Integrin α_vβ₃-targeted gold nanoshells augment tumor vasculature-specific imaging and therapy

Abstract

Purpose

Gold nanoshells (NSs) have already shown great promise as photothermal actuators for cancer therapy. Integrin α_vβ₃ is a marker that is specifically and preferentially overexpressed on multiple tumor types and on angiogenic tumor neovasculature. Active targeting of NSs to integrin α_vβ₃ offers the potential to increase accumulation preferentially in tumors and thereby enhance therapy efficacy.

Methods

Enzyme-linked immunosorbent assay (ELISA) and cell binding assay were used to study the in vitro binding affinities of the targeted nanoconjugate NS–RGDfK. In vivo biodistribution and tumor specificity were analyzed using ⁶⁴Cu-radiolabeled untargeted and targeted NSs in live nude rats bearing head and neck squamous cell carcinoma (HNSCC) xenografts. The potential thermal therapy applications of NS–RGDfK were evaluated by subablative thermal therapy of tumor xenografts using untargeted and targeted NSs.

Results

ELISA and cell binding assay confirmed the binding affinity of NS–RGDfK to integrin α_vβ₃. Positron emission tomography/computed tomography imaging suggested that tumor targeting is improved by conjugation of NSs to cyclo(RGDfK) and peaks at ~20 hours postinjection. In the subablative thermal therapy study, greater biological effectiveness of targeted NSs was implied by the greater degree of tumor necrosis.

Conclusion

The results presented in this paper set the stage for the advancement of integrin α_vβ₃-targeted NSs as therapeutic nanoconstructs for effective cancer therapy.

Keywords:

• nanoparticle
• cyclo(RGDfK)
• cancer
• thermal ablation

Supplementary data

Biodistribution studies

All the animals were used in the imaging studies were anesthetized and then sacrificed at 46 hours postinjection. The organs of interest were removed and wet weighed. The radioactivity in the tissues was measured using a γ-counter (Wallac 1480, Perkin Elmer Life Sciences, Boston, MA, USA). The radioactivity of the tissue samples was calibrated against a known aliquot of the injectate. The percentage injected dose per organ (%ID/organ) values were calculated using the following equation $[\text{activity\hspace{0.17em}in\hspace{0.17em}pellet}/(\text{activity\hspace{0.17em}in\hspace{0.17em}supernatant}+\text{activity\hspace{0.17em}in\hspace{0.17em}pellet})]\times 100$.

Major organs that showed high concentrations of other types of nanoparticles in previous biodistribution studies^1–4 were also subjected to neutron activation analysis (NAA). Portions of tumor, spleen, liver, lung, and kidney tissue were collected, wet weighed, and allowed to decay for 2 weeks. The samples were placed into precleaned and labeled polyethylene irradiation vials. After the wet sample weight was calculated and recorded, the samples were covered and dried under a heat lamp for 48 hours before delivery into the high temperature nuclear reactor core for NAA gold measurements. The procedure of NAA for trace gold quantification in animal tissues has been described elsewhere.⁵ The data were reported as gold mass versus the original wet sample mass.

Table S1 Biodistribution data of ⁶⁴Cu-NS and ⁶⁴Cu-NS–RGDfK in HNSC xenograft-bearing nude rats at 46 hours postinjection.

Figure S1 Neutron activation analysis for concentration of gold in tumor, spleen, liver, lung, and kidney at 46 hours postinjection of NS–PEG (control) and NS–RGDfK.

Acknowledgments

This work was supported by NIST ATP Cooperative Agreement Number 70NANB4H3040 and NIH 1R21CA133691. We thank Pharmaceutical Research and Manufacturers of America Foundation for their support of Dr Xie’s work. We thank Dr Narasimhan Danthi at Molecular Imaging Laboratory of National Institutes of Allergies and Infectious Diseases for kindly providing us with the IAC. We also thank Dr Ting Tung A Chang for his imaging technical support.

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Disclosure

The authors report no conflicts of interest in this work.