Small Molecules Targeting Human UDP-GlcNAc 2-Epimerase

Uridine diphosphate N-acetylglucosamine 2-epimerase (GNE) is a key enzyme in the sialic acid biosynthesis pathway. Sialic acids are primarily terminal carbohydrates on glycans and play fundamental roles in health and disease. In search of effective GNE inhibitors not based on a carbohydrate scaffold, we performed a high-throughput screening campaign of 68,640 drug-like small molecules against recombinant GNE using a UDP detection assay. We validated nine of the primary actives with an orthogonal real-time NMR assay and verified their IC50 values in the low micromolar to nanomolar range manually. Stability and solubility studies revealed three compounds for further evaluation. Thermal shift assays, analytical size exclusion, and interferometric scattering microscopy demonstrated that the GNE inhibitors acted on the oligomeric state of the protein. Finally, hydrogen-deuterium exchange mass spectrometry (HDX-MS) revealed which sections of GNE were shifted upon the addition of the inhibitors. In summary, we have identified three small molecules as GNE inhibitors with high potency in vitro, which serve as promising candidates to modulate sialic acid biosynthesis in more complex systems.

Real-time analysis of endogenous protoporphyrin IX fluorescence from δ-aminolevulinic acid and its derivatives reveals distinct time- and dose-dependent characteristics in vitro

Photodynamic therapy (PDT) and photodiagnosis based on the intracellular production of the photosensitizer protoporphyrin IX (PPIX) by administration of its metabolic precursor -aminolevulinic acid (ALA) achieved their breakthrough upon the clinical approval of MAL (ALA methyl ester) and HAL (ALA hexyl ester). For newly developed ALA derivatives or application in new tumor types, in vitro determination of PPIX formation involves multiparametric experiments covering variable pro-drug concentrations, medium composition, time points of analysis, and cell type(s). This study uses a fluorescence microplate reader with a built-in temperature and atmosphere control to investigate the high-resolution long-term kinetics (72 h) of cellular PPIX fueled by administration of either ALA, MAL, or HAL for each 10 different concentrations. For simultaneous proliferation correction, A431 cells were stably transfected with green fluorescent protein. The results indicate that the peak PPIX level is a function of both, incubation concentration and period: maximal PPIX is generated with 1 to 2-mM ALA/MAL or 0.125-mM HAL; also, the PPIX peak shifts to longer incubation periods with increasing pro-drug concentrations. The results underline the need for detailed temporal analysis of PPIX formation to optimize ALA (derivative)-based PDT or photodiagnosis and highlight the value of environment-controlled microplate readers for automated in vitro analysis.

Abstract LB-113: Non-invasive analysis of drug sensitivity in homo and-heterotypic multicellular tumor spheroids

To gain full benefit of more organotypic tumor culture systems, appropriate assays which enable high-throughput analysis over time without destroying the tissues have to be adopted. Especially read outs for co-culture systems which allow the discrimination of a drug effect on the cancer cell and stroma environment will be of advantage to foster drug testing using more complex 3D models. Here we report the development of microtissue models harboring either fluorescent and/or Luciferase for non-invasive drug sensitivity testing of homotypic and heterotypic tumor spheroids. Microtissues were assayed in microtissue assay plate which allows for biochemical assays and quantitative fluorescence of single multicellular tumor spheroids. Both the fluorescent and secreted luciferase reporter can be measured over time without destroying the tissue allowing for additional end point analysis of interest. HCT116, a colon cancer cell line, was transduced with the reporter genes under the control of a constitutive promoter. To assess the dependency of the fluorescence intensity in accordance to microtissue growth, HCT116-GFP microtissues were assayed over time in a multiplate fluorescence reader. The size profile correlated closely to the increase in fluorescence intensity. For further assay validation the IC50 value were determined by intra-tissue lactate dehydrogenase (LDH) and fluorescence decrease after 72h compound incubation. Reference compounds such as Taxol, Staurosprin and Chlorambucil were tested. The IC50 values from both assays resulted in comparable IC50 values. For non-invasive drug sensitivity testing in heterogenic tumor microtissues HCT116 harboring a secreted Luciferase were combined with a red fluorescent mouse fibroblasts (NIH3T3). Assaying Luciferase on the one hand and red fluorescence intensity on the other allowed discriminating effects on cancer cells and the non-proliferative. Discrimination between specific effects of drug treatment on tumor cells and fibrobast matrix cells is also possible using a two color heterotypic cell model composed of GFP-expressing HTC116 and RFP expressing NIH3T3 cells. Cytotoxic agents targeting either the total cell population or only proliferative cells were tested on the model discriminating the biological response on the two cell populations. To enable the implementation of organotypic cell culture systems at an early time point in the drug development process non-invasive assays. Here, we demonstrate for the first time such a dual cell tumor microtissues system with integrated reporter functions which allows to distinguish effects on different cell populations.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr LB-113. doi:1538-7445.AM2012-LB-113