Synthesis and Characterization of LD2 Peptide Analogs to Inhibit Focal Adhesion Kinase in Cancer

In cancer, various genetic and epigenetic alterations cause cancer cells to hyperproliferate and to bypass the survival and migration mechanisms that typically regulate healthy cells. The focal adhesion kinase (FAK) gene produces FAK, a protein that has been implicated in tumor progression in various cancers. Compared with normal tissue counterparts, FAK is overexpressed in many cancers. FAK is therefore a promising cancer drug target due to its demonstrated role in cancer invasion and metastasis and inhibition of FAK is important to achieve an optimal tumor response. Small molecule FAK inhibitors have been shown to decrease tumor growth and metastasis in several preclinical trials. However, these inhibitors focus narrowly on the enzymatic portion of FAK and neglect its scaffolding function, leaving FAK’s scaffolding of oncogenic drivers intact. Paxillin, a major focal adhesion-associated protein, binds to FAK, enabling it to localize to focal adhesions, and this is essential for FAK’s activation and function. Therefore, disrupting the protein-protein interaction between FAK and paxillin has been hypothesized to prevent tumor progression. The binding of FAK to paxillin at its focal adhesion targeting (FAT) domain is mediated by two highly conserved leucine-rich sequences, the leucine-aspartic acid (LD) motifs LD2 and LD4. The purpose of this project was to develop novel stapled LD2 peptide analogs that target the protein-protein interaction of FAT to LD2. Peptide stapling was performed to enhance the pharmacological performance of the LD2 peptide analogs. Based on the native LD2 peptide sequence, stapled LD2 peptide analogs were developed with the intent to improve efficacy of cell permeability, while maintaining or improving FAK binding. The LD2 peptide analogs were characterized via surface plasmon resonance, fluorescence polarization, immunofluorescence, and circular dichroism spectroscopy. Successful LD2 stapled peptide analogs can be therapeutically relevant inhibitors of the FAT-LD2 protein-protein interaction in cancer and have the potential for greater efficacy in FAK inhibition, proteolytic resistance, and cell permeability, which is key in preventing tumor progression in cancer.