Antitumor histone deacetylase inhibitors suppress cutaneous radiation syndrome: Implications for increasing therapeutic gain in cancer radiotherapy

Microbiome in radiotherapy: an emerging approach to enhance treatment efficacy and reduce tissue injury

Radiotherapy is a widely used cancer treatment that utilizes powerful radiation to destroy cancer cells and shrink tumors. While radiation can be beneficial, it can also harm the healthy tissues surrounding the tumor. Recent research indicates that the microbiota, the collection of microorganisms in our body, may play a role in influencing the effectiveness and side effects of radiation therapy. Studies have shown that specific species of bacteria living in the stomach can influence the immune system's response to radiation, potentially increasing the effectiveness of treatment. Additionally, the microbiota may contribute to adverse effects like radiation-induced diarrhea. A potential strategy to enhance radiotherapy outcomes and capitalize on the microbiome involves using probiotics. Probiotics are living microorganisms that offer health benefits when consumed in sufficient quantities. Several studies have indicated that probiotics have the potential to alter the composition of the gut microbiota, resulting in an enhanced immune response to radiation therapy and consequently improving the efficacy of the treatment. It is important to note that radiation can disrupt the natural balance of gut bacteria, resulting in increased intestinal permeability and inflammatory conditions. These disruptions can lead to adverse effects such as diarrhea and damage to the intestinal lining. The emerging field of radiotherapy microbiome research offers a promising avenue for optimizing cancer treatment outcomes. This paper aims to provide an overview of the human microbiome and its role in augmenting radiation effectiveness while minimizing damage.

Effects of histone acetyltransferase (HAT) and histone deacetylase (HDAC) inhibitors on proliferative, differentiative, and regenerative functions of Toll-like receptor 2 (TLR-2)-stimulated human dental pulp cells (hDPCs)

OBJECTIVES

This in vitro study aimed to modify TLR-2-mediated effects on the paracrine, proliferative, and differentiation potentials of human dental pulp-derived cells using histone acetyltransferase (HAT) and histone deacetylase (HDAC) inhibitors.

MATERIALS AND METHODS

Cell viability was assessed using the XTT assay. Cells were either treated with 10 μg/ml Pam3CSK4 only, or pre-treated with valproic acid (VPA) (3 mM), trichostatin A (TSA) (3 μM), and MG-149 (3 μM) for a total of 4 h and 24 h. Control groups included unstimulated cells and cells incubated with inhibitors solvents only. Transcript levels for NANOG, OCT3-4, FGF-1 and 2, NGF, VEGF, COL-1A1, TLR-2, hβD-2 and 3, BMP-2, DSPP, and ALP were assessed through qPCR.

RESULTS

After 24 h, TSA pre-treatment significantly upregulated the defensins and maintained the elevated pro-inflammatory cytokines, but significantly reduced healing and differentiation genes. VPA significantly upregulated the pro-inflammatory cytokine levels, while MG-149 significantly downregulated them. Pluripotency genes were not significantly affected by any regimen.

CONCLUSIONS

At the attempted concentrations, TSA upregulated the defensins gene expression levels, and MG-149 exerted a remarkable anti-inflammatory effect; therefore, they could favorably impact the immunological profile of hDPCs.

CLINICAL RELEVANCE

Targeting hDPC nuclear function could be a promising option in the scope of the biological management of inflammatory pulp diseases.

The Normal, the Radiosensitive, and the Ataxic in the Era of Precision Radiotherapy: A Narrative Review

(1) Background: radiotherapy is a cornerstone of cancer treatment. When delivering a tumoricidal dose, the risk of severe late toxicities is usually kept below 5% using dose-volume constraints. However, individual radiation sensitivity (iRS) is responsible (with other technical factors) for unexpected toxicities after exposure to a dose that induces no toxicity in the general population. Diagnosing iRS before radiotherapy could avoid unnecessary toxicities in patients with a grossly normal phenotype. Thus, we reviewed iRS diagnostic data and their impact on decision-making processes and the RT workflow; (2) Methods: following a description of radiation toxicities, we conducted a critical review of the current state of the knowledge on individual determinants of cellular/tissue radiation; (3) Results: tremendous advances in technology now allow minimally-invasive genomic, epigenetic and functional testing and a better understanding of iRS. Ongoing large translational studies implement various tests and enriched NTCP models designed to improve the prediction of toxicities. iRS testing could better support informed radiotherapy decisions for individuals with a normal phenotype who experience unusual toxicities. Ethics of medical decisions with an accurate prediction of personalized radiotherapy's risk/benefits and its health economics impact are at stake; (4) Conclusions: iRS testing represents a critical unmet need to design personalized radiotherapy protocols relying on extended NTCP models integrating iRS.

