Radiolabeling optimization and characterization of (68)Ga labeled DOTA-polyamido-amine dendrimer conjugate - Animal biodistribution and PET imaging results

Abstract

The present study describes the optimization of (68)Ga radiolabeling with PAMAM dendrimer-DOTA conjugate. A conjugate (PAMAM-DOTA) concentration of 11.69µM, provided best radiolabeling efficiency of more than 93.0% at pH 4.0, incubation time of 30.0min and reaction temperature ranging between 90 and 100°C. The decay corrected radiochemical yield was found to be 79.4±0.01%. The radiolabeled preparation ([(68)Ga]-DOTA-PAMAM-D) remained stable (radiolabeling efficiency of 96.0%) at room temperature and in serum for up to 4-h. The plasma protein binding was observed to be 21.0%. After intravenous administration, 50.0% of the tracer cleared from the blood circulation by 30-min and less than 1.0% of the injected activity remained in blood by 1.0h. The animal biodistribution studies demonstrated that the tracer excretes through the kidneys and about 0.33% of the %ID/g accumulated in the tumor at 1h post injection. The animal organ's biodistribution data was supported by animal PET imaging showing good 'non-specific' tracer uptake in tumor and excretion is primarily through kidneys. Additionally, DOTA-PAMAM-D conjugation with αVβ3 receptors targeting peptides and drug loading on the dendrimers may improve the specificity of the (68)Ga labeled product for imaging and treating angiogenesis respectively.

Keywords: Angiogenesis; DOTA-NHS; Gallium-68 complexes; Nanoparticles; PAMAM conjugates; Radiolabeling.

Fig. 1

Cytotoxic effects of DOTA–PAMAM-D in BMG cells studied by % cell viability using MTT assay.

Fig. 2

ITLC-SG of the [⁶⁸Ga] DOTA–PAMAM-D: mobile phase 1 M ammonium acetate:methanol (1:1).

Fig. 3

Radiolabeling efficiency (%) of [⁶⁸Ga] DOTA–PAMAM-D calculated at different volumes of buffer.

Fig. 4

Radiolabeling efficiency (%) of [⁶⁸Ga] DOTA–PAMAM-D at different concentrations of conjugate.

Fig. 5

Radiolabeling efficiency (%) of [⁶⁸Ga] DOTA–PAMAM-D with different heating times.

Fig. 6

In vitro and serum stability of [⁶⁸Ga] DOTA–PAMAM-D as a function of time.

Fig. 7

Biodistribution pattern of [⁶⁸Ga] DOTA–PAMAM-D in various organs of normal balb/c mice at three different time intervals (15 min, 30 min and 60 min).

Fig. 8

Biodistribution pattern of [⁶⁸Ga] DOTA–PAMAM-D in various organs of tumor bearing balb/c mice at three different time intervals (15 min, 30 min and 60 min).

Fig. 9

(a) Reconstructed PET/CT imaging in normal Balb/c mice with [⁶⁸Ga] DOTA–PAMAM-D. (b) Reconstructed PET/CT imaging in EAT bearing Balb/c mice with [⁶⁸Ga] DOTA–PAMAM-D.