Fig. 4. Latest designs of PNA–peptide conjugates for cell-specific delivery and overcoming endosomal entrapment. (A) Tumor-specific delivery of a pHLIP conjugated PNA that releases the antisense PNA by cleaving the connecting S–S bond in a reducing environment in cells, which can induce cell apoptosis. (B) Cyclization of the TAT peptide by a PNA–PNA duplex that contains an overhang sequence binding to an antisense PNA. The entire molecular construct is internalized into cells via endocytosis, demonstrating photoirradiation-mediated escape from the endosome and inhibition of telomerase activity.