Mitigation of radiation injury to reproductive system of male mice by Trichostatin A

Trichostatin A (TSA), derived from the bacteria Streptomyces hygroscopicus, is a hydroxamic acid having various biological properties such as histone deacetylase inhibition, anticancer and radiomitigative action. However the mitigative activity of TSA against radiation-induced damages in the mouse reproductive system has not yet been elucidated. The present study unraveled the effects of 2 Gy whole body irradiation (⁶⁰Co γ- radiation) on C57BL/6 mice male reproductive system including structural damages to testes, increase in apoptosis and reduction in germ cell viability, reduced fertility as well as increased genomic instability in the next generation. Moreover, hematological study and micronuclei assay were used to record chances of radiation-induced hematologic cancer and disruption of genomic integrity in F₁ generation. Interestingly, TSA administration 1 and 24 h post-irradiation attenuated radiation-induced morphological damage and cellular apoptosis in testes. In male mice, TSA restored hematological parameters and micronuclei frequency to normal levels, restored sperm viability, and helped them overcome radiation-induced temporary sterility 5 weeks after the irradiation. Thus our results showed that TSA reduced the probability of radiation-induced hematologic cancers as well as genotoxicity and restored genomic integrity in the progenies of paternally exposed mice by reducing radiation-induced apoptosis in spermatogenic cells and restoring cell proliferation. This study suggested that TSA could be used as potential radiomitigator for male reproductive system.

Current and upcoming therapies to modulate skin scarring and fibrosis

Skin is the largest organ of the human body. Being the interface between the body and the outer environment, makes it susceptible to physical injury. To maintain life, nature has endowed skin with a fast healing response that invariably ends in the formation of scar at the wounded dermal area. In many cases, skin remodelling may be impaired, leading to local hypertrophic scars or keloids. One should also consider that the scarring process is part of the wound healing response, which always starts with inflammation. Thus, scarring can also be induced in the dermis, in the absence of an actual wound, during chronic inflammatory processes. Considering the significant portion of the population that is subject to abnormal scarring, this review critically discusses the state-of-the-art and upcoming therapies in skin scarring and fibrosis.

Reactive Oxygen Species Drive Epigenetic Changes in Radiation-Induced Fibrosis

Radiation-induced fibrosis (RIF) develops months to years after initial radiation exposure. RIF occurs when normal fibroblasts differentiate into myofibroblasts and lay down aberrant amounts of extracellular matrix proteins. One of the main drivers for developing RIF is reactive oxygen species (ROS) generated immediately after radiation exposure. Generation of ROS is known to induce epigenetic changes and cause differentiation of fibroblasts to myofibroblasts. Several antioxidant compounds have been shown to prevent radiation-induced epigenetic changes and the development of RIF. Therefore, reviewing the ROS-linked epigenetic changes in irradiated fibroblast cells is essential to understand the development and prevention of RIF.

Rpd3L Contributes to the DNA Damage Sensitivity of Saccharomyces cerevisiae Checkpoint Mutants

DNA replication forks that are stalled by DNA damage activate an S-phase checkpoint that prevents irreversible fork arrest and cell death. The increased cell death caused by DNA damage in budding yeast cells lacking the Rad53 checkpoint protein kinase is partially suppressed by deletion of the EXO1 gene. Using a whole-genome sequencing approach, we identified two additional genes, RXT2 and RPH1, whose mutation can also partially suppress this DNA damage sensitivity. We provide evidence that RXT2 and RPH1 act in a common pathway, which is distinct from the EXO1 pathway. Analysis of additional mutants indicates that suppression works through the loss of the Rpd3L histone deacetylase complex. Our results suggest that the loss or absence of histone acetylation, perhaps at stalled forks, may contribute to cell death in the absence of a functional checkpoint.

