LH2 peptide is a pH-responsive, cell-penetrating peptide dimer with the amino acid sequence LHHLCHLLHHLCHLAG. It increases uptake in tumor cells in slightly acidic environments (such as the tumor microenvironment) through histidine residue protonation (pKa approximately 6). When conjugated with the anticancer agent paclitaxel to form PTX-LH2, it demonstrates superior tumor inhibition compared to paclitaxel alone in a subcutaneous breast tumor model. LH2 peptide holds promise as a delivery vector for cancer research.