89Zr-DFO-J591 for immunoPET of prostate-specific membrane antigen expression in vivo

Abstract

(89)Zr (half-life, 78.41 h) is a positron-emitting radionuclide that displays excellent potential for use in the design and synthesis of radioimmunoconjugates for immunoPET. In the current study, we report the preparation of (89)Zr-desferrioxamine B (DFO)-J591, a novel (89)Zr-labeled monoclonal antibody (mAb) construct for targeted immunoPET and quantification of prostate-specific membrane antigen (PSMA) expression in vivo.

Methods: The in vivo behavior of (89)Zr-chloride, (89)Zr-oxalate, and (89)Zr-DFO was studied using PET. High-level computational studies using density functional theory calculations have been used to investigate the electronic structure of (89)Zr-DFO and probe the nature of the complex in aqueous conditions. (89)Zr-DFO-J591 was characterized both in vitro and in vivo. ImmunoPET in male athymic nu/nu mice bearing subcutaneous LNCaP (PSMA-positive) or PC-3 (PSMA-negative) tumors was conducted. The change in (89)Zr-DFO-J591 tissue uptake in response to high- and low-specific-activity formulations in the 2 tumor models was measured using acute biodistribution studies and immunoPET.

Results: The basic characterization of 3 important reagents-(89)Zr-chloride, (89)Zr-oxalate, and the complex (89)Zr-DFO-demonstrated that the nature of the (89)Zr species dramatically affects the biodistribution and pharmacokinetics. Density functional theory calculations provide a rationale for the observed high in vivo stability of (89)Zr-DFO-labeled mAbs and suggest that in aqueous conditions, (89)Zr-DFO forms a thermodynamically stable, 8-coordinate complex by coordination of 2 water molecules. (89)Zr-DFO-J591 was produced in high radiochemical yield (>77%) and purity (>99%), with a specific activity of 181.7 +/- 1.1 MBq/mg (4.91 +/- 0.03 mCi/mg). In vitro assays demonstrated that (89)Zr-DFO-J591 had an initial immunoreactive fraction of 0.95 +/- 0.03 and remained active for up to 7 d. In vivo biodistribution experiments revealed high, target-specific uptake of (89)Zr-DFO-J591 in LNCaP tumors after 24, 48, 96, and 144 h (34.4 +/- 3.2 percentage injected dose per gram [%ID/g], 38.0 +/- 6.2 %ID/g, 40.4 +/- 4.8 %ID/g, and 45.8 +/- 3.2 %ID/g, respectively). ImmunoPET studies also showed that (89)Zr-DFO-J591 provides excellent image contrast, with tumor-to-muscle ratios greater than 20, for the delineation of LNCaP xenografts between 48 and 144 h after administration.

Conclusion: These studies demonstrate that (89)Zr-DFO-labeled mAbs show exceptional promise as radiotracers for immunoPET of human cancers. (89)Zr-DFO-J591 displays high tumor-to-background tissue contrast in immunoPET and can be used to delineate and quantify PSMA-positive prostate tumors in vivo.

Figure 1

(A) Complexation reaction between [⁸⁹Zr(C₂O₄)₄]⁴⁻ and DFO. (B) DFT-optimized structure of 8-coordinate complex [⁸⁹Zr(HDFO)-cis-(H₂O)₂]²⁺ (3-cis).

Figure 2

PET images showing maximum intensity projection of ⁸⁹Zr-chloride and ⁸⁹Zr-oxalate at 24 h after intravenous administration and dynamic PET images of ⁸⁹Zr-DFO at 1 and 4 min after injection. For maximum-intensity-projection images, upper and lower intensity thresholds were set at 100% and 0%, respectively. Further details are presented in Supplemental Figures 3–6. MIP = maximum intensity projection.

Figure 3

Bar chart showing selected tissue biodistribution data (%ID/g) for uptake of either high- (181.7 ± 1.1 MBq/mg [4.91 ± 0.03 mCi/mg]; 3–4 µg of mAb per mouse) or low-specific-activity (60-fold decrease, 3.04 MBq/mg [0.082 mCi/mg]; 300 µg of mAb per mouse) formulations of ⁸⁹Zr-DFO-J591 (0.55–0.74 MBq [15–20 µCi], in 200 µL of sterile saline for injection) in male athymic nu/nu mice bearing subcutaneous LNCaP (PSMA-positive) or PC-3 (PSMA-negative) tumors.

Figure 4

Temporal immunoPET images of ⁸⁹Zr-DFO-J591 (10.9–11.3 MBq [295–305 µCi], 60–62 µg of mAb, in 200 µL of sterile saline) recorded in LNCaP tumor–bearing (PSMA-positive, left shoulder) (A) and PC-3 tumor–bearing (PSMA-negative, right shoulder) (B) mice between 3 and 144 h after injection. Transverse and coronal planar images intersect center of tumors, and mean tumor-to-muscle ratios derived from volume-of-interest analysis of immunoPET images are given. Upper thresholds of immunoPET have been adjusted for visual clarity, as indicated by scale bars.

Figure 5

Time–activity curves derived by volume-of-interest analysis of immunoPET images showing mean %ID/g tissue uptake vs. time/h for ⁸⁹Zr-DFO-J591 radiotracer accumulation in mice bearing subcutaneous LNCaP (PSMA-positive) or PC-3 (PSMA-negative) tumors. Complete time–activity curve data for ⁸⁹Zr-DFO-J591 immunoPET imaging is given in supplemental materials (Supplemental Tables 9 and 10; Supplemental Figs. 11–13).