body weight, hindlimb muscle mass, and grip strength versus controls. AR-42 suppressed the IL-6/GP130/STAT3 signaling axis in muscle without impacting circulating cytokines. GTx-024-mediated β-catenin target gene regulation was apparent in cachectic mice only when combined with AR-42. Our data suggest cachectic signaling in this model involves catabolic signaling insensitive to anabolic GTx-024 therapy and a blockade of GTx-024-mediated anabolic signaling. AR-42 mitigates catabolic gene activation and restores anabolic responsiveness to GTx-024. Combining GTx-024, a clinically established anabolic therapy, with AR-42, a clinically evaluated HDACi, represents a promising approach to improve anabolic response in cachectic patients.

Histone deacetylase 2 is involved in µ‑opioid receptor suppression in the spinal dorsal horn in a rat model of chronic pancreatitis pain

Chronic pain occurs in ~85–90% of chronic pancreatitis (CP) patients. However, as the pathogenesis of CP pain remains to be fully understood, the current therapies for CP pain remain inadequate. Emerging evidence has suggested that the epigenetic modulations of genes are involved in chronic pain. In the present study, intrapancreatic trinitrobenzene sulfonic acid infusions were used to establish a CP model in rats. Mechanical allodynia was measured with von Frey filaments. Immunofluorescent staining analysis was used to observe the expression changes of histone deacetylase 2 (HDAC2) and µ-opioid receptor (MOR), and intrathecal administration of the selective HDAC2 inhibitor AR-42 was used to assess the underlying mechanisms. The expression levels of c-Jun N-terminal kinase (JNK) in the thoracic spinal cord were detected by western blotting, and the mRNA expression levels of interleukin (IL)1-β, IL-6 and tumor necrosis factor (TNF)-α were detected by reverse transcription-quantitative polymerase chain reaction. The results demonstrated that HDAC2 expression was upregulated during the course of CP induction, while MOR activity in the thoracic spinal dorsal horn was significantly suppressed. Intrathecal infusion of AR-42 significantly attenuated CP-induced mechanical allodynia, with rescued MOR activity. Additionally, HDAC2 facilitated the release of inflammatory cytokines, including IL-1β, IL-6 and TNF-α. These results suggested that the underlying mechanisms of HDAC2 regulating MOR activity under CP induction may occur via promoting the release of inflammatory cytokines, thus activating the JNK signaling pathway. The present study suggested that the epigenetic-regulated disturbance of MOR is dependent on the endogenous analgesia system in CP, which may a provide novel therapeutic strategy for treating pain in CP.

Suppression of Tumor Growth and Muscle Wasting in a Transgenic Mouse Model of Pancreatic Cancer by the Novel Histone Deacetylase Inhibitor AR-42

PURPOSE

Pancreatic ductal adenocarcinoma (PDAC) is the third leading cause of cancer death in the United States. This study was aimed at evaluating the efficacy of AR-42 (formerly OSU-HDAC42), a novel histone deacetylase (HDAC) inhibitor currently in clinical trials, in suppressing tumor growth and/or cancer-induced muscle wasting in murine models of PDAC.

EXPERIMENTAL DESIGN

The in vitro antiproliferative activity of AR-42 was evaluated in six human pancreatic cancer cell lines (AsPC-1, COLO-357, PANC-1, MiaPaCa-2, BxPC-3, SW1990). AsPC-1 subcutaneous xenograft and transgenic KP^fl/flC (LSL-Kras^G12D;Trp53^flox/flox;Pdx-1-Cre) mouse models of pancreatic cancer were used to evaluate the in vivo efficacy of AR-42 in suppressing tumor growth and/or muscle wasting.

RESULTS

Growth suppression in AR-42-treated cells was observed in all six human pancreatic cancer cell lines with dose-dependent modulation of proliferation and apoptotic markers, which was associated with the hallmark features of HDAC inhibition, including p21 upregulation and histone H3 hyperacetylation. Oral administration of AR-42 at 50 mg/kg every other day resulted in suppression of tumor burden in the AsPC-1 xenograft and KP^fl/flC models by 78% and 55%, respectively, at the end of treatment. Tumor suppression was associated with HDAC inhibition, increased apoptosis, and inhibition of proliferation. Additionally, AR-42 as a single agent preserved muscle size and increased grip strength in KP^fl/flC mice. Finally, the combination of AR-42 and gemcitabine in transgenic mice demonstrated a significant increase in survival than either agent alone.

CONCLUSIONS

These results suggest that AR-42 represents a therapeutically promising strategy for the treatment of pancreatic cancer.