Characterization of the dehydrogenase-reductase DHRS2 and its involvement in histone deacetylase inhibition in urological malignancies.

BACKGROUND: Being implicated during tumor migration, invasion, clonogenicity, and proliferation, the nicotinamide adenine dinucleotide (NAD)/-phosphate (NADP)-dependent dehydrogenase/reductase member 2 (DHRS2) has been considered to be induced upon inhibition of histone deacetylases (HDACi). In this study, we evaluated the current knowledge on the underlying mechanisms of the (epi)genetic regulation of DHRS2, as well as its function during tumor progression. METHODS: DHRS2 expression was evaluated on mRNA- and protein-level upon treatment with HDACi by means of qRT-PCR and western blot analyses, respectively. Re-analysis of RNA-sequencing data gained insight into expression of specific DHRS2 isoforms, while re-analysis of ATAC-sequencing data shed light on the chromatin accessibility at the DHRS2 locus. Further examination of the energy and lipid metabolism of HDACi-treated urologic tumor cells was performed using liquid chromatography-mass spectrometry. RESULTS: Enhanced DHRS2 expression levels upon HDACi treatment were directly linked to an enhanced chromatin accessibility at the DHRS2 locus. Particularly the DHRS2 ENST00000250383.11 protein-coding isoform was increased upon HDACi treatment. Application of the HDACi quisinostat only mildly influenced the energy metabolism of urologic tumor cells, though, the analysis of the lipid metabolism showed diminished sphingosine levels, as well as decreased S1P levels. Also the ratios of S1P/sphingosine and S1P/ceramides were reduced in all four quisinostat-treated urologic tumor cells. CONCLUSIONS: With the emphasis on urologic malignancies (testicular germ cell tumors, urothelial, prostate, and renal cell carcinoma), this study concluded that elevated DHRS2 levels are indicative of a successful HDACi treatment and, thereby offering a novel putative predictive biomarker.

Reverse N-Substituted Hydroxamic Acid Derivatives of Fosmidomycin Target a Previously Unknown Subpocket of 1-Deoxy-d-xylulose 5-Phosphate Reductoisomerase (DXR).

Reverse analogs of the phosphonohydroxamic acid antibiotic fosmidomycin are potent inhibitors of the nonmevalonate isoprenoid biosynthesis enzyme 1-deoxy-d-xylulose 5-phosphate reductoisomerase (DXR, IspC) of Plasmodium falciparum. Some novel analogs with large phenylalkyl substituents at the hydroxamic acid nitrogen exhibit nanomolar PfDXR inhibition and potent in vitro growth inhibition of P. falciparum parasites coupled with good parasite selectivity. X-ray crystallographic studies demonstrated that the N-phenylpropyl substituent of the newly developed lead compound 13e is accommodated in a subpocket within the DXR catalytic domain but does not reach the NADPH binding pocket of the N-terminal domain. As shown for reverse carba and thia analogs, PfDXR selectively binds the S-enantiomer of the new lead compound. In addition, some representatives of the novel inhibitor subclass are nanomolar Escherichia coli DXR inhibitors, whereas the inhibition of Mycobacterium tuberculosis DXR is considerably weaker.

Differential Effects of HDAC6 Inhibition Versus Knockout During Hepatic Ischemia-reperfusion Injury Highlight Importance of HDAC6 C-terminal Zinc-finger Ubiquitin-binding Domain.

BACKGROUND: Ischemia-reperfusion injury (IRI) causes significant morbidity in liver transplantation among other medical conditions. IRI following liver transplantation contributes to poor outcomes and early graft loss. Histone/protein deacetylases (HDACs) regulate diverse cellular processes, play a role in mediating tissue responses to IRI, and may represent a novel therapeutic target in preventing IRI in liver transplantation. METHODS: Using a previously described standardized model of murine liver warm IRI, aspartate aminotransferase (AST) and alanine aminotransferase (ALT) levels were assessed at 24 and 48 h after reperfusion to determine the effect of different HDAC inhibitors. RESULTS: Broad HDAC inhibition with trichostatin-A (TSA) was protective against hepatocellular damage (P < 0.01 for AST and P < 0.05 for ALT). Although HDAC class I inhibition with MS-275 provided statistically insignificant benefit, tubastatin-A (TubA), an HDAC6 inhibitor with additional activity against HDAC10, provided significant protection against liver IRI (P < 0.01 for AST and P < 0.001 for ALT). Surprisingly genetic deletion of HDAC6 or -10 did not replicate the protective effects of HDAC6 inhibition with TubA, whereas treatment with an HDAC6 BUZ-domain inhibitor, LakZnFD, eliminated the protective effect of TubA treatment in liver ischemia (P < 0.01 for AST and P < 0.01 for ALT). CONCLUSIONS: Our findings suggest TubA, a class IIb HDAC inhibitor, can mitigate hepatic IRI in a manner distinct from previously described class I HDAC inhibition and requires the HDAC6 BUZ-domain activity. Our data corroborate previous findings that HDAC targets for therapeutic intervention of IRI may be tissue-specific, and identify HDAC6 inhibition as a possible target in the treatment of liver IRI.

