Structural Factors Affecting Binding of Platinum Anticancer Agents with Phospholipids: Influence of Charge and Phosphate Clamp Formation.

Abstract

We report a detailed NMR and DFT study of the interaction of polynuclear platinum anticancer agents (PPCs) with negatively charged phospholipids as a mechanism for their cellular uptake. The reactions of fully 15 N-labelled [{trans-PtCl(NH3 )2 }2 (μ-trans-Pt(NH3 )2 {NH2 (CH2 )6 NH2 }2 )]4+ (15 N-1, 1,0,1/t,t,t) and the dinuclear [{trans-PtCl(NH3 )2 }2 {μ-H2 N(CH2 )6 NH2 }]2+ (15 N-2, 1,1/t,t) with the sodium salt of 1,2-dihexanoyl-sn-glycero-3-phosphate (DHPA) were studied at 298 K, pH ≈5.4, by [1 H,15 N] HSQC 2D NMR spectroscopy. Both 15 N-1 and 15 N-2 form an initial mono-adduct in which the DHPA is coordinated via the phosphate O atom. For the dinuclear 15 N-2, coordination of a second DHPA, in two different orientations, leads to two conformers of the bifunctional adduct. For 15 N-1, coordination of the second DHPA allows the central {PtN4 } coordination unit to bind electrostatically to two additional DHPA molecules via phosphate clamp interactions, in an extended network. For both 1,0,1/t,t,t (1) and 1,1/t,t (2), equilibrium conditions are obtained more slowly (>35 h) than in the presence of phosphate (12 h) and in each case the rate constant for the first step of DHPA binding (kL ) is about 8 times higher than that for phosphate, whereas the rate constants for the reverse reactions are quite similar. Reaction of 15 N-1 with the sodium salt of 1,2-dihexanoyl-sn-glycero-3-[phosphatidyl-l-serine] (DHPS) showed only minor adduct formation via coordination to the N-donor atom of the phosphoserine group.