Animacroxam, a Novel Dual-Mode Compound Targeting Histone Deacetylases and Cytoskeletal Integrity of Testicular Germ Cell Cancer Cells

Mechanisms of cisplatin sensitivity and resistance in testicular germ cell tumors and potential therapeutic agents (Review)

Testicular germ cell tumors (TGCTs) are the most common tumors in men aged 20-40 years and are primarily treated with cisplatin-based drugs. Although TGCTs are highly sensitive to DNA damage induced by cisplatin and show a hypersensitive apoptotic response, cisplatin resistance still exists. Emerging evidence shows that cisplatin resistance in TGCTs is mainly related to the inhibition of apoptotic pathways such as MDM2/p53, OCT4/NOXA, PDGFR/PI3K/AKT, inhibition of cell cycle checkpoints, increased methylation or neddylation and DNA repair balance. In this review, recent advances regarding the mechanisms of TGCTs' sensitivity and resistance to cisplatin were summarized and potential therapeutic agents for cisplatin-resistant TGCTs were presented, providing a new therapeutic strategy for drug-resistant TGCTs.

Novel Thienyl-Based Tyrosine Kinase Inhibitors for the Treatment of Hepatocellular Carcinoma

New medical treatments are urgently needed for advanced hepatocellular carcinoma (HCC). Recently, we showed the anticancer effects of novel thiophene-based kinase inhibitors. In this study, we further characterized the antineoplastic effects and modes of action of the two most promising inhibitors, Thio-Iva and Thio-Dam, and compared their effects with the clinically relevant multi-kinase inhibitor, sorafenib, in HCC cells. Crystal violet staining and real-time cell growth monitoring showed pronounced antiproliferative effects in Huh-7 and SNU-449 cells with IC50 values in the (sub-)micromolar range. Long-term incubation experiments revealed the reduced clonogenicity of Thio-Iva and Thio-Dam-treated HCC cells. LDH-release tests excluded cytotoxicity as an unspecific mode of action of the inhibitors, while flow cytometry analysis revealed a dose-dependent and pronounced G2/M phase cell cycle arrest and cyclin B1 suppression. Additionally, mitochondria-driven apoptosis was observed through the cytosolic increase of reactive oxygen species, a concomitant PARP cleavage, and caspase-3 induction. Both compounds were found to effectively inhibit the capillary tube formation of endothelial EA.hy926 cells in vitro, pointing towards additional antiangiogenic effects. Antiangiogenic and antineoplastic effects were confirmed in vivo by CAM assays. In summary, the thienyl-acrylonitrile derivatives, Thio-Iva and Thio-Dam, exert significant antineoplastic and antiangiogenic effects in HCC cells.

Chimeric HDAC and the cytoskeleton inhibitor broxbam as a novel therapeutic strategy for liver cancer

