A target-based high throughput screen yields Trypanosoma brucei hexokinase small molecule inhibitors with antiparasitic activity. PLoS Negl Trop. Dis

Abstract Background: The parasitic protozoan Trypanosoma brucei utilizes glycolysis exclusively for ATP production during infection of the mammalian host. The first step in this metabolic pathway is mediated by hexokinase (TbHK), an enzyme essential to the parasite that transfers the c-phospho of ATP to a hexose. Here we describe the identification and confirmation of novel small molecule inhibitors of bacterially expressed TbHK1, one of two TbHKs expressed by T. brucei, using a high throughput screening assay

A Target-Based High Throughput Screen Yields Trypanosoma brucei Hexokinase Small Molecule Inhibitors with Antiparasitic Activity

African sleeping sickness is a disease found in sub-Saharan Africa that is caused by the single-celled parasite Trypanosoma brucei. The drugs used widely now to treat infections are 50 years old and notable for their toxicity, emphasizing the need for development of new therapeutics. In the search for potential drug targets, researchers typically focus on enzymes or proteins that are essential to the survival of the infectious agent while being distinct enough from the host to avoid accidental targeting of the host enzyme. This work describes our research on one such trypanosome enzyme, hexokinase, which is a protein that the parasite requires to make energy. Here we describe the results of our search for inhibitors of the parasite enzyme. By screening 220,223 compounds for anti-hexokinase activity, we have identified new inhibitors of the parasite enzyme. Some of these are toxic to trypanosomes while having no effect on mammalian cells, suggesting that they may hold promise for the development of new anti-parasitic compounds

Discovery of Diverse Small Molecule Chemotypes with Cell-Based PKD1 Inhibitory Activity

Protein kinase D (PKD) is a novel family of serine/threonine kinases regulated by diacylglycerol, which is involved in multiple cellular processes and various pathological conditions. The limited number of cell-active, selective inhibitors has historically restricted biochemical and pharmacological studies of PKD. We now markedly expand the PKD1 inhibitory chemotype inventory with eleven additional novel small molecule PKD1 inhibitors derived from our high throughput screening campaigns. The in vitro IC50s for these eleven compounds ranged in potency from 0.4 to 6.1 µM with all of the evaluated compounds being competitive with ATP. Three of the inhibitors (CID 1893668, (1Z)-1-(3-ethyl-5-methoxy-1,3-benzothiazol-2-ylidene)propan-2-one; CID 2011756, 5-(3-chlorophenyl)-N-[4-(morpholin-4-ylmethyl)phenyl]furan-2-carboxamide; CID 5389142, (6Z)-6-[4-(3-aminopropylamino)-6-methyl-1H-pyrimidin-2-ylidene]cyclohexa-2,4-dien-1-one) inhibited phorbol ester-induced endogenous PKD1 activation in LNCaP prostate cancer cells in a concentration-dependent manner. The specificity of these compounds for PKD1 inhibitory activity was supported by kinase assay counter screens as well as by bioinformatics searches. Moreover, computational analyses of these novel cell-active PKD1 inhibitors indicated that they were structurally distinct from the previously described cell-active PKD1 inhibitors while computational docking of the new cell-active compounds in a highly conserved ATP-binding cleft suggests opportunities for structural modification. In summary, we have discovered novel PKD1 inhibitors with in vitro and cell-based inhibitory activity, thus successfully expanding the structural diversity of small molecule inhibitors available for this important pharmacological target

Identification of Inhibitors of \u3cem\u3eTrypanosoma brucei\u3c/em\u3e Hexokinases

