TAT (48–60), GRKKRRQRRRPPQ, is an arginine rich peptide that can cross the cellular membranes and translocate into the nucleus due to a nuclear localization signal within its sequence. TAT has been conjugated to various active agents to mediate their delivery into the cells. Tan et al. utilized TAT-derived peptides (P1, P2, P3) coupled to an anti-HER2 peptide mimetic (AHNP) and STAT3 inhibiting peptide (P1/P2/P3-AHNPSTAT3) to enhance the TAT-dependent internalization and delivery of the therapeutic peptide into different HER2-overexpressing breast cancer cells including MDA-MB-435, SKBr3, and BT-474. The P1 variant (YGRKKRRQRRR) showed highest internalization compared to the other two truncated variants (P2; YGRKKRRQRR) and (P3; YGRKKRRQR) in HER 2-overexpressing SKBr3 cells indicating that arginine residue (R) is important for the increased cellular internalization.