Influence of the Molecular Charge on the Biodistribution of Bombesin Analogues Labeled with the [99mTc(CO)3]-Core

The overexpression of Bombesin (BBS) receptors on a variety of human cancers make them interesting targets for tumor imaging and therapy. Analogues of the neuropeptide BBS have been functionalized with the (NαHis)-chelator for labeling with the 99mTc-tricarbonyl core. The introduction of a βAla-βAla linker between the stabilized BBS binding sequence and the chelator led to increased tumor uptake but still rather unfavorable in vivo properties. Novel polar linkers, with different charge, have been introduced in the molecule and tested for their influence on the biodistribution. The new analogues showed a shift in hydrophilicity from a Log D = 0.9 to Log D values between 0.4 and −2.2. All compounds kept the increased stability in both human plasma (t 1/2 > 16 h) and in tumor cells (t 1/2 = 30−40 min). The compounds with Log D values between +1 and −1 showed the highest binding affinities with K d values of