Peptide–drug conjugate-based novel molecular drug delivery system in cancer

Drug delivery systems are generally believed to comprise drugs and excipients. A peptide–drug conjugate is a single molecule that can simultaneously play multiple roles in a drug delivery system, such as in vivo drug distribution, targeted release, and bioactivity functions. This molecule can be regarded as an integrated drug delivery system, so it is called a molecular drug delivery system. In the context of cancer therapy, a peptide–drug conjugate comprises a tumor-targeting peptide, a payload, and a linker. Tumor-targeting peptides specifically identify membrane receptors on tumor cells, improve drug-targeted therapeutic effects, and reduce toxic and side effects. Payloads with bioactive functions connect to tumor-targeting peptides through linkers. In this review, we explored ongoing clinical work on peptide–drug conjugates targeting various receptors. We discuss the binding mechanisms of tumor-targeting peptides and related receptors, as well as the limiting factors for peptide–drug conjugate-based molecular drug delivery systems. A single peptide–drug conjugate molecule achieves multiple biological functions, which is proposed as a novel drug delivery system, the molecular drug delivery system.Recently, peptide–drug conjugates have been introduced as potential diagnostics and anticancer drugs in the clinic.Aminopeptidase N, integrins, the somatostatin receptor, and several other receptors are major molecular targeting receptors for current peptide–drug conjugate-based molecular drug delivery systems.Solving the problem of oral administration will greatly promote the development of peptide–drug conjugate molecular drug delivery systems.