In light of the current outbreak of Ebola virus disease, there is an urgent need to develop effective therapeutics to treat Ebola infection, and drug repurposing screening is a potentially rapid approach for identifying such therapeutics. We developed a biosafety level 2 (BSL-2) 1536-well plate assay to screen for entry inhibitors of Ebola virus-like particles (VLPs) containing the glycoprotein (GP) and the matrix VP40 protein fused to a beta-lactamase reporter protein and applied this assay for a rapid drug repurposing screen of Food and Drug Administration (FDA)-approved drugs. We report here the identification of 53 drugs with activity of blocking Ebola VLP entry into cells. These 53 active compounds can be divided into categories including microtubule inhibitors, estrogen receptor modulators, antihistamines, antipsychotics, pump/channel antagonists, and anticancer/antibiotics. Several of these compounds, including microtubule inhibitors and estrogen receptor modulators, had previously been reported to be active in BSL-4 infectious Ebola virus replication assays and in animal model studies. Our assay represents a robust, effective and rapid high-throughput screen for the identification of lead compounds in drug development for the treatment of Ebola virus infection.

Mitochondria contain multiple copies of their own 16.6 kb circular genome. To explore the impact of mitochondrial DNA (mtDNA) damage on mitochondrial (mt) function and viability of AML cells, we screened a panel of DNA damaging chemotherapeutic agents to identify drugs that could damage mtDNA. We identified bleomycin as an agent that damaged mtDNA in AML cells at concentrations that induced cell death. Bleomycin also induced mtDNA damage in primary AML samples. Consistent with the observed mtDNA damage, bleomycin reduced mt mass and basal oxygen consumption in AML cells. We also demonstrated that the observed mtDNA damage was functionally important for bleomycin-induced cell death. Finally, bleomycin delayed tumor growth in xenograft mouse models of AML and anti-leukemic concentrations of the drug induced mtDNA damage in AML cells preferentially over normal lung tissue. Taken together, mtDNA-targeted therapy may be an effective strategy to target AML cells and bleomycin could be useful in the treatment of this disease.

Giardiasis is a severe intestinal parasitic disease caused by Giardia lamblia, which inflicts many people in poor regions and is the most common parasitic infection in the United States. Current standard care drugs are associated with undesirable side effects, treatment failures, and an increasing incidence of drug resistance. As follow-up to a high-throughput screening of an approved drug library, which identified compounds lethal to G. lamblia trophozoites, we have determined the minimum lethal concentrations of 28 drugs and advanced 10 of them to in vivo studies in mice. The results were compared to treatment with the standard care drug, metronidazole, in order to identify drugs with equal or better anti-Giardia activities. Three drugs, fumagillin, carbadox, and tioxidazole, were identified. These compounds were also potent against metronidazole-resistant human G. lamblia isolates (assemblages A and B), as determined in in vitro assays. Of these three compounds, fumagillin is currently an orphan drug used within the European Union to treat microsporidiosis in immunocompromised individuals, whereas carbadox and tioxidazole are used in veterinary medicine. A dose-dependent study of fumagillin in a giardiasis mouse model revealed that the effective dose of fumagillin was ∼ 100-fold lower than the metronidazole dose. Therefore, fumagillin may be advanced to further studies as an alternative treatment for giardiasis when metronidazole fails.

Myotonic dystrophy type 1 (DM1) is a dominantly inherited neuromuscular disorder resulting from expression of RNA containing an expanded CUG repeat (CUG(exp)). The pathogenic RNA is retained in nuclear foci. Poly-(CUG) binding proteins in the Muscleblind-like (MBNL) family are sequestered in foci, causing misregulated alternative splicing of specific pre-mRNAs. Inhibitors of MBNL1-CUG(exp) binding have been shown to restore splicing regulation and correct phenotypes in DM1 models. We therefore conducted a high-throughput screen to identify novel inhibitors of MBNL1-(CUG)12 binding. The most active compound was lomofungin, a natural antimicrobial agent. We found that lomofungin undergoes spontaneous dimerization in DMSO, producing dilomofungin, whose inhibition of MBNL1-(CUG)12 binding was 17-fold more potent than lomofungin itself. However, while dilomofungin displayed the desired binding characteristics in vitro, when applied to cells it produced a large increase of CUG(exp) RNA in nuclear foci, owing to reduced turnover of the CUG(exp) transcript. By comparison, the monomer did not induce CUG(exp) accumulation in cells and was more effective at rescuing a CUG(exp)-induced splicing defect. These results support the feasibility of high-throughput screens to identify compounds targeting toxic RNA, but also demonstrate that ligands for repetitive sequences may have unexpected effects on RNA decay.

Mis-sense mutations in the α-subunit of the G-protein, Gsα, cause fibrous dysplasia of bone/McCune-Albright syndrome. The biochemical outcome of these mutations is constitutively active Gsα and increased levels of cAMP. The aim of this study was to develop an assay system that would allow the identification of small molecule inhibitors specific for the mutant Gsα protein, the so-called gsp oncogene. Commercially available Chinese hamster ovary cells were stably transfected with either wild-type (WT) or mutant Gsα proteins (R201C and R201H). Stable cell lines with equivalent transfected Gsα protein expression that had relatively lower (WT) or higher (R201C and R201H) cAMP levels were generated. These cell lines were used to develop a fluorescence resonance energy transfer (FRET)-based cAMP assay in 1536-well microplate format for high throughput screening of small molecule libraries. A small molecule library of 343,768 compounds was screened to identify modulators of gsp activity. A total of 1,356 compounds with inhibitory activity were initially identified and reconfirmed when tested in concentration dose responses. Six hundred eighty-six molecules were selected for further analysis after removing cytotoxic compounds and those that were active in forskolin-induced WT cells. These molecules were grouped by potency, efficacy, and structural similarities to yield 22 clusters with more than 5 of structurally similar members and 144 singleton molecules. Seven chemotypes of the major clusters were identified for further testing and analyses.

