Understanding the Role of Peptides in Modern Therapeutic Research

Peptides are an interesting alternative in drug development. They are larger than traditional small-molecule compounds, still smaller and easier to produce than full-scale proteins, and with different properties and potential uses. This makes them a potential type of molecule with direction to disrupts many areas of drug development and innovation. Its main potential is upgrading current treatments improving their efficacy and reducing side effects.

Reconstitution is where research goes wrong

The part of peptide research that many overlook isn’t the peptide itself – it’s the work in the lab that comes before you can even get started. Most research peptides come to your lab lyophilized, the technical term for freeze-dried. Lyophilization can roughly double a peptide’s shelf life, but the process of bringing that powder back to a solution can be fraught with errors.

And those errors are more common than you might hope. Using the wrong diluent, accidentally introducing contamination, or even just mishandling the temperature of the vial as you’re bringing the powder back into solution can all go a long way toward compromising the integrity of your peptide sample. And you might never even know that you were working with bad data for your entire experiment. 

For one-off solutions or other situations when you know that the entire peptide vial is going to be used on a single preparation, something like sterile water is usually fine. If you’re going to be coming back to this same vial over days or weeks over the course of a multi-dose study, bacteriostatic water is absolutely the standard choice for exactly that reason. The benzyl alcohol that the “bacteriostatic” in bacteriostatic water refers to is in there to keep bacteria from growing in your peptide vial between uses. 

And if you’re going to be coming back to the vial multiple times, working with even a slightly contaminated sample means you can never be sure that the results of your research reflect the peptide itself and not some errant bacteria that was having a good time in the vial. Hospira BAC water is the most commonly recommended option by far because there’s a lot going on with the vial in terms of formulation that you should be able to take for granted. Peptidetest’s bacteriostatic water from Pfizer is a pharmacy-grade product, you know those crucial variables are sorted for you: the benzyl alcohol that keeps the bacteria down in solution and the level to which it’s accurately measured, ensuring the safety and stability of your research, and the vial comes pre-sterilized out of the box.

The shift toward engineered peptide sequences

Historically, the predominant approach to peptide research was the use of naturally occurring peptide sequences. Current practice involves the systematic modification of amino acid residues towards the intended improvement of biological, physical-chemical or pharmacokinetic properties of the peptides. The most often targeted improvement relates to the proteolytic stability of peptides in biological systems. 

Short peptides are quickly degraded (within seconds to minutes) by specific non-specific proteolytic activity. The resulting fast proteolytic degradation of the active substance in vivo often causes the inactivation of a peptide within a short period of time suitable for convenient administration. Frequent dosing quickly leads to patient non-compliance or could render the molecule completely unsuitable for therapeutic use. Other physiological effects of a fast clearance in non-compartmental space can be unphysiological fluctuations in peptide hormone plasma levels or an inability to differentiate between appropriately dosed efficacious levels and overdosing. 

Changes in the amino acid sequence can provide engineered solutions towards the stabilization of peptides against proteolytic degradation. Peptide engineering methods used to enhance in vivo stability include N-terminal acylation, N-terminal protection with a peptidomimetic group, C-terminal amidation, D-amino acid substitution, the introduction of inhibitory stop residues, peptide cyclization, side-chain-to-side-chain cyclization, head-to-tail cyclization, and ester derivatives of amino acids. The most favored strategy by the pharmaceutical industry is amino acid substitution, some of the other modifications are virtually not used at all. 

Other peptides could benefit from N-methyl amino acid replacement. Conversely, PEGylation of peptides which is enjoying a surge in popularity produces water-soluble prodrugs that are slowly degraded in vivo, in order to prolong the therapeutic peptide’s half-life.

Bioavailability and the delivery problem

Peptides have a reputation for being terrible candidates for oral delivery. Our stomach and intestines are full of enzymes that break peptides apart, meaning that when you eat a peptide it gets broken down into its constituent amino acids and never becomes active in your body. For most peptides being used in their laboratory research (insulin being the best-known exception), subcutaneous injection is much more effective.

Handling and cold-chain requirements

Peptides are delicate substances. The application of heat can increase their breakdown. The effects of UV light may be detrimental to the integrity of chemical bonds ensuring the strategic or secondary structure of a given peptide sequence. That knowledge isn’t just a nice-to-know fact – it’s what causes many expensive batches of research chemical to be rejected.

The result? Cold-chain management. Most research peptides are despatched in a sterile, lyophilized powder form and should be stored in a refrigerator at the least from the point of receipt, and in many cases kept in the freezer until the point of use. Post-reconstitution, sterile bacteriostatic diluents have their expiry dates, and reconstituted peptides should be stored in a refrigerator and out of direct light – essentially for the same reasons.

Getting the fundamentals right

Peptides are like precision instruments. The discovery opportunities are there, the therapeutic interest is there, and the development of this market has been underpinned by substantial science and significant investment. However, ultimately all of this potential can only become a reality if the downstream science is as sophisticated as the molecules. The right diluents, meticulous reconstitution, suitable delivery formats, and strict cold-chain logistics are not just that – the difference between real data and false.