Radiosensitization of Triple Negative Breast Cancer with Gold Nanosphere Conjugates Targeting the Folate Receptor

Despite geometric localization capabilities of current radiation therapy (RT) techniques to the tumor, the need for specificity at the cellular level remains. Gold nanoparticles (AuNPs) decorated with tumor-targeting peptides and antibodies can hone in on tumors, get internalized, and sensitize tumors to RT. Extending this paradigm to triple-negative breast cancer (TNBC) has been challenging due to its lack of classical tumor markers. Targeting folate receptor alpha (FRα), overexpressed by MDA-MB-231 TNBC cells, with AuNP-folate conjugates showed substantial AuNP internalization, but mitogenic effects of folate offset anti-tumor effects of AuNP radiosensitization in xenograft mouse studies. To overcome this problem, we switched the targeting moiety on AuNPs from an agonist of FRα, to anti-FRα Ig, an antibody (Ab) that binds to FRα without inducing proliferative or mitogenic effects. Pegylated 20 nm AuNPs (pAuNPs) were synthesized and conjugated to nonspecific rabbit IgG Ab (rAuNPs) or targeted anti-FRα Ab (aAuNPs). AuNPs were characterized by zeta potential, hydrodynamic diameters and absorption spectra. Uptake by MDA-MB-231 cells was analyzed qualitatively using dark field microscopy. In-vitro radiosensitization potential by aAuNPs was assessed via clonogenic assay using clinically relevant, 6MV RT. Surface plasmon resonance peaks of pAuNPs, rAuNPs, and aAuNPs were observed at 521±2 nm. AuNP zeta potentials were: -34±6 mV (bare AuNPs), -8±4 mV (pAuNPs), -1±6 mV (rAuNPs), and -5±5 mV (aAuNPs). Hydrodynamic diameters determined by dynamic light scattering were: 33±12 nm (bare AuNPs), 56±18 nm (pAuNPs), 64±22 nm (rAuNPs), and 62±17 nm (aAuNPs). aAuNPs demonstrated significant radiosensitization with a dose enhancement factor of 1.15 calculated at 10% cell survival relative to RT alone. AuNPs conjugated to anti-FRα Ab sensitize triple negative breast cancer cells to radiation and present a viable strategy to target cancer cells at the molecular level.