spatial-measurements-perfusion-interstitial-fluid-pressure-liposomes

Spatial Measurements of Perfusion, Interstitial Fluid Pressure and Liposomes Accumulation in Solid Tumors

The heterogeneous intra-tumoral accumulation of liposomes is a critical determinant of their efficacy. Both the chaotic tumor microcirculation and ...

Microbubble contrast agents have shown clinical potential for characterising blood flow using 1 to 10 MHz ultrasound; however, scaling their use for similar applications in the mouse with high frequency ultrasound (20 to 60 MHz) has not been addressed. The goal was to determine the utility of microbubbles for mouse imaging with 30 MHz ultrasound by investigating their attenuation and backscatter characteristics as a function of concentration in vitro and dose response in vivo. The agent was exposed to a 30 MHz, 20% bandwidth pulse with a peak negative pressure of 244 kPa. In vitro results showed that the attenuation and backscatter increased linearly for concentrations between 2.8 x 10(6) and 28 x 10(6) bubbles per mL of deionized water. In vivo experiments where performed in the jugular vein of CD-1 mice and time intensity curves were acquired for doses between 10 and 100 microL kg(-1). These doses corresponded to the range of concentrations used in vitro. In vivo results showed that the peak enhancement of the agent increased linearly for doses between 10 and 60 microL kg(-1), the duration of enhancement varied between 200 to 300 s and the integrated enhancement (area under the curve) increased linearly up to 100 microL kg(-1). A maximum enhancement of 13 dB over the blood pool was observed for a dose of 100 microL kg(-1). The intra- and inter-mouse variabilities were 10% to 40% and indicate that further optimisations are required. These results suggest that quantitative contrast flow studies in the mouse using high frequency ultrasound are possible for doses between 10 and 60 microL kg(-1).

Acoustic and kinetic behaviour of definity in mice exposed to high frequency ultrasound.

Microbubble Kontrastmittel zeigten klinische Potenzial f&uuml;r die Charakterisierung der Blutfluss mit 1 bis 10 MHz Ultraschall; jedoch wurde ihre Verwendung f&uuml;r &auml;hnliche Anwendungen in der Maus mit Hochfrequenz-Ultraschall (20 bis 60 MHz) Skalierung nicht behoben. Ziel war es, die N&uuml;tzlichkeit des Mikrobl&auml;schen f&uuml;r Maus-Imaging mit 30 MHz Ultraschall durch ihren D&auml;mpfung und Backscatter-Eigenschaften als eine Funktion der Konzentration in-vitro-Untersuchung zu bestimmen und Dosieren Antwort in-vivo. Der Agent war ein 30 MHz, 20 % Bandbreite Puls mit einer negativen H&ouml;chstdruck von 244 kPa ausgesetzt. In-vitro-Ergebnisse zeigten, dass die D&auml;mpfung und Backscatter linear f&uuml;r Konzentrationen zwischen 2,8 X 10 6 und 28 X 10 6 Blasen pro mL deionisiertem Wasser erh&ouml;ht. In Vivo Experimente durchgef&uuml;hrt in den Jugular Vene von M&auml;usen CD-1 und Intensit&auml;t, die Kurven erworben wurden f&uuml;r Dosen zwischen 10 und 100 MicroL kg(-1) Zeit. Diese Dosen entsprach das Spektrum der Konzentrationen in Vitro verwendet. In Vivo Ergebnisse zeigte, dass die Spitze Verst&auml;rkung des Agents linear f&uuml;r Dosen zwischen 10 und 60 MicroL kg(-1), erh&ouml;ht die Dauer der Erweiterung zwischen 200 und 300 geschwankt erh&ouml;ht s und die integrierte Verst&auml;rkung (Fl&auml;che unter der Kurve) linear bis zu 100 MicroL kg(-1). Eine maximale Leistung von 13 dB &uuml;ber den Blut-Pool wurde f&uuml;r eine Dosis von 100 MicroL kg(-1) beobachtet. Die Intra - und inter - mouse Variabilit&auml;ten waren 10 % bis 40 % und darauf hinweisen, dass weitere Optimierungen erforderlich sind. Diese Ergebnisse legen nahe, dass quantitative Kontrast Flow Studien in der Maus mittels Hochfrequenz-Ultraschall f&uuml;r Dosen zwischen 10 und 60 MicroL kg(-1) m&ouml;glich sind.