Broxbam, also known as N-hydroxy-4-{1-methoxy-4-[4′-(3′-bromo-4′,5′-dimethoxyphenyl)-oxazol-5′-yl]-2-phenoxy} butanamide, is a novel chimeric inhibitor that contains two distinct pharmacophores in its molecular structure. It has been previously demonstrated to inhibit the activity of histone deacetylases (HDAC) and tubulin polymerisation, two critical components required for cancer growth and survival. In the present study, the potential suitability of broxbam for the treatment of liver cancer was investigated. The effects of broxbam on cell proliferation and apoptosis, in addition to the under-lying molecular mechanism of action, were first investigated in primary liver cancer cell lines Huh7, HepG2, TFK1 and EGI1. Real-time proliferation measurements made using the iCEL-Ligence system and viable cell number counting following crystal violet staining) revealed that broxbam time- and dose-dependently reduced the proliferation of liver cancer cell lines with IC₅₀ values <1 µM. In addition, a significant inhibition of the growth of hepatoblastoma microtumours on the chorioallantoic membranes (CAM) of fertilised chicken eggs by broxbam was observed according to results from the CAM assay, suggesting antineoplastic potency in vivo. Broxbam also exerted apoptotic effects through p53- and mitochondria-driven caspase-3 activation in Huh7 and HepG2 cells according to data from western blotting (p53 and phosphorylated p53), mitochondrial membrane potential measurements (JC-1 assay) and fluorometric capsase-3 measurements. Notably, no contribution of unspecific cytotoxic effects mediated by broxbam were observed from LDH-release measurements. HDAC1, -2, -4 and -6 expression was measured by western blotting and the HDAC inhibitory potency of broxbam was next evaluated using subtype-specific HDAC enzymatic assays, which revealed a largely pan-HDAC inhibitory activity with the most potent inhibition observed on HDAC6. Silencing HDAC6 expression in Huh7 cells led to a drop in the expression of the proliferation markers Ki-67 and E2F3, suggesting that HDAC6 inhibition by broxbam may serve a predomi-nant role in their antiproliferative effects on liver cancer cells. Immunofluorescence staining of cytoskeletal proteins (α-tubulin & actin) of broxbam-treated HepG2 cells revealed a pronounced inhibition of tubulin polymerisation, which was accompanied by reduced cell migration as determined by wound healing scratch assays. Finally, data from zebrafish angiogenesis assays revealed marked antiangiogenic effects of broxbam in vivo, as shown by the suppression of subintestinal vein growth in zebrafish embryos. To conclude, the pleiotropic anticancer activities of this novel chimeric HDAC- and tubulin inhibitor broxbam suggest that this compound is a promising candidate for liver cancer treatment, which warrants further pre-clinical and clinical evaluation.

Improved Anticancer Activities of a New Pentafluorothio-Substituted Vorinostat-Type Histone Deacetylase Inhibitor

The development of new anticancer drugs is necessary in order deal with the disease and with the drawbacks of currently applied drugs. Epigenetic dysregulations are a central hallmark of cancerogenesis and histone deacetylases (HDACs) emerged as promising anticancer targets. HDAC inhibitors are promising epigenetic anticancer drugs and new HDAC inhibitors are sought for in order to obtain potent drug candidates. The new HDAC inhibitor SF5-SAHA was synthesized and analyzed for its anticancer properties. The new compound SF5-SAHA showed strong inhibition of tumor cell growth with IC₅₀ values similar to or lower than that of the clinically applied reference compound vorinostat/SAHA (suberoylanilide hydroxamic acid). Target specific HDAC inhibition was demonstrated by Western blot analyses. Unspecific cytotoxic effects were not observed in LDH-release measurements. Pro-apoptotic formation of reactive oxygen species (ROS) and caspase-3 activity induction in prostate carcinoma and hepatocellular carcinoma cell lines DU145 and Hep-G2 seem to be further aspects of the mode of action. Antiangiogenic activity of SF5-SAHA was observed on chorioallantoic membranes of fertilized chicken eggs (CAM assay). The presence of the pentafluorothio-substituent of SF5-SAHA increased the antiproliferative effects in both solid tumor and leukemia/lymphoma cell models when compared with its parent compound vorinostat. Based on this preliminary study, SF5-SAHA has the prerequisites to be further developed as a new HDAC inhibitory anticancer drug candidate.

The chorioallantoic membrane as a bio-barrier model for the evaluation of nanoscale drug delivery systems for tumour therapy

In 2010, the European Parliament and the European Union adopted a directive on the protection of animals used for scientific purposes. The directive aims to protect animals in scientific research, with the final goal of complete replacement of procedures on live animals for scientific and educational purposes as soon as it is scientifically viable. Furthermore, the directive announces the implementation of the 3Rs principle: "When choosing methods, the principles of replacement, reduction and refinement should be implemented through a strict hierarchy of the requirement to use alternative methods." The visibility, accessibility, and the rapid growth of the chorioallantoic membrane (CAM) offers a clear advantage for various manipulations and for the simulation of different Bio-Barriers according to the 3R principle. The extensive vascularisation on the CAM provides an excellent substrate for the cultivation of tumour cells or tumour xenografts which could be used for the therapeutic evaluation of nanoscale drug delivery systems. The tumour can be targeted either by topical application, intratumoural injection or i.v. injection. Different application sites and biological barriers can be examined within a single model.

