Murine photoplethysmography for in vivo estimation of vascular gold nanoshell concentration

Suppression of the reticuloendothelial system using λ-carrageenan to prolong the circulation of gold nanoparticles

AIM

Gold nanoparticles are employed for imaging and treatment of surgically inaccessible tumors owing to their inherent optical absorption and ability to extravasate through intravenous distribution. These nanoparticles are cleared from the blood by the reticuloendothelial system (RES) as expected given their size.

MATERIALS & METHODS

This study demonstrates the effects of RES blockade through the intravenous administration of λ-carrageenan, resulting in a decrease in the median clearance rate from 18.9 (95% CrI: 15.9-22.6) to 11.2 (95% CrI: 8.8-13.9) μl/min and an increase in nanoparticle circulation half-life t(½)( = 264 ± 73 vs 160 ± 22 min; p < 0.01).

RESULTS

This 59.3% decrease in clearance is greater than the 15% previously reported for liposomes [ 1 ].

CONCLUSION

The primary benefit of nontoxic RES blockade is to increase the circulation time, where traditional particle modification is ineffective or impractical.

Simulation of transport and extravasation of nanoparticles in tumors which exhibit enhanced permeability and retention effect

Determining the factors that influence the delivery of sub-micron particles to tumors and understanding the relative importance of each of these factors is fundamental to the optimization of the particle delivery process. In this paper, a model that combines random walk with the pressure driven movement of nanoparticles in a tumor vasculature is presented. Nanoparticle movement in a cylindrical tube with dimensions similar to the tumor's blood capillary with a single pore is simulated. Nanoparticle velocities are calculated as a pressure driven flow over imposed to Brownian motion. The number and percentage of nanoparticles leaving the blood vessel through a single pore is obtained as a function of pore size, nanoparticle size and concentration, interstitial pressure, and blood pressure. The model presented here is able to determine the importance of these controllable parameters and thus it can be used to understand the process and predict the best conditions for nanoparticle-based treatment. The results indicate that the nanoparticle delivery gradually increases with pore size and decreases with nanoparticle size for tumors with high interstitial fluid pressure (in this work we found this behavior for head and neck carcinoma and for metastatic melanoma with interstitial pressures of 18mmHg and 19mmHg, respectively). For tumors with lower interstitial fluid pressure (rectal carcinoma with 15.3mmHg) however, delivery is observed to have little sensitivity to particle size for almost the entire nanoparticle size range. Though an increase in nanoparticle concentration increases the number of nanoparticles being delivered, the efficiency of the delivery (percentage of nanoparticles delivered) is found to remain closely unaffected.

Feasibility of Energy Dispersive X-Ray Fluorescence Determination of Gold in Soft Tissue for Clinical Applications

The feasibility of using EDXRF for a rapid quantitative analysis of gold in tumor tissue has been investigated. The protocol described here demonstrates that sample biopsies can be analyzed in as little as 8 hours, with minimal sample preparation. Samples were prepared by drying a 35 μL aliquot of tissue dissolved in KOH in a standard EDXRF cup on a Prolene® support, producing a thin sample. Calibration curves of XRF peak intensity (CPS/mA) to the gold concentration (0-50 PPM) were prepared for liver, tumor, and a mix of tissue types. A linear regression demonstrated an R² correlation of 0.93. Analysis of experimental samples showed that gold accumulation in tumors (5.8-41.3 PPM) was in agreement with previous studies, where samples were processed using INAA or ICP-MS. This report provides guidance for elemental analysis of gold in tissue in a shorter time span, showing potential for its use in a clinical setting.

Three-wavelength murine photoplethysmography for estimation of vascular gold nanorod concentration

Nanoparticle-assisted photo-thermal (NAPT) ablation has become a new and attractive modality for the treatment of cancerous tumors. This therapy exploits the passive accumulation of intravenously delivered optically resonant metal nanoparticles into tumors, however, the circulating bioavailability of these particles is often unknown. We present a non-invasive optical device capable of monitoring the circulation of optically resonant gold nanorods. The device, referred to as a pulse photometer, uses the technique of multi-wavelength photoplethysmography. We simultaneously report the circulation of gold nanorods and oximetry for six hours post-injection in mice with no anesthesia and remove the probe when not collecting data. The instrument shows good agreement (R(2) = 0.903, n = 30) with ex vivo spectrophotometric analysis of blood samples. The real-time feedback provided has a strong potential for reducing variability and thus improving the efficacy of similar clinical therapies.