Breast cancer is one of the most common malignant tumors among women, which seriously threatens women’s health. Human epidermal growth factor receptor 2 (HER2)-positive breast cancer, characterized by poor prognosis, is an aggressive phenotype accounting for 15–20% of all kinds of breast cancers. Therefore, it has attracted great interest among researchers in discovering targeted therapy drugs countering HER2, and they have been considered as the pivotal therapeutic regimen for HER2-positive breast cancer patients. Nowadays, large progress has been achieved in HER2-targeted drugs, and this review categorizes them into four types according to the drug action mode, including monoclonal antibodies (mAbs), tyrosine kinase inhibitors (TKIs), antibody-drug conjugates (ADCs), and bispecific antibodies (bsAbs). The progress of HER2-targeted drugs reflects the discovery of drug targets, the screening of drug compounds, and the modification of antibodies, which offer diverse medical options and better therapeutic benefits for individual patients. In detail, we focus on the indication, administration, efficacy, strengths, and challenges of HER2-targeted drugs, concerning approved drugs and clinical trials. This review aims to provide significant references for the targeted therapeutic regimen and a more precise treatment strategy for HER2-positive breast cancer.

Cell-penetrating peptides (CPPs) are invaluable tools for delivering various substances into cells by crossing biological membranes. However, the effects of cell-penetrating peptide fusion proteins on the biological activity of antibodies remain to be fully understood. Here, we engineered a recombinant protein, LP-scFv, which combines the single-chain variable region of anti-human epidermal growth factor receptor-2 with a novel and non-oxic cell-penetrating peptide as a leader peptide. The introduction of this leader peptide led to a more than twofold increase in the internalization efficiency of the single-chain antibody, as confirmed using microscopic analysis and flow cytometry. The effects of the single-chain antibodies and LP-scFv on cell viability were evaluated using the MTT assay. Both the single-chain antibodies and LP-scFv reduced the viability of BT474 and NCI-N87 cells in a dose-dependent manner while exhibiting minimal toxicity towards MCF-7 and MCF-10A cells. Further investigation into LP-scFv’s mechanism revealed that the induced leader peptide does not alter the MAPK-ERK1/2 and PI3K/AKT pathways of single-chain antibodies. An enhanced antitumor activity was also confirmed in an NCI-N87 tumor xenograft model in mice with a reduction of 45.2% in tumor growth inhibition (vs. 23.1% for scFv) with a 50 mg/kg dose after orthotopic injection administration, which was equivalent to that of trastuzumab (vs. 55.7% for trastuzumab). Overall, these results indicate that LP-scFv exhibits significant permeation activity in HER2-positive cells to enhance the intracellular dose effect on antitumor activity in vitro and in vivo. This research lays the foundation for designing novel antibody-based therapies for cancer.