LC/MS evaluation of metabolism and membrane transport of bombesin peptides

Combined image guided monitoring the pharmacokinetics of rapamycin loaded human serum albumin nanoparticles with a split luciferase reporter

Imaging guided techniques have been increasingly employed to investigate the pharmacokinetics (PK) and biodistribution of nanoparticle based drug delivery systems. In most cases, however, the PK profiles of drugs could vary significantly from those of drug delivery carriers upon administration in the blood circulation, which complicates the interpretation of image findings. Herein we applied a genetically encoded luciferase reporter in conjunction with near infrared (NIR) fluorophores to investigate the respective PK profiles of a drug and its carrier in a biodegradable drug delivery system. In this system, a prototype hydrophobic agent, rapamycin (Rapa), was encapsulated into human serum albumin (HSA) to form HSA Rapa nanoparticles, which were then labeled with Cy5 fluorophore to facilitate the fluorescence imaging of HSA carrier. Meanwhile, we employed transgenetic HN12 cells that were modified with a split luciferase reporter, whose bioluminescence function is regulated by Rapa, to reflect the PK profile of the encapsulated agent. It was interesting to discover that there existed an obvious inconsistency of PK behaviors between HSA carrier and rapamycin in vitro and in vivo through near infrared fluorescence imaging (NIFRI) and bioluminescence imaging (BLI) after treatment with Cy5 labeled HSA Rapa. Nevertheless, HSA Rapa nanoparticles manifested favorable in vivo PK and tumor suppression efficacy in a follow-up therapeutic study. The developed strategy of combining a molecular reporter and a fluorophore in this study could be extended to other drug delivery systems to provide profound insights for non-invasive real-time evaluation of PK profiles of drug-loaded nanoparticles in pre-clinical studies.

Simultaneous determination of five novel luteinizing hormone-releasing hormone antagonists by LC-MS and pharmacokinetics in rats following cassette dosing

Long acting luteinizing hormone-releasing hormone (LHRH) antagonists designed to be protease-resistant were a series of novel decapeptides structurally similar to LHRH. In the present work, a high-throughput method based on a LC-MS/MS has been developed for the simultaneous determination of pharmacokinetics of five LHRH antagonists in rat via cassette dosing. The method was performed under selected reaction monitoring (SRM) in positive ion mode. The analytes were extracted from rat plasma by liquid-liquid extraction with acetonitrile. Chromatographic separation of the analytes was successfully achieved on a Hypersil Gold (100mm×2.1mm, 3μm) using a mobile phase composed of acetonitrile-water (30:70) containing 0.05% (v/v) formic acid. The result showed good linearity and selectivity were obtained for all antagonists. The limits of quantification of the five LHRH antagonists were from 5 to 10ng/mL. The average extract recoveries in the rat plasma were all over 72%. The intra-day and inter-day precisions (R.S.D. %) were all within 10% and the accuracy was ranged from 92.54 to 109.05%. This method has been successfully applied to the pharmacokinetic studies of the five LHRH antagonists. The results indicated that the plasma drug concentrations versus time curves after intravenous injection of five antagonists via cassette dosing were all fitted to a two-compartment model. The pharmacokinetic parameters of five LHRH antagonists suggested that LY616 could be the more stable candidate drugs and optimized as the candidate drug for further study. Our studies enabled high-throughput rapid screening for pharmacokinetic assessment of new peptide candidates, and provided abundant information on the metabolic properties of these LHRH antagonists.

Rational design of matrix metalloproteinase-13 activatable probes for enhanced specificity

