Targeted chemotherapeutic drug discovery enabled by direct screening of peptide-drug conjugate libraries

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The scientific and medical community has been devoted to investigating different approaches for the treatment of cancer for over 100 years. In the mid-20th century, chemotherapeutic agents were introduced as adjuvant therapy to eliminate remaining cancer cells after surgery and radiation. Such therapies, for many cancer patients, have been able to slow tumor growth or even cure the cancer outright. However, conventional chemotherapy drugs are not able to differentiate between healthy cells and cancer cells, leading to several undesired side effects. In this regard, targeted chemotherapies with drugs that carry ligands for selective binding to specific receptors on cancer cells were developed to address this problem. Conjugating known receptor-targeting peptides to marketed drugs is a reliable method to generate bioactive PDCs as a targeted-delivery strategy. Because the number of known bioactive peptide sequences is limited, cell permeability often decreases after cargo attachment, and peptide-based drugs usually face short plasma half-life time, a streamlined approach for PDC development is needed. In this project, such a strategy is described by direct screening of an unnatural peptide-drug conjugate library in solution, which provides a straight forward approach to revealing de novo peptide sequences of PDC with protease resistance. A peptide library will be generated by SPPS assisted split-and-mix synthesis, followed by sequential Pt(IV) prodrug conjugation and PDC cleavage from solid support to yield a library of PDCs. The transmembrane protein, HER2, is overexpressed on various cancer cell lines and is a tested biological target for cancer treatment. After pull-down experiments for PDC binding to HER2, the mixture will be subjected to nLC-MS/MS for high throughput decoding, finally yielding potential hit PDCs. These PDCs will be prepared with an AFPS and PDC-HER2 binding will be confirmed by BioLayer Interferometry. Additionally, fluorescence microscopy experiments can be used to evaluate PDC internalization and MTT assays can assess their anticancer activity. The validation of hit PDCs offers opportunities to elucidate receptor-mediated internalization mechanisms. Thus, I would like to demonstrate an approach for the direct screening of PDC libraries to discover new, targeted cancer treatments as well as to develop molecular tools for elucidating new biology.