Autophagy in the HTR-8/SVneo Cell Oxidative Stress Model Is Associated with the NLRP1 Inflammasome

We investigated whether there was activation of NLRP1 inflammasomes and excessive autophagy in oxidative stress damage. And we further demonstrate whether there is a cascade relationship between the activation of NLRP1 inflammasomes and the phenomenon of excessive autophagy. To observe the expression level of the NLRP1 inflammasome group in the pathological process of trophoblast cell oxidative stress, western blot, immunofluorescence, and qRT-PCR were performed. Autophagy in trophoblast cells after the action of H₂O₂ was detected by using normal trophoblast cells' NLRP1-specific activator (MDP) as a positive control. The presence of excessive autophagy was determined by comparing it with the autophagy-related proteins in normal trophoblast cells. Through siRNA-NLRP1, we investigated the role of oxidative stress and the NLRP1 inflammasome in autophagy in cells. 100 μmol MDP for 24 hours can be used as the optimal concentration of the NLRP1 activator. In human placental trophoblast oxidative stress, the model group significantly increased the expression level of inflammasome IL-1β, CASP1, and NLRP1, compared with the control group NLRP3, and LC3-II, Beclin-1, ATG5, ATG7, and p62 overactivated the autophagy ability of cells. After the activation of NLRP1, the expression of these inflammasomes increased, accompanied by the decrease in autophagy. After the expression of NLRP1 was silenced by RNAi, the expression of inflammasome IL-1β, CASP1, and NLRP3 was also decreased. Still, the autophagy level was increased, which was manifested by the high expression of LC3-II, Beclin-1, ATG5, and ATG7 and the decrease in p62. Trophoblast cells showed the expression of NLRP1 protein and excessive autophagy under oxidative stress. Simultaneously, the NLRP1 inflammasome of trophoblast cells in the state of oxidative stress was correlated with autophagy. Inflammasome activation and autophagy were shown to be linked and to influence each other mutually. These may also provide new therapeutic targets in a pathological pregnancy.

Between a Rock and a Hard Place: An Epigenetic-Centric View of Testicular Germ Cell Tumors

Simple Summary

This minireview focuses on the role of epigenetics in testicular cancer. A working model is developed that postulates that epigenetic features that drive testicular cancer malignancy also enable these tumors to be cured at a high rate with chemotherapy. Chemoresistance may occur by epigenetic uncoupling of malignancy and chemosensitivity, a scenario that may be amenable to epigenetic-based therapies.

Abstract

Compared to many common solid tumors, the main genetic drivers of most testicular germ cell tumors (TGCTs) are unknown. Decades of focus on genomic alterations in TGCTs including awareness of a near universal increase in copies of chromosome 12p have failed to uncover exceptional driver genes, especially in genes that can be targeted therapeutically. Thus far, TGCT patients have missed out on the benefits of targeted therapies available to treat most other malignancies. In the past decade there has been a greater appreciation that epigenetics may play an especially prominent role in TGCT etiology, progression, and hypersensitivity to conventional chemotherapy. While genetics undoubtedly plays a role in TGCT biology, this mini-review will focus on the epigenetic “states” or features of testicular cancer, with an emphasis on DNA methylation, histone modifications, and miRNAs associated with TGCT susceptibility, initiation, progression, and response to chemotherapy. In addition, we comment on the current status of epigenetic-based therapy and epigenetic biomarker development for TGCTs. Finally, we suggest a unifying “rock and a hard place” or “differentiate or die” model where the tumorigenicity and curability of TGCTs are both dependent on common but still ill-defined epigenetic states.

