Studies of topoisomerase-specific antitumor drugs in human lymphocytes using rabbit antisera against recombinant human topoisomerase II polypeptide.

A complementary DNA fragment of the human DNA topoisomerase II gene was cloned into a T7 expression vector and overproduced in Escherichia coli. Rabbit polyclonal antibodies were raised against the recombinant topoisomerase II polypeptide which corresponds to the C-terminal one-third of human topoisomerase II polypeptide. Using the antiserum, DNA topoisomerase II levels were measured by immunoblotting human lymphocytes following phytohemagglutinin (PHA) stimulation. Our results showed that the intracellular topoisomerase II but not the topoisomerase I level increased in parallel with the entry of cells into proliferation. At least a 100-fold increase in topoisomerase II was observed at 50 h after PHA stimulation. As topoisomerase II levels increased upon PHA stimulation, DNA damage induced by teniposide (VM26) increased in parallel, as measured by both DNA synthesis inhibition and chromosomal aberrations. However, the damage induced by camptothecin also increased upon PHA stimulation, while the level of topoisomerase I remained relatively constant. Our results suggest that, in addition to cellular contents of topoisomerases, the state of cell proliferation is another important determinant of drug action.