Discovering and improving novel peptide therapeutics.
ABSTRACT Peptides have a number of advantages over small molecules in terms of specificity and affinity for targets, and over antibodies in terms of size. However, sensitivity to serum and tissue proteases coupled with short serum half-life has resulted in few recombinant library derived peptides, making the transition from lead to drug on the market. Recently, a series of technologies have been developed to address both these issues: selection methodologies addressing protease resistance have been developed that when combined with methods such as pegylation antibody Fc attachment and binding to serum albumin look likely to finally turn therapeutic peptides into a widely accepted drug class.
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ABSTRACT: Glucagon-like peptide (GLP-1) increases insulin secretion but is rapidly degraded (half-life: 2 min in circulation). GLP-1 analogue, exenatide (Byetta) has a longer half-life (3.3-4 h) with potent insulinotropic effects but requires cold storage, daily abdominal injections with short shelf life. Because patients with diabetes take >60 000 injections in their life time, alternative delivery methods are highly desired. Exenatide is ideal for oral delivery because insulinotropism is glucose dependent, with reduced risk of hypoglycaemia even at higher doses. Therefore, exendin-4 (EX4) was expressed as a cholera toxin B subunit (CTB)-fusion protein in tobacco chloroplasts to facilitate bioencapsulation within plant cells and transmucosal delivery in the gut via GM1 receptors present in the intestinal epithelium. The transgene integration was confirmed by PCR and Southern blot analysis. Expression level of CTB-EX4 reached up to 14.3% of total leaf protein (TLP). Lyophilization of leaf material increased therapeutic protein concentration by 12- to 24-fold, extended their shelf life up to 15 months when stored at room temperature and eliminated microbes present in fresh leaves. The pentameric structure, disulphide bonds and functionality of CTB-EX4 were well preserved in lyophilized materials. Chloroplast-derived CTB-EX4 showed increased insulin secretion similar to the commercial EX4 in beta-TC6, a mouse pancreatic cell line. Even when 5000-fold excess dose of CTB-EX4 was orally delivered, it stimulated insulin secretion similar to the intraperitoneal injection of commercial EX4 but did not cause hypoglycaemia in mice. Oral delivery of the bioencapsulated EX4 should eliminate injections, increase patient compliance/convenience and significantly lower their cost.Plant Biotechnology Journal 10/2012; 11(1). DOI:10.1111/pbi.12008 · 5.68 Impact Factor
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ABSTRACT: Peptide therapeutics (PTs) is generally regarded as highly effective macromolecule therapeutics at very low concentrations. The main issues surrounding the administration of PTs is guaranteeing that they are bioavailable, reach the desired therapeutic index and distribute throughout the body effectively. The oral administration, a non-invasive route, of PTs is considered a major complication due to inadequate oral absorption through biological membranes such as the small intestine epithelium due to presystemic proteolytic enzymatic activity. PTs bioavailability is further diminished in the systemic circulation due to low stability in the plasma and rapid excretion from the body. Many alternative routes can be considered non-invasive such as transdermal and nasal routes, but this review focuses on the oral route, specifically the small intestine region of the gastrointestinal tract. Although this region has the highest density of proteolytic enzymes, it contains tight junctions which have the lowest trans-epithelial electrical resistance throughout the body; thus paracellular transport of these large PTs can be achieved more readily. The use of a natural polysaccharide polymer, such as trimethyl chitosan (TMC), which enhances the bioavailability of these PTs through the small intestine, will also be discussed in great detail. TMC has been considered because it could potentially solve many of the mechanistic and chemical problems associated with oral therapeutic peptide administration. The safety of orally administered PTs through the small intestinal epithelium employing a polymer such as TMC is also discussed as this is a significant issue for regulatory bodies.International Journal of Peptide Research and Therapeutics 04/2012; 18(3). DOI:10.1007/s10989-012-9299-7 · 0.83 Impact Factor
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ABSTRACT: Peptide and protein drugs have evolved in recent years into mainstream therapeutics, representing a significant portion of the pharmaceutical market. Peptides and proteins exhibit highly diverse structures, broad biological activities as hormones, neurotransmitters, structural proteins, metabolic modulators and therefore have a significant role as both therapeutics and biomarkers. Understanding the metabolism of synthetic or biotechnologically derived peptide and protein drugs is critical for pharmaceutical development as metabolism has a significant impact on drug efficacy and safety. Although the same principles of pharmacokinetics and metabolism of small molecule drugs apply to peptide and protein drugs, there are few notable differences. Moreover, the study of peptide and protein drug metabolism is a rather complicated process which requires sophisticated analytical techniques, and mass spectrometry based approaches have provided the capabilities for efficient and reliable quantification, characterization, and metabolite identification. This review article will focus on the current use of mass spectrometry for the study of the metabolism of peptide and protein drugs.Mass Spectrometry Reviews 01/2012; 31(1):110-33. DOI:10.1002/mas.20340 · 8.05 Impact Factor