Point mutations in β-glucocerebrosidase (GCase) can result in a deficiency of both GCase activity and protein in lysosomes thereby causing Gaucher Disease (GD). Enzyme inhibitors such as isofagomine, acting as pharmacological chaperones (PCs), increase these levels by binding and stabilizing the native form of the enzyme in the endoplasmic reticulum (ER), and allow increased lysosomal transport of the enzyme. A high-throughput screen of the 50 000-compound Maybridge library identified two, non-carbohydrate-based inhibitory molecules, a 2,4-diamino-5-substituted quinazoline (IC50 5 μM) and a 5-substituted pyridinyl-2-furamide (IC50 8 μM). They raised the levels of functional GCase 1.5–2.5-fold in N370S or F213I GD fibroblasts. Immunofluorescence confirmed that treated GD fibroblasts had decreased levels of GCase in their ER and increased levels in lysosomes. Changes in protein dynamics, monitored by hydrogen/deuterium-exchange mass spectrometry, identified a domain III active-site loop (residues 243–249) as being significantly stabilized upon binding of isofagomine or either of these two new compounds; this suggests a common mechanism for PC enhancement of intracellular transport.

The bifunctional GlmU protein catalyzes the formation of UDP-N-acetylglucosamine in a two-step reaction using the substrates glucosamine-1-phosphate, acetyl coenzyme A, and UTP. This metabolite is a common precursor to the synthesis of bacterial cell surface carbohydrate polymers, such as peptidoglycan, lipopolysaccharide, and wall teichoic acid that are involved in the maintenance of cell shape, permeability, and virulence. The C-terminal acetyltransferase domain of GlmU exhibits structural and mechanistic features unique to bacterial UDP-N-acetylglucosamine synthases, making it an excellent target for antibacterial design. In the work described here, we have developed an absorbance-based assay to screen diverse chemical libraries in high throughput for inhibitors to the acetyltransferase reaction of Escherichia coli GlmU. The primary screen of 50,000 drug-like small molecules identified 63 hits, 37 of which were specific to acetyltransferase activity of GlmU. Secondary screening and mode-of-inhibition studies identified potent inhibitors where compound binding within the acetyltransferase active site was requisite on the presence of glucosamine-1-phosphate and were competitive with the substrate acetyl coenzyme A. These molecules may represent novel chemical scaffolds for future antimicrobial drug discovery. In addition, this work outlines the utility of catalytic variants in targeting specific activities of bifunctional enzymes in high-throughput screens.The acetylated amino-sugar N-acetylglucosamine (GlcNAc) is a metabolite of central importance to the biosynthesis of the bacterial cell envelope. The activated form of GlcNAc, UDPGlcNAc, is at a branchpoint between the synthesis of three key bacterial biosynthetic pathways: peptidoglycan and lipid A and lipopolysaccharide in gram-negative bacteria, and teichoic acid in gram-positive bacteria. This activated precursor is necessary for the assembly of these molecules on the intracellular face of the cytoplasmic membrane, and perturbing UDP-GlcNAc synthesis can have grave effects on the fitness of the bacteria. Both peptidoglycan and lipid A are necessary for cell viability (13, 24), while lipopolysaccharide and teichoic acid contribute to the virulence of bacterial pathogens (23,28). Hence, the discrete inhibition of UDP-GlcNAc biosynthesis would simultaneously target multiple essential and virulence-determining pathways.Although UDP-GlcNAc is an essential metabolite in both eukaryotes and prokaryotes, distinct differences in biosynthesis observed between UDP-GlcNAc synthases from members of each kingdom can be exploited for selective inhibition of prokaryotic UDP-GlcNAc synthesis. In bacteria, UDP-GlcNAc is efficiently synthesized from the glycolysis intermediate fructose-6-phosphate in four enzymatic steps beginning with amidation to glucosamine-6-phosphate followed by isomerization to glucosamine-1-phosphate (GlcN-1-P) by the GlmS and GlmM enzymes (2). The 456-amino-acid bifunctional enzyme GlmU then catalyzes the two final steps of UDP-GlcNAc synthesis: the...

Glutamate is an important signaling molecule in a wide variety of tissues. Aberrant glutamatergic signaling disrupts normal tissue homeostasis and induces several disruptive pathological conditions including pain. Breast cancer cells secrete high levels of glutamate and often metastasize to bone. Exogenous glutamate can disrupt normal bone turnover and may be responsible for cancer-induced bone pain (CIBP). CIBP is a significant co-morbidity that affects quality of life for many advanced-stage breast cancer patients. Current treatment options are commonly accompanied by serious side-effects that negatively impact patient care. Identifying small molecule inhibitors of glutamate release from aggressive breast cancer cells advances a novel, mechanistic approach to targeting CIBP that could advance treatment for several pathological conditions. Using high-throughput screening, we investigated the ability of approximately 30,000 compounds from the Canadian Compound Collection to reduce glutamate release from MDA-MB-231 breast cancer cells. This line is known to secrete high levels of glutamate and has been demonstrated to induce CIBP by this mechanism. Positive chemical hits were based on the potency of each molecule relative to a known pharmacological inhibitor of glutamate release, sulfasalazine. Efficacy was confirmed and drug-like molecules were identified as potent inhibitors of glutamate secretion from MDA-MB-231, MCF-7 and Mat-Ly-Lu cells.

