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" This is something that might deserve a closer
evaluation, " cautioned Haas. " For example,
homologous lipids may be considered, which
are identical in structure except for one
nitrogen atom in the head group which can
be permanently charged or ionizable. If they
are ionizable the charge can be switched by
adjusting the pH. This impacts packing. "
" SAXS provides accurate information on the pH
dependent structural changes inside nanoparticles
comprising either permanently charged
or ionizable lipid. This allows one to determine
a structural equivalent to pKa values with high
resolution and purpose, " said Haas. " By variation
of mixing ratios between lipids and RNA these
values can be accurately fine-tuned. This can be
helpful along with chemical synthesis of a lipid
library. You can tailor the library based on composition
and other aspects of the LPX system, which
allows easier and more accurate adjustment of
parameters to optimize endosomal processing. "
There is also another straightforward approach
to modulate particle characteristics and activity,
added Haas. " If you mix RNA and liposomes in
different ratios, you can find conditions where
you obtain colloidally-stable particles either with
an excess of negative or positive charge, " he said.
Animal experiment using luciferase as a reporter
gene demonstrated that LPXs formed at an
excess of positive charge (liposomes) resulted in
high transfection efficacy in the lung, whereas
those formed with an excess of negative charge
(RNA) showed high expression in the spleen. " Just
by changing that one physical parameter you
can change organ efficacy, " emphasized Haas.
Such insight allowed initiation of various clinical
studies in the field of cancer immunotherapy.
Thorough characterization of the particles by
SAXS and other measurements were helpful to
accurately determine critical quality attributes as
a basis for manufacturing of the drug products.
Clinical Product Development
" After you have identified your formulation
the development work begins. Now you
have to refine all of the parameters and
justify them, " said Haas. He recommends
review of the FDA Liposome Drug Products
guidance that details the requirements for
characterization and data generation.
" For liposome manufacturing, when it comes to
process development, you start with something
adapted for lab-scale experiments, " said Haas.
" Since this process may change as it is scaled
up into a GMP environment you need to
control, detail, and justify all process parameters
with more accuracy and care than what
was done for the formulation experiments. "
In order to follow up with the requirements
in the guidances, extensive characterization
and thorough understanding of structural
and functional coherencies inside the product
in development is mandatory. Here, SAXS
and other measurements for extended | 27


Table of Contents for the Digital Edition of Cytiva_Jan2022_mRNAVaccinesANewEra

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