Synthesis and biological evaluation of hydantoin derivatives as potent antiplasmodial agents.

Malaria, a devastating disease, has claimed numerous lives and caused considerable suffering, with young children and pregnant women being the most severely affected group. However, the emergence of multidrug-resistant strains of Plasmodium and the adverse side effects associated with existing antimalarial drugs underscore the urgent need for the development of novel, well-tolerated, and more efficient drugs to combat this global health threat. To address these challenges, six new hydantoins derivatives were synthesized and evaluated for their in vitro antiplasmodial activity. Notably, compound 2c exhibited excellent inhibitory activity against the tested Pf3D7 strain, with an IC50 value of 3.97 ± 0.01 nM, three-fold better than chloroquine. Following closely, compound 3b demonstrated an IC50 value of 27.52 ± 3.37 µM against the Pf3D7 strain in vitro. Additionally, all the hydantoins derivatives tested showed inactive against human MCR-5 cells, with an IC50 value exceeding 100 µM. In summary, the hydantoin derivative 2c emerges as a promising candidate for further exploration as an antiplasmodial compound.

Activity of alkoxyamide-based histone deacetylase inhibitors against Plasmodium falciparum malaria parasites.

There are more than 240 million cases of malaria and 600,000 associated deaths each year, most due to infection with Plasmodium falciparum parasites. While malaria treatment options exist, new drugs with novel modes of action are needed to address malaria parasite drug resistance. Protein lysine deacetylases (termed HDACs) are important epigenetic regulatory enzymes and prospective therapeutic targets for malaria. Here we report the antiplasmodial activity of a panel of 17 hydroxamate zinc binding group HDAC inhibitors with alkoxyamide linkers and different cap groups. The two most potent compounds (4a and 4b) were found to inhibit asexual P. falciparum growth with 50% inhibition concentrations (IC50's) of 0.07 µM and 0.09 µM, respectively, and demonstrated >200-fold more selectivity for P. falciparum parasites versus human neonatal foreskin fibroblasts (NFF). In situ hyperacetylation studies demonstrated that 4a, 4b and analogs caused P. falciparum histone H4 hyperacetylation, suggesting HDAC inhibition, with structure activity relationships providing information relevant to the design of new Plasmodium-specific aliphatic chain hydroxamate HDAC inhibitors.

Regulation of STING activity in DNA sensing by ISG15 modification.

Sensing of human immunodeficiency virus type 1 (HIV-1) DNA is mediated by the cyclic GMP-AMP synthase-stimulator of interferon genes (cGAS-STING) signaling axis. Signal transduction and regulation of this cascade is achieved by post-translational modifications. Here we show that cGAS-STING-dependent HIV-1 sensing requires interferon-stimulated gene 15 (ISG15). ISG15 deficiency inhibits STING-dependent sensing of HIV-1 and STING agonist-induced antiviral response. Upon external stimuli, STING undergoes ISGylation at residues K224, K236, K289, K347, K338, and K370. Inhibition of STING ISGylation at K289 suppresses STING-mediated type Ⅰ interferon induction by inhibiting its oligomerization. Of note, removal of STING ISGylation alleviates gain-of-function phenotype in STING-associated vasculopathy with onset in infancy (SAVI). Molecular modeling suggests that ISGylation of K289 is an important regulator of oligomerization. Taken together, our data demonstrate that ISGylation at K289 is crucial for STING activation and represents an important regulatory step in DNA sensing of viruses and autoimmune responses.

