Stability of a cisplatin-chondroitin sulfate A complex in plasma and kidney in terms of protein binding

Determination of unbound platinum concentrations in human plasma using ultrafiltration and precipitation methods

Quantification of the unbound portion of platinum (Pt) in human plasma is important for assessing the pharmacokinetics of the chemotherapeutic drug cisplatin. In this study, we sought to compare the recovery of unbound Pt using Nanosep® filters to 1) traditional filters (Centrifree®, Centrisart®, Amicon®) or trichloroacetic acid (TCA) protein precipitation, and 2) unbound, bound, and total Pt concentrations in clinical specimens. For the tested filters, the impact of 1) molecular weight cut-offs, 2) centrifugation force, and 3) total Pt concentration on Pt binding in human plasma was evaluated. Pt was quantified using inductively coupled-plasma mass spectrometry. In human plasma spiked with 0.9 μg/mL Pt, the percent of unbound Pt increased at higher centrifugation speeds. By comparison, the percent of unbound Pt was highest (42.1%) following TCA protein precipitation. When total Pt was ≤0.9 μg/mL, unbound Pt (∼20-30%) was consistent across filters. Conversely, when plasma was spiked with Pt exceeding 0.9 μg/mL, the percent of unbound Pt increased from 36.5 to 48% using ultrafiltration, compared to 63.4% to 79% with TCA precipitation. In patients receiving cisplatin-containing chemotherapy, the fraction of unbound Pt at concentrations exceeding 0.9 μg/mL ranged between 35 and 90%. Moreover, the unbound fraction of Pt in plasma correlated with the concentration of unbound (R2 = 0.738) and total Pt (R2 = 0.335). In summary, this study demonstrates that 1) the percent of unbound Pt is influenced by total and unbound Pt levels in vitro and in clinical specimens, and 2) ultrafiltration with Nanosep® filters is a feasible method for quantifying unbound Pt concentrations in human plasma.

Capillary electrophoretic methods in the development of metal-based therapeutics and diagnostics: new methodology and applications

In recent years, capillary electrophoresis (CE) has matured to a standard method in medicinal inorganic chemistry. More and more steps of the drug discovery process are followed by CE. However, not only the number of applications has steadily increased but also the variety of used methodology has significantly broadened and, as compared to a few years ago, a wider scope of separation modes and hyphenated systems has been used. Herein, a summary of the newly utilized CE methods and their applications in metallodrug research in the timeframe 2006-2011 is presented, following related reviews from 2003 and 2007 (Electrophoresis, 2003, 24, 2023-2037; Electrophoresis 2007, 28, 3436-3446). Areas covered include impurity profiling, quality control of pharmaceutical formulations, lipophilicity estimation, interactions between metallodrugs and proteins or nucleotides, and characterization and also quantification of metabolites in biological matrices and real-world samples.

Toxicodynamic evaluation of a cisplatin-chondroitin sulfate complex using a perfused kidney and human proximal tubular cells

Cisplatin (CDDP) is an anticancer drug. The clinical limitations associated with CDDP have stimulated the development of macromolecular drug-carrier systems, in attempts to decrease its toxicity. A complex (CDDP-CSA-23) between CDDP and chondroitin sulfate (CSA), a natural polysaccharide with a mean molecular weight of 23 kDa, proved to have the same anticancer activity as CDDP. A toxicodynamic study was performed on perfused kidneys to determine the effect of CDDP-CSA-23 on renal functions and the extent of platinum accumulation. The results showed that CDDP-CSA-23 attenuates the reduction in urine flow and creatinine clearance induced by CDDP. Moreover, significantly lower amounts of platinum were excreted into the urine in the case of CDDP-CSA-23, compared with CDDP alone. Meanwhile, CDDP-CSA-23 effectively retarded the rapid perfusion of platinum into kidney tissues, as occurs when CDDP is being perfused alone. The cytoprotective effects of CDDP-CSA on human proximal tubular (HK-2) cells were examined by measuring the growth of HK-2 cells in the presence of CDDP or CDDP-CSA-23. Interestingly, CDDP-CSA-23 was found to have a significantly reduced cytotoxicity, compared to CDDP. These results suggest that CDDP-CSA-23 greatly decreased the negative effects of CDDP on glomerular filtration and tubular transport in kidneys at early stages of its administration.

Spectroscopic studies of interactions of chondroitin sulfates with cisplatin

Complexation of cisplatin (CDDP) and chondroitin sulfate A (CSA) or C (CSC) has been reported to reduce the nephrotoxicity of CDDP. However the mechanism of interaction between CDDP and CSA or CSC was not known. In this study, spectroscopic analyses including NMR were carried out to examine the complexation interactions of CSA and CSC with CDDP. The time-dependent changes in the UV spectra indicate that CSA and CSC effectively complexes with CDDP in aqueous solution and that the reaction occurs subsequent to the hydrolysis of CDDP. The time-dependent change results measured by capillary electrophoresis showed that complexation of chondroitin sulfate (CS) followed first-order reaction kinetics and that the rate of CDDP hydrolysis in the complexation for both CSA and CSC was the same. These results suggested that the mechanism of complexation was a two-step process with monoaqua formation proved to be the first step, which was also the reaction rate controlling step. Moreover, NMR data suggested that the carboxylic and sulfate groups of CS played an important role in its interaction with CDDP.

Molecular-weight-dependent pharmacokinetics and cytotoxic properties of cisplatin complexes prepared with chondroitin sulfate A and C

In order to screen out an optimum complex for reducing the nephrotoxicity of cisplatin (CDDP), we investigated and compared CDDP-chondroitin sulfate complexes to CDDP in terms of in vivo pharmacokinetics and in vitro cytotoxicity. The polymeric carriers used in the study were chondroitin sulfate A (CSA, 4-sulfate) with mean molecular weights of 10 kDa (CSA-1) and 23 kDa (CSA-2), and chondroitin sulfate C (CSC, 6-sulfate) with mean molecular weights of 8 kDa (CSC-1) and 25 kDa (CSC-2). The resultant complexes (CDDP-CSA-1, CDDP-CSA-2, CDDP-CSC-1 and CDDP-CSC-2) were administered intravenously to rats. The obtained plasma concentration-time curves during the 3 h period studied for all complexes are biphasic. The plasma dispositions of complexes were dependent on the molecular sizes with urinary excretion as main elimination pathway. CDDP-CSA-1 and CDDP-CSC-1 were unable to effectively increase the plasma retention of platinum due to rapid renal excretion. Furthermore, CDDP-CSA-1 disappeared from plasma more quickly than CDDP-CSC-1. CDDP-CSA-2 and CDDP-CSC-2, with similar urinary excretion as CDDP, gave rise to approximately five and four-fold increase in AUC(0-3 h) values, respectively, than that was achieved with native CDDP treatment. Biodistribution was compared between CDDP-CSA-2 and CDDP-CSC-2. Both complexes effectively suppressed the extensive distribution of CDDP into most tissues, especially kidney. However, CDDP-CSC-2 showed less reduction effect than CDDP-CSA-2. In addition, a significantly higher accumulation in tumor tissue was found with the administration of CDDP-CSA-2 than CDDP. Moreover, CSA complexes displayed an IC(50) of 6 microM Pt-equivalents against SW4800 human colon cancer cells, similar to that of CDDP, whereas CSC complexes were less active than CDDP. These studies indicate that the complex prepared with CSA, which is greater than 20 kDa of molecular size, is superior to that of CSC, exhibiting improved pharmacokinetics and similar pharmacological activity to the native drug.