eBook: Analytical Method and QC Testing Strategies for Biologics Production - 19

clinical impact (i.e. aggregation), and attributes that
have a relationship with the critical attribute, which
should be assessed independently of their potential
to promote aggregation.6
Another example is charge
heterogeneity. Charge isoforms may arise from
different post-translational modifications (PTMs) of the
protein such as N/C terminal processing, deamidation,
oxidation and disulfide heterogeneity.15
Depending
on the location of the affected residues, potency may
be affected.16
In some cases, acidic and basic protein
species may exhibit different clearance rates from the
main species.17
In practice, it is often not possible to generate and
isolate product variants with a single PTM for direct
assessment of biological impact. Some attrbutes may
only be evaluated through profile-based analysis (e.g.
charge variants). Product variants never detected or
observed only at low abundance during development
may not pose significant risk to a program to warrant
further tracking. Overall, the CQA risk ranking is used
to drive execution of additional structure-function
studies for further delineation of the impact on safety
and efficacy of the drug and progressively decrease
uncertainty. Preliminary acceptable ranges for CQAs
can be defined from findings of these studies.
For impact assessment of process-related impurities,
the focus is often on safety and toxicity concerns.
However, in some cases impurities such as
intracellular enzymes, metal ions and nonmetallic
leachables may cause product degradation or
protein modifications, which in turn might impact
function.18,19
For host cell proteins (HCPs), proteomics
profiling by LC-MS techniques allow identification
and impact assessment of individual HCPs.20
Process
additives undergo an assessment based on worstcase
assumptions of their level in a product dose,
while toxicology data and the additives' history of use
in the industry is also considered.4
For the uncertainty factor, the level of reliance on in
vitro vs. in vivo data should be considered, as well as
the availability of molecule-specific data pertaining to
potency and PK, the relevance of data leveraged from
related molecules, and the range of clinical exposure.
By evaluating attribute criticality solely on the basis
of impact and uncertainty to safety and efficacy, the
product
risk assessment only needs to be revised
when new information is discovered regarding the
properties of the attributes themselves, and not every
time a process change is made.
Process Capability and
Stability Information
With the CQA criticality ranking as a foundation, a
second level of risk assessment can be performed
to consider occurrence.4
This takes into account the
likelihood (or frequency of failure) of maintaining a CQA
within its acceptable limits under the range of process
and storage conditions of interest. Manufacturing
process and formulation development efforts are
thus focused on improving process performance via
controlling the process parameters, material attributes
and procedural controls that are linked to the CQAs.
Results from stability studies (real-time, accelerated
and forced degradation) demonstrate the primary
degradation mechanisms of the biotherapeutic and
inform understanding of the impact to CQAs during
routine storage and handling as well as excursions.21,22
The process/stability impact ranking tool may consist
of 3-5 levels, and the resultant occurrence scores
are combined (via multiplication) with the criticality
score for each CQA. The overall output is a listing
of CQAs based on residual risk after process control
19
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