Based on our identification of a polypeptide (Angiopep-7) that is efficiently transported to cells such as liver, lung, kidney, spleen, and muscle, the invention provides polypeptides, conjugates including the polypeptides, and methods for treating diseases associated with these cell types. Unlike other aprotinin related polypeptides identified herein (including Angiopep-3, Angiopep-4a Angiopep-4b Angiopep-5, and Angiopep-6) which efficiently cross the blood-brain barrier (BBB), Angiopep-7 is not efficiently transported across the BBB.
