EFFECT OF METHOTREXATE ON CELL-PROLIFERATION IN DEVELOPING HAMSTER MOLAR TOOTH GERMS IN-VITRO

Amongst the most frequently used drugs for the treatment of acute lymp hoblastic leukaemia (ALL) belongs methotrexate (MTX), an inhibitor of pyrimidine (thymidine) synthesis. We examined effects of MTX on cell p roliferation during tooth morphogenesis in organ culture by exposing h amster molar tooth germs to 10(-7) to 10(-3) M MTX for 24 h. In the pr esence of serum, only the highest concentration of MTX (10(-3) M) indu ced a small, non-significant decrease in cell mass without histologica l changes but, unexpectedly increased uptake of [H-3]thymidine. In ser umless conditions increase in cell mass (dry weight) and incorporation of [H-3]thymidine was lower than in serum-supplemented conditions. Ex posure to MTX in serumless conditions reduced the increase in cell mas s even further without histological changes and, again, strongly enhan ced incorporation of [H-3]thymidine to the same proportion as measured in the serum-supplemented cultures exposed to MTX. The data suggest t hat only exposure to high levels of MTX reduces proliferation activity , shown by reduction in cell mass. The enhanced [H-3]thymidine uptake under MTX exposure was explained by blockage of the internal biosynthe sis of thymidine, by which action more radiolabel was taken up from th e medium. The data also suggest that serum contains (growth) factors t hat stimulate cell proliferation, thereby increasing cell mass and [H- 3]thymidine incorporation.