Longitudinal microSPECT/CT imaging and pharmacokinetics of synthetic luteinizing hormone-releasing hormone (LHRH) vaccine in rats

Background: Luteinizing hormone-releasing hormone (LHRH)-derived decapeptide-based vaccines have been used in studies of immunocastration and immunotherapy of prostate cancer, but no image data are available on the kinetics of vaccines post injection (p.i.). Therefore, an 131 I radiolabeled LHRH-derived immunogen was developed to visualize and evaluate the retention of LHRH-derived vaccines in rats. Materials and Methods: The LHRH immunogens, which contained equal moles of 131 I-p607E, p667 and p500, were formulated with an equal volume of an adjuvant, Montanide ISA50. MicroSPECT/CT imaging was performed to visualize the retention of the radiolabeled immunogen up to 30 days after intramuscular inoculation of 25 Ig immunogens. The pharmacokinetics, distribution and excretion were also evaluated. Results: The radiochemical purity of 131 I-p607E was 97.85±2.12%. The longitudinal microSPECT/CT imaging revealed that most 131 I-p607E was retained at the injected