TGF‐β1 Conjugated to Gold Nanoparticles Results in Protein Conformational Changes and Attenuates the Biological Function

Abstract

Gold nanoparticles (AuNPs) are widely used as carriers or therapeutic agents due to their great biocompatibility and unique physical properties. Transforming growth factor-beta 1 (TGF-β1), a member of the cysteine-knot structural superfamily, plays a pivotal role in many diseases and is known as an immunosuppressive agent that attenuates immune response resulting in tumor growth. The results reported herein reflect strong interactions between TGF-β1 and the surface of AuNPs when incubated with serum-containing medium, and demonstrate a time- and dose-dependent pattern. Compared with other serum proteins that can also bind to the AuNP surface, AuNP-TGFβ1 conjugate is a thermodynamically favored compound. Epithelial cells undergo epithelial-mesenchymal transition (EMT) upon treatment with TGF-β1; however, treatment with AuNPs reverses this effect, as detected by cell morphology and expression levels of EMT markers. TGF-β1 is found to bind to AuNPs through S-Au bonds by X-ray photoelectron spectroscopy. Fourier transform infrared spectroscopy is employed to analyze the conformational changes of TGF-β1 on the surface of AuNPs. The results indicate that TGF-β1 undergoes significant conformational changes at both secondary and tertiary structural levels after conjugation to the AuNP surface, which results in the deactivation of TGF-β1 protein. An in vivo experiment also shows that addition of AuNPs attenuates the growth of TGF-β1-secreting murine bladder tumor 2 cells in syngeneic C3H/HeN mice, but not in immunocompromised NOD-SCID mice, and this is associated with an increase in the number of tumor-infiltrating CD4⁺ and CD8⁺ T lymphocytes and a decrease in the number of intrasplenic Foxp3(+) lymphocytes. The findings demonstrate that AuNPs may be a promising agent for modulating tumor immunity through inhibiting immunosuppressive TGF-β1 signaling.

Nanotechnology platforms for cancer immunotherapy

“…Mirkin et al (Radovic-Moreno et al, 2015) found that AuNP-CpG formulated with OVA induced elevated IgG2a antibody titers and also improved T cell activation, leading to reduced tumor growth and improved survival in a lymphoma model system. Moreover, according to previous reports Tsai et al, 2013;Yen, Hsu, & Tsai, 2009), AuNPs also tended to interact with DCs, leading to the expression of immunostimulant cytokines (IL-1, IL-6, IL-12, IFN-α, and TNF-α) and down-regulation of immunosuppressive chemokines (TGF-β1 and IL-10). Activation of DCs by AuNPs was also indicated by the increased phagocytic activity of DCs and enhanced maturation and activation of T cells-related immune responses (Dykman & Khlebtsov, 2011).…”

Gold nanoparticle mediated cancer immunotherapy

“…43 The absorption of the cytokine to the nanoparticle surface also induced a conformational change that reduced the biological activity of TGF-β1, thereby reducing epithelial-mesenchymal transition of murine mammary gland cells in vitro . Finally, the group demonstrated that AuNPs could inhibit tumor growth when MBT-2 cells were implanted in mice in the presence of AuNPs, The particles were shown to reduce the systemic concentration of TGF-β1 as well as the concentration of the immune suppressive cytokine IL-10.…”

“…Overall, their results demonstrate that AuNPs can attenuate TGF-β1 signaling and subsequently promote an anti-tumor immune response. 43 Further studies on AuNP interactions with other immune modulating cytokines can potential yield new immune therapeutic applications for AuNPs.…”

Targeting cancer stem cells by using the nanoparticles

“…132 In this context, Tsai et al found that AuNPs could selectively capture TGF-β1 through S-Au binding between cysteine and disulfides residues resulting in deactivation of TGF-β signaling pathway. 133 Interestingly, they also found that the immunosuppressive function of TGF-β was significantly attenuated by AuNPs and resulted in an increased number and frequency of tumor-infiltrating T lymphocytes. 133 These results demonstrate that AuNPs may be a promising immune modulator by inhibiting immunosuppressive function of TGF-β1 signaling pathway.…”

“…133 Interestingly, they also found that the immunosuppressive function of TGF-β was significantly attenuated by AuNPs and resulted in an increased number and frequency of tumor-infiltrating T lymphocytes. 133 These results demonstrate that AuNPs may be a promising immune modulator by inhibiting immunosuppressive function of TGF-β1 signaling pathway.…”