Hematopoietic stem and progenitor cell differentiation are blocked in acute myeloid leukemia (AML) resulting in cytopenias and a high risk of death. Most patients with AML become resistant to treatment due to lack of effective cytotoxic and differentiation promoting compounds. High MN1 expression confers poor prognosis to AML patients and induces resistance to cytarabine and alltrans-retinoic acid (ATRA) induced differentiation. Using a high-throughput drug screening, we identified the dihydrofolate reductase (DHFR) antagonist pyrimethamine to be a potent inducer of apoptosis and differentiation in several murine and human leukemia cell lines. Oral pyrimethamine treatment was effective in two xenograft mouse models and specifically targeted leukemic cells in human AML cell lines and primary patient cells, while CD34+ cells from healthy donors were unaffected. The antileukemic effects of PMT could be partially rescued by excess folic acid, suggesting an oncogenic function of folate metabolism in AML. Thus, our study identifies pyrimethamine as a candidate drug that should be further evaluated in AML treatment.

Introduction: Hematopoietic stem/progenitor cell differentiation is blocked in acute myeloid leukemia (AML) resulting in cytopenias and high risk of death. Most patients with AML become resistant to treatment due to lack of effective cytotoxic and differentiation fostering compounds. High expression of MN1 confers poor prognosis to AML patients and induces resistance to cytarabine and all-trans-retinoic acid (ATRA) induced differentiation. We thus set out to identify compounds which could potentially overcome the differentiation block in AML. Methods: Based on the above concepts and in an effort to identify novel compounds which are potent inducers of differentiation and apoptosis in AML, high-throughput drug screening was employed in the MN1 leukemic model. A total of 3580 bioactive compounds were tested in duplicate at a concentration of 2.5 µM using alamar blue fluorescence as readout. As MN1 cells are resistant to ATRA (at 1µM and even 10µM ATRA), the drug screening was performed in the presence of a clinically relevant dose of ATRA (1 µM) to identify compounds that concurrently act with the cytotoxic and/or differentiating effects of ATRA. To determine whether a compound was effective as monotherapy or if it synergized with ATRA, we also performed a validation phase study in which the IC50 of each candidate compound was tested alone and in combination with ATRA. Fifty-four inhibitors were chosen from the primary screen for further validation based on presumed mechanism of action and novelty. The shortlisted compound pyrimethamine (PMT) was validated for its differentiation and apoptosis promoting effects in various murine and human AML models. Results: Our high-throughput drug screening identified 117 compounds, which reduced MN1 leukemic cell proliferation by more than 80% above the ATRA-treated control in both replicates (inhibitors), 8 borderline inhibitors (one replicate with more than 80% inhibition and one with 74 to 80% inhibition), and 35 outliers, which inhibited cell proliferation by 80% or more in only one replicate. The biologic processes most frequently targeted by the 117 inhibitors were DNA replication (n=26), microtubule assembly (n=12), NF-kB pathway (n=8), dihydrofolate reductase (DHFR, n=3) and heat shock protein 90 (HSP90). Dihydrofolate reductase inhibitors, pyrimethamine and amethopterin/methotrexate emerged as top hits from the screening and preliminary validation studies. Validation studies identified the antifolate pyrimethamine (PMT) that potently induced apoptosis and differentiation in several murine and human leukemic cell lines when administered as a single agent. The cytotoxic effects of pyrimethamine were reversed by addition of an excess of folic acid whereas induction of myeloid differentiation at higher concentrations of pyrimethamine was not mediated through DHFR inhibition. We further evaluated the effect of pyrimethamine in an in vivo xenograft mouse model by subcutaneously inducing tumors with HL60 and THP1 cell lines. Oral pyrimethamine treatment significantly reduced tumor volumes after 14, 19 and 24 days post-transplantation and at death compared to solvent treated mice (P<0.01). The effect of pyrimethamine was further assessed in primary human AML cells and normal CD34+ cells by CFC assays. Colony numbers from primary AML cells, but not normal CD34+ bone marrow cells, were significantly reduced by pyrimethamine as compared to solvent control. Thus, our study identifies pyrimethamine as a candidate drug that is a potent and specific inducer of apoptosis and differentiation with the property of specifically targeting leukemic cells. Conclusion: Our high-throughput drug screening identified pyrimethamine as a potent and specific antileukemic compound and reinforces targeting of folate metabolism as a treatment strategy in acute myeloid leukemia. Disclosures No relevant conflicts of interest to declare.

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