The new InsP<inf>3</inf>Kinase inhibitor BIP-4 is competitive to InsP<inf>3</inf> and blocks proliferation and adhesion of lung cancer cells

Abstract

© 2015 Elsevier Inc. All rights reserved. As ectopic expression of the neuronal inositol-1,4,5-trisphosphate-3-kinase A (InsP<inf>3</inf>Kinase) in tumor cells increases the metastatic potential, InsP<inf>3</inf>Kinase is an interesting target for tumor therapy. Recently, we have identified a membrane-permeable InsP<inf>3</inf>Kinase inhibitor (BAMB-4) exhibiting an IC50-value of 20 μM. Here we characterized a new InsP<inf>3</inf>Kinase inhibitor which shows a 130-fold lower IC50 value (157 ± 57 nM) as compared to BAMB-4. We demonstrate that this nitrophenolic compound, BIP-4, is non-competitive to ATP but competitive to InsP<inf>3</inf>, thus exhibits a high selectivity for inhibition of InsP<inf>3</inf>Kinase activity. Docking analysis suggested a putative binding mode of this molecule into the InsP<inf>3</inf>Kinase active site. Determination of cellular uptake in lung cancer cells (H1299) revealed that 6% of extracellular BIP-4 is internalized by non-endosomal uptake, showing that BIP-4 is not trapped inside endo/lysosomes but is available to inhibit cellular InsP<inf>3</inf>Kinase activity. Interestingly, we found that BIP-4 mediated inhibition of InsP<inf>3</inf>Kinase activity in the two lung cancer cell lines H1299 and LN4323 inhibited proliferation and adhesion at IC50 values of 3 μM or 2 μM, respectively. InsP<inf>3</inf>Kinase inhibition did not alter ATP-induced calcium signals but significantly reduced the level of Ins(1,3,4,5,6)P<inf>5</inf>. From these data we conclude that the inhibitory effect of BIP-4 on proliferation and adhesion of lung cancer cells does not result from alterations of calcium but from alterations of inositol phosphate signals. In summary, we reveal that inhibition of cellular InsP<inf>3</inf>Kinase by BIP-4 impairs proliferation and adhesion and therefore BIP-4 might be a promising compound to reduce the metastatic potential of lung carcinoma cells.