The behavior of cancer cells is strongly influenced by the properties of extracellular microenvironments, including topology, mechanics and composition. As topological and mechanical properties of the extracellular matrix are hard to access and control for in-depth studies of underlying mechanisms in vivo, defined biomimetic in vitro models are needed. Herein we show, how pore size and fibril diameter of collagen I networks distinctively regulate cancer cell morphology and invasion. Three-dimensional collagen I matrices with a tight control of pore size, fibril diameter and stiffness were reconstituted by adjustment of concentration and pH value during matrix reconstitution. At first, a detailed analysis of topology and mechanics of matrices using confocal laser scanning microscopy, image analysis tools and force spectroscopy indicate pore size and not fibril diameter as the major determinant of matrix elasticity. Secondly, by using two different breast cancer cell lines (MDA-MB-231 and MCF-7), we demonstrate collagen fibril diameter--and not pore size--to primarily regulate cell morphology, cluster formation and invasion. Invasiveness increased and clustering decreased with increasing fibril diameter for both, the highly invasive MDA-MB-231 cells with mesenchymal migratory phenotype and the MCF-7 cells with amoeboid migratory phenotype. As this behavior was independent of overall pore size, matrix elasticity is shown to be not the major determinant of the cell characteristics. Our work emphasizes the complex relationship between structural-mechanical properties of the extracellular matrix and invasive behavior of cancer cells. It suggests a correlation of migratory and invasive phenotype of cancer cells in dependence on topological and mechanical features of the length scale of single fibrils and not on coarse-grained network properties.

Monocytes enter sites of microbial or sterile inflammation as the first line of defense of the immune system and initiate pro-inflammatory effector mechanisms. We show that activation with bacterial lipopolysaccharide (LPS) induces them to undergo a metabolic shift toward aerobic glycolysis, similar to the Warburg effect observed in cancer cells. At sites of inflammation, however, glucose concentrations are often drastically decreased, which prompted us to study monocyte function under conditions of glucose deprivation and abrogated Warburg effect. Experiments using the Seahorse Extracellular Flux Analyzer revealed that limited glucose supply shifts monocyte metabolism toward oxidative phosphorylation, fueled largely by fatty acid oxidation at the expense of lipid droplets. While this metabolic state appears to provide sufficient energy to sustain functional properties like cytokine secretion, migration, and phagocytosis, it cannot prevent a rise in the AMP/ATP ratio and a decreased respiratory burst. The molecular trigger mediating the metabolic shift and the functional consequences is activation of AMP-activated protein kinase (AMPK). Taken together, our results indicate that monocytes are sufficiently metabolically flexible to perform pro-inflammatory functions at sites of inflammation despite glucose deprivation and inhibition of the LPS-induced Warburg effect. AMPK seems to play a pivotal role in orchestrating these processes during glucose deprivation in monocytes.

Defined biomimetic three-dimensional (3D) matrices are needed to decipher the complex cellular signalling during wound healing at high resolution in vitro. Soluble factors like TGF-β1 and adhesion promoting structural components of the extracellular matrix (ECM) are known to be key regulators of fibroblast behaviour. The ECM component fibronectin (FN) bears a complex function as adhesion promoter, fibrillar element and soluble factor binder. However, its implementation in biomimetic 3D matrices is frequently ill defined. To study the impact of FN on fibroblast cellular function under differentiating conditions (TGF-β1 stimulation), we functionalized 3D collagen I matrices with FN using two strategies: co-assembly and adsorptive immobilization. In comparison to co-assembly, adsorptive immobilization provided no alteration in collagen microstructure as well as mechanical properties. Moreover, this approach provided a controllable FN amount and a homogenous distribution of FN throughout collagen networks. A strong interplay of FN amount and TGF-β1 stimulation on fibroblast function was found in terms of proliferation, migration and myofibroblast differentiation. High levels of FN alone reduced proliferation and showed no effect on differentiation of fibroblasts, but increased migration. In contrast, fibroblast stimulation with high amounts of FN together with TGF-β1 increased proliferation. Independent of FN, the TGF-β1 stimulation enhanced mRNA expression of matrix components like collagen type I alpha 1 chain (Coll I(a1), FN with extra domain A (EDA-FN) and reduced cell migration. The latter cell behaviour indicated a FN independent differentiation into a myofibroblast phenotype. Overall, our 3D biomimetic matrices allow dissecting the overlapping action of the ECM protein FN and the soluble factor TGF-β1 on fibroblast proliferation, migration and differentiation in 3D microenvironments. Furthermore, this model enables the mimicking of important steps of the in vivo wound healing process in vitro.

The transcription factor STAT5b is a target for tumour therapy. We recently reported catechol bisphosphate and derivatives such as Stafib-1 as the first selective inhibitors of the STAT5b SH2 domain. Here, we demonstrate STAT5b binding of catechol bisphosphate by solid-state nuclear magnetic resonance, and report on rational optimization of Stafib-1 (Ki = 44 nM) to Stafib-2 (Ki = 9 nM). The binding site of Stafib-2 was validated using combined isothermal titration calorimetry (ITC) and protein point mutant analysis, representing the first time that functional comparison of wild-type versus mutant protein by ITC has been used to characterize the binding site of a small-molecule ligand of a STAT protein with amino acid resolution. The prodrug Pomstafib-2 selectively inhibits tyrosine phosphorylation of STAT5b in human leukaemia cells and induces apoptosis in a STAT5-dependent manner. We propose Pomstafib-2, which currently represents the most active, selective inhibitor of STAT5b activation available, as a chemical tool for addressing the fundamental question of which roles the different STAT5 proteins play in various cell processes.