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.