Quantification of Plasmodium falciparum HRP-2 as an alternative method to [3H]hypoxanthine incorporation to measure the parasite reduction ratio in vitro.

In the absence of a highly efficacious vaccine, chemotherapy remains the cornerstone to control malaria morbidity and mortality. The threat of the emergence of parasites resistant to artemisinin-based combination therapies highlights the need for new antimalarial drugs ideally with superior properties. The killing rate reflects the speed of action of antimalarial drugs, which can be measured in vitro through the parasite reduction ratio (PRR) assay to shortlist interesting candidates. As a standard, the in vitro PRR assay is performed by measuring [3H]hypoxanthine incorporation of Plasmodium falciparum. This methodology is restricted to specialised laboratories owing to the handling of radioactive material. In this work, we describe a sandwich enzyme-linked immunosorbent assay to detect P. falciparum histidine-rich protein 2 (HRP-2) as an alternative methodology to assess the PRR. We first validated the methodology with established antimalarial drugs (artesunate, chloroquine, pyrimethamine and atovaquone) by comparing our results with previous results of the [3H]hypoxanthine incorporation readout provided by an expert laboratory, and subsequently assessed the speed of action of four new antimalarial candidates (compound 22, chlorotonil A, boromycin and ivermectin). The HRP-2 PRR assay achieved comparable results to the [3H]hypoxanthine incorporation readout in terms of parasite growth rate over time, lag phase and parasite clearance time. In addition, parasite growth following drug exposure was quantified after 7, 14, 21 and 28 days of recovery time. In conclusion, the PRR assay based on HRP-2 is similar to [3H]hypoxanthine in determining a drug's parasite killing rate and can be widely used in all research laboratories.

Tacedinaline (CI-994), a class I HDAC inhibitor, targets intrinsic tumor growth and leptomeningeal dissemination in MYC-driven medulloblastoma while making them susceptible to anti-CD47-induced macrophage phagocytosis via NF-kB-TGM2 driven tumor inflammation.

BACKGROUND: While major advances have been made in improving the quality of life and survival of children with most forms of medulloblastoma (MB), those with MYC-driven tumors (Grp3-MB) still suffer significant morbidity and mortality. There is an urgent need to explore multimodal therapeutic regimens which are effective and safe for children. Large-scale studies have revealed abnormal cancer epigenomes caused by mutations and structural alterations of chromatin modifiers, aberrant DNA methylation, and histone modification signatures. Therefore, targeting epigenetic modifiers for cancer treatment has gained increasing interest, and inhibitors for various epigenetic modulators have been intensively studied in clinical trials. Here, we report a cross-entity, epigenetic drug screen to evaluate therapeutic vulnerabilities in MYC amplified MB, which sensitizes them to macrophage-mediated phagocytosis by targeting the CD47-signal regulatory protein α (SIRPα) innate checkpoint pathway. METHODS: We performed a primary screen including 78 epigenetic inhibitors and a secondary screen including 20 histone deacetylase inhibitors (HDACi) to compare response profiles in atypical teratoid/rhabdoid tumor (AT/RT, n=11), MB (n=14), and glioblastoma (n=14). This unbiased approach revealed the preferential activity of HDACi in MYC-driven MB. Importantly, the class I selective HDACi, CI-994, showed significant cell viability reduction mediated by induction of apoptosis in MYC-driven MB, with little-to-no activity in non-MYC-driven MB, AT/RT, and glioblastoma in vitro. We tested the combinatorial effect of targeting class I HDACs and the CD47-SIRPa phagocytosis checkpoint pathway using in vitro phagocytosis assays and in vivo orthotopic xenograft models. RESULTS: CI-994 displayed antitumoral effects at the primary site and the metastatic compartment in two orthotopic mouse models of MYC-driven MB. Furthermore, RNA sequencing revealed nuclear factor-kB (NF-κB) pathway induction as a response to CI-994 treatment, followed by transglutaminase 2 (TGM2) expression, which enhanced inflammatory cytokine secretion. We further show interferon-γ release and cell surface expression of engulfment ('eat-me') signals (such as calreticulin). Finally, combining CI-994 treatment with an anti-CD47 mAb targeting the CD47-SIRPα phagocytosis checkpoint enhanced in vitro phagocytosis and survival in tumor-bearing mice. CONCLUSION: Together, these findings suggest a dynamic relationship between MYC amplification and innate immune suppression in MYC amplified MB and support further investigation of phagocytosis modulation as a strategy to enhance cancer immunotherapy responses.

