Gametocyte-specific and all-blood-stage transmission-blocking chemotypes discovered from high throughput screening on Plasmodium falciparum gametocytes.

Blocking Plasmodium falciparum human-to-mosquito transmission is essential for malaria elimination, nonetheless drugs killing the pathogenic asexual stages are generally inactive on the parasite transmissible stages, the gametocytes. Due to technical and biological limitations in high throughput screening of non-proliferative stages, the search for gametocyte-killing molecules so far tested one tenth the number of compounds screened on asexual stages. Here we overcome these limitations and rapidly screened around 120,000 compounds, using not purified, bioluminescent mature gametocytes. Orthogonal gametocyte assays, selectivity assays on human cells and asexual parasites, followed by compound clustering, brought to the identification of 84 hits, half of which are gametocyte selective and half with comparable activity against sexual and asexual parasites. We validated seven chemotypes, three of which are, to the best of our knowledge, novel. These molecules are able to inhibit male gametocyte exflagellation and block parasite transmission through the Anopheles mosquito vector in a standard membrane feeding assay. This work shows that interrogating a wide and diverse chemical space, with a streamlined gametocyte HTS and hit validation funnel, holds promise for the identification of dual stage and gametocyte-selective compounds to be developed into new generation of transmission blocking drugs for malaria elimination.

Inhibiting pathologically active ADAM10 rescues synaptic and cognitive decline in Huntington's disease.

A disintegrine and metalloproteinase 10 (ADAM10) is implicated in synaptic function through its interaction with postsynaptic receptors and adhesion molecules. Here, we report that levels of active ADAM10 are increased in Huntington's disease (HD) mouse cortices and striata and in human postmortem caudate. We show that, in the presence of polyglutamine-expanded (polyQ-expanded) huntingtin (HTT), ADAM10 accumulates at the postsynaptic densities (PSDs) and causes excessive cleavage of the synaptic protein N-cadherin (N-CAD). This aberrant phenotype is also detected in neurons from HD patients where it can be reverted by selective silencing of mutant HTT. Consistently, ex vivo delivery of an ADAM10 synthetic inhibitor reduces N-CAD proteolysis and corrects electrophysiological alterations in striatal medium-sized spiny neurons (MSNs) of 2 HD mouse models. Moreover, we show that heterozygous conditional deletion of ADAM10 or delivery of a competitive TAT-Pro-ADAM10709-729 peptide in R6/2 mice prevents N-CAD proteolysis and ameliorates cognitive deficits in the mice. Reduction in synapse loss was also found in R6/2 mice conditionally deleted for ADAM10. Taken together, these results point to a detrimental role of hyperactive ADAM10 at the HD synapse and provide preclinical evidence of the therapeutic potential of ADAM10 inhibition in HD.

Development and optimization of a binding assay for histone deacetylase 4 using surface plasmon resonance.

Histone deacetylase 4 (HDAC4) is a histone deacetylase profoundly involved in cell differentiation and in the pathogenesis of cancer. The histone deacetylase inhibitors are a new, promising class of anticancer agents. The screening of molecular interactions involving determination of the affinity of drug candidates is an integral part of the drug discovery process. Here we report the development of an assay using surface plasmon resonance for the analysis of HDAC4-small molecule interactions. We describe a new cloning and purification strategy that can be used to set up surface plasmon resonance experiments with other recombinant proteins.

Optimization of a series of potent and selective ketone histone deacetylase inhibitors.

Histone deacetylase (HDAC) inhibitors offer a promising strategy for cancer therapy and the first generation HDAC inhibitors are currently in the clinic. Herein we describe the optimization of a series of ketone small molecule HDAC inhibitors leading to potent and selective class I HDAC inhibitors with good dog PK.

2-Trifluoroacetylthiophene oxadiazoles as potent and selective class II human histone deacetylase inhibitors.

Trifluoroacetylthiophene carboxamides have recently been reported to be class II HDAC inhibitors, with moderate selectivity. Exploration of replacements for the carboxamide with bioisosteric pentatomic heteroaromatic like 1,3,4-oxadiazoles, 1,2,4-oxadiazoles and 1,3-thiazoles, led to the discovery that 2-trifluoroacetylthiophene 1,3,4-oxadiazole derivatives are very potent low nanomolar HDAC4 inhibitors, highly selective over class I HDACs (HDAC 1 and 3), and moderately stable in HCT116 cell culture.

2-Trifluoroacetylthiophenes, a novel series of potent and selective class II histone deacetylase inhibitors.

The identification of class II HDAC inhibitors has been hampered by lack of efficient enzyme assays, in the preceding paper two assays have been developed to improve the efficiency of these enzymes: mutating an active site histidine to tyrosine, or by the use of a trifluoroacetamide lysine substrate, allowing screening to identify class II HDAC inhibitors. Herein, 2-trifluoroacetylthiophenes have been demonstrated to inhibit class II HDACs, resulting in the development of a series of 5-(trifluoroacetyl)thiophene-2-carboxamides as novel, potent and selective class II HDAC inhibitors. X-ray crystal structures of the HDAC 4 catalytic domain with a bound inhibitor demonstrate these compounds are active site inhibitors and bind in their hydrated form.

Development of a Broadly Applicable Assay for Measurement of Glycan-Directed Enzymatic Activity.

Glycosylation is a key posttranslational modification that tags protein to membranes, organelles, secretory pathways, and degradation. Aberrant protein glycosylation is present both in acquired diseases, such as cancer and neurodegeneration, and in congenital disorders of glycosylation (CDGs). Consequently, the ability to interrogate the activity of enzymes that can modify protein glycan moieties is key for drug discovery projects aimed at finding modulators of these enzymes. To date, low-throughput technologies such as SDS-PAGE and mass spectrometry have been used, which are not suitable for compound screening in drug discovery. In the present work, a broadly applicable time-resolved fluorescence resonance energy transfer (TR-FRET) assay was developed that can determine the activity of endoglycosidase enzymes in high-throughput formats. The assay was validated using PNGaseF and EndoH as tool deglycosylases. Even though the current setup is based on the recognition of glycans that bind concanavalin A (ConA), the assay concept can be adapted to glycans that bind other lectins.

Discovery of a Selective Series of Inhibitors of Plasmodium falciparum HDACs.

The identification of a new series of P. falciparum growth inhibitors is described. Starting from a series of known human class I HDAC inhibitors a SAR exploration based on growth inhibitory activity in parasite and human cells-based assays led to the identification of compounds with submicromolar inhibition of P. falciparum growth (EC50 < 500 nM) and good selectivity over the activity of human HDAC in cells (up to >50-fold). Inhibition of parasital HDACs as the mechanism of action of this new class of selective growth inhibitors is supported by hyperacetylation studies.

A series of novel, potent, and selective histone deacetylase inhibitors.

Histone deacetylase (HDAC) inhibitors offer a promising strategy for cancer therapy and the first generation HDAC inhibitors are currently in clinical trials. A structurally novel series of HDAC inhibitors based on the natural cyclic tetrapeptide Apicidin is described. Selected screening of the sample collection looking for L-2-amino-8-oxodecanoic acid (L-Aoda) derivatives identified a small acyclic lead molecule 1 with the unusual ketone zinc binding group. SAR studies around this lead resulted in optimization to potent, low molecular weight, selective, non-hydroxamic acid HDAC inhibitors, equipotent to current clinical candidates.