Development and validation of a method to determine the unbound paclitaxel fraction in human plasma

Efficacy and safety evaluation of albumin-bound paclitaxel chemotherapy in East Asian patients with gynecological tumors based on the degree of paclitaxel binding to patient plasma

Nab-PTX is a special dosage form of antitumor drug that is different from other injections. In order to explore the efficacy and safety of albumin-bound paclitaxel, we developed an analytical method with UPLC-MS/MS to quantify the total and free paclitaxel in plasma, and prospectively evaluate the impact of unbound fraction fu (%) on the prognosis and adverse reactions of patients with gynecological tumors. From 2020.10 to 2021.10, a total of 116 patients with gynecological tumors were included, application of albumin-bound paclitaxel combined with platinum chemotherapy drugs, the blood collection time is 18-30 h after nab-PTX intravenous infusion. The collection time and the start (end) time of intravenous drip are recorded correctly, and a high-precision and sensitive UPLC-MS/MS method for the simultaneous determination of total and free paclitaxel was established. With fu (%) = Cunbound/Ctotal as the evaluation index, the concentration of total paclitaxel and free paclitaxel were determined by UPLC-MS/MS. The value of fu (%) was closely related to clinical adverse reactions, neutropenia, thrombocytopenia, leukopenia and bone marrow suppression. Neurotoxicity was statistically remarkable (P up0.001), and fu (%) has a significant correlation with clinical efficacy (P up0.001). We have developed a highly precise, highly sensitive and specific UPLC-MS/MS method for the simultaneous determination of binding and free albumin-bound paclitaxel concentrations in patients' serum. In addition, we found that fu (%) could be used as the detection index. The higher the fu (%) was, the more taxol could be free, the more adverse reactions related to toxic events occurred in patients.

Randomized crossover pharmacokinetic study of solvent-based paclitaxel and nab-paclitaxel

PURPOSE

Abraxane (ABI-007) is a 130-nm albumin-bound (nab) particle formulation of paclitaxel, devoid of any additional excipients. We hypothesized that this change in formulation alters the systemic disposition of paclitaxel compared with conventional solvent-based formulations (sb-paclitaxel; Taxol), and leads to improved tolerability of the drug.

PATIENTS AND METHODS

Patients with malignant solid tumors were randomized to receive the recommended single-agent dose of nab-paclitaxel (260 mg/m(2) as a 30-minute infusion) or sb-paclitaxel (175 mg/m(2) as a 3-hour infusion). After cycle 1, patients crossed over to the alternate treatment. Pharmacokinetic studies were carried out for the first cycle of sb-paclitaxel and the first two cycles of nab-paclitaxel.

RESULTS

Seventeen patients were treated, with 14 receiving at least one cycle each of nab-paclitaxel and sb-paclitaxel. No change in nab-paclitaxel pharmacokinetics was found between the first and second cycles (P = 0.95), suggesting limited intrasubject variability. Total drug exposure was comparable between the two formulations (P = 0.55) despite the dose difference. However, exposure to unbound paclitaxel was significantly higher after nab-paclitaxel administration, due to the increased free fraction (0.063 +/- 0.021 versus 0.024 +/- 0.009; P < 0.001).

CONCLUSION

This study shows that paclitaxel disposition is subject to considerable variability depending on the formulation used. Because systemic exposure to unbound paclitaxel is likely a driving force behind tumoral uptake, these findings explain, at least in part, previous observations that the administration of nab-paclitaxel is associated with augmented antitumor efficacy compared with solvent-based paclitaxel.

Comparative in vitro degradation of the human hemorphin LVV-H7 in mammalian plasma analysed by capillary zone electrophoresis and mass spectrometry

