Recent advances have unveiled new frontiers in cancer treatment through the design and application of hydrocarbon-stapled peptides aimed at disrupting the focal adhesion kinase (FAK)-paxillin interaction, promising to improve clinical outcomes for patients where conventional therapies have failed.
Focal adhesion kinase, commonly overexpressed across many solid tumors, is integral to several hallmarks of cancer, including proliferation and metastasis. Its traditional inhibitors have largely proven ineffective, as they often target the kinase domain—the site necessary for its scaffolding activities—leading to limited therapeutic benefits. Researchers at the University of Arizona have taken a revolutionary approach by targeting the protein-protein interaction (PPI) between FAK's focal adhesion targeting (FAT) domain and paxillin, utilizing the structural design of chemically-stabilized peptides.
The recent study focuses on the design of specific peptide inhibitors, termed stapled peptides, derived from the paxillin LD2 sequence, known for its interaction with FAK. Employing structural biology techniques, such as X-ray crystallography, the team created peptide 1907, which displayed markedly improved binding affinity—over 100 times greater—compared to the native LD2 sequence. These peptides were chemically altered to contain hydrocarbon staples, which stabilize their alpha-helical structure and significantly increase their efficacy within biological systems.
Research methods included surface plasmon resonance (SPR) and fluorescence polarization assays to demonstrate the improved binding capabilities of the peptides. The boldest new class identified, lead peptide 2012, included modifications for enhanced cell permeability and protease resistance. This myristoylated version showed pronounced efficacy, yielding reduced cancer cell viability and prompting apoptosis, all the way down to IC50 values as low as 0.80 µM, matching its binding affinity at the target site.
Upon testing the lead inhibitor 2012 against various melanoma cell lines, results indicated not only effective disruption of FAK localization to focal adhesions but also superior results relative to traditional FAK kinase inhibitors. Unlike the latter, which significantly increased the proportion of FAK-containing focal adhesions, 2012 effectively diminished this figure, highlighting its unique therapeutic mechanism.
This targeting of specific molecular frameworks has prompted the authors to refer to it as the first reliable strategy for hitting previously classified undruggable targets. "This is the first indication of targeting the FAT-paxillin complex to provide selective anti-cancer responses, indicating it's possible to drug previously undruggable targets," remarked the researchers. These peptides not only demonstrate promise as effective cancer therapeutics but also promise few off-target effects compared to standard kinase inhibitors.
The investigation underscored the importance of structural modifications, detailing how the presence of hydrocarbon staples serves to optimize drug delivery and binding specificity. Initial studies have shown significant pharmacokinetic advantages as seen through the excellent plasma half-life displayed by peptide 2012, reinforcing its potential for clinical translation.
With these findings, the research sets the stage for future studies exploring the use of FAK-targeted therapies across various cancers, potentially establishing hydrocarbon-stapled peptides as valuable assets within the oncology pharmaceutical arsenal. Further research may involve expansion beyond melanoma cells to encompass varied tumor types, offering hope for targeted treatments with fewer side effects and higher patient tolerability.