Reversible and irreversible interactions of a cisplatin analog bearing a 1,2-diphenylethylenediamine ligand with plasma and plasma proteins in vitro.
The cisplatin analog [meso-1,2-bis(2,6-dichloro-4-hydroxyphenyl) ethylenediamine]dichloroplatinum(II) [PtCl2(1)], by virtue of its estrogenic 1,2-diphenylethylenediamine ligand 1, was intended to function as a cytotoxic estrogen. This article reports on the reversible and irreversible interactions of this compound with plasma and plasma proteins in vitro. At 37 degrees C [PtCl2(1)] is > 99% reversibly bound to proteins in plasma. At 0 degree C [PtCl2(1)] reversibly binds to albumin at specific binding sites not shared by 1. By use of HPLC the in vitro half-life of total [PtCl2(1)] in plasma was found to be 35 min at 37 degrees C, which is approximately 1/3 the half-life reported for cisplatin under similar conditions. To understand this decreased stability, irreversible reactions of [PtCl2(1)] with albumin and plasma globulins were investigated. The reaction rate of [PtCl2(1)] with albumin is independent of the protein concentration and is comparable to the rate of the first Pt-Cl hydrolysis reaction. Thus, [PtCl2(1)], like cisplatin, reacts irreversibly with albumin through a solvent-assisted SN2 substitution pathway. Because the hydrolysis rate for [PtCl2(1)] is 40% slower than for cisplatin, irreversible reactions of [PtCl2(1)] with albumin cannot account for the decreased stability of the compound in plasma. alpha-Globulins undergo substitution reactions with [PtCl2(1)] by both solvent-assisted and direct SN2 pathways. The half-life of [PtCl2(1)] in the presence of alpha-globulins at concentrations normally present in plasma (6-16 g/liter) is from 41 to 22 min.(ABSTRACT TRUNCATED AT 250 WORDS)
Bednarski
P J
PJ
Lehrstuhl für Pharmazeutische Chemie II, Fakultät Chemie-Pharmazie, Universität Regensburg, Germany.
Kratochwil
N A
NA
Otto
A M
AM
D000510:Alpha-Globulins / Q000378:metabolism; D000970:Antineoplastic Agents / Q000378:metabolism*; D001798:Blood Proteins / Q000378:metabolism*; D005029:Ethylenediamines / Q000097:blood; D006801:Humans; D007700:Kinetics; D009944:Organoplatinum Compounds / Q000097:blood / Q000378:metabolism*; D011485:Protein Binding; D012710:Serum Albumin, Bovine / Q000378:metabolism
D000510:Alpha-Globulins; D000970:Antineoplastic Agents; D001798:Blood Proteins; D005029:Ethylenediamines; D009944:Organoplatinum Compounds; C078283:(1,2-bis(2,6-dichloro-4-hydroxyphenyl)ethylenediamine)dichloroplatinum (II); D012710:Serum Albumin, Bovine; C007305:1,2-dianilinoethane