A LC-MS/MS method to monitor the concentration of HYD-PEP06, a RGD-modified Endostar mimetic peptide in rat blood

HYD-PEP06 is a novel RGD-modified Endostar mimetic peptide with 30 amino acids that is intended to suppress the formation of neoplasm vessels. This assay was developed and validated to monitor the level of the peptide HYD-PEP06 in rat blood, using liquid chromatography tandem mass spectrometry (LC-MS/MS). HYD-PEP10, another peptide similar to the analyte, was used as an internal standard (IS). A triple quadrupole mass spectrometry in Multiple Reaction Monitoring (MRM) mode and an electrospray interface (ESI) in the positive mode were used for MS analysis. The analysis was optimized with addition of 0.3% formic acid (FA) into the mobile phase as well as with a needle washing solution to overcome the carryover effect. In addition, the carryover was reduced by optimizing the mobile phase gradient. Methanol was used as a diluent of working solutions to avoid any adsorption. Methanol:acetonitrile (1:1, v:v) containing 0.3% FA was employed to precipitate the blood samples. Unknown blood samples must be placed in ice bath immediately, and precipitating agents should be added within 30 min to ensure the stability of blood samples. The assay was established and validated. This method showed a good linear relationship for the HYD-PEP06 in the range of 10 ng·mL^-1 to 2000 ng·mL^-1, with R > 0.99. HYD-PEP06 was determined with accuracy values (RE%) of -5.06%-8.54%, intra- and inter-day precisions (RSD%) of 3.13%-4.87% and 4.81%-9.42%. The method was successfully in monitoring the concentration of HYD-PEP06 in rat blood.

Retinal Electrophysiology Is a Viable Preclinical Biomarker for Drug Penetrance into the Central Nervous System

Objective. To examine whether retinal electrophysiology is a useful surrogate marker of drug penetrance into the central nervous system (CNS). Materials and Methods. Brain and retinal electrophysiology were assessed with full-field visually evoked potentials and electroretinograms in conscious and anaesthetised rats following systemic or local administrations of centrally penetrant (muscimol) or nonpenetrant (isoguvacine) compounds. Results. Local injections into the eye/brain bypassed the blood neural barriers and produced changes in retinal/brain responses for both drugs. In conscious animals, systemic administration of muscimol resulted in retinal and brain biopotential changes, whereas systemic delivery of isoguvacine did not. General anaesthesia confounded these outcomes. Conclusions. Retinal electrophysiology, when recorded in conscious animals, shows promise as a viable biomarker of drug penetration into the CNS. In contrast, when conducted under anaesthetised conditions confounds can be induced in both cortical and retinal electrophysiological recordings.

Utilization of DBS within drug discovery: a simple 2D-LC–MS/MS system to minimize blood- and paper-based matrix effects from FTA elute™ DBS

Background: Dried blood spot-based bioanalysis potentially introduces novel matrix effects that need to be eliminated or controlled. Within nonregulatory drug discovery these can be defined as ≤20% and ≤30% for nominal peak area, respectively. Results: Controlling matrix effects for a panel of compounds by simple 1D-HPLC–MS/MS was not achievable and the optimization of 2D-HPLC–MS/MS is reported here. Simple inclusion of a ‘trapping’ stage was not sufficient to improve matrix effects and optimization of the reconstitution solvent, reconstitution volume and injection volume was required for a generic system to be developed. Conclusion: A generic 2D-LC–MS/MS system has been developed that eliminates paper-based matrix effects and eliminates or controls dried blood spot matrix effects for a panel of compounds extracted from FTA Elute™ with methanol.