dihydropyridines and Brain-Neoplasms

Glioma-initiating cells (GIC) are considered the underlying cause of recurrences of aggressive glioblastomas, replenishing the tumor population and undermining the efficacy of conventional chemotherapy. Here we report the discovery that inhibiting T-type voltage-gated Ca

Topics: Amino Acids; Animals; Biological Transport; Brain Neoplasms; Calcium Channel Blockers; Calcium Channels, T-Type; Cell Death; Cell Line, Tumor; Dihydropyridines; Glioma; Humans; Mice; Mycotoxins; Neoplastic Stem Cells; Potassium Channels, Calcium-Activated; Proteomics; Sodium; Unfolded Protein Response

Evidence has accumulated that classic L-type Ca2+ channel blockers with a dihydropyridine structure also inhibit T-type Ca2+ channels in certain types of central and peripheral neurons and in smooth muscle cells, albeit with a lower potency. Thus beneficial therapeutic effects of dihydropyridines in cardiovascular and neurological diseases may not only be associated with L-type but also with T-type Ca2+ channel blockade. Little is known about the exact order of potency of dihydropyridine derivatives at T-type Ca2+ channels. Here we investigate the efficacy and potency of four therapeutically used compounds, i.e. nifedipine, nimodipine, nicardipine, niguldipine, in the neuroblastoma-glioma cell line NG108-15. For comparative purposes the Ca2+ channel agonist Bay K 8644 was included. Ca2+ channel currents were measured with the whole-cell voltage clamp technique. Subtype Ca2+ channel currents were separated by clamp protocol and selective blockers. T-type Ca2+ channel currents were inhibited with decreasing potency in the order niguldipine > nicardipine > nimodipine > nifedipine (IC50-values 244 nM, 2.5 microM, 9.8 microM, 39 microM), whereas L-type Ca2+ channel currents were blocked with similar potency (IC50 for nicardipine 75 nM). Bay K 8644 increased T-type Ca2+ channel current at nanomolar concentrations (i.e. 95 +/- 16% increase by 300 nM). T-type Ca2+ channel block was completely reversible with exception of the block by niguldipine. Our results indicate a variability of two orders of magnitude in potency of T-type Ca2+ channel block by the dihydropyridine derivatives investigated. It is speculated that the relation between the L- and T-type Ca2+ channel block may determine the therapeutic profile of a dihydropyridine derivative.

Topics: Animals; Brain Neoplasms; Calcium Channel Blockers; Cell Differentiation; Dihydropyridines; Glioma; Hybrid Cells; Membrane Potentials; Mice; Neuroblastoma; Rats; Tumor Cells, Cultured

Ca2+ channel currents were recorded in undifferentiated human neuroblastoma (SH-SY5Y) cells with the whole-cell patch-clamp technique, using 10 mM Ba2+ as charge carrier. Currents were only evoked by depolarizations to -30 mV or more positive (holding potential -80 mV), inactivated partially during 200 ms depolarizing steps, and were abolished by 150 microM Cd2+. Currents could be enhanced by Bay K-8644 and partially inhibited by nifedipine, suggesting that they arose in part due to activation of L-type Ca2+ channels. Currents were also inhibited by the marine snail peptide omega-conotoxin GVIA (omega-CgTx). At a concentration of 10 nM inhibition by omega-CgTx was reversible, but at higher concentrations blockade was always irreversible. Although current inhibition by nifedipine was maximal at 1 microM, supramaximal concentrations reduced the inhibitory actions of omega-CgTx in a concentration-dependent manner. Ca2+ channel currents evoked from a holding potential of -50 mV showed no inactivation during 200 ms depolarizations but declined in amplitude with successive depolarizing steps (0.2 Hz). Current amplitudes could be restored by returning the holding potential to -80 mV. Currents evoked from -50 mV were inhibited by nifedipine and omega-CgTx to a similar degree as those evoked from -80 mV. Our results indicate that undifferentiated SH-SY5Y cells possess L- and N-type Ca2+ channels which can be distinguished pharmacologically but cannot be separated by using depolarized holding potentials. Furthermore, these data suggest that nifedipine has a novel action to inhibit blockade of N-type channels by omega-CgTx.

Topics: Brain Neoplasms; Calcium Channel Blockers; Calcium Channels; Cell Differentiation; Dihydropyridines; Humans; Membrane Potentials; Neuroblastoma; omega-Conotoxin GVIA; Patch-Clamp Techniques; Peptides; Tumor Cells, Cultured