Development of Hplc Conditions for Valid Determination of Hydrolysis Products of Cisplatin

Abstract

In water, the antineoplastic drug cisplatin, cis-[PtCl2(NH3)2] (1) hydrolyses slowly to the aqua complexes cis-[Pt(NH3)2Cl(H2O)]+ (2) and, to a small extent, cis-[Pt(NH3)2(H2O)2]2+ (3), which are thought to play an important role in the metabolism of cisplatin. HPLC is a useful technique for monitoring 2 and 3, but only if the components of the mobile phase used in the reverse phase HPLC technique are unreactive toward these aqua complexes under the conditions of the experiment. 15N Nuclear magnetic resonance (NMR) with samples highly enriched (>98%) in 15N has been used to check the reactivity of 2 and 3 toward substances commonly used as components of the mobile phase. The results reported herein indicate that acetonitrile, often used as an organic modifier, reacts readily with 2 and 3. Methanol, also commonly employed, is much less reactive. Carboxylic acids RCO2H (R = CH3, H, CF3), which are frequently used to adjust pH of the mobile phase, also react readily with 2 and 3. Trifluoromethanesulfonic acid ("triflic acid"), CF3SO3H, is unreactive. Neither hexanesulfonic acid nor sodium dodecyl sulfate (SDS), used as "ion-pairing agents", reacts significantly with 2 or 3 under the experimental conditions, but SDS gives better peak separation. Commercial SDS must, however, be purified from chloride contamination. From our studies, optimal conditions for HPLC separation of 1, 2, and 3, with a C18 stationary phase at 37 degrees C, require an aqueous mobile phase with 3% v/v methanol, 0.05 mM SDS, and pH 2.5 (adjusted with triflic acid). This technique was then used to measure levels of 1, 2, and 3 in ultrafiltered serum after incubation for various times with cisplatin at 37 degrees C.