A Review of Clinical Radioprotection and Chemoprotection for Oral Mucositis

The first tenet of medicine, "primum non nocere" or "first, do no harm", is not always compatible with oncological interventions e.g., chemotherapy, targeted therapy and radiation, since they commonly result in significant toxicities. One of the more frequent and serious treatment-induced toxicities is mucositis and particularly oral mucositis (OM) described as inflammation, atrophy and breakdown of the mucosa or lining of the oral cavity. The sequelae of oral mucositis (OM), which include pain, odynodysphagia, dysgeusia, decreased oral intake and systemic infection, frequently require treatment delays, interruptions and discontinuations that not only negatively impact quality of life but also tumor control and survivorship. One potential strategy to reduce or prevent the development of mucositis, for which no effective therapies exist only best supportive empirical care measures, is the administration of agents referred to as radioprotectors and/or chemoprotectors, which are intended to differentially protect normal but not malignant tissue from cytotoxicity. This limited-scope review briefly summarizes the incidence, pathogenesis, symptoms and impact on patients of OM as well as the background and mechanisms of four clinical stage radioprotectors/chemoprotectors, amifostine, palifermin, GC4419 and RRx-001, with the proven or theoretical potential to minimize the development of mucositis particularly in the treatment of head and neck cancers.

Histone Deacetylase Inhibitor Induced Radiation Sensitization Effects on Human Cancer Cells after Photon and Hadron Radiation Exposure

Suberoylanilide hydroxamic acid (SAHA) is a histone deacetylase inhibitor, which has been widely utilized throughout the cancer research field. SAHA-induced radiosensitization in normal human fibroblasts AG1522 and lung carcinoma cells A549 were evaluated with a combination of γ-rays, proton, and carbon ion exposure. Growth delay was observed in both cell lines during SAHA treatment; 2 μM SAHA treatment decreased clonogenicity and induced cell cycle block in G1 phase but 0.2 μM SAHA treatment did not show either of them. Low LET (Linear Energy Transfer) irradiated A549 cells showed radiosensitization effects on cell killing in cycling and G1 phase with 0.2 or 2 μM SAHA pretreatment. In contrast, minimal sensitization was observed in normal human cells after low and high LET radiation exposure. The potentially lethal damage repair was not affected by SAHA treatment. SAHA treatment reduced the rate of γ-H2AX foci disappearance and suppressed RAD51 and RPA (Replication Protein A) focus formation. Suppression of DNA double strand break repair by SAHA did not result in the differences of SAHA-induced radiosensitization between human cancer cells and normal cells. In conclusion, our results suggest SAHA treatment will sensitize cancer cells to low and high LET radiation with minimum effects to normal cells.

Trichostatin A inhibits radiation-induced epithelial-to-mesenchymal transition in the alveolar epithelial cells

Radiation-induced pneumonitis and fibrosis are major complications following thoracic radiotherapy. Epithelial-to-mesenchymal transition (EMT) plays an important role in tissue injury leading to organ fibrosis, including lung. Our previous studies have reported that radiation can induce EMT in the type II alveolar epithelial cells in both in vitro and in vivo. HDAC inhibitors are a new family of anti-cancer agents currently being used in several clinical trials. In addition to their intrinsic anti-tumor properties, HDAC inhibition is also important in other human diseases, including fibrosis and radiation-induced damage. In this study, we evaluated the effect of Trichostatin A (TSA), a HDAC inhibitor, on radiation-induced EMT in type II alveolar epithelial cells (RLE-6TN). Pre-treatment of RLE-6TN cells with TSA inhibited radiation-induced EMT-like morphological alterations including elevated protein level of α-SMA and Snail, reduction of E-cadherin expression, enhanced phosphorylation of GSK3β and ERK1/2, increased generation of ROS. Radiation enhanced the protein level of TGF-β1, which was blocked by N-acetylcysteine, an antioxidant. Treating cells with SB-431542, TGF-β1 type I receptor inhibitor, diminished radiation-induced alterations in the protein levels of p-GSK-3β, Snail-1 and α-SMA, suggesting a regulatory role of TGF-β1 in EMT. Pre-incubation of cells with TSA showed significant decrease in the level of TGF-β1 compared to radiation control. Collectively, these results demonstrate that i] radiation-induced EMT in RLE-6TN cells is mediated by ROS/MEK/ERK and ROS/TGF-β1 signaling pathways and ii] the inhibitory role of TSA in radiation-induced EMT appears to be due, at least in part, to its action of blocking ROS and TGF-β1 signaling.

