Less than 0.5% of intravenously injected drugs reach
tumors, contributing to side effects. To limit damage to healthy cells, various delivery vectors have been formulated; yet, previously developed vectors suffer from poor penetration into solid
tumors. This issue was resolved by the discovery of
HN-1 peptide isolated via biopanning a phage-display library. HN-1 targets human
head and neck squamous cell carcinoma (
HNSCC) (breast, thyroid; potentially lung, cervix, uterine,
colon cancer), translocates across the cell membrane, and efficiently infiltrates solid
tumors.
HN-1 peptide has been conjugated to various anticancer drugs and imaging agents though the identity of its receptor remained enigmatic.
AIM:
HN-1 peptide was synthesized and purified using reverse-phase high-performance liquid chromatography and gel electrophoresis. The predicted mass was confirmed by mass spectroscopy. To image the 3-dimensional structure of
HN-1 peptide, PyMOL was used. Molecular modeling was also performed with PEP-FOLD3 software via RPBS bioinformatics web portal (INSERM, France). The immunohistochemistry results of
discoidin domain receptor 1 (
DDR1) protein were obtained from the publicly accessible database in the Human
Protein Atlas portal, which contained the images of immunohistochemically labeled human
cancers and the corresponding normal tissues.
RESULTS: The clues that led to DDR1 involved in
metastasis as the putative receptor mediating HN-1 endocytosis are the following: (1) HN-1 is internalized in
phosphate-buffered saline and its uptake is competitively inhibited; (2) HN-1 (
TSPLNIHNGQKL) exhibits similarity with a stretch of
amino acids in alpha5
beta3 integrin (KLLITIHDRKEF). Aside from two identical residues (Ile-His) in the middle, the overall distribution of polar and nonpolar residues throughout the sequences is nearly identical. As HN-1 sequence lacks the
Arg-Gly-Asp motif recognized by
integrins, HN-1 may interact with an "
integrin-like" molecule. The tertiary structure of both
peptides showed similarity at the 3-dimensional level; (3) HN-1 is internalized by attached cells but not by suspended cells. As culture plates are typically coated with
collagen,
collagen-binding receptor (expressed by adherent but not suspended cells) may represent the receptor for HN-1; (4) DDR1 is highly expressed in
head and neck cancer (or
breast cancer) targeted by HN-1; (5) Upon activation by
collagen, DDR1 becomes internalized and compartmentalized in endosomes consistent with the determination of 'energy-dependent
clathrin-mediated endocytosis' as the HN-1 entry route and the identification of HN-1 entrapped vesicles as endosomes; and (6) DDR1 is essential for the development of mammary glands consistent with the common embryonic lineage rationale used to identify
breast cancer as an additional target of HN-1. In summary,
collagen-activated
tyrosine kinase receptor DDR1 overexpressed in
HNSCC assumes a critical role in
metastasis. Further studies are warranted to assess
HN-1 peptide's interaction with DDR1 and the therapeutic potential of treating metastatic
cancer. Additionally, advances in delivery (conformation, endocytic mechanism, repertoire of targeted
cancers of HN-1
peptide), tracking (HN-1 conjugated imaging agents), and activity (HN-1 conjugated therapeutic agents) are described.
CONCLUSION: