Tracking the elusive antiestrogenic effect of melatonin: a new methodological approach.
OBJECTIVE
Detection of the antiestrogenic effect of melatonin on various breast cancer cell lines and its dependence of the differential expression of estrogen receptors (ERalpha and ERbeta) and melatonin receptors (mt1 and RZRalpha).


METHODS
Dose-response curves of estradiol were determined in 6 different breast cancer cell lines using a colorimetric proliferation assay in the absence or presence of various melatonin concentrations.


METHODS
In order to detect the minor growth inhibitory effect of melatonin, a simple yet novel approach was employed: instead of incubating cells at single estradiol-concentrations at increasing melatonin levels, breast cancer cells were grown in microwell-plates for 4 days at increasing concentrations of estradiol (10(-12)M - 10(-10)M) in the absence or presence of melatonin (10(-9)M - 10(-8)M). Cell number was determined using Alamar blue and colorimetry. RT-PCR was performed for the expression of ERalpha, ERbeta, RZRalpha and mt1.


RESULTS
Melatonin at concentrations of 10(-9)M and 5 x 10(-9)M shifted the dose-response curves of estradiol to higher concentrations. Responsiveness to melatonin depended on expression of ERalpha but not on ERbeta. mRNA of ERbeta was not detectable in the breast cancer cell lines used. Only small amounts of mt1 transcripts were detectable in MCF-7 cells of one source. In MCF-7 cells transfected with the mt1 gene and in an ovarian cancer cell line mt1 was expressed at significant levels. RZRalpha was expressed in all tested cell lines at different amounts.


CONCLUSIONS
The growth of all ERalpha-positive breast cancer cell lines can be inhibited by melatonin. The effect in most cell lines is weak yet clearly reproducible. RZRalpha clearly contributes to the growth inhibitory effect of melatonin.
Girgert
Rainer
R
Dept. of Gynecology and Obstetrics, University of Ulm, Prittwitzstrasse 43, D-89075 Ulm, Germany. rainer.girgert@medizin.uni-ulm.de
Bartsch
Christian
C
Hill
Steven M
SM
Kreienberg
Rolf
R
Hanf
Volker
V
D000276:Adjuvants, Immunologic / Q000494:pharmacology*; D001943:Breast Neoplasms; D002455:Cell Division / Q000187:drug effects; D045744:Cell Line, Tumor / Q000166:cytology / Q000187:drug effects / Q000502:physiology; D004347:Drug Interactions; D004958:Estradiol / Q000494:pharmacology*; D047628:Estrogen Receptor alpha; D047629:Estrogen Receptor beta; D005260:Female; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D006801:Humans; D008550:Melatonin / Q000494:pharmacology*; D057094:Nuclear Receptor Subfamily 1, Group F, Member 1; D018160:Receptors, Cytoplasmic and Nuclear; D011960:Receptors, Estrogen / Q000235:genetics; D044094:Receptors, Melatonin / Q000235:genetics; D018168:Receptors, Retinoic Acid / Q000235:genetics; D015534:Trans-Activators
D000276:Adjuvants, Immunologic; D047628:Estrogen Receptor alpha; D047629:Estrogen Receptor beta; D057094:Nuclear Receptor Subfamily 1, Group F, Member 1; D018160:Receptors, Cytoplasmic and Nuclear; D011960:Receptors, Estrogen; D044094:Receptors, Melatonin; D018168:Receptors, Retinoic Acid; D015534:Trans-Activators; D004958:Estradiol; D008550:Melatonin