Effect of molecular size on interstitial pharmacokinetics and tissue catabolism of antibodies

Abstract

Advances in antibody engineering have enabled the construction of novel molecular formats in diverse shapes and sizes, providing new opportunities for biologic therapies and expanding the need to understand how various structural aspects affect their distribution properties. To assess the effect of antibody size on systemic pharmacokinetics (PK) and tissue distribution with or without neonatal Fc receptor (FcRn) binding, we evaluated a series of non-mouse-binding anti-glycoprotein D monoclonal antibody formats, including IgG [~150 kDa], one-armed IgG [~100 kDa], IgG-HAHQ (attenuated FcRn binding) [~150 kDa], F(ab')₂ [~100 kDa], and F(ab) [~50 kDa]. Tissue-specific concentration-time profiles were corrected for blood content based on vascular volumes and normalized based on interstitial volumes to allow estimation of interstitial concentrations and interstitial:serum concentration ratios. Blood correction demonstrated that the contribution of circulating antibody on total uptake was greatest at early time points and for highly vascularized tissues. Tissue interstitial PK largely mirrored serum exposure profiles. Similar interstitial:serum ratios were obtained for the two FcRn-binding molecules, IgG and one-armed IgG, which reached pseudo-steady-state kinetics in most tissues. For non-FcRn-binding molecules, interstitial:serum ratios changed over time, suggesting that these molecules did not reach steady-state kinetics during the study. Furthermore, concentration-time profiles of both intact and catabolized molecule were measured by a dual tracer approach, enabling quantification of tissue catabolism and demonstrating that catabolism levels were highest for IgG-HAHQ. Overall, these data sets provide insight into factors affecting preclinical distribution and may be useful in estimating interstitial concentrations and/or catabolism in human tissues.

Keywords: Monoclonal antibody (mAb); distribution; interstitial; neonatal Fc receptor (FcRn); pharmacokinetics; size; tissue.

Figure 1.

Schematic of molecules. IgG1-HAHQ has mutations H310A and H435Q in the Fc region that ablate FcRn binding. F(ab’)₂ and F(ab) have no Fc region.

Figure 2.

continued.

Figure 2.

Blood, serum, and uncorrected tissue concentration–time profiles of antibody variants detected by radioactivity in terms of (a) ¹²⁵I (intact only) or (b) ¹¹¹In (intact plus catabolized) after a single IV injection (5 mg/kg) in C57Bl/6 mice. Concentrations are reported in %ID/mL or %ID/g.

Figure 3.

Blood correction of selected tissue concentration–time profiles of antibody variants detected by radioactivity in terms of ¹²⁵I (intact only) after a single IV injection (5 mg/kg) in C57Bl/6 mice. Solid circles are uncorrected while hollow circles are blood corrected values. The proportion of antibody in blood and interstitial compartments is depicted in red and green, respectively. Concentrations are reported in %ID/g.

Figure 4.

Tissue interstitial fluid concentration–time profiles of antibody variants detected by radioactivity in terms of ¹²⁵I (intact only) after a single IV injection (5 mg/kg) in C57Bl/6 mice. Interstitial concentrations were not calculated for tissues with highly fenestrated capillaries (e.g., liver, spleen) or for eyes that are composed mostly of vitreous matter. Concentrations are reported in µg/mL.

Figure 5.

continued.

Figure 5.

Tissue interstitial:serum concentration ratios over time for FcRn-binding (a) and FcRn-non-binding (b) antibody variants after a single IV injection (5 mg/kg) in C57Bl/6 mice. Interstitial concentrations detected by radioactivity in terms of ¹²⁵I (intact only) were normalized to serum concentrations (¹²⁵I) for all molecules except for F(ab), for which ¹¹¹In serum concentrations were used for normalization due to contamination of ¹²⁵I serum signal by catabolites escaping the kidneys.

Figure 6.

Effect of molecule size on tissue catabolism of antibody variants. Tissue catabolism may be approximated as the difference (highlighted in yellow) between ¹¹¹In (intact plus catabolized) and ¹²⁵I (intact only) after a single IV injection (5 mg/kg) in C57Bl/6 mice. Concentrations are reported in %ID/g. Data for intact (¹²⁵I) F(ab) (bottom row, hollow symbols) should be interpreted with caution as tissue levels are contaminated by ¹²⁵I-labeled catabolites escaping the kidneys.

Figure 7.

Population mean compartmental model fits to all available blood (red curves and circles) and plasma (blue curves and circles) PK data. Supplemental Table 1 shows final fitted population mean parameter values and AUC_0-168h values for each molecule.