The human hemorphin LVV-H7 (L32VVYPWTQRF41) is a hemoglobin-beta, -gamma, -delta or -epsilon chain derived cationic decapeptide of the micro-opioid receptor binding family. It exhibits potential pharmacological value relevant, for example, for blood pressure regulation, learning performance and Alzheimer's disease. The regulatory potency is strictly dependent on the length of the amino acid sequence which is sensitive towards proteinases from tissues and plasma. To analyse LVV-H7 in vitro degradation in mammalian plasma, a novel multi-component quantitative capillary zone electrophoretic (CZE) procedure was applied, combined with qualitative metabolite profiling by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). In all types of plasma, LVV-H7 was N-terminally truncated generating four metabolites (M1-M4) with an intact C-terminus: M1 (V33VYPWTQRF41), M2 (V34YPWTQRF41), M3 (Y35PWTQRF41) and M4 (W37TQRF41). In EDTA plasma these degradation products were detected exclusively, whereas in citrate and heparin plasma four further metabolites appeared resulting from additional C-terminal cleavage of the dipeptide R40F41: M5 (L32VVYPWTQ39), M6 (V33VYPWTQ39), M7 (V34YPWTQ39) and M8 (Y35PWTQ39). In the presence of selective proteinase inhibitors aminopeptidase M and angiotensin-converting enzyme (for N- and C-terminal truncation, respectively) were identified as plasma enzymes responsible for hemorphin degradation. Furthermore, striking inter-mammalian species distinctions were detected revealing strongly differing degradation velocities but similar metabolite patterns.

Development of a Physiology-Based Whole-Body Population Model for Assessing the Influence of Individual Variability on the Pharmacokinetics of Drugs

In clinical development stages, an a priori assessment of the sensitivity of the pharmacokinetic behavior with respect to physiological and anthropometric properties of human (sub-) populations is desirable. A physiology-based pharmacokinetic (PBPK) population model was developed that makes use of known distributions of physiological and anthropometric properties obtained from the literature for realistic populations. As input parameters, the simulation model requires race, gender, age, and two parameters out of body weight, height and body mass index. From this data, the parameters relevant for PBPK modeling such as organ volumes and blood flows are determined for each virtual individual. The resulting parameters were compared to those derived using a previously published model (P(3)M). Mean organ weights and blood flows were highly correlated between the two models, despite the different methods used to generate these parameters. The inter-individual variability differed greatly especially for organs with a log-normal weight distribution (such as fat and spleen). Two exemplary population pharmacokinetic simulations using ciprofloxacin and paclitaxel as model drugs showed good correlation to observed variability. A sensitivity analysis demonstrated that the physiological differences in the virtual individuals and intrinsic clearance variability were equally influential to the pharmacokinetic variability but were not additive. In conclusion, the new population model is well suited to assess the influence of individual physiological variability on the pharmacokinetics of drugs. It is expected that this new tool can be beneficially applied in the planning of clinical studies.

Quantification of [3H]docetaxel in feces and urine: development and validation of a combustion method

Most radiolabeled biological samples require extensive sample preparation to reduce quenching interference before quantification of radioactivity is possible. Clearly, a more rapid and simple method ensuring a constant count rate and optimal counting efficiency has important advantages. We report on the development and analytical method validation of a rapid and simple combustion method to quantify [3H]docetaxel excreted in human feces and urine. A 3-day validation procedure was performed; quality control (QC) samples, prepared in blank feces and urine, were combusted 5 times and aliquots of the produced tritiated combustion water were counted in a liquid scintillation counter. The validation runs demonstrated adequate precision (below 7.6%) across all QC levels. Sensitivity at the lowest QC level was excellent and recovery of radioactivity constant (ranging from 85 to 91.8%). Clinical applicability of the method was tested in a cancer patient receiving docetaxel and a tracer amount of [3H]docetaxel; during the first 72 h after [3H]docetaxel infusion, 60% of total radioactivity was excreted in the collected feces and urine, which is within the expected range. Combustion of tritiated feces and urine samples is a simple, rapid, sensitive, precise and reproducible method with high recovery. It can be applied to quantify [3H]docetaxel excretion after i.v. administration.

Binding studies of taxanes to human serum albumin by bioaffinity chromatography and circular dichroism

The binding to human serum albumin (HSA) of the antitumoural drug paclitaxel and of several structural analogues has been characterized by bioaffinity chromatography and circular dichroism. A ranking of the taxanes was obtained for their affinity to the protein by measuring their retention times on an albumin chromatographic column. This also allowed the calculation of the drug bound percentage. Affinity resulted significantly affected by the nature of the isoserinic side chain, the presence of the 1,14-carbonate moiety and the substituent at C-7, showing that the hydrophobicity of the drug is fundamental in the binding process. The analysis demonstrated that the organic solvent highly alters the interaction mechanism of taxanes to the protein and so the affinity results. Circular dichroism experiments supported this hypothesis. Furthermore, taxanes binding to the serum carrier was characterized by displacement chromatography, by adding into the mobile phase selected competitors, (S)-ibuprofen and valproic acid, that are known to bind to specific binding sites on HSA. These experiments established a non-cooperative binding mechanism.

