Kinetic and thermodynamic characterization of camptothecin hydrolysis at physiological pH in the absence and presence of human serum albumin

Abstract

To accurately derive the kinetic and thermodynamic parameters governing the hydrolysis of the lactone ring at physiological pH, a derivative spectrophotometric technique was used for the simultaneous estimation of lactone and carboxylate forms of camptothecin (CPT). The hydrolysis of the CPT-lactone and the lactonization of CPT-carboxylate at 310.15 K followed a first-order decay with apparent rate constants equal to 0.0279 ± 0.0016 min −1 and 0.0282 ± 0.0024 min −1 , respectively. The activation energy associated with the hydrolysis of the CPT-lactone and the lactonization of the CPT-carboxylate as calculated from the Arrhenius equation was 89.18 ± 0.84 and 86.49 ± 2.7 kJ mol −1 , respectively. The enthalpy and entropy of the thermodynamically favored hydrolysis reaction were on average 10.49 kJ mol −1 and 48.00 J K −1 mol −1 , respectively. The positive enthalpy and entropy values of the CPT-lactone hydrolysis indicate that the reaction is endothermic and entropically driven. The stability of CPTlactone in the presence of human serum albumin (HSA) was also analyzed. Notwithstanding the much faster hydrolysis of the CPT-lactone in the presence of HSA at various temperatures, the energy of activation was determined to be similar to the one estimated in the absence of HSA, suggesting that HSA does not catalyze the hydrolysis reaction, but it merely binds, sequesters, and stabilizes the CPT-carboxylate species. C 2009 Wiley Periodicals, Inc. Int J Chem Kinet 41: 704-

Thermodynamic Studies and Loading of 7-Ethyl-10-hydroxycamptothecin into Mesoporous Silica Particles MCM-41 in Strongly Acidic Solutions

“…[1][2][3][4][5][6][7] Their therapeutic promise is exemplified by the variety of malignancies that have shown promise for treatment and the fact that two analogues, Topotecan and Irrinotecan, have already been approved for clinical use by the FDA. 8,9 The camptothecin analog 7-ethyl-10-hydroxy-camptothecin (SN38) is in fact the potent biologically relevant moiety of the Irrinotecan prodrug, but its very low solubility precluded its efficient pharmaceutical development.…”

Kinetic and thermodynamic analysis of 9‐nitrocamptothecin hydrolysis at physiological pH in the presence and absence of human serum albumin

“…In our recent publications, we have shown that firstderivative excitation spectroscopy is capable of simultaneously quantifying lactone and carboxylate species during camptothecin hydrolysis [35,36]. As reported in the literature [38,39] and as we have found in our Results are reported as the average values and standard uncertainties calculated from three independent experiments.…”

“…These results are somewhat different when compared to the CPT hydrolysis, that is, E a of CPT alone and in the presence of HSA was 89.18 and 80.66 kJ mol −1 , respectively. In addition, to the smaller difference in the energy of activation, the CPT hydrolysis in the presence of HSA was 100% regardless of the temperature of the reaction [36]. The role of HSA in 9NC hydrolysis was further investigated by fluorescence quenching measurements in an attempt to gain further insight into the disproportionally increased hydrolysis of 9NC at physiological temperatures.…”

“…Furthermore, it is reported that in the presence of human serum albumin (HSA), CPT converts to inactive carboxylate form at a much faster rate than when dissolved in phosphate-buffered saline (PBS) of physiological pH [30]. Several reports have studied the hydrolysis kinetics of the camptothecin and its analogues at physiological pH and temperature [31][32][33][34][35][36], but to our knowledge the kinetics and thermodynamics of the hydrolysis reaction of 9NC has not yet been reported.…”

“…In this work, we have developed a real-time nonperturbing method based on first derivative UV spectroscopy for the simultaneous determination of nonequilibrium concentrations of 9NC lactone and 9NC carboxylate species at different temperatures in PBS and in the presence of HSA [35,36]. The thermodynamics of the 9NC hydrolysis was supplemented with protein affinity studies conducted at physiological temperature, thus providing a scientific explanation to the facilitated hydrolysis of the 9NC compound in the presence of HSA.…”