Optimization of RGD-Containing Cyclic Peptides against αvβ3 Integrin

Abstract

We have previously reported the use of one-bead-one-compound (OBOC) combinatorial technology to develop a disulfide cyclic, Arg-Gly-Asp containing octapeptide LXW7 (cGRGDdvc), that targets αvβ3 integrin with high affinity and specificity (Mol Cancer Ther, 9:2714–23, 2010). αvβ3 integrin is known to be over-expressed in many cancers and in tumor vasculature, and it has been established as a cancer therapeutic target. To further optimize LXW7, we have performed systematic structure activity relationship (SAR) studies. Based on the results, two highly focused OBOC peptide libraries were designed, synthesized and screened against αvβ3 integrin transfected K562 cells. One of the best ligands, LXW64 was found to have 6.6-fold higher binding affinity than LXW7, and showed preferential binding to cells expressing αvβ3 integrin. In addition to binding strongly to U-87MG glioblastoma cells in vitro, LXW64 also targets U-87MG xenografts implanted in nude mice, indicating that it is an excellent vehicle for delivery of cytotoxic payload to tumors and tumor blood vessels that overexpress αvβ3 integrin.

Tumor-targeting peptides from combinatorial libraries

“…OBOC library can also be used for discovery of cell penetrating peptide ligands, but a cleavable linker and a reporting probe are needed in between the library compound and beads; (iv) OBOC combinatorial libraries are based on synthetic chemistry; therefore, it enables incorporation of D-amino acids, unnatural amino acids, many other organic building blocks, and investigation of cyclic, turned or branched peptides and secondary structures which can confer enhanced resistance to proteolytic degradation, a key requirement for clinical applications; (v) tumor-targeting ligands identified by OBOC library approach are not limited to peptides, but also N -methylated peptides [108], glycopeptides [109-111], peptide tertiary amides [112,113], peptidomimetics [114,115], and peptoids [116]; and (vi) the OBOC method can be used for rapid optimization of the initial lead compounds, whether they are native or identified from biological or synthetic peptide libraries. In OBOC method, each library compound is tethered to the solid support via a linker such as polyethylene glycol.…”

“…Further optimization of LXW7 led to development of LXW64 with sequence cGRGDd-nal1-c (where nal1 stands for D-1-naphthylalanine). LXW64 exhibits 6.6-fold more potent binding affinity against ανβ3-expressing U-87MG cell in vitro and better in vivo tumor targeting compared to LXW7 [108]. …”

Tumor-penetrating peptide fused to a pro-apoptotic peptide facilitates effective gastric cancer therapy

“…anticancer drugs by providing peptides with high affinity and specificity, and in addition they typically have low interaction with the immune system and good tumor and tissue penetration (19). In the targeted delivery of anticancer drugs into cancer tissue the ability to penetrate deep into the solid tumor tissue can potentially be a great challenge for the targeted therapeutic (3).…”

Targeting Integrins in Cancer Nanomedicine: Applications in Cancer Diagnosis and Therapy

“…The cyclic RGD (cRGD) peptides display higher activity than the linear RGD peptides due to a less flexible conformational structure that resists proteolysis [88,89]. To enhance the biological properties and pharmacokinetics of RGD peptides, including their affinity, various strategies have been used to modify the structure of RGD peptides, such as altering their structure [90] and the stereochemical configuration of the constituent amino acids [91], introducing other amino acids to flank the RGD sequence [92], and N-methylation [93,94]. The modification of NPs with RGD peptides could increase their binding affinity to specific integrins.…”