Akustische und kinetische Verhalten der Definity bei M&auml;usen, Hochfrequenz-Ultraschall ausgesetzt.

This paper presents the design of a micro-CT guided small animal robotic needle positioning system. In order to simplify the robotic design and maintain a small targeting error, a novel implementation of the remote center of motion is used in the system. The system has been developed with the objective of achieving a mean targeting error of <200 Î¼m while maintaining a high degree of user friendliness.

3D image-guided robotic needle positioning system for small animal interventions.

In vivo and direct imaging of the murine spinal cord and its vasculature using multimodal (optical and acoustic) imaging techniques could significantly advance preclinical studies of the spinal cord. Such intrinsically high resolution and complementary imaging technologies could provide a powerful means of quantitatively monitoring changes in anatomy, structure, physiology and function of the living cord over time after traumatic injury, onset of disease, or therapeutic intervention. However, longitudinal in vivo imaging of the intact spinal cord in rodent models has been challenging, requiring repeated surgeries to expose the cord for imaging or sacrifice of animals at various time points for ex vivo tissue analysis. To address these limitations, we have developed an implantable spinal cord window chamber (SCWC) device and procedures in mice for repeated multimodal intravital microscopic imaging of the cord and its vasculature in situ. We present methodology for using our SCWC to achieve spatially co-registered optical-acoustic imaging performed serially for up to four weeks, without damaging the cord or induction of locomotor deficits in implanted animals. To demonstrate the feasibility, we used the SCWC model to study the response of the normal spinal cord vasculature to ionizing radiation over time using white light and fluorescence microscopy combined with optical coherence tomography (OCT) in vivo. In vivo power Doppler ultrasound and photoacoustics were used to directly visualize the cord and vascular structures and to measure hemoglobin oxygen saturation through the complete spinal cord, respectively. The model was also used for intravital imaging of spinal micrometastases resulting from primary brain tumor using fluorescence and bioluminescence imaging. Our SCWC model overcomes previous in vivo imaging challenges, and our data provide evidence of the broader utility of hybridized optical-acoustic imaging methods for obtaining multiparametric and rich imaging data sets, including over extended periods, for preclinical in vivo spinal cord research.

A spinal cord window chamber model for in vivo longitudinal multimodal optical and acoustic imaging in a murine model.

Liposomes have proven to be a viable drug delivery strategy resulting in significant increases in tumor accumulation of drugs via exploitation of the enhanced permeability and retention (EPR) effect. However, significant variability has been observed in their bulk tumor accumulation and intra-tumoral distribution. The heterogeneous accumulation of liposomes in solid tumors is largely believed to result from the chaotic morphology and physiology of tumor blood vessels. Thus, tumor perfusion imaging may provide a novel method to predict the accumulation and resulting therapeutic effect of liposome formulations. In this study, dynamic contrast enhanced computed tomography (DCE-CT) was employed to quantitatively estimate the intra-tumoral distribution of perfusion and anatomical CT was used to map the spatio-temporal accumulation of a CT-liposome contrast agent. A statistically significant positive correlation was found between quantitative and semi-quantitative measures of tumor perfusion (i.e. K(trans), vp, and AUC(iox)) and liposome accumulation (AUC(lipo) and C(peak)) in two mouse xenograft models of human cervical cancer. Specifically, it was found that regions with higher K(trans),vp, and AUC(iox) had greater liposome accumulation. These findings demonstrate that DCE-CT measurements of tumor perfusion may be an important technique for selecting patients that are likely to respond to liposome and potentially other nanoparticle-based therapies.

Tumor perfusion imaging predicts the intra-tumoral accumulation of liposomes.

Tumor hypoxia is a negative prognostic factor in multiple cancers, due in part to its role in causing resistance to radiotherapy. Hypoxia arises in tumor regions distal to blood vessels as oxygen is consumed by more proximal tumor cells. Reducing the rate of oxygen consumption is therefore a potential strategy to reduce tumor hypoxia. We hypothesized that the anti-diabetic drug metformin, which reduces oxygen consumption through inhibition of mitochondrial complex I, would improve radiation response by increasing tumor oxygenation.

Reprogramming metabolism with metformin improves tumor oxygenation and radiotherapy response.

