BackgroundHemostasis is a critical and active function of the blood mediated by platelets. Therefore, the prevention of pathological platelet aggregation is of great importance as well as of pharmaceutical and medical interest. Endogenous platelet inhibition is predominantly based on cyclic nucleotides (cAMP, cGMP) elevation and subsequent cyclic nucleotide-dependent protein kinase (PKA, PKG) activation. In turn, platelet phosphodiesterases (PDEs) and protein phosphatases counterbalance their activity. This main inhibitory pathway in human platelets is crucial for countervailing unwanted platelet activation. Consequently, the regulators of cyclic nucleotide signaling are of particular interest to pharmacology and therapeutics of atherothrombosis. Modeling of pharmacodynamics allows understanding this intricate signaling and supports the precise description of these pivotal targets for pharmacological modulation.ResultsWe modeled dynamically concentration-dependent responses of pathway effectors (inhibitors, activators, drug combinations) to cyclic nucleotide signaling as well as to downstream signaling events and verified resulting model predictions by experimental data. Experiments with various cAMP affecting compounds including anti-platelet drugs and their combinations revealed a high fidelity, fine-tuned cAMP signaling in platelets without cross-talk to the cGMP pathway. The model and the data provide evidence for two independent feedback loops: PKA, which is activated by elevated cAMP levels in the platelet, subsequently inhibits adenylyl cyclase (AC) but as well activates PDE3. By multi-experiment fitting, we established a comprehensive dynamic model with one predictive, optimized and validated set of parameters. Different pharmacological conditions (inhibition, activation, drug combinations, permanent and transient perturbations) are successfully tested and simulated, including statistical validation and sensitivity analysis. Downstream cyclic nucleotide signaling events target different phosphorylation sites for cAMP- and cGMP-dependent protein kinases (PKA, PKG) in the vasodilator-stimulated phosphoprotein (VASP). VASP phosphorylation as well as cAMP levels resulting from different drug strengths and combined stimulants were quantitatively modeled. These predictions were again experimentally validated. High sensitivity of the signaling pathway at low concentrations is involved in a fine-tuned balance as well as stable activation of this inhibitory cyclic nucleotide pathway.ConclusionsOn the basis of experimental data, literature mining and database screening we established a dynamic in silico model of cyclic nucleotide signaling and probed its signaling sensitivity. Thoroughly validated, it successfully predicts drug combination effects on platelet function, including synergism, antagonism and regulatory loops.

S100/calgranulins (S100A8, S100A9 and S100A12) are key players of innate immune function and elevated levels are a characteristic feature of acute and chronic inflammation, and inflammation-associated carcinogenesis. However, reduced S100A8 and S100A9 expression has been detected for squamous cell carcinoma, including the head and neck region (HNSCC), which originate from mucosal epithelia with abundant expression of both proteins under physiological conditions. In contrast to S100A8 and S100A9, only sparse information is available for S100A12 and a comparative study of all three S100/calgranulins in HNSCC is still missing. We analyzed S100/calgranulin protein levels in a retrospective patient cohort (n 5 131) of oropharyngeal squamous cell carcinoma (OPSCC) by immunohistochemical staining of tissue microarrays. Common characteristics of all three S100/calgranulins were: (i) abundant expression in supra-basal keratinocytes of normal mucosa with predominant nuclear staining, (ii) low expression in 30.4-51.9% of primary OPSCCs and (iii) variable accumulation of S100/calgranulin-positive immune cells in the tumor stroma. These features were associated with histopathological characteristics, such as tumor grade, lymph node metastasis and tumor stage. Furthermore, univariate and multivariate analysis revealed worse overall survival of OPSCC patients with simultaneous reduction of S100A8 and S100A12 expression, while expression of S100A9 or presence of the S100A8/S100A9 heterodimer had no impact, suggesting distinct regulation and function of individual S100/ calgranulins in the pathogenesis of HNSCCs.Head and neck squamous cell carcinoma (HNSCC) is one of the most prevalent human malignancies worldwide characterized by high mortality and high morbidity.

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