The reactions of cisplatin [cis-diamminedichloroplatinum(II), CDDP] with glutathione (GSH) and drug thiols were investigated at 37°C in 100 mM Tris-NO3, pH ∼7.4, using a clinically relevant concentration of CDDP (33 μM), a large excess of GSH (16.5 mM), and [NaCl] of 4.62 mM. The conditions were designed to mimic passage of CDDP through the cytosol. The reactions were studied by UV-absorption spectroscopy, high-pressure liquid chromatography (HPLC), and atomic absorption spectroscopy. The initial rates, detected by UV absorbance, confirmed that the reactions are first order in [CDDP]. The HPLC peak corresponding to CDDP was analyzed for platinum content by atomic absorption spectroscopy, which decreased exponentially with time, confirming that the reactions are first order in [CDDP] and allowing determination of the pseudo first order rate constants (k1). For reaction of the dichloro form of CDDP with GSH, the k1 value was ∼2.2 × 10-4 s-1 (t1/2 of ∼53 min), giving the second order rate constant value (k2) of ∼1.3 × 10-2 M-1 s-1. Reaction of a mixture of the aquated forms of CDDP with GSH gave a lower k1 value (∼0.9 × 10-4 s-1). Reaction of CDDP with sodium 2-mercaptoethanesulfonate (mesna) gave a k1 value of ∼1.8 × 10-4 s-1 (t1/2 of ∼65 min and k2 of ∼1.1 × 10-2 M-1 s-1). Reaction of CDDP with S-2-(3-aminopropylamino)ethanethiol (WR-1065) gave a k1 value of ∼12.0 × 10-4 s-1 (t1/2 of ∼10 min and k2 of ∼7.3 × 10-2 M-1 s-1). The relatively slow reaction rate of CDDP with GSH is consistent with the efficient DNA platination by CDDP in the presence of millimolar concentration of GSH in the cytosol.
ASJC Scopus subject areas
- Pharmaceutical Science