A human trophoblastic isozyme (lactate dehydrogenase-Z) associated with choriocarcinoma

A unique electrophoretic form of lactate dehydrogenase (LDH-Z), formerly observed in a choriocarcinoma cell line (JEG-3) and first-trimester placenta, has been shown to be the same as that produced in hydatidiform mole and term placenta. We have also observed LDH-Z in second-trimester placenta, choriocarcinoma metastasized to the liver, and five of five additional independently derived (from different patients) choriocarcinoma cell lines. The only exception to the production of LDH-Z in a choriocarcinoma was in the cell line BEWO, which was established from the same tumor as JEG-3. Since BEWO has been in culture for over 200 passages more than any of the independently derived lines, its lack of LDH-Z is viewed as being consistent with the loss of certain expressional characteristics upon such long-term culture. Analysis of JEG-3 subclones revealed the expression of LDH-Z to be independent of the products of the LDH-A genetic locus. Present data do not allow us to determine whether LDH-Z is the product of a newly discovered LDH locus or is a modified form of the product of the LDH-B locus. LDH-Z has not been observed in other human tissues, nor have we observed it in homogenates prepared from over 60 cell lines established from a wide variety of human neoplasms. We therefore conclude that LDH-Z is an isozyme associated with human choriocarcinoma and is indicative of the trophoblastic origin of the cells.