The Rational Design, Synthesis, Characterization, and Biological Evaluation of Cancer-Targeting Immunostimulatory Peptide-Protein Conjugates and Tripeptides

With the advent of cancer immunotherapy and the rise in applications of synthetic biologics, there has been a steady decline in the incidence of cancer. Despite this trend, there is an anticipated 1.7 million new cancer cases with an estimated 610,000 deaths expected by the end of 2018.2 Therefore, the call for continued efforts in creating more effective treatment options are still in high demand. In this thesis, the rational design of a semi-synthetic cancer-targeting immunostimulatory peptide-protein bioconjugate—using N-succinimidyl carbamate chemistry is described. This bio-orthogonal chemistry approach was used to conjugate the synthetic Pep42, cancer-targeting peptide (CTP) and the immunostimulatory recombinant B7H6 tumor associated antigen (TAA). Also reported within this thesis is the design, synthesis and biological evaluation of bifunctional tripeptides composed of the CTP and TAA targeting and effector ligands, respectively. The purported CTP was anticipated to bind to cell surface GRP78—a phenotype found exclusively in several cancers, while the TAA, was expected to bind and activate NKp30, an activating natural cytotoxicity receptor (NCR) found on the surface of NK cells. In this manner, the cancer-targeting immunostimulatory peptide-protein conjugates and tripeptides were hypothesized to behave as bifunctional antibody mimics, targeting and activating NK cells towards selective tumor cytolysis. Using Fmoc-SPPS, we have generated a library of tripeptides that were isolated and characterized by RP-LC/MS and UV/Vis spectroscopy. Using flow cytometry, the preliminary data confirmed tripeptide-GRP78 binding of the HepG2 cells and tripeptide-NKp30 binding of NK92-MI cells. We anticipate the specific binding of the tripeptides to their intended targets will provide the best candidates for translating our cancer immunotherapy approach in-vivo.