Abstract
Constitutively activated signal transducer and activator of transcription 3 (STAT3) factor is an important therapeutic target in head and neck cancer (HNC). Despite early promising results, a reliable systemic delivery system for STAT3- targeted oligonucleotide (ODN) drugs is still needed for future clinical translation of anti-STAT3 therapies. We engineered and tested a novel ODN duplex/gold nanoparticle (AuNP)-based system carrying a therapeutic STAT3 decoy (STAT3d) payload. This strategy is two-pronged because of the additive STAT3 antagonism and radiosensitizing properties of AuNP. The specificity to head and neck cancer cell surface was imparted by using a nucleolin aptamer (NUAP) that was linked to AuNP for taking the advantage of an aberrant presentation of a nuclear protein nucleolin on the cell surface. STAT3d and nucleolin aptamer constructs were independently linked to AuNPs via Au-S bonds. The synthesized AuNP constructs (AuNP-NUAP-STAT3d) exhibited internalization in cells that was quantified by using radiolabeled STAT3d. AuNP-NUAP-STAT3d showed radiosensitizing effect in human HNC FaDu cell culture experiments that resulted in an increase of cell DNA damage as determined by measuring γ-H2AX phosphorylation levels by flow cytometry. The radiosensitization study also demonstrated that AuNP-NUAP-STAT3d as well as STAT3d alone resulted in the efficient inhibition of A431 cell proliferation. While FaDu cells did not show instant proliferation inhibition after incubating with AuNP-NUAP-STAT3d, the cell DNA damage in these cells showed nearly a 50% increase in AuNP-NUAP-STAT3d group after treating with radiation. Compared with anti-EGFR humanized antibody (Cetuximab), AuNP-NUAP-STAT3d system had an overall stronger radiosensitization effect in both A431 and FaDu cells.