TECHNICAL NOTE
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Recall that a positive k
D
is considered favorable to
biologics researchers aiming to reduce the self-
association behavior of their candidates. With this
in mind, in the case of NISTmAb it is preferable to
work with the antibody in the buffer without salt
supplemented, as it demonstrates a positive k
D
and therefore a decreased tendency towards self-
association at higher concentrations.
Conclusion
The DLS capabilities of the Prometheus Panta allow
researchers to measure the self-association propensity
of their biologics, which enables them to make better
decisions about their protein therapeutics. The self-
interaction or diffusion-interaction parameter k
D
is a
useful indicator of how a protein-based therapeutic will
behave at higher concentrations, which is important
for scale-up and delivery. This information allows
researchers to select better candidates or optimize
formulations prior to scale-up and manufacture.
The k
D
is calculated from DLS experiments run at low
concentrations and used to extrapolate behavior
at high concentrations, such as those used for
subcutaneous injections in a clinical setting. High
viscosity can lead to difficulty administering a biologic
Impact of formulation on determined k
D
Altering the buffer, such as by changing the pH or
supplementing with salt, can have dramatic effects on
a protein's self-association behavior. To demonstrate
this, we evaluated the NISTmAb in two different buffers,
both 12.5 mM Histidine pH 6.0, one without additional
salts and one supplemented with 150 mM NaCl. Figure 2
shows how adding salt to the buffer affects the diffusive
behaviour of NISTmAb.
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2 4 6 8 1
Concentration (mg/ml)
k
D
= 17.9 ml/g
k
D
= -5.1 ml/g
Diffusion
Coefficient
(µm2/s)
Figure 2: Plot of concentration vs diffusion coefficient for k
D
determination of
NISTmAb in two different buffers. NISTmAb was prepared in 12.5 mM histidine
pH 6 (purple) or 12.5 mM histidine pH 6 + 150 mM NaCl (teal) at 10, 8, 6, 4, 2,
and 1 mg /ml; 10 measurements were obtained in high sensitivity mode on
three different capillaries for each concentration and a fit line was plotted.
