The term “dPEG^®” is Quanta BioDesign’s trademarked acronym for “discrete polyethylene glycol” or “discrete PEG”. The “discrete” portion of the dPEG® trademark indicates single molecular weight PEG technology. Like traditional PEGs, our products contain an amphiphilic^[1] backbone of repeating ethylene oxide units. However, traditional PEGs are not single compounds. Quanta BioDesign invented and manufactures these monodisperse PEG products using our proprietary synthetic and purification processes.

What is PEGylation?

PEGylation is the process adding polyethylene glycol (PEG) to a molecule or surface, often through covalent modification of the targeted molecule or surface. Molecules and surfaces that have been modified by PEGylation are called PEGylated. Any surface containing appropriate functional groups can be PEGylated. Gold, silver, iron, and silica are examples of surfaces that are often PEGylated for use in diagnostic, therapeutic, or theranostic applications. The list of molecules that are PEGylated is enormously long and continually expanding. Examples of the types of molecules that are PEGylated include small molecule therapeutic drugs, peptides, proteins, the carbohydrate coats of glycoproteins, oligonucleotides, and lipids.

The benefits of PEGylation include increased water solubility, increased hydrodynamic volume, decreased immunogenicity, and extended circulation in vivo in the bloodstream due to reduced renal clearance. In addition to reducing renal clearance, PEGylation also often modifies the biodistribution and pharmacokinetics of therapeutic, theranostic, and diagnostic molecules.

Traditional PEGs

Specifically, traditional PEG products are prepared by polymerization processes. Any polymerized PEG product is a Poisson distribution of chain lengths and molecular weights.^[2],[3] This distribution was formerly known as the polydispersity index (PDI), but is now known as the dispersity index or simply dispersity (indicated by the symbol “Đ”)^[4]. The reported molecular weight is an average molecular weight, and Đ (or PDI) gives an indication of the range of molecular weights in the sample. Disperse samples have Đ > 1 and are a heterogeneous mixture of sizes and molecular weights. High M.W. (>50 kDa) traditional PEG has Đ up to 1.1. Lower M.W. traditional PEG has Đ in the range of 1.01 – 1.05. These numbers represent broad distributions of molecular weights.^[5],[6],[7]

dPEG^® Products Are Different

Our dPEG^® products are quite different from traditional PEGs, because of our proprietary, patent-protected processes. Each dPEG^® product represents a single compound with a unique, specific, single molecular weight (MW). See Figure 1.

Figure 1

Figure 1: Side-by-side comparison of actual mass spectra from a traditional, dispersed PEG (left spectrum) and a dPEG^® of equivalent mass from Quanta BioDesign (right spectrum). The mass spectrum on the left is of PEG1000. It has M_w = 1027 Daltons; M_n = 888 Daltons; and Đ = 1.16. The masses in this dispersed PEG range from 600 – 1,500 Daltons. The mass spectrum on the right is of Quanta BioDesign product number 10317, amino-dPEG^®₂₄-acid, the structure of which is shown across the top of the two mass spectra. PN10317 is a single molecular weight compound with a single, discrete chain length. The molecular weight of PN10317 is 1146.355 Daltons. Because it has no dispersity, Đ = 1.

A Wide Variety of Functional Groups and Architectures for dPEG^® Products

Our dPEG^® products are synthesized from high purity building blocks (e.g. diethylene glycol, triethylene glycol, or tetraethylene glycol) in a series of stepwise reactions to provide specific MWs, organic moieties, functional groups (see Figure 2), and architectures (see Figure 3) suited for a wide variety of applications. From these building blocks, we produce homobifunctional and heterobifunctional crosslinkers, homotetrafunctional and homohexafunctional crosslinkers, biotinylation reagents, fluorescent tags, surface modification reagents, and specialized products designed for modification of pharmacokinetics (PK) and biodistribution (BD). Our products contain methoxy, alcohol, and carboxylic acid end-capping; various protective groups for reactive moieties (e.g., methoxytrityl, Fmoc, boc, etc.); various functional groups for conjugation to amines, thiols, alcohols, carboxylic acids, ketones, aldehydes, alkynes, and azides; and a wide variety of organic moieties (i.e., biotin, lipoamide, fluorescein, DOTA, etc.).

All dPEG^® products contain linear chains of two to seventy-two ethylene oxide units. We also build branched structures consisting of three to nine of these linear chains. Our proprietary synthetic processes maintain homogeneity of our products in the range of 200 Da to 16 kDa. Our Sidewinder™ line of products was designed by Quanta BioDesign’s scientists to provide new ways to incorporate the beneficial properties and advantages of dPEG^® products into diagnostic and therapeutic applications. One clear application for these products is fine-tuning PK and BD of diagnostic and therapeutic products. These novel dPEG^® products are not possible with traditional disperse PEG products.

References

[1] The term “amphiphilic” means that the compound is soluble in both water (or aqueous buffer) and organic solvents. All PEG products that do not contain hydrophobic substituents are soluble in water and in a variety of organic solvents. The addition of hydrophobic groups to PEG reduces the water solubility of some PEG products.

[2] Flory, P. J. Molecular Size Distribution in Ethylene Oxide Polymers. J. Am. Chem. Soc. 1940, 62, 1561−1565. https://doi.org/10.1021/ja01863a066.

[3] Herzberger, J.; Niederer, K.; Pohlit, H.; Seiwert, J.; Worm, M.; Wurm, F. R.; Frey, H. Polymerization of Ethylene Oxide, Propylene Oxide, and Other Alkylene Oxides: Synthesis, Novel Polymer Architectures, and Bioconjugation. Chem. Rev. 2016, 116, 2170-2243. https://doi.org/10.1021/acs.chemrev.5b00441.

[4] Gilbert, R. G.; Hess, M.; Jenkins, A. D.; Jones, R. G.; Kratochvíl, P.; Stepto, R. F. T. Dispersity in polymer science (IUPAC Recommendations 2009). Pure Appl. Chem. 2009, 81, 351–353. https://doi.org/10.1351/PAC-REC-08-05-02. See also, Stepto, R. F. T. Erratum. Pure Appl. Chem. 2009, 81, 779. https://doi.org/10.1351/PAC-REC-08-05-02_erratum.

[5] Veronese, F. M.; Mero, A.; Pasut, G. Protein PEGylation, Basic Science and Biological Applications. In PEGylated Protein Drugs: Basic Science and Clinical Applications; Veronese, F. M., Ed.; Milestones in Drug Therapy; Birkhäuser Basel: Basel, 2009; pp 11–31. https://doi.org/10.1007/978-3-7643-8679-5_2.

[6] Jevsevar, S; Kunstejl, M; Porekar, V.G. PEGylation of therapeutic proteins. Biotechnology Journal 2010, 5(1) 113-128. DOI: 10.1002/biot.200900218.

[7] For example, dextran with Đ=2 is considered “low dispersity” today. Previously dextran had even higher dispersity than that. See, Pasut, G. Polymers for Protein Conjugation. Polymers 2014, 6(1), 160–178. https://doi.org/10.3390/polym6010160.