Novel homing peptides as powerful theranostic tools for targeting central nervous system (CNS) tumors

This thesis is centered on homing peptides targeting the central nervous system (CNS) tumors, focusing on glioblastoma (GBM) and brain metastases (BM). Both GBM and BM represent an unmet medical need with dismal prognosis. GBM is the most malignant primary brain tumor in adults with bulky and highly infiltrative tumors. BM is a secondary brain tumor commonly originating from aggressive solid tumors, including triple negative (TN) and HER2+ breast cancers, melanoma, and non-small cell lung cancers (NSCLC). In addition, other solid cancer types are at risk of developing brain metastases. Despite the better outcomes for cancer patients due to improved systemic therapy, there are still increasing incidences of about 4-6 million new BM patients annually. BM are multifocal and highly infiltrative tumors that are very difficult to detect and due to the technical challenges of removing the invasive tumor masses in the brain, BM patients are mostly not eligible for neurosurgery! . Similar ly, the total surgical removal of GBM tumor is impossible thereby leaving behind highly invasive tumor cells. Identifying homing peptides that selectively target these invasive tumor cells would allow the development of novel targeted therapies against malignant brain tumors. In the first subproject, an alanine scan for a GBM homing peptide, ACooP, was performed by substituting each amino acid residue in the sequence with alanine in a sequential order to generate 13 novel peptides. A binding study of each peptide variant with the ACooP target protein, the recombinant fatty acid binding protein 3/mammary-derived growth inhibitor (FABP3/MDGI), was performed by using microscale thermophoresis (MST) and surface plasmon resonance (SPR) to investigate the necessity of each amino acid in binding. This sequence activity relationship (SAR) study would aid the future development of targeted therapies against GBM or other CNS tumor-related malignancies. In the second subproject, ACooP was conjugated to Fluorine-18 to develop a novel radiopeptide for targeted PET imaging and utilized for the in vitro visualization of FABP3/MDGI expressing brain metastases in lung cancer patient tissue samples. In the third subproject, I described the discovery of a novel 9-amino acid long BM homing peptide identified via an in vivo phage display screen using preclinical brain metastases model that I created for the study. The peptide was briefly designated as ‘RVA’ and branded a new patent named 'Navigator'. Moreover, I identified peroxiredoxin 1 (PRDX1) as the binding partner for RVA after photoaffinity crosslinking and mass spectrophotometric studies. In a proof-of-concept study, RVA was modified as a molecular probe or conjugated to cytotoxic agents for theranostic applications in preclinical BM models.