The inhibition of receptor-mediated and voltage-dependent calcium entry by the antiproliferative L-651,582.
L-651,582, 5-amino-[4-(4-chlorobenzoyl)-3,5-dichlorobenzyl]-1,2,3-triazole-4- carboxamide, an antiproliferative and antiparasitic agent previously shown to affect 45Ca2+ uptake into mammalian cells, inhibits both receptor-mediated and voltage-dependent calcium entry in well characterized in vitro systems. Indo 1 fluorescence measurements of cytosolic calcium levels indicate that the drug has no effect on the initial transient release of internal stores of calcium stimulated by fMet-Leu-Phe in rat polymorphonuclear leukocytes. It does decrease the levels maintained subsequently, however, indicating blockage of calcium influx through receptor-operated channels. L-651,582 also blocks the stimulation of leukotriene B4 (LTB4) production by fMet-Leu-Phe with an IC50 = 0.5 micrograms/ml equal to that for calcium entry inhibition. The LTB4 inhibition is likely due to calcium entry inhibition since L-651,582 does not inhibit calmodulin or enzymes producing arachidonate metabolites. L-651,582 also inhibits potassium-stimulated 45Ca2+ influx into GH3 cells with an IC50 of 0.5 microgram/ml, indicating a block of voltage-gated L-type calcium channels. Patch voltage clamp measurements of current through L- and T-type calcium in guinea pig atrial cells also indicate that L-651,582 is a calcium antagonist. Block of L-type calcium channels is voltage-dependent, and the apparent dissociation constant for the high affinity state is 0.2 micrograms/ml. The IC50 for block of T-type calcium channels is 1.4 micrograms/ml. The inhibition of cellular proliferation and the production of arachidonate metabolites by L-651,582 may be the result of the nearly equipotent block of receptor-operated and voltage-gated calcium channels.
Hupe
D J
DJ
Department of Enzymology, Merck Institute for Therapeutic Research, Rahway, New Jersey 07065.
Boltz
R
R
Cohen
C J
CJ
Felix
J
J
Ham
E
E
Miller
D
D
Soderman
D
D
Van Skiver
D
D
D000620:Aminoimidazole Carboxamide / Q000031:analogs & derivatives* / Q000494:pharmacology; D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology*; D001095:Arachidonic Acids / Q000378:metabolism; D002118:Calcium / Q000037:antagonists & inhibitors; D015220:Calcium Channels / Q000187:drug effects*; D006168:Guinea Pigs; D006325:Heart Atria / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D015640:Ion Channel Gating / Q000187:drug effects*; D009240:N-Formylmethionine Leucyl-Phenylalanine / Q000378:metabolism; D009504:Neutrophils / Q000378:metabolism; D051381:Rats; D014230:Triazoles
D000970:Antineoplastic Agents; D001095:Arachidonic Acids; D015220:Calcium Channels; D014230:Triazoles; D000620:Aminoimidazole Carboxamide; D009240:N-Formylmethionine Leucyl-Phenylalanine; C062058:carboxyamido-triazole; D002118:Calcium