Pulsed high intensity focused ultrasound increases penetration and therapeutic efficacy of monoclonal antibodies in murine xenograft tumors.

The success of radioimmunotherapy for solid tumors remains elusive due to poor biodistribution and insufficient tumor accumulation, in part, due to the unique tumor microenvironment resulting in heterogeneous tumor antibody distribution. Pulsed high intensity focused ultrasound (pulsed-HIFU) has previously been shown to increase the accumulation of (111)In labeled B3 antibody (recognizes Lewis(y) antigen). The objective of this study was to investigate the tumor penetration and therapeutic efficacy of pulsed-HIFU exposures combined with (90)Y labeled B3 mAb in an A431 solid tumor model. The ability of pulsed-HIFU (1 M Hz, spatial averaged temporal peak intensity=2685 W cm(-2); pulse repetition frequency=1 Hz; duty cycle=5%) to improve the tumor penetration and therapeutic efficacy of (90)Y labeled B3 mAb ((90)Y-B3) was evaluated in Le(y)-positive A431 tumors. Antibody penetration from the tumor surface and blood vessel surface was evaluated with fluorescently labeled B3, epi-fluorescent microscopy, and custom image analysis. Tumor size was monitored to determine treatment efficacy, indicated by survival, following various treatments with pulsed-HIFU and/or (90)Y-B3. The pulsed-HIFU exposures did not affect the vascular parameters including microvascular density, vascular size, and vascular architecture; although 1.6-fold more antibody was delivered to the solid tumors when combined with pulsed-HIFU. The distribution and penetration of the antibodies were significantly improved (p-value<0.05) when combined with pulsed-HIFU, only in the tumor periphery. Pretreatment with pulsed-HIFU significantly improved (p-value<0.05) survival over control treatments.

Investigation of cellular and molecular responses to pulsed focused ultrasound in a mouse model.

Continuous focused ultrasound (cFUS) has been widely used for thermal ablation of tissues, relying on continuous exposures to generate temperatures necessary to induce coagulative necrosis. Pulsed FUS (pFUS) employs non-continuous exposures that lower the rate of energy deposition and allow cooling to occur between pulses, thereby minimizing thermal effects and emphasizing effects created by non-thermal mechanisms of FUS (i.e., acoustic radiation forces and acoustic cavitation). pFUS has shown promise for a variety of applications including drug and nanoparticle delivery; however, little is understood about the effects these exposures have on tissue, especially with regard to cellular pro-homing factors (growth factors, cytokines, and cell adhesion molecules). We examined changes in murine hamstring muscle following pFUS or cFUS and demonstrate that pFUS, unlike cFUS, has little effect on the histological integrity of muscle and does not induce cell death. Infiltration of macrophages was observed 3 and 8 days following pFUS or cFUS exposures. pFUS increased expression of several cytokines (e.g., IL-1α, IL-1ß, TNFα, INFγ, MIP-1α, MCP-1, and GMCSF) creating a local cytokine gradient on days 0 and 1 post-pFUS that returns to baseline levels by day 3 post-pFUS. pFUS exposures induced upregulation of other signaling molecules (e.g., VEGF, FGF, PlGF, HGF, and SDF-1α) and cell adhesion molecules (e.g., ICAM-1 and VCAM-1) on muscle vasculature. The observed molecular changes in muscle following pFUS may be utilized to target cellular therapies by increasing homing to areas of pathology.

In vitro investigations into enhancement of tPA bioavailability in whole blood clots using pulsed-high intensity focused ultrasound exposures.

Investigations were carried out on the manner by which pulsed-high intensity focused ultrasound (HIFU) enhances the effectiveness of tissue plasminogen activator (tPA) in whole blood clots, in vitro. Scanning electronic microscope (SEM) of the surface of the clots showed that the exposures increased exposed fibrin, as well as the number of openings to more interior regions. These findings were supported by fluorescent antibody labeling of tPA in frozen sections of clots treated post-HIFU. Here, improved accumulation at the surface and penetration of the tPA into the clots were observed in those treated with HIFU. Fluorescence recovery after photobleaching was also performed, indicating that the diffusion coefficient increased 6.3-fold for fluorescently labeled dextrans, comparable in size to tPA, in the HIFU-treated clots. Improved understanding of the manner by which pulsed--HIFU exposures can improve the effectiveness of thrombolytics will help optimize the exposures for this application and potentially facilitate translation to the clinic.

Investigations into pulsed high-intensity focused ultrasound-enhanced delivery: preliminary evidence for a novel mechanism.

Pulsed high-intensity focused ultrasound (HIFU) exposures without ultrasound contrast agents have been used for noninvasively enhancing the delivery of various agents to improve their therapeutic efficacy in a variety of tissue models in a nondestructive manner. Despite the versatility of these exposures, little is known about the mechanisms by which their effects are produced. In this study, pulsed-HIFU exposures were given in the calf muscle of mice, followed by the administration of a variety of fluorophores, both soluble and particulate, by local or systemic injection. In vivo imaging (whole animal and microscopic) was used to quantify observations of increased extravasation and interstitial transport of the fluorophores as a result of the exposures. Histological analysis indicated that the exposures caused some structural alterations such as enlarged gaps between muscle fiber bundles. These effects were consistent with increasing the permeability of the tissues; however, they were found to be transient and reversed themselves gradually within 72 h. Simulations of radiation force-induced displacements and the resulting local shear strain they produced were carried out to potentially explain the manner by which these effects occurred. A better understanding of the mechanisms involved with pulsed HIFU exposures for noninvasively enhancing delivery will facilitate the process for optimizing their use.

Evaluation of pulsed high intensity focused ultrasound exposures on metastasis in a murine model.

High intensity focused ultrasound (HIFU) may be employed in two ways: continuous exposures for thermal ablation of tissue (> 60 degrees C), and pulsed-exposures for non-ablative effects, including low temperature hyperthermia (37-45 degrees C), and non thermal effects (e.g. acoustic cavitation and radiation forces). Pulsed-HIFU effects may enhance the tissue's permeability for improved delivery of drugs and genes, for example, by opening up gaps between cells in the vasculature and parenchyma. Inducing these effects may improve local targeting of therapeutic agents, however; concerns exist that pulsed exposures could theoretically also facilitate dissemination of tumor cells and exacerbate metastases. In the present study, the influence of pulsed-HIFU exposures on increasing metastatic burden was evaluated in a murine model with metastatic breast cancer. A preliminary study was carried out to validate the model and determine optimal timing for treatment and growth of lung metastases. Next, the effect of pulsed-HIFU on the metastatic burden was evaluated using quantitative image processing of whole-lung histological sections. Compared to untreated controls (2/15), a greater number of mice treated with pulsed-HIFU were found to have lungs "overgrown" with metastases (7/15), where individual metastases grew together such that they could not accurately be counted. Furthermore, area fraction of lung metastases (area of metastases/area of lungs) was approximately 30% greater in mice treated with pulsed-HIFU; however, these differences were not statistically significant. The present study details the development of an animal model for investigating the influence of interventional techniques or exposures (such as pulsed HIFU) on metastatic burden.

Response variability in attention-deficit disorders.

Reaction times in a mental rotation task were measured across a diverse population that sorted into two groupings based on overall variability. Although both the low- and the high-variance groups produced data that displayed the trends typical of mental rotation, the two groups' reaction time sequences had very different autocorrelation functions. Power spectra derived from the two groups' data showed the presence of distinctive noise processes with long memory. Normal levels of variance were associated with 1/f noise, whereas high-variance data had substantial traces of random walk contour. These findings provide new perspectives on cognitive assessments of attention dysfunction.