Carbamate kinase from Giardia lamblia is an essential enzyme for the survival of the organism. The enzyme catalyzes the final step in the arginine dihydrolase pathway converting ADP and carbamoyl phosphate to ATP and carbamate. We previously reported that disulfiram, a drug used to treat chronic alcoholism, inhibits G. lamblia CK and kills G. lamblia trophozoites in vitro at submicromolar IC50 values. Here, we examine the structural basis for G. lamblia CK inhibition of disulfiram and its analog, thiram, their activities against both metronidazole-susceptible and metronidazole-resistant G. lamblia isolates, and their efficacy in a mouse model of giardiasis. The crystal structure of G. lamblia CK soaked with disulfiram revealed that the compound thiocarbamoylated Cys-242, a residue located at the edge of the active site. The modified Cys-242 prevents a conformational transition of a loop adjacent to the ADP/ATP binding site, which is required for the stacking of Tyr-245 side chain against the adenine moiety, an interaction seen in the structure of G. lamblia CK in complex with AMP-PNP. Mass spectrometry coupled with trypsin digestion confirmed the selective covalent thiocarbamoylation of Cys-242 in solution. The Giardia viability studies in the metronidazole-resistant strain and the G. lamblia CK irreversible inactivation mechanism show that the thiuram compounds can circumvent the resistance mechanism that renders metronidazole ineffectiveness in drug resistance cases of giardiasis. Together, the studies suggest that G. lamblia CK is an attractive drug target for development of novel antigiardial therapies and that disulfiram, an FDA-approved drug, is a promising candidate for drug repurposing.

Myotonic dystrophy (DM) is a multi-system neuromuscular disorder for which there is no treatment. We have developed a medium throughput phenotypic assay, based on the identification of nuclear foci in DM patient cell lines using in situ hybridization and high-content imaging to screen for potentially useful therapeutic compounds. A series of further assays based on molecular features of DM have also been employed. Two compounds that reduce and/or remove nuclear foci have been identified, Ro 31-8220 and chromomycin A3. Ro 31-8220 is a PKC inhibitor, previously shown to affect the hyperphosphorylation of CELF1 and ameliorate the cardiac phenotype in a DM1 mouse model. We show that the same compound eliminates nuclear foci, reduces MBNL1 protein in the nucleus, affects ATP2A1 alternative splicing and reduces steady-state levels of CELF1 protein. We demonstrate that this effect is independent of PKC activity and conclude that this compound may be acting on alternative kinase targets within DM pathophysiology. Understanding the activity profile for this compound is key for the development of targeted therapeutics in the treatment of DM.

The ability to control pre-mRNA splicing with small molecules could facilitate the development of therapeutics or cell-based circuits that control gene function. Myotonic dystrophy type 1 is caused by the dysregulation of alternative pre-mRNA splicing due to sequestration of muscleblind-like 1 protein (MBNL1) by expanded, non-coding r(CUG) repeats (r(CUG)(exp)). Here we report two small molecules that induce or ameliorate alternative splicing dysregulation. A thiophene-containing small molecule (1) inhibits the interaction of MBNL1 with its natural pre-mRNA substrates. Compound (2), a substituted naphthyridine, binds r(CUG)(exp) and displaces MBNL1. Structural models show that 1 binds MBNL1 in the Zn-finger domain and that 2 interacts with UU loops in r(CUG)(exp). This study provides a structural framework for small molecules that target MBNL1 by mimicking r(CUG)(exp) and shows that targeting MBNL1 causes dysregulation of alternative splicing, suggesting that MBNL1 is thus not a suitable therapeutic target for the treatment of myotonic dystrophy type 1.

The anti-fibrotic, vasodilatory and pro-angiogenic therapeutic properties of recombinant relaxin peptide hormone have been investigated in several diseases, and recent clinical trial data has shown benefit in treating acute heart failure. However, the remodelling capacity of these peptide hormones is difficult to study in chronic settings because of their short half-life and the need for intravenous administration. Here we present the first small-molecule series of human relaxin/insulin-like family peptide receptor 1 agonists. These molecules display similar efficacy as the natural hormone in several functional assays. Mutagenesis studies indicate that the small molecules activate relaxin receptor through an allosteric site. These compounds have excellent physical and in vivo pharmacokinetic properties to support further investigation of relaxin biology and animal efficacy studies of the therapeutic benefits of relaxin/insulin-like family peptide receptor 1 activation.

Evaluation of compound activity in vitro is crucial to drug discovery efforts and require that the compounds be accurately and reliably titrated and dispensed to the assay wells. The HP D300 dispenser uses inkjet technology to achieve small-volume dispensing that allows concentration-response testing using the direct dilution paradigm. Although inkjet technology has been long in existence, it is new to the field of screening and drug development. We have evaluated the D300 dispenser in a biochemical assay, a cell-based reporter gene assay, and a cytotoxicity assay. The software for this instrument is user friendly, and the compound-dispensing process is streamlined. However, a limitation is that this dispenser is currently applicable to only 96-well and 384-well plate formats and not to 1536-well high-density plates. Our results indicate that the D300 generates clean and reproducible results that correlate with those produced with more commonly used instruments such as the pin tool. We found that the instrument is useful and can improve the throughput of compound dispensing in 96-well and 384-well plates.