Screening, identification and therapeutic evaluation of STAT3- and albumin-targeted aptides

Abstract

Peptide molecules that can specifically bind to targets with high affinity have diagnostic and therapeutic potential, and have emerged as alternatives to antibodies in market. However, the peptides with sufficient affinity and specificity for antigens of interest may not be present or readily isolated. Therefore, our group have developed peptide scaffold, termed ‘aptide’, that show high affinity and selectivity for specific target protein. In this thesis, I describe the application of this scaffold technology to the peptide inhibitor for cancer therapy. Further-more, I isolated human serum albumin specific aptide with potential for improving half-life of peptide drug.

In chapter 2. In this chapter, I described STAT3-targeting aptide for cancer therapy. STAT3 promotes the survival, proliferation, metastasis, immune escape and drug resistance of cancer cells, making its targeting an appealing prospect. However, while multiple inhibitors of STAT3 and its regulatory or effector pathway elements have been developed, bioactive agents have been somewhat elusive. Here, I described the identification of a specific STAT3-binding peptide ($APT_{STAT3}$) through phage display of a novel `aptide` library. $APT_{STAT3}$ bound STAT3 with high specificity and affinity (~231 nM). Addition of a cell-penetrating motif to the peptide to yield $APT_{STAT3}-9R$ enabled uptake by murine B16F1 melanoma cells. Treatment of various types of cancer cells with $APT_{STAT3}-9R$ blocked STAT3 phosphorylation and reduced expression of STAT targets, including cyclin D1, Bcl-xL, and survivin. As a result, $APT_{STAT3}-9R$ suppressed the viability and proliferation of cancer cells. Furthermore, intratumoral injection of $APT_{STAT3}-9R$ exerted potent antitumor activity in both xenograft and allograft tumor models. This results offer a preclinical proof of concept for $APT_{STAT3}$ as a tractable agent for translation to target the broad array of cancers harbouring constitutively activated S...