Persister state-directed transitioning and vulnerability in melanoma

Melanoma is a highly plastic tumor characterized by dynamic interconversion of different cell identities depending on the biological context. Melanoma cells with high expression of the H3K4 demethylase KDM5B (JARID1B) rest in a slow-cycling, yet reversible persister state. Over time, KDM5Bhigh cells can promote rapid tumor repopulation with equilibrated KDM5B expression heterogeneity. The cellular identity of KDM5Bhigh persister cells has not been studied so far, missing an important cell state-directed treatment opportunity in melanoma. Here, we have established a doxycycline-titratable system for genetic induction of permanent intratumor expression of KDM5B and screened for chemical agents that phenocopy this effect. Transcriptional profiling and cell functional assays confirmed that the dihydropyridine 2-phenoxyethyl 4-(2-fluorophenyl)-2,7,7-trimethyl-5-oxo-1,4,5,6,7,8-hexa-hydro-quinoline-3-carboxylate (termed Cpd1) supports high KDM5B expression and directs melanoma cells towards differentiation along the melanocytic lineage and to cell cycle-arrest. The high KDM5B state additionally prevents cell proliferation through negative regulation of cytokinetic abscission. Moreover, treatment with Cpd1 promoted the expression of the melanocyte-specific tyrosinase gene specifically sensitizing melanoma cells for the tyrosinase-processed antifolate prodrug 3-O-(3,4,5-trimethoxybenzoyl)-(-)-epicatechin (TMECG). In summary, our study provides proof-of-concept for a dual hit strategy in melanoma, in which persister state-directed transitioning limits tumor plasticity and primes melanoma cells towards lineage-specific elimination.

Context-Specific and Proximity-Dependent Labeling for the Proteomic Analysis of Spatiotemporally Defined Protein Complexes with Split-BioID

Proximity-dependent labeling techniques such as BioID and APEX2 allow the biotinylation of proteins proximal to a protein of interest in living cells. Following streptavidin pulldown and mass spectrometry analysis, this enables the identification of native protein-protein interactions. Here we describe split-BioID, a protein-fragment complementation assay that increases the resolution of BioID. Using this technique, context-specific protein complexes can be resolved.

Abstract 3054: Tracing EMT with fluorescent biosensors (chromobodies) in living cancer cells

Epithelial-mesenchymal transition (EMT) is a complex cellular program, involved in the progression of epithelial cancers to a metastatic stage. During this process characteristic epithelial marker proteins are repressed in favor of mesenchymal biomarkers, such as the intermediate filament protein vimentin. There is an ongoing need for reliable cell-based EMT model systems, which can be adapted to screening campaigns for novel anti-metastatic therapies. Imaging-based screening systems are restricted to endpoint immunofluorescence studies that provide only little information about the dynamics of the process, or to ectopic expression of EMT markers, fused to fluorescent proteins. However, overexpression of EMT marker proteins, particularly vimentin, have been shown to influence the EMT phenotype of the cells.

Here we introduce chromobodies as an innovative technology to monitor EMT in living non-small lung cancer cells. Chromobodies are fluorescently-labeled single-domain-antibodies that are functional within in living cells and directly target endogenous proteins. We generated chromobodies against the EMT biomarkers vimentin, actin and β-catenin and stably introduced them into the genome of A549 cells. Upon induction of EMT with transforming growth factor β (TGF- β), we could visualize the dynamic reorganization of endogenous vimentin, actin and β-catenin in the established EMT chromobody models in 2D as well as 3D cell culture. By means of these chromobody cell lines we further developed a 2D high content analysis system to visualize and quantify spatiotemporal changes of the endogenous biomarkers vimentin and actin during the EMT process. In a proof-of-principle screen, using known EMT-affecting reagents (e.g. TGF receptor I inhibitors LY364947 and SB505124) as well as EMT-unrelated agents, we were able to show that this high content analysis system can be applied to select compounds that inhibit TGF-β-induced EMT.

In summary, live cell imaging of EMT markers with chromobodies provides a novel versatile approach to study EMT in real time and allows the identification of EMT inhibitors as potential candidates for anti-metastatic therapies by high content screening.

Citation Format: Julia Maier, Theresa Plaga, Stefanie Egetemaier, Bjoern Traenkle, Ulrich Rothbauer. Tracing EMT with fluorescent biosensors (chromobodies) in living cancer cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3054. doi:10.1158/1538-7445.AM2017-3054