The unicellular eukaryote Trypanosoma brucei (T. brucei) is the causative agent of human African trypanosomiasis (HAT), a disease that annually infects ~500,000 people in sub-Saharan Africa resulting in 50,000 – 70,000 deaths per year. Without treatment, HAT is fatal. Unfortunately, current treatments are limited in availability, have toxic side effects, are difficult to administer and are not well characterized in terms of their mechanism of action. Thus, the lack of affordable, safe, and effective therapies for those with African trypanosomiasis makes the identification of molecular target-specific chemotypes a priority in our effort to understand the mechanisms involved with parasite growth and viability, as well as for future therapeutic development. The probe identified from this effort, ML205, is a stable, small molecule possessing submicromolar activity (IC50 = 0.98 μM) against a defined T. brucei hexokinase 1 (rTbHK1) target. The probe was not toxic to mammalian cells (IMR-90 cells, EC50 \u3e 25 μM) and mechanistic studies revealed that the probe operates with mixed inhibition with respect to ATP

A Small Molecule Screen Exposes mTOR Signaling Pathway Involvement in Radiation-Induced Apoptosis

Individuals are at risk of exposure to acute ionizing radiation (IR) from a nuclear accident or terrorism, but we lack effective therapies to mitigate the lethal IR effects. In the current study, we exploited an optimized, cell-based, high throughput screening assay to interrogate a small molecule library comprising 3437 known pharmacologically active compounds for mitigation against IR-induced apoptosis. Thirty-three library compounds significantly reduced apoptosis when administered 1 h after 4 Gy IR. Two- or three-dimensional computational structural analyses of the compounds indicated only one or two chemical clusters with most of the compounds being unique structures. The mechanistic target of rapamycin complex 1 (mTORC1) inhibitor, rapamycin, was the most potent compound, and it mitigated apoptosis by 50% at 200 ± 50 pM. Other mTOR inhibitors, namely everolimus, AZD8055, and torin 1, also suppressed apoptosis, providing additional pharmacological evidence for mTOR pathway involvement in regulating cell death after IR. Everolimus and torin 1 treatment after IR decreased the S phase population and enforced both G₁ and G₂ phase arrest. This prorogation of cell cycle progression was accompanied by decreased IR-induced DNA damage measured by γH2AX phosphorylation at Ser139. RNA interference-mediated knockdown of the respective mTORC1 and mTORC2 subunits, Raptor or Rictor, also mitigated IR-induced apoptosis. Collectively, this study suggests a central role for the mTOR signaling in the cytotoxic response to IR and offers a useful platform to probe for additional agents

Ebselen and SID 17387000 inhibit TbHK activity from parasite cell lysate and cause a reduction in cellular G6P levels in BSF parasites.

<p>Increasing amounts of (A.) ebselen or (B.) SID 17387000 were incubated with 2×10⁵ BSF cell equivalents for 15 min at RT and HK assays were performed as described in the Materials and <a href="http://www.plosntds.org/article/info:doi/10.1371/journal.pntd.0000659#s2" target="_blank">Methods</a>. (C.) Growth in the presence of Ebselen or SID 17387000 causes a reduction in cellular G6P levels. BSF parasites (1×10⁷) were cultured for 1 or 4 hours in the presence of 30 µM or 1 µM (10-fold the EC₅₀) ebselen or SID 17387000 followed by lysate preparation and comparison of G6P levels to an equivalent number of untreated parasites <a href="http://www.plosntds.org/article/info:doi/10.1371/journal.pntd.0000659#pntd.0000659-Haanstra1" target="_blank">[14]</a>.</p

Comparison of structural similarities of HTS hits to licensed compounds used against HAT and to known TbHK1 inhibitors.

1<p>Reviewed in <a href="http://www.plosntds.org/article/info:doi/10.1371/journal.pntd.0000659#pntd.0000659-Zhang1" target="_blank">[13]</a>.</p>2<p>Similarity coefficient was determined using the Tanimoto coefficient. Compounds with values greater than 80% are considered highly structurally similar.</p>3<p><a href="http://www.plosntds.org/article/info:doi/10.1371/journal.pntd.0000659#pntd.0000659-Chambers1" target="_blank">[4]</a>.</p>4<p>Lyda and Morris, unpublished.</p