New 3-Aryl-2-(2-thienyl)acrylonitriles with High Activity Against Hepatoma Cells

New 2-(thien-2-yl)-acrylonitriles with putative kinase inhibitory activity were prepared and tested for their antineoplastic efficacy in hepatoma models. Four out of the 14 derivatives were shown to inhibit hepatoma cell proliferation at (sub-)micromolar concentrations with IC50 values below that of the clinically relevant multikinase inhibitor sorafenib, which served as a reference. Colony formation assays as well as primary in vivo examinations of hepatoma tumors grown on the chorioallantoic membrane of fertilized chicken eggs (CAM assay) confirmed the excellent antineoplastic efficacy of the new derivatives. Their mode of action included an induction of apoptotic capsase-3 activity, while no contribution of unspecific cytotoxic effects was observed in LDH-release measurements. Kinase profiling of cancer relevant protein kinases identified the two 3-aryl-2-(thien-2-yl)acrylonitrile derivatives 1b and 1c as (multi-)kinase inhibitors with a preferential activity against the VEGFR-2 tyrosine kinase. Additional bioinformatic analysis of the VEGFR-2 binding modes by docking and molecular dynamics calculations supported the experimental findings and indicated that the hydroxy group of 1c might be crucial for its distinct inhibitory potency against VEGFR-2. Forthcoming studies will further unveil the underlying mode of action of the promising new derivatives as well as their suitability as an urgently needed novel approach in HCC treatment.

Epigenetic alterations of testicular germ cell tumours

PURPOSE OF REVIEW

Testicular germ cell tumours (TGCTs) exhibit, in contrast to other cancer types, a relatively low mutational burden. However, numerous epigenetic alterations have been shown to impact TGCT. In this review, we summarize the most relevant findings of the past 2 years.

RECENT FINDINGS

Recent studies focused on the functions of microRNAs and the impact of aberrant DNA methylation. Moreover, several epigenetic drugs with antineoplastic effects in TGCTs were identified.

SUMMARY

Aberrant DNA methylation and differentially expressed microRNAs have an important effect on TGCT pathogenesis. Moreover, differential DNA methylation patterns were found to be specific for different TGCT subtypes. Various microRNAs, such as miR-371a-3p, were found to be highly sensitive and specific biomarkers for TGCT. The epigenetic drugs guadecitabine, animacroxam, and JQ1 showed promising effects on TGCT in preclinical in-vivo and in-vitro studies.

Epigenetic alterations as therapeutic targets in Testicular Germ Cell Tumours : current and future application of 'epidrugs'

Testicular germ cell tumours (TGCTs) are heterogeneous neoplasms mostly affecting young-adult men. Despite high survival rates, some patients with disseminated disease acquire cisplatin resistance, entailing the need for less toxic therapies. Epigenetic alterations constitute an important feature of TGCTs, which are also implicated in resistance mechanism(s). These alterations might be used as potential targets to design epigenetic drugs. To date, several compounds have been explored and evaluated regarding therapeutic efficacy, making use of pre-clinical studies with in vitro and in vivo models, and some have already been explored in clinical trials. This review summarizes the several epigenetic mechanisms at play in these neoplasms, the current challenges in the field of TGCTs and critically reviews available data on 'epidrugs' in those tumours.

Antitumor and antiangiogenic activity of the novel chimeric inhibitor animacroxam in testicular germ cell cancer

Chimeric inhibitors, which merge two drug pharmacophores in a single molecule have become a prominent approach for the design of novel anticancer compounds. Here, we examined animacroxam, which combines histone deacetylase (HDAC) inhibitory and cytoskeleton‐interfering pharmacophores, in testicular germ cell tumors (TGCT). The effectiveness of animacroxam was compared to that of the commonly applied chemotherapeutic cisplatin as well as the clinically approved HDAC inhibitor vorinostat. The antineoplastic and antiangiogenic effects of animacroxam on TGCT in vivo were assessed through exploratory animal studies and a modified chorioallantoic membrane assay, revealing that animacroxam has significant antitumor activity in TGCT. A novel positron emission tomography/MR‐imaging approach was applied to determine tumor volume and glucose [2‐fluoro‐2‐deoxy‐d‐glucose (18F‐FDG)] uptake in TGCT tumors, revealing reduced glucose uptake in animacroxam‐treated TGCTs and showing a dose‐dependent suppression of glycolytic enzymes, which led to a breakdown in glycolytic energy production. Furthermore, the observed antiangiogenic effects of animacroxam were related to its ability to inhibit endothelial cell–cell communication, as the expression of gap junction‐forming connexin 43 was strongly suppressed, and gap‐junctional intercellular mass transport was reduced. Our data suggest that the chimeric HDAC inhibitor animacroxam may become a promising candidate for the treatment of solid cancers and may serve as an interesting alternative to platinum‐based therapies.