Anti-fibrotic effects of valproic acid: role of HDAC inhibition and associated mechanisms

Tissue injuries and pathological insults produce oxidative stress, genetic and epigenetic alterations, which lead to an imbalance between pro- and anti-fibrotic molecules, and subsequent accumulation of extracellular matrix, thereby fibrosis. Various molecular pathways play a critical role in fibroblasts activation, which promotes the extracellular matrix production and accumulation. Recent reports highlighted that histone deacetylases (HDACs) are upregulated in various fibrotic disorders and play a central role in fibrosis, while HDAC inhibitors exert antifibrotic effects. Valproic acid is a first-line anti-epileptic drug and a proven HDAC inhibitor. This review provides the current research and novel insights on antifibrotic effects of valproic acid in various fibrotic conditions with an emphasis on the possible strategies for treatment of fibrosis.

Radiosensitization by the histone deacetylase inhibitor PCI-24781

PURPOSE

PCI-24781 is a novel broad spectrum histone deacetylase inhibitor that is currently in phase I clinical trials. The ability of PCI-24781 to act as a radiation sensitizer and the mechanisms of radiosensitization were examined.

EXPERIMENTAL DESIGN

Exponentially growing human SiHa cervical and WiDr colon carcinoma cells were exposed to 0.1 to 10 micromol/L PCI-24781 in vitro for 2 to 20 h before irradiation and 0 to 4 h after irradiation. Single cells and sorted populations were analyzed for histone acetylation, H2AX phosphorylation, cell cycle distribution, apoptotic fraction, and clonogenic survival.

RESULTS

PCI-24781 treatment for 4 h increased histone H3 acetylation and produced a modest increase in gammaH2AX but negligible cell killing or radiosensitization. Treatment for 24 h resulted in up to 80% cell kill and depletion of cells in S phase. Toxicity reached maximum levels at a drug concentration of approximately 1 micromol/L, and cells in G(1) phase at the end of treatment were preferentially spared. A similar dose-modifying factor (DMF(0.1) = 1.5) was observed for SiHa cells exposed for 24 h at 0.1 to 3 micromol/L, and more radioresistant WiDr cells showed less sensitization (DMF(0.1) = 1.2). Limited radiosensitization and less killing were observed in noncycling human fibroblasts. Cell sorting experiments confirmed that depletion of S-phase cells was not a major mechanism of radiosensitization and that inner noncycling cells of SiHa spheroids could be sensitized by nontoxic doses. PCI-24781 pretreatment increased the fraction of cells with gammaH2AX foci 24 h after irradiation but did not affect the initial rate of loss of radiation-induced gammaH2AX or the rate of rejoining of DNA double-strand breaks.

CONCLUSIONS

PCI-24781 shows promise as a radiosensitizing agent that may compromise the accuracy of repair of radiation damage.

Cell cycle checkpoint signaling involved in histone deacetylase inhibition and radiation-induced cell death

In breast cancer, radiation has a central role in the treatment of brain metastasis, although tumor sensitivity might be limited. The tumor cell defense response to ionizing radiation involves activation of cell cycle checkpoint signaling. Histone deacetylase (HDAC) inhibitors, agents that cause hyperacetylation of histone proteins and thereby aberrations in the chromatin structure, may also override the DNA damage defense response and facilitate the radiation-induced mitotic cell death. In experimental metastasis models, the human breast carcinoma cell line MA-11 invariably disseminates to the central nervous system. We compared profiles of in vitro MA-11 cell cycle response to ionizing radiation and HDAC inhibition. After radiation exposure, the G2-M phase accumulation and the preceding repression of the G2 phase regulatory factors Polo-like kinase-1 and cyclin B1 required intact G2 checkpoint signaling through the checkpoint kinase CHK1, whereas the similar phenotypic changes observed with HDAC inhibition did not. MA-11 cells did not show radiation-induced expression of the G1 cell cycle inhibitor p21, indicative of a defective G1 checkpoint and consistent with a point mutation detected in the tumor suppressor TP53 gene. Increase in the p21 level, however, was observed with HDAC inhibition. Following pretreatment with the HDAC inhibitor, the efficiency of clonogenic regrowth after irradiation was reduced, which is in accordance with the concept of increased probability of mitotic cell death when the chromatin structure is disrupted. Among molecular cell cycle-targeted drugs currently in the pipeline for testing in early-phase clinical trials, HDAC inhibitors may have therapeutic potential as radiosensitizers.