Functional quality of peptide drugs

The quality of peptides might affect its functionality, and vica versa, the desired functionality determines the required quality (QbD principles). It was demonstrated that even small changes in a peptide sequence by one or two amino acids can convert a receptor agonist, respectively antagonist, into an antagonist, respectively agonist. The quality of a peptide drug mainly depends on its impurity profile, with the emphasis on related impurities, but other quality parameters may be critical as well for specific peptides, e.g. its secondary structure. These impurities may be biomedically active, altering the desired efficacy or inducing unwanted toxicity. We have recently demonstrated that synthesis impurities are responsible for the observed functional effects in a tissue model, instead of the peptide itself. Regulatory authorities have set up guidances or have legally established specification limits to assure a consistent purity of these peptide drugs once in clinical use. Nonetheless, quality control of peptides has to be a standard procedure in scientific research and early drug development to draw correct conclusions

Receptor and blood-brain barrier characterization of opioid peptides in drug research and early development

The penetration of the blood–brain barrier (BBB) combined with the receptor-subtype selectivity determines the medical activity of opioid peptides within the central nervous system (CNS). The opioid receptor-subtype selectivity can be assessed not only by the classic radio-ligand binding methods, but also by novel techniques such as SAW (surface acoustic wave) measuring binding kinetics. Pharmacokinetics include metabolic stability, brain influx and efflux characteristics, as well as brain capillary retention. Metabolic stability is evaluated by in vitro kinetic studies using different target tissues. When applying the in vivo mouse model, the influx transfer constant from serum into mouse brain is determined by multiple time regression, while the efflux kinetics are investigated with the intra-cerebroventricular injection technique. Furthermore, brain parenchyma-capillary cell distribution is evaluated by capillary depletion. Finally, the in vivo antinociceptive activity can be quantified in a mouse model. Since the evaluation of opioid peptides as potential therapeutic or diagnostic CNS agents requires the consideration of these opposing criteria, the CNS-functional drugability of opioid peptides is evaluated using a desirability criterion combining these different requirements. Information about the BBB behaviour of peptides, including the opioid peptides, are found in the database Brainpeps, which can also be used for QSPR

Stability-indicating HPLC-DAD/UV-ESI/MS impurity profiling of the anti-malarial drug lumefantrine

<p>Abstract</p> <p>Background</p> <p>Lumefantrine (benflumetol) is a fluorene derivative belonging to the aryl amino alcohol class of anti-malarial drugs and is commercially available in fixed combination products with β-artemether. Impurity characterization of such drugs, which are widely consumed in tropical countries for malaria control programmes, is of paramount importance. However, until now, no exhaustive impurity profile of lumefantrine has been established, encompassing process-related and degradation impurities in active pharmaceutical ingredients (APIs) and finished pharmaceutical products (FPPs).</p> <p>Methods</p> <p>Using HPLC-DAD/UV-ESI/ion trap/MS, a comprehensive impurity profile was established based upon analysis of market samples as well as stress, accelerated and long-term stability results. <it>In-silico </it>toxicological predictions for these lumefantrine related impurities were made using Toxtree^®and Derek^®.</p> <p>Results</p> <p>Several new impurities are identified, of which the desbenzylketo derivative (DBK) is proposed as a new specified degradant. DBK and the remaining unspecified lumefantrine related impurities are predicted, using Toxtree^®and Derek^®, to have a toxicity risk comparable to the toxicity risk of the API lumefantrine itself.</p> <p>Conclusions</p> <p>From unstressed, stressed and accelerated stability samples of lumefantrine API and FPPs, nine compounds were detected and characterized to be lumefantrine related impurities. One new lumefantrine related compound, DBK, was identified and characterized as a specified degradation impurity of lumefantrine in real market samples (FPPs). The <it>in-silico </it>toxicological investigation (Toxtree^®and Derek^®) indicated overall a toxicity risk for lumefantrine related impurities comparable to that of the API lumefantrine itself.</p

Chemical quality control of peptide functionality testing in tissue baths

The biological functionality of peptides is often tested by tissue bath studies. However, chemical integrity of the peptide is not assured during this evaluation, blurring the final functionality conclusions. We investigated adsorption and degradation of several model peptides with different structures by subjecting these peptides to tissue bath testing with guinea pig ileum. HPLC-UV was used for quantification, while HPLC-ESI/iontrap MSn was used for identification purposes. We demonstrated that adsorption as well as degradation can occur. After tissue bath experiments, a recovery range of 6% to 94% was observed. Some peptides did not show any significant adsorption nor degradation. The majority exhibited adsorption only, whereas some other peptides did show only chemical/metabolic degradation, but the total mass balance results did point no adsorption losses. Overall, our findings call for a general quality control system when functionality of peptides is studied

Purity profiling and the associated functional effects of a new peptide

Peptides show great pharmaceutical potential as active drugs and diagnostics in several clinical areas such as endocrinology, obstetrics or oncology. The search towards novel lead-peptides with a biological function has thus attracted renewed interest. Within a collaborative, multidisciplinary approach investigating the mouse peptidomics [1], new peptides were identified with the potential of serving as a basis towards new peptidic drugs. Tissue organ bath tests were used for functional screening of these newly identified peptides, obtained in sufficient quantity by chemical synthesis. One of these new peptides, SBO215_7, was identified to induce baseline contractions in longitudinal smooth muscle preparations of the guinea pig ileum (GPI). However, unlike the initially tested crude peptide, the pure peptide (> 95% purity) could not induce the previously observed baseline contractions. Peptide purity (crude vs. > 95% purity) will thus influence the final outcome of the functionality testing. Nevertheless, this quality aspect is generally neglected in this phase of investigation, leading to wrong fail/pass decisions. The crude peptide was synthesized by three different world-wide suppliers and characterized in comparison with the high-purity (> 95%) peptide. Their purity profile was investigated using HPLC-UV/DAD-ESI/MSn allowing purity quantification as well as identification of the related impurities. Each of the three suppliers had a different major impurity, with only a few impurities in common. Moreover, differences in GPI-contraction behaviour was observed between the different peptide suppliers and qualities. We thus demonstrated that the quality of peptides is an important aspect in their functional screening using tissue organ bath experiments