Date of Award


Document Type


Degree Name

Doctor of Philosophy (Ph.D.)


Pharmaceutical and Chemical Sciences

First Advisor

Xiaoling Li

First Committee Member

Bhaskara Jasti

Second Committee Member

Xin Guo

Third Committee Member

John Livesey

Fourth Committee Member

Jay Wu


Peptides have been used as targeting ligands in targeted drug delivery. Conjugating peptides to cytotoxicity agents via a linker to build peptide-drug conjugate (PDC) is a promising targeting strategy. The binding affinity of the peptide ligand and the receptor plays a crucial role in the PDC targeted drug delivery. Although the ligand binding which can be used in targeted drug delivery has been established conceptually, the quantitative or semi-quantitative contribution of binding affinity in targeting efficiency has not been fully explored. The optimal range of binding affinity of the peptide for targeted delivery remains unknown. Therefore, there is a lack of knowledge on the relationship between the peptide binding affinity and targeted drug delivery efficiency. The major steps in peptide drug delivery include cellular binding, cellular internalization, and tumor cells killing. In this study, three EGFR-targeting peptides with binding affinity levels ranging from 22 nM to 1.25 μM were selected to study their targeted drug delivery efficiency. The cellular binding study of FITC labeled peptides showed that peptide GE11 with the highest binding affinity had the highest cellular binding among three peptides. PEP11 peptide showed enhanced cellular binding compared to the L1 peptide. Moreover, GE11 also showed the selectivity of cellular binding between EGFR-positive cells and EGFR-negative cells. The cellular distribution showed that GE11-FITC could be successfully internalized into cells. The uptake mechanism studies demonstrated that the cellular uptake of GE11-FITC was based on receptor-mediated endocytosis, meaning that the cellular binding of GE11 was able to trigger the endocytosis. MMAE, a non-selective anticancer agent, was conjugated to the peptides through a protease-sensitive linker. The cytotoxicity assay showed that GE11-MMAE had the highest drug delivery efficiency and selectivity of three peptides, with 200 folds lower IC50 value than MMAE in EGFR-positive cells and 1000 times lower in EGFR-negative cells. PEP11-MMAE also showed an enhanced drug delivery than MMAE and L1-MMAE. L1-MMAE failed to show a significant difference with MMAE. Cellular binding kinetics results revealed that GE11-FITC had a higher rate of cellular uptake than PEP11-FITC.

In conclusion, in the range from micromolar to the nanomolar, higher binding affinity of peptide ligand will contribute to higher cellular binding, targeted drug delivery efficiency, and cellular uptake rate. These results suggest that in EGFR-targeting delivery, the nanomolar level binding affinity is necessary for peptides to be used as targeting moiety in the targeted drug delivery. This study provides a starting point for further quantitative probing of the optimal binding affinity for designing and developing peptide ligand-based targeted delivery.





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