Determination of unbound docetaxel and paclitaxel in plasma by ultrafiltration and liquid chromatography–tandem mass spectrometry

This work describes the development of a straightforward method for the determination of free docetaxel and paclitaxel in plasma. The separation of bound and unbound drug was performed with ultrafiltration. Different ultrafiltration devices were evaluated, especially regarding non-specific binding to the device. The most appropriate device for this application was selected and a procedure to counteract non-specific binding to the ultrafiltrate collection cup was developed. This consisted of a wash procedure with methyl t-butyl ether. A liquid/liquid extraction with methyl t-butyl ether was performed and samples were analysed with a previously developed liquid chromatography-tandem mass spectrometry procedure. The method used a Merck Purospher Star RP-18 column (55 mm x 2.0 mm, 3-microm particle size) and electrospray in the positive mode. A triple quadrupole instrument was used to monitor MRM transitions. Small modifications to this procedure were made to ensure adequate sensitivity. Within- and between-day reproducibility did not exceed 15% and accuracy ranged between 94.4 and 102.5%. The calibration range of the method was from 0.4 to 100 ng/ml both for paclitaxel and docetaxel. Finally, a fast and relatively simple method could be developed.

Application of solid-phase microextraction in the investigation of protein binding of pharmaceuticals

Protein-drug interactions of seven common pharmaceuticals were studied using solid-phase microextraction (SPME). SPME can be used in such investigations on the condition that no analyte depletion occurs. In multi-compartment systems (e.g. a proteinaceous matrix) only the free portion of the analyte is able to partition into the SPME fiber. In addition if no sample depletion occurs, the bound drug-free drug equilibria are not disturbed. In the present study seven pharmaceuticals (quinine, quinidine, naproxen, ciprofloxacin, haloperidol, paclitaxel and nortriptyline) were assayed by SPME. For quantitative purposes SPME was validated first in the absence of proteins. Calibration curves were constructed for each drug by HPLC-fluorescence and HPLC-UV analysis. SPME was combined to HPLC off-line, desorption occurring in HPLC inserts filled with 200 microL methanol. Binding of each drug to human serum albumin was studied independently. Experimental results were in agreement with literature data and ultrafiltration experiments, indicating the feasibility of the method for such bioanalytical purposes.

Altered Pharmacokinetics of Paclitaxel in Experimental Hepatic or Renal Failure

PURPOSE

The aim of this study was to investigate the effect of hepatic or renal insufficiency on the pharmacokinetics of paclitaxel in rats.

METHODS

Rats were treated with carbon tetrachloride (CCl4; 0.5 ml/kg) to induce hepatic failure or were subjected to 5/6 nephrectomy (5/6 Nx) to induce renal failure. Paclitaxel (3 mg/kg) was administered intravenously or intraportally. Testosterone 6beta-hydroxylase activity, which is a marker of CYP3A activity, was measured in rat liver microsomes from CCl4-treated or 5/6 Nx rats.

RESULTS

After paclitaxel was administered intravenously, total body clearance was significantly reduced by 73% and 34% relative to each control value in CCl4-treated and 5/6 Nx rats, respectively (control, 1.82+/-0.42 vs. CCl4-treated, 0.49+/-0.11; sham, 1.54+/-0.07 vs. 5/6 Nx, 1.01+/-0.12 L h(-1) kg(-1); mean+/-SE, n = 5 to 6). Testosterone 6beta-hydroxylase activity was reduced by 92% and 59% relative to each control value in rat liver microsomes from CCl4-treated and 5/6 Nx rats, respectively. After the intraportal administration of paclitaxel, apparent clearance was reduced by 85% relative to control value in rats with hepatic failure, while that in rats with renal failure was the same as the reduction in systemic clearance.

CONCLUSIONS

These results suggested that not only hepatic failure but also renal failure could modify the pharmacokinetics of paclitaxel in vivo.