Abstract: Described herein are peptides and variants thereof as well as peptide constructs comprising peptides conjugated to, linked to, or fused to agents, wherein the peptides and peptide constructs are capable of binding TfR. Binding of a peptide or peptide construct as described herein to TfR can enable transcytosis across an endothelial layer, e.g., the blood brain barrier, or the crossing of a cell membrane. Pharmaceutical compositions and uses of peptides and peptide constructs, as well as methods of designing and manufacturing such peptides and peptide constructs, to treat a disease or condition are also described herein.

Abstract: Peptides that home, distribute to, target, are directed to, or accumulate in tumors, cancers, or diseased cells are disclosed. Peptides that cross the blood brain barrier and home, distribute to, target, are directed to, or accumulate in the brain and in a specific region of the brain are also disclosed. Pharmaceutical compositions and uses for peptides or peptide-active agent complexes comprising such peptides are additionally disclosed. Such compositions can be formulated for targeted or untargeted delivery of a drug to a target region, tissue, structure or cell. Targeted compositions of the disclosure can deliver peptide or peptide-active agent complexes to target regions, tissues, structures or cells targeted by the peptide.