Chemical synthesis and biological activity of a novel fluorescent etoposide derivative

Abstract

The antineoplastic activity of etoposide resides in its ability to poison the nuclear enzyme DNA topoisomerase II (topo II). The factors that control the cellular entry and subcellular distribution of etoposide remain poorly understood. Therefore, we have synthesized a novel fluorescence-labeled etoposide (Bodipyetoposide) by coupling 4,4-difluoro-5,7-dimethyl-4-bora-3a, 4a-diaza-s-indacene-3-propionylethylenediamine (Bodipy) to 4'-benzyloxycarbonyl-4'-demethylepipodophyllotoxin beta-D-glucopyranoside, a precursor of etoposide. Bodipy-etoposide retained the ability to stabilize topo II-DNA covalent complexes in isolated nuclei, although it was significantly less potent and efficacious than etoposide. The growth inhibitory activity of Bodipy-etoposide was also approximately 200-fold less than that of etoposide in human leukemia K562 and DU-145 prostatic carcinoma cells. Nonetheless, etoposide-resistant K/VP.5 and K/VP.5-1 leukemia cells were cross-resistant to Bodipy-etoposide compared with parental K562 cells. Analysis by flow cytometry revealed a concentration-dependent Bodipy-etoposide cell association with no significant difference in drug association in the etoposide-resistant cell lines relative to the parental K562 cells. Using confocal laser scanning microscopy, we found significant cytoplasmic perinuclear localization of Bodipy-etoposide. Thus, Bodipy-etoposide displays promise as a tool to probe the factors controlling entry and subcellular distribution of etoposide-like compounds in live cells.