Improved radiopharmaceutical based on 99mTc-Bombesin–folate for breast tumour imaging

BackgroundClinical studies in women using technetium-99m (99mTc)-Bombesin have shown successful radionuclide imaging of breast tumours overexpressing gastrin-releasing peptide receptors (GRPRs). Recent studies have demonstrated that most breast tumours overexpress folate receptors (FR&agr;). AimThe aim of this work was to synthesize the Lys1(&agr;,&ggr;-Folate)-Lys3(99mTc-EDDA/HYNIC)-Bombesin (1–14) conjugate (99mTc-Bombesin–Folate), as well as to assess the in-vitro and in-vivo potential of the radiopharmaceutical to target FR&agr; and GRPR. MethodsLys1Lys3(HYNIC)-Bombesin (1–14) was conjugated to folic acid and the product was purified by size-exclusion high-performance liquid chromatography. Ultraviolet–visible spectroscopy, Fourier transform infrared spectroscopy and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry were used for chemical characterization. 99mTc labelling was performed using ethylenediamine-N,N′-diacetic acid/tricine as coligands. In-vitro binding studies were carried out in T47D breast cancer cells (positive for FR&agr; and GRPR). Biodistribution studies and micro-single-photon emission computed tomography/computed tomography imaging were carried out on athymic mice with T47D-induced tumours. ResultsHigh-performance liquid chromatography analyses indicated that the radioconjugate was obtained with high radiochemical purity (96±2.1%). In-vitro and in-vivo results showed significant uptake of the radiopharmaceutical in T47D cells and tumours (5.43% ID/g), which was significantly inhibited by preincubation with cold folic acid or cold Bombesin. ConclusionThe 99mTc-Bombesin–folate heterobivalent radiopharmaceutical significantly enhances in-vivo tumour uptake because of the concomitant interaction with FR&agr; and GRPR.