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Translation of RNA Medicines from Design to Clinic
from the endosome following cellular uptake.
To manufacture the nanoparticles, the RNA
dissolved in buffer, and lipids dissolved in ethanol
are rapidly mixed at precise ratios, to induce
self-assembly into particles with the desired
properties. Further process steps, comprising
buffer adjustment, addition of stabilizers,
concentration adjustment and sterile filtration
may be involved to obtain the end product.
After determining various physico-chemically
characteristics for quality control, the biological
activity is measured in cell or animal models. The
correlation between particle characteristics and
biology is used as a basis for system optimization.
In lipid-based delivery systems some general
features are considered to be related to activity.
One is the capacity to undergo transitions
between phase states, e.g., hexagonal, inverse
hexagonal, or lamellar. Lipids where the transition
between lamellar and hexagonal phases
is facilitated are considered to be particularly
helpful for uptake or release across bilayer
membranes. Another important aspect is
the pKa value of ionizable lipids, which is
decisive for pH dependent changes of the
particle characteristics in circulation and
during endosomal processing after uptake.
Two examples of lipid-based delivery systems are
lipoplexes (LPXs) and lipid nanoparticles (LNPs).
LPXs are made by mixing preformed cationic
liposomes with RNA to form a lamellar-like
lipoplex stack. In contrast, LNPs are formed by
26 |
mixing lipids (an ionizable lipid, a helper lipid,
and a grafted lipid) in ethanolic solution with
RNA in an acidic buffer to complex the RNA and
form the LNP in one step. Permanently cationic
LPXs are thought to be more cytotoxic than LNPs,
which are largely uncharged at physiological pH.
This reduces serum interactions and thus also
reduces one main cause of potential toxicity.
Alnylam's Onpattroâ„¢ for the treatment of
polyneuropathy caused by hereditary ATTR
(hATTR) amyloidosis and the Moderna
mRNA-1273 and Pfizer-BioNTech BNT162b2
SARS-CoV-2 vaccines all use ionizable cationic
lipids formed by precipitation in ethanol.
The two systems differ in their internal structure,
which can be demonstrated by small angle x-ray
scattering (SAXS) where the sample is irradiated
with an x-ray beam and the scattered light
collected. Scattering profiles are displayed as a
function of the angle or the momentum transfer.
" From this profile you can determine if a Bragg
peak is present along with its height and area
to get quantitative information on the internal
organization of your particle to assist system
specification and optimization, " explained Haas.
The LPX structure is characterized by a narrow and
well-defined Bragg peak whereas the LNP peak
is broader, indicating a lower degree of internal
organization. A further difference between
LNPs and LPXs is that typically in the former
ionizable lipids are used, while LPXs typically
comprise permanently charged cationic lipids.


Table of Contents for the Digital Edition of Cytiva_Jan2022_mRNAVaccinesANewEra

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