[Effects of biorhythm regulator melatonin on DNA synthesis in short-term cultures of human malignant tumors].

The cytotoxic action of melatonin on DNA synthesis was studied in short-term human tumor tissue cultures. Twenty tumors (ovarian, renal, colorectal, gastric, skin, testicular, thyroid, adrenal gland, endometrial, cervical uterus ones, and melanoma) were isolated from patients at surgery. The effect of melatonin (concentrations of 5 x 10(-5) M to 5 x 10(-13) M on the level of 3H-thymidine incorporation into tumor tissue DNA (4-hour exposure) was evaluated. After exposure, 3H-thymidine was added to the medium for an hour. The quantity of DNA was determined in the hydrolysate by spectrometry; the level of 3H-thymidine incorporation into DNA was radiometrically evaluated by a scintillation counter. The quantity corresponding to 3H-thymidine incorporation per unit of DNA was determined. The control group and the melatonin-treated groups were compared by ANOVA. Melatonin inhibited DNA synthesis in 11 (55%) of the 20 tumors and was ineffective in 9 (45%) of the 20 ones. Melatonin-sensitive tumors were as follows: endometrial CA (33% vs 75% inhibition, p < 0.01), gastric CA (71% inhibition, p < 0.05), adrenal gland CA (38% inhibition, p < 0.01). Ovarian, cervical, skin CA and melanoma were unresponsive to melatonin. Renal cell CA, colonic and rectal CA were sensitive in some cases. In sensitive tumors, melatonin was effective even at concentrations of 5 x 10(-13) M to 5 x 10(-7) M. Thus, melatonin has an oncostatic effect on some human tumors in vitro occasionally at physiological concentrations.