Comparison of receptor-mediated endocytosis kinetics between wild-type t-PA and recombinant pamiteplase in isolated rat hepatocytes and liver cell plasma membranes.
1. Differences in receptor-mediated endocytosis kinetics between pamiteplase, an engineered t-PA, and an unmodified rt-PA were examined using liver cell plasma membranes and isolated rat hepatocytes. 2. Whereas the binding site of pamiteplase on hepatocytes was the same as that of rt-PA, the Kd of pamiteplase was 5.1-7.7 times larger than that of rt-PA, indicating a lower affinity of pamiteplase for the t-PA receptor. 3. ke for pamiteplase measured using parenchymal cells or non-parenchymal cells was slightly smaller than that for rt-PA, whereas kon for pamiteplase were much lower than that of rt-PA, suggesting that the interaction between pamiteplase and the receptor is slower than that of rt-PA because of its structural modification. 4. Therefore, the difference in drug disposition between pamiteplase and rt-PA is mainly due to the difference in the hepatic clearance caused by a change in the interaction rate between the ligand and its cell-surface receptor.
Oikawa
K
K
Drug Metabolism Laboratories, Yamanouchi Pharmaceutical Co., Ltd., Tokyo, Japan. oikawa@yamanouchi.co.jp
Watanabe
T
T
Higuchi
S
S
D000818:Animals; D001667:Binding, Competitive / Q000187:drug effects; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D004705:Endocytosis / Q000502:physiology*; D022781:Hepatocytes / Q000187:drug effects / Q000378:metabolism*; D066298:In Vitro Techniques; D007457:Iodine Radioisotopes; D007700:Kinetics; D008297:Male; D010960:Plasminogen Activators / Q000494:pharmacology*; D051381:Rats; D011916:Rats, Inbred F344; D011994:Recombinant Proteins / Q000494:pharmacology; D010959:Tissue Plasminogen Activator / Q000494:pharmacology*
D007457:Iodine Radioisotopes; D011994:Recombinant Proteins; D010960:Plasminogen Activators; D010959:Tissue Plasminogen Activator; C085027:pamiteplase