Studies of methotrexate‐induced limb dysplasias utilizing a 51chromium release assay

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Abstract
The folate antagonist methotrexate (MTX), widely used in chemotherapy, is a well‐documented teratogen. However, the mechanism by which it exerts its effects is still unclear. Specifically, we have examined the cytotoxicity of MTX in vivo and in vitro and have looked at the relationship between cytotoxicity and teratogenesis. The chick embryo was utilized to examine the effects of the drug administered to carefully staged embryos. Embryos were exposed at stages 18–22 and examined on day 11 of incubation. Wings were malformed in a stage‐dependent manner while legs were affected similarly at each stage used. A modification of the 51chromium‐release assay was used to test the toxicity of MTX to limb cells in vitro. None of the tissues tested showed measurable toxicity in vitro even though the drug kills cells in vivo, thereby suggesting that MTX may be metabolized differently in vitro. Malformations induced by MTX do not seem to be due to changes in the amount of cell death taking place in the limb but may be caused by a transient inhibition of cell division.