Mechanism of action and spectrum of cell lines sensitive to a doxorubicin-transferrin conjugate.
A transferrin-doxorubicin conjugate exhibited greatly increased cytotoxicity relative to unconjugated doxorubicin toward a variety of cultured tumor cell lines. An L929 cell line selected for doxorubicin resistance was as sensitive to the transferrin-doxorubicin conjugate as was the parental unselected line. Quantitative measurements of doxorubicin fluorescence in single L929 cells showed that uptake was similar in amount when cells were exposed to equivalent concentrations of doxorubicin presented either free or as the transferrin-doxorubicin conjugate. However, unconjugated drug fluorescence was distributed in membranes, cytoplasm and nucleus, whereas conjugate fluorescence was confined mainly to the cytoplasmic compartment. In as much as NADPH-dependent free radical formation is a known mechanism of doxorubicin cytotoxicity, localization in the vicinity of NADPH production might facilitate this cytotoxic pathway. Neither cytotoxicity nor uptake of the conjugate quantified by doxorubicin fluorescence was significantly blocked by excess free transferrin, and the conjugate was not concentrated in the plasma membrane at 4 degrees C. These findings suggest that conjugate internalization is not entirely dependent on transferrin receptor binding.
Lai
B T
BT
Department of Pathology and Laboratory Medicine, Staten Island University Hospital, NY 10305, USA.
Gao
J P
JP
Lanks
K W
KW
D000230:Adenocarcinoma / Q000188:drug therapy / Q000378:metabolism; D000818:Animals; D002295:Carcinoma, Transitional Cell / Q000188:drug therapy / Q000378:metabolism; D004317:Doxorubicin / Q000493:pharmacokinetics* / Q000627:therapeutic use; D004338:Drug Combinations; D019008:Drug Resistance, Neoplasm; D006801:Humans; D051379:Mice; D008856:Microscopy, Fluorescence; D014018:Tissue Distribution; D014168:Transferrin / Q000493:pharmacokinetics* / Q000627:therapeutic use; D014407:Tumor Cells, Cultured / Q000378:metabolism*
D004338:Drug Combinations; D014168:Transferrin; D004317:Doxorubicin