Over 40 Years of Fosmidomycin Drug Research: A Comprehensive Review and Future Opportunities.

To address the continued rise of multi-drug-resistant microorganisms, the development of novel drugs with new modes of action is urgently required. While humans biosynthesize the essential isoprenoid precursors isopentenyl diphosphate (IPP) and dimethylallyl diphosphate (DMAPP) via the established mevalonate pathway, pathogenic protozoa and certain pathogenic eubacteria use the less well-known methylerythritol phosphate pathway for this purpose. Important pathogens using the MEP pathway are, for example, Plasmodium falciparum, Mycobacterium tuberculosis, Pseudomonas aeruginosa and Escherichia coli. The enzymes of that pathway are targets for antiinfective drugs that are exempt from target-related toxicity. 2C-Methyl-D-erythritol 4-phosphate (MEP), the second enzyme of the non-mevalonate pathway, has been established as the molecular target of fosmidomycin, an antibiotic that has so far failed to be approved as an anti-infective drug. This review describes the development and anti-infective properties of a wide range of fosmidomycin derivatives synthesized over the last four decades. Here we discuss the DXR inhibitor pharmacophore, which comprises a metal-binding group, a phosphate or phosphonate moiety and a connecting linker. Furthermore, non-fosmidomycin-based DXRi, bisubstrate inhibitors and several prodrug concepts are described. A comprehensive structure-activity relationship (SAR) of nearly all inhibitor types is presented and some novel opportunities for further drug development of DXR inhibitors are discussed.

Fractal dimension of the aortic annulus: a novel predictor of paravalvular leak after transcatheter aortic valve implantation.

To evaluate the prognostic relevance of aortic annulus (AA) and left ventricular outflow tract (LVOT) Fractal dimension (FD). FD is a mathematical concept that describes geometric complexity of a structure and has been shown to predict adverse outcomes in several contexts. Computed tomography (CT) scans from the SOLVE-TAVI trial, which, in a 2 × 2 factorial design, randomized 447 patients to TAVI with the balloon-expandable Edwards Sapien 3 or the self-expanding Medtronic Evolut R, and conscious sedation or general anesthesia, were analyzed semi-automatically with a custom-built software to determine border of AA and LVOT. FD was measured by box counting using grid calibers between 0.8 and 6.75 mm and was compared between patients with none/trivial and mild/moderate paravalvular regurgitation (PVR). Overall, 122 patients had CT scans sufficient for semi-automatic PVR in 30-day echocardiography. PVR was none in 65(53.3%) patients, trace in 9(7.4%), mild in 46(37.7%), moderate in 2(1.6%) and severe in 0 patients. FD determined in diastolic images was significantly higher in patients with mild/moderate PVR (1.0558 ± 0.0289 vs. 1.0401 ± 0.0284, p = 0.017). Annulus eccentricity was the only conventional measure of AA and LVOT geometry significantly correlated to FD (R = 0.337, p < 0.01). Area under the curve (AUC) of diastolic annular FD for prediction of mild/moderate PVR in ROC analysis was 0.661 (0.542-0.779, p = 0.014). FD shows promise in prediction of PVR after TAVI. Further evaluation using larger patient numbers and refined algorithms to better understand its predictive performance is warranted.Trial Registration: www.clinicaltrials.gov , identifier: NCT02737150, date of registration: 13.04.2016.

The Novel Class IIa Selective Histone Deacetylase Inhibitor YAK540 Is Synergistic with Bortezomib in Leukemia Cell Lines.

