Mauldin S K, Plescia M, Richard F A, Wyrick S D, Voyksner R D, Chaney S G
Department of Biochemistry and Nutrition, School of Medicine, University of North Carolina, Chapel Hill 27599.
Biochem Pharmacol. 1988 Sep 1;37(17):3321-33. doi: 10.1016/0006-2952(88)90646-6.
Previous studies of platinum(II) compounds with bidentate leaving ligands have emphasized the contrast between the stability of the bidentate leaving ligand in vitro (T1/2 greater than 11 days in water) and the apparent reactivity of these bidentate platinum compounds in vivo. However, none of these studies actually measured the stability of these compounds in tissue culture medium (or in any other reaction mixture resembling in vivo conditions). The experiments described in this paper were designed to measure the stability and fate of (d,l-trans-1,2-diaminocyclohexane)malonatoplatinum(II) [Pt(mal)(trans-dach)] in RPMI-1640 tissue culture medium. The T1/2 for displacement of the malonate ligand in this medium was 9.5 hr at 37 degrees. Of the inorganic anions present in the medium, chloride accounted for the greatest displacement of the malonate ligand. However, at the concentrations with which it is found in tissue culture medium and in blood, bicarbonate was nearly as effective as chloride at displacing the malonate ligand. This observation is of particular significance because the bicarbonatoplatinum complex is unstable and the bicarbonate displacement reaction appears to represent a major non-enzymatic pathway for the formation of the biologically active aquated platinum complexes. At the concentrations with which they occur inside the cell, phosphates may play a similar role. Of the amino acids present in the medium, glutathione and the sulfur-containing amino acids were 50- to 400-fold more effective at displacing the malonate ligand than the other amino acids in RPMI-1640 medium. In the case of methionine, the reaction with Pt(mal)(trans-dach) was shown to be a direct displacement (SN2) reaction at physiological methionine concentrations. When Pt(mal)(trans-dach) was incubated at 37 degrees for 24 hr in RPMI-1640 medium, the major transformation products formed were (d,l-trans-1,2-diaminocyclohexane)methionineplatinum(II) (38%), other amino acid-platinum complexes (19%), and (d,l,-trans-1,2-diaminocyclohexane)dichloroplatinum(II) (14%). Eleven percent of the Pt(mal)(trans-dach) remained intact. Mass spectrometry and 1H-NMR indicated that the (d,l-trans-1,2-diaminocyclohexane)methionineplatinum(II) complexes that formed in RPMI-1640 medium consisted of approximately 60% of the bidentate mono-methionine complex coordinated to platinum at the sulfur and alpha-amino positions and 40% of the bis-methionine complex, presumably coordinated at the sulfurs.(ABSTRACT TRUNCATED AT 400 WORDS)
先前对带有双齿离去配体的铂（II）化合物的研究强调了双齿离去配体在体外的稳定性（在水中半衰期大于11天）与这些双齿铂化合物在体内的明显反应活性之间的差异。然而，这些研究均未实际测量这些化合物在组织培养基中（或在任何其他类似于体内条件的反应混合物中）的稳定性。本文所述的实验旨在测量（d，l-反式-1,2-二氨基环己烷）丙二酸铂（II）[Pt（mal）（反式-dach）]在RPMI-1640组织培养基中的稳定性和归宿。在该培养基中丙二酸配体的取代半衰期在37℃时为9.5小时。培养基中存在的无机阴离子中，氯离子对丙二酸配体的取代作用最大。然而，在组织培养基和血液中发现的浓度下，碳酸氢根在取代丙二酸配体方面几乎与氯离子一样有效。这一观察结果具有特别重要的意义，因为碳酸氢根铂络合物不稳定，碳酸氢根取代反应似乎代表了形成生物活性水合铂络合物的主要非酶途径。在细胞内存在的浓度下，磷酸盐可能起类似作用。培养基中存在的氨基酸中，谷胱甘肽和含硫氨基酸在取代RPMI-1640培养基中的丙二酸配体方面比其他氨基酸有效50至400倍。就蛋氨酸而言，在生理蛋氨酸浓度下，与Pt（mal）（反式-dach）的反应显示为直接取代（SN2）反应。当Pt（mal）（反式-dach）在RPMI-1640培养基中于37℃孵育24小时时，形成的主要转化产物为（d，l-反式-1,2-二氨基环己烷）蛋氨酸铂（II）（38%）、其他氨基酸-铂络合物（19%）和（d，l-反式-1,2-二氨基环己烷）二氯铂（II）（14%）。11%的Pt（mal）（反式-dach）保持完整。质谱和1H-NMR表明，在RPMI-1640培养基中形成（d，l-反式-1,2-二氨基环己烷）蛋氨酸铂（II）络合物约60%为双齿单蛋氨酸络合物，其硫和α-氨基位置与铂配位，40%为双蛋氨酸络合物，推测在硫原子处配位。（摘要截于400字）