The discovery of the enhanced permeability and retention (EPR) effect has resulted in the development of nanomedicines, including liposome-based formulations of drugs, as cancer therapies. The use of liposomes has resulted in substantial increases in accumulation of drugs in solid tumors; yet, significant improvements in therapeutic efficacy have yet to be achieved. Imaging of the tumor accumulation of liposomes has revealed that this poor or variable performance is in part due to heterogeneous inter-subject and intra-tumoral liposome accumulation, which occurs as a result of an abnormal transport microenvironment. A mathematical model that relates liposome accumulation to the underlying transport properties in solid tumors could provide insight into inter and intra-tumoral variations in the EPR effect. In this paper, we present a theoretical framework to describe liposome transport in solid tumors. The mathematical model is based on biophysical transport equations that describe pressure driven fluid flow across blood vessels and through the tumor interstitium. The model was validated by direct comparison with computed tomography measurements of tumor accumulation of liposomes in three preclinical tumor models. The mathematical model was fit to liposome accumulation curves producing predictions of transport parameters that reflect the tumor microenvironment. Notably, all fits had a high coefficient of determination and predictions of interstitial fluid pressure agreed with previously published independent measurements made in the same tumor type. Furthermore, it was demonstrated that the model attributed inter-subject heterogeneity in liposome accumulation to variations in peak interstitial fluid pressure. These findings highlight the relationship between transvascular and interstitial flow dynamics and variations in the EPR effect. In conclusion, we have presented a theoretical framework that predicts inter-subject and intra-tumoral variations in the EPR effect based on fundamental properties of the tumor microenvironment and forms the basis for transport modeling of liposome drug delivery.

A mathematical model of the enhanced permeability and retention effect for liposome transport in solid tumors.

Existing paradigms in nano-based drug delivery are currently being challenged. Assessment of bulk tumor accumulation has been routinely considered an indicative measure of nanomedicine potency. However, it is now recognized that the intratumoral distribution of nanomedicines also impacts their therapeutic effect. At this time, our understanding of the relationship between the bulk (i.e., macro-) tumor accumulation of nanocarriers and their intratumoral (i.e., micro-) distribution remains limited. Liposome-based drug formulations, in particular, suffer from diminished efficacy in vivo as a result of transport-limiting properties, combined with the heterogeneous nature of the tumor microenvironment. In this report, we perform a quantitative image-based assessment of macro- and microdistribution of liposomes. Multi-scalar assessment of liposome distribution was enabled by a stable formulation which co-encapsulates an iodinated contrast agent and a near-infrared fluorescence probe, for computed tomography (CT) and optical microscopy, respectively. Spatio-temporal quantification of tumor uptake in orthotopic xenografts was performed using CT at the bulk tissue level, and within defined sub-volumes of the tumor (i.e., rim, periphery and core). Tumor penetration and relative distribution of liposomes were assessed by fluorescence microscopy of whole tumor sections. Microdistribution analysis of whole tumor images exposed a heterogeneous distribution of both liposomes and tumor vasculature. Highest levels of liposome uptake were achieved and maintained in the well-vascularized tumor rim over the study period, corresponding to a positive correlation between liposome and microvascular density. Tumor penetration of liposomes was found to be time-dependent in all regions of the tumor however independent of location in the tumor. Importantly, a multi-scalar comparison of liposome distribution reveals that macro-accumulation in tissues (e.g., blood, whole tumor) may not reflect micro-accumulation levels present within specific regions of the tumor as a function of time.

Spatial and temporal mapping of heterogeneity in liposome uptake and microvascular distribution in an orthotopic tumor xenograft model.

The heterogeneous intra-tumoral accumulation of liposomes has been linked to both the chaotic tumor microcirculation and to elevated interstitial fluid pressure (IFP). Here, we explored the relationship between tumor microcirculation, IFP, and the intra-tumoral accumulation of liposomes. Measurements of the tumor microcirculation using perfusion imaging, IFP using a novel image-guided robotic needle positioning system, and the intra-tumoral distribution of liposomes using volumetric micro-CT imaging were performed in mice bearing subcutaneous and orthotopic MDA-MB-231 tumors. Intra-tumoral perfusion and IFP were substantially different between the two tumor implantation sites. Tumor perfusion and not vascular permeability was found to be the primary mediator of the intra-tumoral accumulation of CT-liposomes. A strong relationship was observed between the radial distribution of IFP, metrics of tumor perfusion, and the intra-tumoral accumulation of liposomes. Tumors with elevated central IFP that decreased at the periphery had low perfusion and low levels of CT-liposome accumulation that increased towards the periphery. Conversely, tumors with low and radially uniform IFP exhibited higher levels of tumor perfusion and CT-liposome accumulation. Both tumor perfusion and elevated IFP exhibit substantial intra-tumoral heterogeneity and both play an integral role in mediating the intra-tumoral accumulation of liposomes through a complex interactive effect. Measuring IFP in the clinical setting remains challenging and these results demonstrate that tumor perfusion imaging alone provides a robust non-invasive method to identify factors that contribute to poor liposome accumulation and may allow for pre-selection of patients that are more likely to respond to nanoparticle therapy.