The treatment of leukemias, especially acute myeloid leukemia (AML), is still a challenge as can be seen by poor 5-year survival of AML. Therefore, new therapeutic approaches are needed to increase the treatment success. Epigenetic aberrations play a role in pathogenesis and resistance of leukemia. Histone deacetylase (HDAC) inhibitors (HDACIs) can normalize epigenetic disbalance by affecting gene expression. In order to decrease side effects of so far mainly used pan-HDACIs, this paper introduces the novel highly selective class IIa HDACI YAK540. A synergistic cytotoxic effect was observed between YAK540 and the proteasome inhibitor bortezomib (BTZ) as analyzed by the Chou-Talalay method. The combination of YAK540 and BTZ showed generally increased proapoptotic gene expression, increased p21 expression, and synergistic, caspase 3/7-mediated apoptosis. Notably, the cytotoxicity of YAK540 is much lower than that of pan-HDACIs. Further, combinations of YAK540 and BTZ are clearly less toxic in non-cancer HEK293 compared to HL-60 leukemia cells. Thus, the synergistic combination of class IIa selective HDACIs such as YAK540 and proteasome inhibitors represents a promising approach against leukemias to increase the anticancer effect and to reduce the general toxicity of HDACIs.

Impact of moderate or severe left ventricular outflow tract calcification on clinical outcomes of patients with severe aortic stenosis undergoing transcatheter aortic valve implantation with self- and balloon-expandable valves: a post hoc analysis from the SOLVE-TAVI trial.

BACKGROUND: Left ventricular outflow tract (LVOT) calcification has been associated with worse outcomes in patients undergoing transcatheter aortic valve implantation (TAVI) and may influence the selection of prosthetic valve type. AIMS: We aimed to evaluate the impact of LVOT calcification on outcomes after TAVI with a self-expanding valve (SEV) versus a balloon-expandable valve (BEV). METHODS: Patients of the SOLVE-TAVI trial, randomised to Edwards SAPIEN 3 or Medtronic Evolut R, were divided according to LVOT calcification into no/mild (≤1 calcium nodule extending <5 mm and covering <10% of the LVOT perimeter) and moderate/severe LVOT calcification groups. The primary endpoint was a composite of death, stroke, moderate/severe paravalvular regurgitation, permanent pacemaker implantation and annulus rupture at 30 days. Additional endpoints included all-cause and cardiovascular mortality at 1 year. RESULTS: Out of 416 eligible patients, moderate/severe LVOT calcification was present in 143 (34.4%). Moderate/severe LVOT calcification was associated with significantly longer fluoroscopy time and higher rates of pre- and post-dilation. Regardless of the LVOT calcification group, there was no significant difference in the primary endpoint associated with the valve type (no/mild LVOT calcification group: SEV 25.0% vs BEV 27.0%; hazard ratio [HR] 1.10, 95% confidence interval [95% CI]: 0.68-1.73; p=0.73 and moderate/severe LVOT calcification group: SEV 25.0% vs BEV 19.4%; HR 0.76, 95% CI: 0.38-1.61; p=0.49), no significant interaction between LVOT calcification and valve type (pint=0.29) and no differences between SEV vs BEV within LVOT calcification groups regarding 1-year all-cause and cardiovascular mortality. CONCLUSIONS: Moderate/severe LVOT calcification was associated with longer fluoroscopy time and an increased need for pre- and post-dilation, but not with a higher incidence of early and mid-term adverse clinical outcomes, regardless of valve type. (ClinicalTrials.gov: NCT02737150).

Total Synthesis of the Antimycobacterial Natural Product Chlorflavonin and Analogs via a Late-Stage Ruthenium(II)-Catalyzed ortho-C(sp2)-H-Hydroxylation.

The continuous, worldwide spread of multidrug-resistant (MDR) and extensively drug-resistant (XDR) tuberculosis (TB) endanger the World Health Organization's (WHO) goal to end the global TB pandemic by the year 2035. During the past 50 years, very few new drugs have been approved by medical agencies to treat drug-resistant TB. Therefore, the development of novel antimycobacterial drug candidates to combat the threat of drug-resistant TB is urgent. In this work, we developed and optimized a total synthesis of the antimycobacterial natural flavonoid chlorflavonin by selective ruthenium(II)-catalyzed ortho-C(sp2)-H-hydroxylation of a substituted 3'-methoxyflavonoid skeleton. We extended our methodology to synthesize a small compound library of 14 structural analogs. The new analogs were tested for their antimycobacterial in vitro activity against Mycobacterium tuberculosis (Mtb) and their cytotoxicity against various human cell lines. The most promising new analog bromflavonin exhibited improved antimycobacterial in vitro activity against the virulent H37Rv strain of Mtb (Minimal Inhibitory Concentrations (MIC90) = 0.78 µm). In addition, we determined the chemical and metabolic stability as well as the pKa values of chlorflavonin and bromflavonin. Furthermore, we established a quantitative structure-activity relationship model using a thermodynamic integration approach. Our computations may be used for suggesting further structural changes to develop improved derivatives.

