Abstract
The pharmacokinetic (PK) behavior of monoclonal antibodies (mAbs) is influenced by target-mediated drug disposition (TMDD), off-target effects, anti-drug antibody formation, and interaction with Fc receptors such as FcRn. All of these interactions hold the potential to impact mAb biodistribution. Near-infrared (nIR) fluorescent probes offer a complementary approach to radionuclides to characterize drug disposition. Notably, the use of FDA-approved IRDye800® (IR800; LI-COR®) as a protein labeling agent in preclinical work holds the potential for quantitative tissue analysis. Here, we tested the utility of IR800 dye as a quantitative mAb tracer during pharmacokinetic analysis in both plasma and tissues using a model mouse monoclonal IgG1 (8C2) labeled with ≤ 1.5 molecules of IR800. The plasma PK parameters derived from a mixture of IR800-8C2 and 8C2 dosed intravenously to C57BL/6 mice at 8 mg/kg exhibited a large discrepancy in exposure dependent on the method of quantitation (CLplasma = 56.9 mL/day/kg (nIR fluorescence detect) versus 16.8 mL/day/kg (ELISA)). The disagreement between measurements suggests that the PK of 8C2 is altered by IR800 dye. Additionally, direct fluorescence analysis of homogenized tissues revealed several large differences in IR800-8C2 tissue uptake when compared with a previously published study using 125I-8C2 (Abuqayyas et al., 2012), most notably an over 4-fold increase in liver concentration. Finally, the utility of IR800 in combination with whole body imaging was examined by comparison of IR800-8C2 levels observed in animal saggital cross sections to those measured in homogenized tissues. Our results represent the first PK analysis in both mouse plasma and tissues of an IR800-mAb conjugate and suggest that mAb disposition is significantly altered by IR800 conjugation.
- The American Society for Pharmacology and Experimental Therapeutics