Edition 1 / March 2021
In response to the COVID-19 pandemic, mRNA (messenger RNA) vaccines have catapulted to center stage of the pharmaceutical and biotechnology industry. As of early 2021, there are eight ongoing human trials for mRNA vaccines led by Moderna, BioNTech / Pfizer, CureVac, Sanofi / TranslateBio, Arcturus / Duke-NUS Medical School (Singapore), Imperial College (London), Chulalongkorn University (Thailand), and Providence Therapeutics.
In terms of SARS-CoV-2 infection in 2020, two of these clinical trials announced interim phase 3 results that reported an efficacy of greater than 94% reduction of infection after the administration of 2 doses (30 μg for Pfizer/BioNtech or 100 μg for Moderna). Both vaccines were developed using an mRNA sequence that encodes for a spike protein immunogen, delivered in a Lipid NanoParticle (LNP).
Through a process known as transcription, an RNA copy of a DNA sequence is made which creates a given protein. This copy – now called mRNA (messenger RNA) – travels from the nucleus of the cell to the part of the cell known as the cytoplasm, which houses ribosomes. Ribosomes are complex machinery in the cells that are responsible for making proteins. Then, through another process known as translation, ribosomes ‘read’ the mRNA, and follow the instructions, creating the protein step by step. The cell then expresses the protein (the Spike Glycoprotein, in the case of the coronavirus SARS-CoV-2) and it, in turn, carries out its designated function in the cell or body.
The Spike (S) Glycoprotein of SARS-CoV-2, which plays a key role in the receptor recognition and cell membrane fusion process, is composed of two subunits, S1 and S2. The S1 subunit contains a receptor-binding domain that recognizes and binds to the host receptor angiotensin-converting enzyme 2, while the S2 subunit mediates viral cell membrane fusion by forming a six-helical bundle via the two-heptad repeat domain. With a size of 180–200 kDa, the S protein consists of an extracellular N-terminus, a transmembrane (TM) domain anchored in the viral membrane, and a short intracellular C-terminal segment.
The recent success of mRNA vaccines in SARS-CoV-2 clinical trials is in part due to the development of Lipid NanoParticle (LNP) delivery systems that not only efficiently express the mRNA-encoded immunogen after intramuscular injection, but also play a role as adjuvants and in vaccine reactogenicity.
1) Role of Cationic Lipids
Cationic Lipids are critical to the self-assembly process of the Lipid NanoParticle itself, the ability of it to be introduced (or inserted or enter or travel) into cells, and the escape of the mRNA from the endosome. They are the functional lipid components of the Drug Product.
When incorporated into Lipid NanoParticles (LNP), they help regulate the endosomal release of the RNA. During Drug Product manufacturing, introduction of an aqueous mRNA solution to an ethanolic lipid mixture containing the Cationic Lipid at a specific pH leads to an electrostatic interaction between the negatively charged RNA backbone and the positively charged Cationic Lipid, which then leads to the encapsulation of the RNA Drug Substance, resulting in particle formation. Once the Lipid NanoParticle has been introduced into the cell, the low pH of the endosome renders the Lipid NanoParticle (LNP) fusogenic, allowing the release of RNA into the cytosol.
Typical examples of Cationic Lipids are:
2) Role of Phospholipids
The Phospholipid component provides a stable bilayer-forming structure to balance the non-bilayer propensity of the Cationic Lipid, eventually forming a stable bilayer underneath the PEG surface. Examples include:
3) Role of Cholesterol
Cholesterol stabilizes the Lipid NanoParticle (LNP) structures and facilitates endosome escape. The major source of cholesterol today comes from the wool grease of sheep.
In 2011, EMA published a revised guidance to minimize the risk of transmitting animal spongiform encephalopathy agents via human and veterinary medicinal products (EMA/410/01 rev.3). Transmissible Spongiform Encephalopathies (TSEs) are chronic degenerative nervous diseases characterised by the accumulation of an abnormal isoform of a cellular glycoprotein.
TSE Diseases in Animals include:
At CordenPharma, we only manufacture non-animal origin cholesterol, called CP BotaniChol, with a synthesis process that starts from plant derivative materials that are chemically converted into the final cholesterol. With such an approach, we avoid any potential animal source of contamination. CordenPharma is a trusted and reliable source of gram and bulk (Kg, MT) supply of this vegetal-derived Cholesterol in GMP grade, suitable for parenteral use, but not exclusively.
4) Role of PEG Lipids
The primary function of PEGylated Lipid is to form a protective hydrophilic layer that sterically stabilises the LNP, which contributes to storage stability, reduces nonspecific binding to proteins, and prolongs the circulation time after in vivo administration. Because higher PEG content reduces cellular uptake and interaction with the endosomal membrane, PEG content should be very well controlled. Examples include:
At CordenPharma, PEGylated lipids are currently produced at large-scale, allowing MT kg annual delivery worldwide.
The entire CordenPharma organization is honored to support the emergence of these synthetic mRNA-based vaccines with long-standing expertise in the manufacture & supply of specialized critical Lipid excipients and components. We look forward to the great strides the Pharma Industry is making over the coming months and years to provide life-saving vaccines and critical medications to patients.
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