Abstract
Understanding a drug's whole-body biodistribution and tumor targeting can provide important information regarding efficacy, safety, and dosing parameters. Current methods to evaluate biodistribution include in vivo imaging technologies like positron electron tomography and single-photon emission computed tomography or ex vivo quantitation of drug concentrations in tissues using autoradiography and standard biochemical assays. These methods use radioactive compounds or are cumbersome and do not give whole-body information. Here, for the first time, we show the utility of fluorescence molecular tomography (FMT) imaging to determine the biodistribution and targeting of an antibody-drug conjugate (ADC). An anti-5T4-antibody (5T4-Ab) and 5T4-ADC were conjugated with a near-infrared (NIR) fluorophore VivoTag 680XL (VT680). Both conjugated compounds were stable as determined by SEC-HPLC and plasma stability studies. Flow cytometry and fluorescence microscopy studies showed that VT680-conjugated 5T4-ADC specifically bound 5T4-expressing cells in vitro and also exhibited a similar cytotoxicity profile as the unconjugated 5T4-ADC. In vivo biodistribution and tumor targeting in an H1975 subcutaneous xenograft model demonstrated no significant differences between accumulation of VT680-conjugated 5T4-Ab or 5T4-ADC in either normal tissues or tumor. In addition, quantitation of heart signal from FMT imaging showed good correlation with the plasma pharmacokinetic profile suggesting that it (heart FMT imaging) may be a surrogate for plasma drug clearance. These results demonstrate that conjugation of VT680 to 5T4-Ab or 5T4-ADC does not change the behavior of native biologic, and FMT imaging can be a useful tool to understand biodistribution and tumor-targeting kinetics of antibodies, ADCs, and other biologics. Mol Cancer Ther; 15(10); 2530-40. ©2016 AACR.
Highlights
The biodistribution of a therapeutic agent provides significant insights regarding the drug's therapeutic efficacy, on- and offtarget potential toxicities, clearance mechanisms, half-life and metabolism as well as information for designing next-generation therapeutic agents with superior safety and efficacy [1,2,3,4,5]
In order to minimize the effects of fluorophore conjugation to the 5T4-Ab or 5T4-antibody–drug conjugate (ADC), we developed a conjugation protocol that would yield a DOL of approximately 3 VivoTag 680XL (VT680) molecules per antibody
We demonstrated that fluorescence molecular tomography (FMT) is a useful imaging modality to evaluate the biodistribution and tumor targeting of biologics
Summary
The biodistribution of a therapeutic agent provides significant insights regarding the drug's therapeutic efficacy, on- and offtarget potential toxicities, clearance mechanisms, half-life and metabolism as well as information for designing next-generation therapeutic agents with superior safety and efficacy [1,2,3,4,5]. Biodistribution studies are performed using radiolabeled compounds in rodents and collecting tissues at various time points after injection to quantitate the drug concentration. This method is labor intensive and requires the synthesis of radiolabeled compounds, specialized facilities to perform studies, and the use of a large number of animals. A major disadvantage of this method is that not every tissue or compartment of the body can be evaluated. Note: Supplementary data for this article are available at Molecular Cancer Therapeutics Online (http://mct.aacrjournals.org/).
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