Establishment and Evaluation of Dual HDAC/BET Inhibitors as Therapeutic Options for Germ Cell Tumors and Other Urological Malignancies.

Urological malignancies represent major challenges for clinicians, with annually rising incidences. In addition, cisplatin treatment induced long-term toxicities and the development of therapy resistance emphasize the need for novel therapeutics. In this study, we analyzed the effects of novel histone deacetylase (HDAC) and bromodomain and extraterminal domain-containing (BET) inhibitors to combine them into a potent HDAC-BET-fusion molecule and to understand their molecular mode-of-action. Treatment of (cisplatin-resistant) germ cell tumors (GCT), urothelial, renal, and prostate carcinoma cells with the HDAC, BET, and dual inhibitors decreased cell viability, induced apoptosis, and affected the cell cycle. Furthermore, a dual inhibitor considerably decreased tumor burden in GCT xenograft models. On a molecular level, correlating RNA- to ATAC-sequencing data indicated a considerable induction of gene expression, accompanied by site-specific changes of chromatin accessibility after HDAC inhibitor application. Upregulated genes could be linked to intra- and extra-cellular trafficking, cellular organization, and neuronal processes, including neuroendocrine differentiation. Regarding chromatin accessibility on a global level, an equal distribution of active or repressed DNA accessibility has been detected after HDAC inhibitor treatment, questioning the current understanding of HDAC inhibitor function. In summary, our HDAC, BET, and dual inhibitors represent a new treatment alternative for urological malignancies. Furthermore, we shed light on new molecular and epigenetic mechanisms of the tested epi-drugs, allowing for a better understanding of the underlying modes-of-action and risk assessment for the patient.

Development of a First-in-Class Small-Molecule Inhibitor of the C-Terminal Hsp90 Dimerization.

Heat shock proteins 90 (Hsp90) are promising therapeutic targets due to their involvement in stabilizing several aberrantly expressed oncoproteins. In cancerous cells, Hsp90 expression is elevated, thereby exerting antiapoptotic effects, which is essential for the malignant transformation and tumor progression. Most of the Hsp90 inhibitors (Hsp90i) under investigation target the ATP binding site in the N-terminal domain of Hsp90. However, adverse effects, including induction of the prosurvival resistance mechanism (heat shock response or HSR) and associated dose-limiting toxicity, have so far precluded their clinical approval. In contrast, modulators that interfere with the C-terminal domain (CTD) of Hsp90 do not inflict HSR. Since the CTD dimerization of Hsp90 is essential for its chaperone activity, interfering with the dimerization process by small-molecule protein-protein interaction inhibitors is a promising strategy for anticancer drug research. We have developed a first-in-class small-molecule inhibitor (5b) targeting the Hsp90 CTD dimerization interface, based on a tripyrimidonamide scaffold through structure-based molecular design, chemical synthesis, binding mode model prediction, assessment of the biochemical affinity, and efficacy against therapy-resistant leukemia cells. 5b reduces xenotransplantation of leukemia cells in zebrafish models and induces apoptosis in BCR-ABL1+ (T315I) tyrosine kinase inhibitor-resistant leukemia cells, without inducing HSR.

Assessing the Anthelmintic Candidates BLK127 and HBK4 for Their Efficacy on Haemonchus contortus Adults and Eggs, and Their Hepatotoxicity and Biotransformation.

