Detecting peptidic drugs, drug candidates and analogs in sports doping: current status and future directions

Random phage display peptide libraries and affinity selective methods were used to isolate small peptides that bind to and activate the receptor for the cytokine erythropoietin (EPO). In a panel of in vitro biological assays, the peptides act as full agonists and they can also stimulate erythropoiesis in mice. These agonists are represented by a 14- amino acid disulfide-bonded, cyclic peptide with the minimum consensus sequence YXCXXGPXTWXCXP, where X represents positions allowing occupation by several amino acids. The amino acid sequences of these peptides are not found in the primary sequence of EPO. The signaling pathways activated by these peptides appear to be identical to those induced by the natural ligand. This discovery may form the basis for the design of small molecule mimetics of EPO.

Biotechnology increasingly delivers highly promising protein-based biopharmaceutical candidates to the drug development funnel. For successful biopharmaceutical drug development, reliable bioanalytical methods enabling quantification of drugs in biological fluids (plasma, urine, tissue, etc.) are required to generate toxicokinetic (TK), pharmacokinetic (PK), and bioavailability data. A clear observable trend is that liquid chromatography coupled to (tandem) mass spectrometry (LC-MS(/MS)) is more and more replacing ligand binding assays (LBA) for the bioanalytical determination of protein-based biopharmaceuticals in biological matrices, mainly due to improved selectivity and linear dynamic ranges. Practically all MS-based quantification methods for protein-based biopharmaceuticals traditionally rely on (targeted) proteomic techniques and include "seven critical factors": (1) internal standardization, (2) protein purification, (3) enzymatic digestion, (4) selection of signature peptide(s), (5) peptide purification, (6) liquid chromatographic separation and (7) mass spectrometric detection. For this purpose, the variety of applied strategies for all "seven critical factors" in current literature on MS-based protein quantification have been critically reviewed and evaluated. Special attention is paid to the quantification of therapeutic monoclonal antibodies (mAbs) in serum and plasma since this is a very promising and rapidly expanding group of biopharmaceuticals. Additionally, the review aims to predict the impact of strategies moving away from traditional protein cleavage isotope dilution mass spectrometry (PC-IDMS) toward approaches that are more dedicated to bioanalysis. Copyright © 2013 Elsevier B.V. All rights reserved.

Human chorionic gonadotropin (hCG) is mainly used for detection and monitoring of pregnancy and pregnancy-related disorders but it is also an extremely sensitive and specific marker for trophoblastic tumors of placental and germ cell origin. Thus treatment of relapsing choriocarcinomas and testicular germ cell tumors is often initiated on the basis of rising hCG levels even in the absence of clinical or histological evidence of a relapse. While these tumors mostly produce the intact heterodimeric hormone consisting of an alpha (hCGalpha), and a beta subunit (hCGbeta), many nontrophoblastic tumors produce only hCGbeta This is usually a sign of aggressive disease and elevated serum levels of hCGbeta are strongly associated with poor prognosis. Elevated serum levels are observed in 45-60% of patients with biliary and pancreatic cancer and in 10-30% of most other cancers. Methods that detect hCG and hCGbeta together are mainly used for measurement of hCG-like immunoreactivity in serum. However, the reference range for hCG is 5-8 fold higher than that for hCGbeta and thus moderately elevated levels can be identified only with a specific and sensitive hCGbeta assay.