GRP and pachyonychia congenita: These findings explain why the positively charged [99 mTc]-labeled bombesin analog [25] displays high affinity to GRP receptor and high accumulation in PC-3 tumors whereas non-positively charged analogs, such as 64Cu-labeled DOTA-Aoc-BN(7–14) [35] or 111In-labeled DOTA-[Lys3] BN [36] show low affinities.