As a widely distributed parasitic nematode of ruminants, Haemonchus contortus has become resistant to most anthelmintic classes, there has been a major demand for new compounds against H. contortus and related nematodes. Recent phenotypic screening has revealed two compounds, designated as BLK127 and HBK4, that are active against H. contortus larvae. The present study was designed to assess the activity of these compounds against H. contortus eggs and adults, hepatotoxicity in rats and sheep, as well as biotransformation in H. contortus adults and the ovine liver. Both compounds exhibited no inhibitory effect on the hatching of eggs. The benzyloxy amide BLK127 significantly decreased the viability of adults in sensitive and resistant strains of H. contortus and showed no hepatotoxic effect, even at the highest concentration tested (100 µM). In contrast, HBK4 had no impact on the viability of H. contortus adults and exhibited significant hepatotoxicity. Based on these findings, HBK4 was excluded from further studies, while BLK127 seems to be a potential candidate for a new anthelmintic. Consequently, biotransformation of BLK127 was tested in H. contortus adults and the ovine liver. In H. contortus, several metabolites formed via hydroxylation, hydrolysis and glycosidation were identified, but the extent of biotransformation was low, and the total quantity of the metabolites formed did not differ significantly between the sensitive and resistant strains. In contrast, ovine liver cells metabolized BLK127 more extensively with a glycine conjugate of 4-(pentyloxy)benzoic acid as the main BLK127 metabolite.

Antiproliferation and Antiencystation Effect of Class II Histone Deacetylase Inhibitors on Acanthamoeba castellanii.

Acanthamoeba is a ubiquitous and free-living protozoan pathogen responsible for causing Acanthamoeba keratitis (AK), a severe corneal infection inflicting immense pain that can result in permanent blindness. A drug-based treatment of AK has remained arduous because Acanthamoeba trophozoites undergo encystment to become highly drug-resistant cysts upon exposure to harsh environmental conditions such as amoebicidal agents (e.g., polyhexanide, chloroquine, and chlorohexidine). As such, drugs that block the Acanthamoeba encystation process could result in a successful AK treatment. Histone deacetylase inhibitors (HDACi) have recently emerged as novel therapeutic options for treating various protozoan and parasitic diseases. Here, we investigated whether novel HDACi suppress the proliferation and encystation of Acanthamoeba. Synthetic class II HDACi FFK29 (IIa selective) and MPK576 (IIb selective) dose-dependently decreased the viability of Acanthamoeba trophozoites. While these HDACi demonstrated a negligible effect on the viability of mature cysts, Acanthamoeba encystation was significantly inhibited by these HDACi. Apoptosis was slightly increased in trophozoites after a treatment with these HDACi, whereas cysts were unaffected by the HDACi exposure. The viability of human corneal cells was not affected by HDACi concentrations up to 10 µmol/L. In conclusion, these synthetic HDACi demonstrated potent amoebicidal effects and inhibited the growth and encystation of Acanthamoeba, thus highlighting their enormous potential for further development.

QSAR Classification Models for Prediction of Hydroxamate Histone Deacetylase Inhibitor Activity against Malaria Parasites.

Malaria, caused by Plasmodium parasites, results in >400,000 deaths annually. There is no effective vaccine, and new drugs with novel modes of action are needed because of increasing parasite resistance to current antimalarials. Histone deacetylases (HDACs) are epigenetic regulatory enzymes that catalyze post-translational protein deacetylation and are promising malaria drug targets. Here, we describe quantitative structure-activity relationship models to predict the antiplasmodial activity of hydroxamate-based HDAC inhibitors. The models incorporate P. falciparum in vitro activity data for 385 compounds containing a hydroxamic acid and were subject to internal and external validation. When used to screen 22 new hydroxamate-based HDAC inhibitors for antiplasmodial activity, model A7 (external accuracy 91%) identified three hits that were subsequently verified as having potent in vitro activity against P. falciparum parasites (IC50 = 6, 71, and 84 nM), with 8 to 51-fold selectivity for P. falciparum versus human cells.

Designing HDAC-PROTACs: lessons learned so far.

Proteolysis-targeting chimeras (PROTACs) are a powerful tool to hijack the endogenous ubiquitin-proteasome system (UPS) and to degrade the intracellular proteins of therapeutic importance. Recently, two heterobifunctional degraders targeting hormone receptors headed into phase II clinical trials. Compared to traditional drug design and common modes of action, the PROTAC approach offers new opportunities for the drug research field. Histone deacetylase inhibitors (HDACi) are well-established drugs for the treatment of hematological malignancies. The integration of HDAC binding motifs in PROTACs explores the possibility of targeted, chemical HDAC degradation. This review provides an overview and a perspective about the key steps in the structure development of HDAC-PROTACs. In particular, the influence of the three canonical PROTAC elements on HDAC-PROTAC efficacy and selectivity are discussed, the HDACi, the linker and the E3 ligase ligand.