Because of the important roles that matrix metalloproteinases (MMPs) play in tumor invasion and metastasis, various activatable optical probes have been developed to visualize MMP activities in vitro and in vivo. Our recently developed MMP-13 activatable probe, l-MMP-P12, has been successfully applied to image the expression and inhibition of MMPs in a xenografted tumor model [Zhu, L., et al. (2011) Theranostics 1, 18-27]. In this study, to further optimize the in vivo behavior of the proteinase activatable probe, we tracked and profiled the metabolites by a high-resolution liquid chromatography-mass spectrometry (LC-MS) system. Two major metabolites that contributed to the fluorescence recovery were identified. One was specifically cleaved between glycine (G(4)) and valine (V(5)) by MMP, while the other one was generated by nonspecific cleavage between glycine (G(7)) and lysine (K(8)). To visualize the MMP activity more accurately and specifically, a new probe, D-MMP-P12, was designed by replacing the l-lysine with d-lysine in the MMP substrate sequence. The metabolic profile of the new probe, D-MMP-P12, was further characterized by in vitro enzymatic assay, and no nonspecific metabolite was found by LC-MS. Our in vivo optical imaging also demonstrated that D-MMP-P12 had a tumor-to-background ratio (TBR, 5.55 ± 0.75) significantly higher than that of L-MMP-P12 (3.73 ± 0.31) 2 h postinjection. The improved MMP activatable probe may have the potential for drug screening, tumor diagnosis, and therapy response monitoring. Moreover, our research strategy can be further extended to study other protease activatable probes.

Evaluation of fluorine-labeled gastrin-releasing peptide receptor (GRPR) agonists and antagonists by LC/MS

An LC/MS method was used to evaluate 2-fluoropropionyl (FP) and 4-fluorobenzoyl (FB) modified bombsin peptides: GRPR agonist [Aca-QWAVGHLM-NH(2)] and antagonist [fQWAVGHL-NHEt], and their hydrophilic linker modified counterparts with the attachment of GGGRDN sequence. This study developed strategies to evaluate the in vitro receptor mediated cell uptake and metabolic profile of the various GRPR agonists and antagonists. We identified the metabolites produced by rat hepatocytes and quantitatively analyzed the uptake and internalization of the ligands in PC-3 human prostate cancer cells. The major metabolites of both GRPR agonists and antagonists were the result of peptide bond hydrolysis between WA and AV. The agonists also formed a unique metabolite resulting from hydrolysis of the C-terminal amide. The antagonists showed significantly higher stability against metabolism compared to the agonists in rat hepatocytes. The directly modified agonists (FP-BBN and FB-BBN) had higher internalization with similar cell binding compared to the unmodified agonist (BBN), whereas the hydrophilic linker modified agonists (G-BBN and FG-BBN) had much lower total cell uptake. The labeled antagonists (FP-NBBN, FB-NBBN, G-NBBN and FP-G-NBBN) displayed lower internalization. The optimal imaging agent will depend on the interplay of ligand metabolism, cellular uptake, and internalization in vivo.

Structural modifications of ⁹⁹mTc-labelled bombesin-like peptides for optimizing pharmacokinetics in prostate tumor targeting

PURPOSE

The main goal of the present study was to investigate the importance of the addition of a positively charged aa in the naturally occurring bombesin (BN) peptide for its utilization as radiodiagnostic agent, taking into consideration the biodistribution profile, the pharmacokinetic characteristics and the tumor targeting ability.

METHODS

Two BN-derivatives of the general structure [M-chelator]-(spacer)-BN(2-14)-NH(2), where M: (99m)Tc or (185/187)Re, chelator: Gly-Gly-Cys-, spacer: -(arginine)(3)-, M-BN-A; spacer: -(ornithine)(3)-, M-BN-O; have been prepared and evaluated as tumor imaging agents.

RESULTS

The peptides under study presented high radiolabelling efficiency (>98%), significant stability in human plasma (>60% intact radiolabelled peptide after 1h incubation) and comparable receptor binding affinity with the standard [(125)I-Tyr(4)]-BN. Their internalization rates in the prostate cancer PC-3 cells differed, although the amount of internalized peptide was the same. The biodistribution and the dynamic γ-camera imaging studies in normal and PC-3 tumor-bearing SCID mice have shown significant tumor uptake, combined with fast blood clearance, through the urinary pathway.

CONCLUSION

The addition of the charged aa spacer in the BN structure was advantageous for biodistribution, pharmacokinetics and tumor targeting ability, because it reduced the upper abdominal radioactivity levels and increased tumor/normal tissue contrast ratios.