The intra-tumoral relationship between microcirculation, interstitial fluid pressure and liposome accumulation.

Functional and molecular imaging has become increasingly used to evaluate interpatient and intrapatient tumor heterogeneity. Imaging allows for assessment of microenvironment parameters including tumor hypoxia, perfusion and proliferation, as well as tumor metabolism and the intratumoral distribution of specific molecular markers. Imaging information may be used to stratify patients for targeted therapies, and to define patient populations that may benefit from alternative therapeutic approaches. It also provides a method for non-invasive monitoring of treatment response at earlier time-points than traditional cues, such as tumor shrinkage. Further, companion diagnostic imaging techniques are becoming progressively more important for development and clinical implementation of targeted therapies. Imaging-based companion diagnostics are likely to be essential for the validation and FDA approval of targeted nanotherapies and macromolecular medicines. This review describes recent clinical advances in the use of functional and molecular imaging to evaluate the tumor microenvironment. Additionally, this article focuses on image-based assessment of distribution and anti-tumor effect of nano- and macromolecular systems.

Integration of imaging into clinical practice to assess the delivery and performance of macromolecular and nanotechnology-based oncology therapies.

The tumor microenvironment has an important influence on cancer biological and clinical behavior and radiation treatment (RT) response. However, RT also influences the tumor microenvironment in a complex and dynamic manner that can either reinforce or inhibit this response and the likelihood of long-term disease control in patients. It is increasingly evident that the interplay between RT and the tumor microenvironment can be exploited to enhance the accumulation and intra-tumoral distribution of nanoparticles, mediated by changes to the vasculature and stroma with secondary effects on hypoxia, interstitial fluid pressure (IFP), solid tissue pressure (STP), and the recruitment and activation of bone marrow-derived myeloid cells (BMDCs). The use of RT to modulate nanoparticle drug delivery offers an exciting opportunity to improve antitumor efficacy. This review explores the interplay between RT and the tumor microenvironment, and the integrated effects on nanoparticle drug delivery and efficacy.

Article	Year
Acoustic and kinetic behaviour of definity in mice exposed to high frequency ultrasound. Ultrasound in medicine & biology\| PubMed ID: 18950930	2009
3D image-guided robotic needle positioning system for small animal interventions. Medical physics\| PubMed ID: 23298100	2013
A spinal cord window chamber model for in vivo longitudinal multimodal optical and acoustic imaging in a murine model. PloS one\| PubMed ID: 23516432	2013
Tumor perfusion imaging predicts the intra-tumoral accumulation of liposomes. Journal of controlled release : official journal of the Controlled Release Society\| PubMed ID: 24021358	2013
Reprogramming metabolism with metformin improves tumor oxygenation and radiotherapy response. Clinical cancer research : an official journal of the American Association for Cancer Research\| PubMed ID: 24141625	2013
A mathematical model of the enhanced permeability and retention effect for liposome transport in solid tumors. PloS one\| PubMed ID: 24312530	2013
Spatial and temporal mapping of heterogeneity in liposome uptake and microvascular distribution in an orthotopic tumor xenograft model. Journal of controlled release : official journal of the Controlled Release Society\| PubMed ID: 25862513	2015
The intra-tumoral relationship between microcirculation, interstitial fluid pressure and liposome accumulation. Journal of controlled release : official journal of the Controlled Release Society\| PubMed ID: 26070245	2015
Integration of imaging into clinical practice to assess the delivery and performance of macromolecular and nanotechnology-based oncology therapies. Journal of controlled release : official journal of the Controlled Release Society\| PubMed ID: 26403800	2015
Radiation effects on the tumor microenvironment: Implications for nanomedicine delivery. Advanced drug delivery reviews\| PubMed ID: 27262923	2016

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