Technetium-99m RP527, a GRP analogue for visualisation of GRP receptor-expressing malignancies: a feasibility study

Gastrin-releasing peptide (GRP) receptor scintigraphy could allow predictio n of response to GRP receptor-targeted treatment options, early non-invasiv e diagnosis and in vivo prognostic stratification of GRP receptor-positive tumours. This study reports on the imaging characteristics and efficacy for tumour detection of technetium-99m RP527, a Tc-99m chelated targeting pept ide derived from bombesin, which binds GRP receptors with high affinity. Te n patients (four men and six women, mean age 56.4 years) either suffering f rom metastasised prostate (n, number of patients = 4) or breast carcinoma ( n=1) or presenting with a clinical diagnosis high ly suggestive for breast carcinoma (n=5) were included in the study. In the latter five patients, Tc -99m-RP527 scintigraphy was performed prior to diagnostic, e.g. biopsy, and staging examinations. Final diagnosis in these patients was breast carcino ma in all five. In all patients, whole-body planar scans and tomographic im ages were acquired 1 h and 5-6 h post injection of 555 MBq Tc-99m-RP527 and tumour to normal tissue (T/N) ratios determined. Tc-99m-RP527 showed speci fic uptake in four of six breast and one of four prostate carcinomas. T/N r atios derived from planar and tomographic images increased significantly (P <0.01) from 1.65 (SD 1.53) and 3.35 (SD 3.04) to 2.58 (SD 1.26) and 7.23 (S D 8.46), respectively. T/N ratios derived from tomographic images were cons istently higher (P<0.01). The data presented suggest that Tc-99m-RP527 resu lts in specific tumour localisation and exhibits good imaging characteristi cs with a good T/N ratio that may be further enhanced by single-photon emis sion tomography.