dihydropyridines and Adrenal-Cortex-Neoplasms

Blockade of a mineralocorticoid receptor is a clinically useful approach to the prevention of cardiovascular disease. The present study was designed to evaluate the effect of azelnidipine, a unique dihydropyridine Ca(2+) channel blocker, on aldosterone production in the human adrenocortical cell line NCI-H295R. Azelnidipine inhibited angiotensin II- and KCl-induced expression of steroid 11beta-hydroxylase, steroid 18-hydroxylase, and the alpha1H subunit of the T-type Ca(2+) channel, and suppressed steroid biosynthesis in H295R cells by the same amount as efonidipine. On the basis of these findings, azelnidipine appears to suppress steroid biosynthesis in H295R cells beyond the blockade of L-type calcium channels.

Topics: Adrenal Cortex Neoplasms; Adrenocortical Carcinoma; Aldosterone; Angiotensin II; Azetidinecarboxylic Acid; Calcium Channel Blockers; Calcium Channels, L-Type; Calcium Channels, T-Type; Cell Line, Tumor; Cytochrome P-450 CYP11B2; Dihydropyridines; Gene Expression Regulation; Humans; Nitrophenols; Organophosphorus Compounds; Potassium Chloride; Steroid 11-beta-Hydroxylase

In this report we use both whole cell and perforated patch clamp recording techniques to characterize calcium and potassium channels in Y-1 adrenocortical cells in order to assess their responsiveness to ACTH. Both transient and long-lasting components of an inward calcium current were identified which were similar to T and L-type Ca2+ currents. With Ba2+ as the charge carrier, the transient current activated at voltages more hyperpolarized than -50 mV with V1/2 for activation at -78.1 mV, and for steady state inactivation at -52.3 mV. The L-type current activated at -20 mV, with a V1/2 for activation at -29.9 mV and steady state inactivation at -44.2 mV. Under perforated patch conditions the response was shifted to more depolarized voltages. Both currents were responsive to agents which usually affect T- or L-type Ca2+ currents. The transient current was completely blocked by 50 microM lanthanum or 200 microM nickel and partially blocked by 300 mM amiloride. Cadmium (100 microM) and nifedipine (300 nM) completely blocked the long-lasting current while omega-conotoxin GVIA (1992 nM) inhibited the current by only 20-25%. The agonist, Bay K 8644 was stimulatory at 50 nM. Both transient and sustained outward potassium currents similar to A-type and delayed rectifier currents, respectively, were present. The transient current demonstrated fast activation at voltages more positive than -10 mV, inactivation with continued depolarization and steady state inactivation at V1/2 = -50 mV. The sustained current activated rapidly and had minimal inactivation with continued depolarization. The transient current was blocked by 5 mM 4AP and the sustained by 25 mM TEA. While Y-1 cells contain both calcium and potassium currents similar to those found in other adrenocortical cells, none of the currents were affected by ACTH or AII, secretagogues which stimulate steroidogenesis. These data, combined with the inability of both Ca2+ and K+ channel blockers to alter ACTH-induced steroidogenesis as reported earlier, suggests that neither calcium nor potassium currents are responsive to ACTH in Y-1 cells.

Topics: Adrenal Cortex; Adrenal Cortex Neoplasms; Adrenocorticotropic Hormone; Angiotensin II; Animals; Calcium Channel Blockers; Calcium Channels; Dihydropyridines; Electric Stimulation; Electrophysiology; Mice; omega-Conotoxin GVIA; Patch-Clamp Techniques; Peptides; Potassium Channel Blockers; Potassium Channels; Tumor Cells, Cultured

P-Glycoprotein (Pgp), product of the mdr-1 gene, is a 130- to 180-kDa plasma membrane phosphoglycoprotein which mediates multidrug resistance in cell culture by increasing efflux of the natural product chemotherapeutic agents. High levels of expression of mdr-1/Pgp are found in both the normal adrenal and adrenocortical cancers. By RNA in situ hybridization the expression in adrenocortical cancer is shown to be widely distributed. The present study demonstrates that decreased drug accumulation mediated by mdr-1/Pgp can be overcome by clinically achievable concentrations of mitotane (o,p'-DDD). The increase in drug accumulation with the addition of mitotane is due at least in part to a decrease in drug efflux and results in an increase in cytotoxicity when agents of the natural product class are used. This effect is observed in cells with a broad range of mdr-1/Pgp expression, including levels comparable to those found in most adrenocortical cancers. Similar increases in drug accumulation can be demonstrated in an unselected adrenocortical cancer cell line that expresses mdr-1/Pgp. The finding that multidrug resistance mediated by mdr-1/Pgp can be reversed by mitotane provides a rational basis for exploring the use of mitotane in combination with natural product chemotherapeutic agents in adrenocortical cancer.

Topics: Adrenal Cortex Neoplasms; Affinity Labels; Antineoplastic Agents; ATP Binding Cassette Transporter, Subfamily B, Member 1; Azides; Cell Survival; Dactinomycin; Dihydropyridines; Drug Resistance; Gene Expression; Humans; Membrane Glycoproteins; Mitotane; Nucleic Acid Hybridization; RNA, Messenger; Tumor Cells, Cultured; Vinblastine