Utility of a human FcRn transgenic mouse model in drug discovery for early assessment and prediction of human pharmacokinetics of monoclonal antibodies

Abstract

Therapeutic antibodies continue to develop as an emerging drug class, with a need for preclinical tools to better predict in vivo characteristics. Transgenic mice expressing human neonatal Fc receptor (hFcRn) have potential as a preclinical pharmacokinetic (PK) model to project human PK of monoclonal antibodies (mAbs). Using a panel of 27 mAbs with a broad PK range, we sought to characterize and establish utility of this preclinical animal model and provide guidance for its application in drug development of mAbs. This set of mAbs was administered to both hemizygous and homozygous hFcRn transgenic mice (Tg32) at a single intravenous dose, and PK parameters were derived. Higher hFcRn protein tissue expression was confirmed by liquid chromatography-high resolution tandem mass spectrometry in Tg32 homozygous versus hemizygous mice. Clearance (CL) was calculated using non-compartmental analysis and correlations were assessed to historical data in wild-type mouse, non-human primate (NHP), and human. Results show that mAb CL in hFcRn Tg32 homozygous mouse correlate with human (r(2) = 0.83, r = 0.91, p < 0.01) better than NHP (r(2) = 0.67, r = 0.82, p < 0.01) for this dataset. Applying simple allometric scaling using an empirically derived best-fit exponent of 0.93 enabled the prediction of human CL from the Tg32 homozygous mouse within 2-fold error for 100% of mAbs tested. Implementing the Tg32 homozygous mouse model in discovery and preclinical drug development to predict human CL may result in an overall decreased usage of monkeys for PK studies, enhancement of the early selection of lead molecules, and ultimately a decrease in the time for a drug candidate to reach the clinic.

Keywords: Allometric scaling; FcRn; Human PK prediction; IgG; Neonatal Fc Receptor; PK; clearance; hFcRn transgenic mice; mAb; monoclonal antibody; pharmacokinetics.

Figure 1.

Panel of mAbs Used in Study. Interspecies CL for therapeutic mAbs. Panels A, B and C depict the 27 mAbs examined in this study, including 21 Pfizer mAbs (•) and 6 marketed mAbs () and the CL values (mL/hr/kg) for human (15/27), NHP (26/27), and WT mouse (17/27), respectively. Mean CL value are depicted for each species. Symbols depict definitive linear CL values (•), apparent linear CL values (▪) and non-linear (▴). Of the 27 collected mAbs: 24 are IgG1 and 3 are IgG2; 16 have soluble ligand targets, 9 have membrane bound targets, and 2 target both soluble and membrane bound receptor targets; 12 are fully human, 13 are humanized, and 2 are chimeric.

Figure 2.

hFcRn Tg Mouse Strain Comparisons. PK profile results of Tg32 hemizygous and homozygous, Tg276 homozygous, WT C57Bl/6 and FcRn KO mice following administration of (A) mAb 14, (B) mAb 04 and (C) mAb17. (D) PK profile overlay in FcRn KO mice for mAb04 and mAb17. (E) PK parameters for mAb14, mAb04 and mAb17 in NHP and each mouse model. Data is depicted as the mean ± standard deviation for 3-6 animals/group for panels A-D.

Figure 3.

hFcRn Tissue Expression Profile in Tg32 Hemizygous and Homozygous Mice. Significant expression differences between homozygous and hemizygous genotypes were analyzed using an unpaired Mann-Whitney test where significance is indicated as single asterisk (*) for p < 0.1 and double asterisk (**) for p < 0.05.

Figure 4.

hFcRn Tg32 PK Differentiation in Framework Mutations. CL correlation between (A) Tg32 hemizygous and (B) homozygous mouse to NHP for 4 pairs of parent and FcRn+ mAbs (mAb01, mAb02, mAb07, mAb14) and (C) Summary of CL and T1/2 PK parameters for each parent and FcRn+ mAb in Tg32 hemizygous and homozygous mice and NHP. Statistical significance determined using a Student's paired t-test (*p < 0.05 and ** p < 0.01).

Figure 5.

Correlation of mAb CL in Rodents to mAb CL in NHP. Linear correlation graphs of (A) WT mouse CL to NHP CL for 15/27 mAbs, (B) Tg32 hemizygous mouse CL to NHP CL for 25/27 mAbs and (C) Tg32 homozygous CL to NHP CL for 23/27 mAbs. Tg32 mouse CL results are shown as the mean ± standard deviation for 3-6 animals/group. Symbols: •, definitive linear CL values; ▪, apparent linear CL in NHP only; ▴, apparent linear CL in rodent only; ♦, apparent linear CL in both NHP and rodent. •, Pfizer mAbs , marketed therapeutic mAbs.

Figure 6.

Correlation of mAb CL in Rodents vs Human and NHP vs Human. Linear correlation graphs of (A) WT mouse CL to human CL for 11/27 mAbs, (B) NHP CL to human CL for 15/27 mAbs, (C) Tg32 hemizygous CL to human CL for 15/27 mAbs and D) Tg32 homozygous CL to human CL for 15/27 mAbs. MAbs shown in panels B, C, and D represent the same 15 mAbs. Tg32 mouse CL results are shown as the mean ± standard deviation for 3-6 animals/group. Symbols: •, definitive linear CL values; ▴, apparent linear CL in rodent or NHP; ▪apparent linear CL in human; ♦, apparent linear CL in rodent or NHP and human. •, Pfizer mAbs, , marketed therapeutic mAbs.

Figure 7.

Single Species Allometric Scaling of CL for mAbs. Allometric Scaling for mAbs in NHP (15/27mAbs), WT mice (11/27mAbs), and hFcRn Tg32 hemizygous and homozygous mice (15/27 mAbs), comparing a standard scaling exponent of 0.75 (top row) to an empirically derived best fit exponent (middle row) per animal model. Results are plotted against a line of unity (solid black line) ± 2-fold error (dotted gray lines) where accuracy is described as the percentage (%) of mAbs predicted within 2-fold of the line of unity. Symbols: •, definitive linear CL values; ▴, apparent linear CL in rodent or NHP; ▪, apparent linear CL in human; ♦ apparent linear CL in rodent or NHP and human. •, training data set. , test set, marketed therapeutic mAbs.

Figure 8.

Utility of hFcRn Tg32 Mouse Model. (A) Current timeline for utility of NHP PK studies in preclinical development. (B) Suggested timeline for utility of hFcRn Tg32 PK studies, showing earlier use in discovery and application of allometric scaling using the exponent 0.93 to scale to human PK. (C) Use and selection of hemizygous vs homozygous Tg32 model.