Cellular uptake of a novel cytotoxic agent, cryptophycin-52, by human THP-1 leukemia cells and H-125 lung tumor cells.

Cryptophycin (CP) is a newly developed anticancer agent isolated from the terrestrial cyanobacteria of the genus Nostoc. CP is a mitotic inhibitor, causing cells to accumulate in mitosis with the disappearance of intracellular microtubules. In this report, we studied the interaction and uptake of a new synthetic CP analog, CP-52, with 2 human tumor cell lines, THP-1 and H-125. In vitro colony-forming assay showed that CP-52 has antiproliferative activity against THP-1 and H-125 cell lines with IC50 of 0.1 ng/ml and 20 microg/ml, respectively; i.e., THP-1 cells are 200,000 times more sensitive to CP-52 than H-125 cells. The uptake of CP-52 by the target cells was carried out using tritiated CP-52 (3H-CP-52). The uptake of 3H-CP-52 by both THP-1 and H-125 cells was rapid, reaching a maximum within 20 min. Dissociation experiments showed that CP-52 interacts with the target cells irreversibly, presumably by binding to specific cellular sites with high affinity. With increasing doses of 3H-CP-52, the uptake was found to be saturable, reaching a steady state as the concentrations of 3H-CP-52 were raised to about 20 microg/ml. Under this condition, the maximal values of CP-52 uptake by THP-1 and H-125 cells was estimated to be 27 and 136 ng/10(5) cells, respectively. The uptake and accumulation of 3H-CP-52 with the target cells was effectively inhibited by prior treatment with unlabeled CP-52 and, to a lesser extent, vinblastine and taxol but not adriamycin, colchicine or mitomycin. In addition, the binding of 3H-CP-52 to purified tubulin was inhibited by vinblastine but not taxol. This finding suggested that CP-52 and taxol interact and bind to distinct regions of tubulin molecules. Further, it suggests that, in addition to tubulin, other intracellular and/or membrane components are involved in mediating the binding of CP-52.