As a drug type, peptides offer certain benefits, such as specificity and potency, but they also present challenges, such as poor stability and short half-life. Recent partnerships among large pharmaceutical companies and specialized companies as well as advances from academia are seeking to resolve these problems.
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Peptides as drugs
Peptides and proteins have the size and functionality to effectively modulate intracellular protein–protein interactions, but they often do not permeate cells and therefore are used to modulate extracellular targets such as receptors (1, 2). The majority of peptide candidates target extracellular molecules with less than 10% binding to intracellular targets, according to a recent analysis of the peptide drug pipeline by the Peptide Therapeutics Foundation (3). The most common extracellular targets were G-protein coupled receptors (GPCR), which include nearly 1000 transmembrane proteins that activate cellular response. During 2000–2008, 60% of peptides entering clinical development targeted GPCRs, and most had agonist activity (3).
Although a small portion of total drug candidates, the number of peptide drugs entering clinical development has increased during the past several decades, according to the Peptide Therapeutics Foundation analysis, which excluded insulins (3). The study found that the average number of new peptide candidates entering clinical development in the 1970s was 1.2 per year and rose to 4.6 per year in the 1980s, 9.7 per year in the 1990s, and 16.8 per year through 2000–2008 (3). During 2000–2008, peptides entering clinical study were most frequently treatments for cancer and metabolic disorders (including diabetes and obesity), respectively, representing 18% and 17% of peptide drug development. Decreases were observed for peptides studied as therapies for treating allergies, immunological disorders and cardiovascular diseases (3).
Patricia Van Arnum
On a commercial level, several peptide-based therapeutics have reached blockbuster status, defined as having sales of $1 billion or more, or near blockbuster status (3). These drugs, using 2011 global sales figures from company annual financial reports, include:
- Teva Pharmaceutical's Copaxone (glatiramer acetate), an L-glutamic acid polymer with L-alanine, L-lysine and L-tyrosine (2011 global sales of $3.6 billion)
- Abbott's Lupron (leuprolide acetate), a synthetic nonapeptide analog of the naturally occurring gonadotropin-releasing hormone (GnRH or luteinizing hormone-releasing hormone [LHRH]) (2011 global sales of $810 million)
- AstraZeneca's Zoladex (goserelin acetate), a decadpeptide and GnRH agonist and synthetic analog of a naturally occurring LHRH) (2011 global sales of $1.1 billion)
- Novartis' Sandostatin (octreotide acetate), a cyclic octapeptide with pharmacologic actions mimicking those of the natural hormone somatostatin (2011 global sales of $1.4 billion)
- Eli Lilly/Amylin Pharmaceuticals' Byetta (exenatide), a 39-amino acid peptide amide (2011 global sales, Eli Lilly, $423 million, Amylin, $518 million)
- Forteo (teriparatide recombinant), which contains recombinant human parathyroid hormone (1–34), is also called rhPTH (1–34). It has an identical sequence to the 34 N-terminal amino acids (the biologically active region) of the 84-amino acid human parathyroid hormone (2011 global sales of $951 million) (4–9).