Narrow band imaging of squamous cell carcinoma tumors using topically delivered anti-EGFR antibody conjugated gold nanorods

BACKGROUND

Nanoparticles have recently gained interest as exogenous contrast agents in a variety of biomedical applications related to cancer detection and treatment. The objective of this study was to determine the potential of topically administered antibody conjugated gold nanorods (GNRs) for imaging squamous cell carcinomas (SCCs) of the skin using near-infrared narrowband imaging (NBI). Near-infrared (NIR) NBI images narrow wavelength bands to enhance contrast from plasmonic particles in a wide field portable and noncontact device that is clinically compatible for real-time tumor imaging and tumor margin demarcation.

STUDY DESIGN

We conjugated GNRs to Cetuximab, a clinically approved humanized antibody that targets the epidermal growth factor receptor (EGFR), which is overexpressed on the surface of many tumor cells, especially SCCs. We excised subcutaneous xenografts of SCCs (A431) from Swiss nu/nu mice and divided the tumors into two groups: (1) the targeted group (Cetuximab conjugated GNRs) and (2) the control group (polyethylene glycol-conjugated GNRs). After topical application of particles and incubation for 30 minutes, the tumors were washed and imaged using NBI. In addition, we performed two-photon imaging to quantify the binding of EGFR targeted GNRs in tumors and their depth profile.

RESULTS

The NBI images showed a visual increase in contrast from tumors after topical administration of targeted GNR. Targeted GNR tumors showed increased contrast compared to tumors administered with the control GNR. There was a statistically significant increase in mean pixel intensity (∼2.5×) from targeted GNR tumors (n = 6). Two-photon microscopy images of targeted GNRs confirmed their binding affinity to the EGF receptors over expressed in the A431 tumors.

CONCLUSION

We have demonstrated that a topical application of gold nanorods targeted specifically to tumor growth factor receptors results in a significantly higher image contrast compared to nontargeted gold nanorods. These results demonstrate the feasibility of near-infrared NBI to image and demarcate tumor margins during surgical resection using topical administration of targeted GNR.

In vivo tumor targeting of gold nanoparticles: effect of particle type and dosing strategy

Gold nanoparticles (GNPs) have gained significant interest as nanovectors for combined imaging and photothermal therapy of tumors. Delivered systemically, GNPs preferentially accumulate at the tumor site via the enhanced permeability and retention effect, and when irradiated with near infrared light, produce sufficient heat to treat tumor tissue. The efficacy of this process strongly depends on the targeting ability of the GNPs, which is a function of the particle’s geometric properties (eg, size) and dosing strategy (eg, number and amount of injections). The purpose of this study was to investigate the effect of GNP type and dosing strategy on in vivo tumor targeting. Specifically, we investigated the in vivo tumor-targeting efficiency of pegylated gold nanoshells (GNSs) and gold nanorods (GNRs) for single and multiple dosing. We used Swiss nu/nu mice with a subcutaneous tumor xenograft model that received intravenous administration for a single and multiple doses of GNS and GNR. We performed neutron activation analysis to quantify the gold present in the tumor and liver. We performed histology to determine if there was acute toxicity as a result of multiple dosing. Neutron activation analysis results showed that the smaller GNRs accumulated in higher concentrations in the tumor compared to the larger GNSs. We observed a significant increase in GNS and GNR accumulation in the liver for higher doses. However, multiple doses increased targeting efficiency with minimal effect beyond three doses of GNPs. These results suggest a significant effect of particle type and multiple doses on increasing particle accumulation and on tumor targeting ability.

Alkyl passivation and amphiphilic polymer coating of silicon nanocrystals for diagnostic imaging

A method to produce biocompatible polymer-coated silicon nanocrystals for medical imaging is shown. Silica-embedded Si nanocrystals are formed by HSQ thermolysis. The nanocrystals are then liberated from the oxide and terminated with Si-H bonds by HF etching, followed by alkyl monolayer passivation by thermal hydrosilylation. The Si nanocrystals have an average diameter of 2.1 nm ± 0.6 nm and photoluminesce with a peak emission wavelength of 650 nm, which lies within the transmission window of 650-900 nm that is useful for biological imaging. The hydrophobic Si nanocrystals are then coated with an amphiphilic polymer for dispersion in aqueous media with the pH ranging between 7 and 10 and an ionic strength between 30 mM and 2 M, while maintaining a bright and stable photoluminescence and a hydrodynamic radius of only 20 nm. Fluorescence imaging of polymer-coated Si nanocrystals in biological tissue is demonstrated, showing the potential for in vivo imaging.

Near-infrared narrow-band imaging of gold/silica nanoshells in tumors

Gold nanoshells (GNS) are a new class of nanoparticles that can be optically tuned to scatter or absorb light from the near-ultraviolet to near-infrared (NIR) region by varying the core (dielectric silica)/shell (gold) ratio. In addition to spectral tunability, GNS are inert and bioconjugatable, making them potential labels for in vivo imaging and therapy of tumors. We report the use of GNS as exogenous contrast agents for enhanced visualization of tumors using narrow-band imaging (NBI). NBI takes advantage of the strong NIR absorption of GNS to distinguish between blood and nanoshells in the tumor by imaging in narrow wavelength bands in the visible and NIR, respectively. Using tissue-simulating phantoms, we determined the optimum wavelengths to enhance contrast between blood and GNS. We then used the optimum wavelengths for ex vivo imaging of tumors extracted from human colon cancer xenograft bearing mice injected with GNS. Systemically delivered GNS accumulated passively in tumor xenografts by the enhanced permeability and retention (EPR) effect. Ex vivo NBI of tumor xenografts demonstrated heterogeneous distribution of GNS with a clear distinction from the tumor vasculature. The results of this study demonstrate the feasibility of using GNS as contrast agents to visualize tumors using NBI.