Dual effect of tamoxifen, an anti-breast-cancer drug, on intracellular Ca(2+) and cytotoxicity in intact cells.
The effect of tamoxifen on Ca(2+) signaling and viability in Madin Darby canine kidney (MDCK) cells was investigated by using fura-2 as a Ca(2+) probe. Tamoxifen evoked a rise in cytosolic free Ca(2+) levels ([Ca(2+)](i)) concentration-dependently between 1 and 50 microM with an EC50 of 10 microM. The response was decreased by extracellular Ca(2+) removal. In Ca(2+)-free medium, pretreatment with 5 microM tamoxifen abolished the [Ca(2+)](i) increase induced by the endoplasmic reticulum Ca(2+) pump inhibitor thapsigargin (1 microM), but pretreatment with brefeldin A (50 microM; a Ca(2+) mobilizer of the Golgi complex), thapsigargin (an inhibitor of the endoplasmic reticulum Ca(2+) pump), and carbonylcyanide m-chlorophenylhydrazone (CCCP; a mitochondrial uncoupler), only partly inhibited tamoxifen-induced [Ca(2+)](i) increases. This suggests that tamoxifen released Ca(2+) from multiple pools. Addition of 3 mM Ca(2+) induced a [Ca(2+)](i) rise after pretreatment with 5 microM tamoxifen in Ca(2+)-free medium. Inhibiting inositol 1,4,5-trisphosphate formation with the phospholipase C inhibitor U73122 (2 microM) did not alter 5 microM tamoxifen-induced Ca(2+) release. The [Ca(2+)](i) increase induced by 5 microM tamoxifen was not altered by La(3+), nifedipine, verapamil, or diltiazem. Tamoxifen (1-10 microM) decreased cell viability in a concentration- and time-dependent manner. Tamoxifen (5 microM) also increased [Ca(2+)](i) in neutrophils, bladder cancer cells, and prostate cancer cells from humans and glioma cells from rats. Collectively, it was found that tamoxifen increased [Ca(2+)](i) in MDCK cells by releasing Ca(2+) from multiple Ca(2+) stores in a manner independent of the production of inositol 1,4, 5-trisphosphate and also by triggering Ca(2+) influx from extracellular space. The [Ca(2+)](i) increase was accompanied by cytotoxicity.
Jan
C R
CR
Department of Medical Education and Research, Kaohsiung Veterans General Hospital, Kaohsiung, Taiwan. crjan@isca.vghks.gov.tw
Cheng
J S
JS
Chou
K J
KJ
Wang
S P
SP
Lee
K C
KC
Tang
K Y
KY
Tseng
L L
LL
Chiang
H T
HT
D000818:Animals; D018931:Antineoplastic Agents, Hormonal / Q000494:pharmacology*; D001943:Breast Neoplasms / Q000188:drug therapy*; D002118:Calcium / Q000378:metabolism*; D002470:Cell Survival / Q000187:drug effects; D004285:Dogs; D004305:Dose-Response Relationship, Drug; D005260:Female; D006801:Humans; D008297:Male; D051381:Rats; D013629:Tamoxifen / Q000494:pharmacology*; D014407:Tumor Cells, Cultured
D018931:Antineoplastic Agents, Hormonal; D013629:Tamoxifen; D002118:Calcium