Biomeasures and mechanistic modeling highlight PK/PD risks for a monoclonal antibody targeting Fn14 in kidney disease

Figures & data

Figure 1. The mechanistic SoA model developed for predicting target coverage on membrane Fn14 in kidney in the presence of circulating soluble Fn14.

Figure 2. Experimental measures for mFn14 and sFn14 levels in human. Left bar: concentration of mFn14 in human kidney tissue from diabetic nephropathy patients. Right bar: concentration of sFn14 in human serum from healthy subjects. The bar height represents the mean value and error bar represents the standard deviation. The y-axis is in log scale.

Figure 3. Pulse-chase experiment for determining serum turnover rate of sFn14. a: Chromatograms at selected time points showing the growth and decay of the newly synthesized peptide (blue) ratio to light peptide (red). b: The enrichment of heavy leucine (▪) and heavy sFn14 peptide (▴) in human serum and the corresponding fitted curves. The graph is from one representative subject. Accordingly, the calculated average half-life of sFn14 was 5 ± 0.5 hours in three human subjects.

Table 1. Model parameters for mechanistic SoA model.

Parameter	Definition	Units	Value	Reference
Sp0	sFn14 baseline concentration in plasma	nM	1.7	Measured value in healthy volunteers by MS
Ts0	mFn14 baseline concentration in kidney	nM	63	Measured value in diabetic nephropathy patients by MS
kintT	Internalization rate of mFn14 in kidney	hr^−1	0.014-1.4	A range of internalization half-life of 0.5 to 50 hr was investigated
kintDT	Internalization rate of mFn14-mAb complex in kidney	hr^−1	0.014-1.4	Assumed same internalization rate as mFn14
kelS	Elimination rate of sFn14 in plasma	hr^−1	0.14	A half-life of 5 hr in healthy subjects by SIL pulse chase study
kelDs	Elimination rate for drug-sFn14 complex in plasma	hr^−1	0.0035	Assumed same elimination rate as mAb for soluble target
kD	Binding affinity of anti-Fn14 mAb	nM	0.3	Predicted optimal KD
Kon	on rate for anti-Fn14 mAb binding	M^−1×hr^−1	3.6	Maximum on-rate controlled by diffusion limit of antibody (1)
kelD	Elimination rate constant of the anti-Fn14 mAb	hr-1	0.0035	Typical mAb PK parameter
kptD	Distribution rate constant of anti-Fn14 mAb from plasma to peripheral compartment	hr^−1	0.0078	Typical mAb PK parameter
ktpD	Distribution rate constant of anti-Fn14 mAb from peripheral compartment to plasma	hr^−1	0.0079	Typical mAb PK parameter
kpsd	Distribution rate constant of anti-Fn14 mAb from plasma to into SoA	hr^−1	0.043	Based on the assumption that antibody distribution into tissue is driven by lymphatic flow, which is 0.2% of blood flow ($C{L}_{DPs}$= 124.6 ml/h *0.2% = 0.25 ml/h) (2,3) and $k_{psD}=\frac{C{L}_{DPs}}{V_p}$
kspd	Distribution rate constant of anti-Fn14 mAb from SoA to plasma	hr^−1	4.21	Back-calculated based on tissue mAb concentration is about 30% of plasma concentration (4,5)

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Figure 4. Simulated relationship between required dose and K_d of anti-Fn14 mAb as a function of 1) mFn14 half-life in kidney (0.5, 5, or 50 hours as illustrated in panels), 2) pre-specified target coverage (90% or 50% as illustrated as blue or yellow curve), and 3) sFn14 concentrations (baseline level in healthy subjects to 10 times baseline, as expressed in width of bands). Optimal K_d of anti-Fn14 mAb is the K_d at which the required dose is the lowest (illustrated as vertical lines).

Figure 5. Projection of Fn14 target coverage in human plasma and kidney with subcutaneous administration.