This paper presents cytotoxicity data of selected imidazolium ionic liquids evaluated in vitro on the human tumor cell line HeLa. It was found that for 1-n-butyl-3-methylimidazolium entities the toxicity depends strongly on the associated anion; EC50 values are lowest for tetrafluoroborate. No direct dependence of the reduced effect concentration was found on elongating the short, methyl chain to ethyl or n-hexyl. Only for the ionic liquid with an n-decyl chain, the longest one studied, did higher hydrophobicity result in a EC50 one order of magnitude lower than that obtained with the n-butyl entity. The effect concentrations of imidazolium ionic liquids in the HeLa system used are lower than the values obtained for conventional organic solvents such as dichloromethane, toluene or xylene.

Ecto-5'-nucleotidase (eN, CD73) mediates extracellular adenosine production from 5'-AMP. Non-enzymatic functions of eN have also been reported. The aim of the study was to investigate the role of ecto-5'-nucleotidase in aggressive melanoma behaviour. Analysis of the involvement of eN in adhesion, migration and invasion revealed eN functions unknown to date. We found that following eN blockade by concanavalin A, the strength of adhesion to different ECM proteins was not altered, but at the same time the invasion ability of the cells was decreased. On the other hand, knocking down eN in melanoma cells did not influence cell invasion but abolished their migration on tenascin C (TnC). Ecto-5'-nucleotidase seems to fulfil a more distinct role as a receptor than as an enzyme in the cell interaction and mobility on TnC. Ecto-5'-nucleotidase activates also focal adhesion kinase and enhances the formation of complexes upon cell adhesion to TnC. All these observations prove that an eN-TnC complex is involved in cell migration and invasion and thus in the regulation of melanoma progression.

Ecto-5'-nucleotidase is a GPI-anchored enzyme localized in cell membrane lipid rafts. Although it is highly expressed in many tumour cells, its specific function during tumorigenesis is unclear. We have found that, among different melanoma cells, upregulated expression of ecto-5'-nucleotidase is associated with a highly invasive phenotype. Analysis of other cell membrane proteins involved in melanoma adhesion and metastasis demonstrated that expression of alpha5, beta1, beta3-integrin subunits and CD44 was elevated gradually in accordance with increasing metastatic potential. Expression of alphav-integrin and caveolin-1 was seen mostly in cells derived from metastatic melanomas. Furthermore, in contrast to N-cadherin, which was unaltered in all lines, we could not detect E-cadherin in any cell type. Functional assays demonstrated that highly expressed ecto-5'-nucleotidase is a catalytically competent protein that is very sensitive to inhibition by concanavalin A. The interaction with concanavalin A also caused increased association of ecto-5'-nucleotidase-rich lipid rafts with much heavier cytoskeletal complexes as determined by density gradient centrifugation. A similar shift towards heavier cytoskeletal fractions also took place with other proteins coexpressed with ecto-5'-nucleotidase, such as alphav, alpha5, beta1 and beta3-integrins, caveolin-1 and CD44. As ConA-induced clustering may reflect the interactions of membrane proteins with extracellular matrix, we also analysed the effect of several extracellular matrix proteins on the in-situ activity of ecto-5'-nucleotidase in WM9 cells and found that tenascin C strongly inhibited ecto-5'-nucleotidase activity and adenosine generation from AMP. We also developed WM9 cells with reduced ecto-5'-nucleotidase expression and tested differences in cell adhesion on various extracellular matrix proteins. WM9 cells attached significantly weaker to tenascin C layer. These observations indicate that expression of ecto-5'-nucleotidase correlates with a number of metastasis-related markers and thus may have a function in this process. Furthermore, our data suggest that, in addition to generating adenosine, ecto-5'-nucleotidase may have independent roles in adhesion and interaction with extracellular matrix components in melanoma.

A soluble 5'-nucleotidase was purified 200-fold from pigeon heart. The enzyme (1) had an apparent molecular mass close to 150 kDa, (2) had a neutral pH optimum and hydrolysed a wide range of nucleoside 5'-monophosphates with a 15-fold preference for AMP over IMP, (3) at near-physiological concentrations of AMP was activated by ADP but not by ATP, (4) was inhibited by high Mg2+ concentration and high ionic strength, (5) was weakly inhibited by p-nitrophenol phosphate and Pi, and (6) was non-competitively inhibited more potently by 5'-deoxy-5'-isobutylthioinosine than by 5'-deoxy-5'-isobutylthioadenosine, but not by [alpha,beta-methylene]ADP. The data show that the enzyme is distinct from the ecto-5'-nucleotidase and from the previously purified IMP-specific 5'-nucleotidase. They also predict that the enzyme is activated during ATP catabolism and hence will generate a more-than-linear increase in the adenosine-formation rate in response to an increase in cytosolic AMP concentration.

CD73 (ecto-5'-nucleotidase), a cell surface enzyme hydrolyzing AMP to adenosine, was lately demonstrated to play a direct role in tumor progression including regulation of tumor vascularization. It was also shown to stimulate tumor macrophage infiltration. Interstitial adenosine, accumulating in solid tumors due to CD73 enzymatic activity, is recognized as a main mediator regulating the production of pro- and anti-angiogenic factors, but the engagement of specific adenosine receptors in tumor progression in vivo is still poorly researched. We have analyzed the role of high affinity adenosine receptors A1, A2A, and A3 in B16F10 melanoma progression using specific agonists (CCPA, CGS-21680 and IB-MECA, respectively). We limited endogenous extracellular adenosine background using CD73 knockout mice treated with CD73 chemical inhibitor, AOPCP (adenosine α,β-methylene 5’-diphosphate). Activation of any adenosine receptor significantly inhibited B16F10 melanoma growth but only at its early stage. At 14th day of growth, the decrease in tumor neovascularization and MAPK pathway activation induced by CD73 depletion was reversed by all agonists. Activation of A1AR primarily increased angiogenic activation measured by expression of VEGF-R2 on tumor blood vessels. However, mainly A3AR activation increased both the microvessel density and expression of pro-angiogenic factors. All agonists induced significant increase in macrophage tumor infiltration, with IB-MECA being most effective. This effect was accompanied by substantial changes in cytokines regulating macrophage polarization between pro-inflammatory and pro-angiogenic phenotype. Our results demonstrate an evidence that each of the analyzed receptors has a specific role in the stimulation of tumor angiogenesis and confirm significantly more multifaceted role of adenosine in its regulation than was already observed. They also reveal previously unexplored consequences to extracellular adenosine signaling depletion in recently proposed anti-CD73 cancer therapy.