Epigenetic treatment combinations to effectively target cisplatin-resistant germ cell tumors: past, present, and future considerations

BACKGROUND

Type II germ cell tumors represent the most common solid malignancy in men aged 15-45 years. Despite high cure rates of >90% over all stages, 10-15% of advanced patients develop treatment resistance and potentially succumb to their disease. Treatment of refractory germ cell tumors remains unsatisfactory, and new approaches are needed to further improve outcomes.

OBJECTIVES

With this narrative review, we highlight epigenetic mechanisms related to resistance to standard systemic treatment, which may act as promising targets for novel combined epigenetic treatment approaches.

MATERIALS AND METHODS

A comprehensive literature search of PubMed and MEDLINE was conducted to identify original and review articles on resistance mechanisms and/or epigenetic treatment of germ cell tumors in vitro and in vivo. Review articles were hand-searched to identify additional articles.

RESULTS

Distinct epigenetic phenomena have been linked to chemotherapy resistance in germ cell tumors, among which DNA hypermethylation, histone acetylation, and bromodomain proteins appear as promising targets for therapeutic exploitation. Inhibitors of key regulators, for example DNA methyltransferases (e.g. decitabine, guadecitabine), histone deacetylases (e.g. romidepsin), and bromodomain proteins (e.g. JQ1) decreased cell viability, triggered apoptosis, and growth arrest. Additionally, these epigenetic drugs induced differentiation and led to loss of pluripotency and re-sensitization towards cisplatin in cell lines and animal models.

DISCUSSION

Epigenetic treatments hold promise to (i) reduce the treatment burden of and (ii) overcome resistance to standard cisplatin-based chemotherapy. Combined approaches may enhance activity, while the ideal target and treatment combination of epigenetic drugs, either with another epigenetic agent or conventional cytotoxic agents need to be defined.

CONCLUSION

Epigenetic (combination) treatment for germ cell tumors should be further explored in pre-clinical and clinical research for its potential to further improve germ cell tumor treatment.

Oxazole-Bridged Combretastatin A-4 Derivatives with Tethered Hydroxamic Acids: Structure⁻Activity Relations of New Inhibitors of HDAC and/or Tubulin Function

New inhibitors of tubulin polymerization and/or histone deacetylase (HDAC) activity were synthesized by attaching alkyl tethered hydroxamic acid appendages of varying length to oxazole-bridged combretastatin A-4 analogous caps. While their antiproliferative and microtubule disrupting effect was most pronounced for derivatives with short spacers, HDAC inhibition was strongest for those with longer spacers. These findings were further supported by computational methods such as structure-based docking experiments exploring the target interactions of the derivatives with varying linkers. For instance, compounds featuring short four-atom spacers between cap and hydroxamic acid inhibited the growth of various cancer cell lines and human endothelial hybrid cells with IC₅₀ values in the low nanomolar range. In line with their ability to inhibit the microtubule assembly, four- and five-atom spacered hydroxamic acids caused an accumulation of 518A2 melanoma cells in G2/M phase, whereas a compound featuring a six-atom spacer and performing best in HDAC inhibition, induced a G1 arrest in these cells. All these beneficial anticancer activities together with their selectivity for cancer cells over non-malignant cells, point out the great potential of these novel pleiotropic HDAC and tubulin inhibitors as drug candidates for cancer therapy.