Cisplatin, hydrolysis

Platinum speciation using IPC-ICP-MS has been achieved by Zhao et al. [50], An ODS C18 column and 1-heptanesulfonate ion-pairing reagent at pH 2.6 were used to separate the metabolites of cisplatin and cisplatin hydrolysis products. The low pH was required in order to retain thiol containing complexes. All complexes were resolved and urine and blood samples were analyzed by the speciation method. 

The time-dependence of the [1H,15N] 2D-NMR spectra can also be used to determine the hydrolysis rates for each individual chloride ligand in the dichloride complex and in the monoaqua monochloro complex, by fitting the curves of the concentration changes of each species with time [14], The NMR spectrum of 15N-cisplatin in water at 310 K for 40 h (at equilibrium) contains [1H,15N] resonances assignable to unreacted cisplatin, the monoaqua and diaqua adducts in a ratio of 0.64 0.35 0.01, respectively, from which an equilibrium constant of 2.72 for the first stage of cisplatin hydrolysis was calculated [13]. 

Figure 4 Hydrolysis scheme for cisplatin-based anticancer agents. Where L = U = NH3 cisplatin is indicated. When L = NH3 and V = 2-picoline or cha the rates of aquation of the trans-chloride ligands are different.

Fig. 2. Ligand substitution as a prodrug strategy for metallochem-otherapeutics (a) general scheme of prodrug activation by ligand substitution hydrolysis of a metal—halide bond is a typical activation pathway of metal-based anticancer drugs, as exemplified by the activation of cisplatin (b) and a ruthenium—arene complex (c).

The bifunctional amine-tethered ruthenium(II) arene complexes [Ru(r6 ti1-C6H5CH2(CH2)i1NH2)C12] (n = 1,2) (13a,b) show two consecutive hydrolysis steps to yield the mono- and bis-aqua complexes (64). At extracellular chloride concentrations, the majority of the complexes could be expected to be present as the mono-aqua adduct. Equilibrium constants were determined for both steps (for 13b, Ki = 145 mM K2 = 5.4 mM) and found to be considerably higher than those of cisplatin, which also has two reactive sites available. 

The conversion of the monofunctional adducts into bifunctional lesions depends drastically on the structure of the Pt drug. Obviously, Pt compounds exhibiting trans geometry form different bisadducts than cisplatin and hence, a different spectrum of antitumor activity is expected. Mechanistically, the formation and possible isomerization of bisadducts are not well understood. The assumption that hydrolysis of the second leaving group controls the formation of bisadduct may be an oversimplification. Studies with model compounds as well as with oligonucleotides have indicated that a certain nucleobase may be a powerful nucleophile toward Pt(II) if spatially in a correct position. Unfortunately, our knowledge on these interactions is at present very limited. 

Rate constants determined during the reaction of cisplatin with DNA. b kla corresponds to the hydrolysis of CL trans to the c-CeHnNH2, and kib to the hydrolysis of Cl" trans to NH3. 

This route gives a much better yield and a purer compound than when K2[PtCl4] is treated with ammonia directly. A disadvantage, however, is the necessity to use silver salts (usually nitrate) with overnight stirring, resulting in the possibility of side products formed by hydrolysis of the intermediate aqua species cis-[Pt(NH3)2(H20)2]2+.12 We here present a rapid and facile one-step synthesis of cisplatin. The experimental conditions are based on Lebedinsky s method,8 slightly modified as specified. 

Fig. 6. Hydrolysis scheme of cisplatin the final dimerization (or even trimerization) occurs only at high pH and in concentrated solutions8,35)...

So, in aqueous solution cisplatin will loose Cl-, and an aqua or/and hydroxo (at high pH) ligand becomes coordinated. In the body, the Cl- concentration outside cells is rather high (about 100 mM), and therefore hydrolysis is largely prevented there. Inside cells, however, the Cl- concentration is about 4 mM, promoting the hydrolysis process. According to calculations by Martin35), the aquated species in the body fluids is present only for a few percent, whereas it amounts to about 50% of the total present inside the cell. 

Studies of cisplatin bound to DNA have also been reported by others. Eastman111,112) has used radiolabeled PtCl2(en) to detect and quantify the adducts after enzymatic hydrolysis. Johnson113,114) has used an acid-catalyzed depurination followed by electrophoresis. Rahn115) used radiolabeled platinum compounds for detection, whereas Olinsky and Walter116) have used the SnCl2 method to quantify the amounts of the various cisplatin-DNA adducts. 

P. Shearan, J. M. F. Alvarez, N. Zayed, and M. R. Smyth, HPI separation of cisplatin and its hydrolysis products on aluminudi and application to studies of their interaction with cysteine, Bio [ med. Chromatogr., 4 78 (1990). 

Gold(III) organometallics are isoelectronic with cisplatin-like Ptn complexes. For example, complex 10 hydrolyses in water [123] and has shown activity in human tumour xenograft models [124]. However, its mechanism of action is different from that of cisplatin [124,125]. The role of hydrolysis as an activation step for this class of compounds is not yet clear. 

The mechanism of action of cisplatin is believed to involve activation via hydrolysis inside cells where the Cl- concentration is much lower (ca. 4 him) than outside cells (ca. 100 him) [10]. Ptn-OH2 bonds are more reac-... 

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