Tumor blood flow differs between mouse strains: consequences for vasoresponse to photodynamic therapy

Diffuse correlation spectroscopy: current status and future outlook

Diffuse correlation spectroscopy (DCS) has emerged as a versatile, noninvasive method for deep tissue perfusion assessment using near-infrared light. A broad class of applications is being pursued in neuromonitoring and beyond. However, technical limitations of the technology as originally implemented remain as barriers to wider adoption. A wide variety of approaches to improve measurement performance and reduce cost are being explored; these include interferometric methods, camera-based multispeckle detection, and long path photon selection for improved depth sensitivity. We review here the current status of DCS technology and summarize future development directions and the challenges that remain on the path to widespread adoption.

Phosphorescent NIR emitters for biomedicine: applications, advances and challenges

Application of NIR (near-infrared) emitting transition metal complexes in biomedicine is a rapidly developing area of research. Emission of this class of compounds in the "optical transparency windows" of biological tissues and the intrinsic sensitivity of their phosphorescence to oxygen resulted in the preparation of several commercial oxygen sensors capable of deep (up to whole-body) and quantitative mapping of oxygen gradients suitable for in vivo experimental studies. In addition to this achievement, the last decade has also witnessed the increased growth of successful alternative applications of NIR phosphors that include (i) site-specific in vitro and in vivo visualization of sophisticated biological models ranging from 3D cell cultures to intact animals; (ii) sensing of various biologically relevant analytes, such as pH, reactive oxygen and nitrogen species, RedOx agents, etc.; (iii) and several therapeutic applications such as photodynamic (PDT), photothermal (PTT), and photoactivated cancer (PACT) therapies as well as their combinations with other therapeutic and imaging modalities to yield new variants of combined therapies and theranostics. Nevertheless, emerging applications of these compounds in experimental biomedicine and their implementation as therapeutic agents practically applicable in PDT, PTT, and PACT face challenges related to a critically important improvement of their photophysical and physico-chemical characteristics. This review outlines the current state of the art and achievements of the last decade and stresses the most promising trends, major development prospects, and challenges in the design of NIR phosphors suitable for biomedical applications.

A Focus on "Bio" in Bio-Nanoscience: The Impact of Biological Factors on Nanomaterial Interactions

Bio-nanoscience research encompasses studies on the interactions of nanomaterials with biological structures or what is commonly referred to as the biointerface. Fundamental studies on the influence of nanomaterial properties, including size, shape, composition, and charge, on the interaction with the biointerface have been central in bio-nanoscience to assess nanomaterial efficacy and safety for a range of biomedical applications. However, the state of the cells, tissues, or biological models can also influence the behavior of nanomaterials at the biointerface and their intracellular processing. Focusing on the "bio" in bio-nano, this review discusses the impact of biological properties at the cellular, tissue, and whole organism level that influences nanomaterial behavior, including cell type, cell cycle, tumor physiology, and disease states. Understanding how the biological factors can be addressed or exploited to enhance nanomaterial accumulation and uptake can guide the design of better and suitable models to improve the outcomes of materials in nanomedicine.

Blood Flow Measurements Enable Optimization of Light Delivery for Personalized Photodynamic Therapy

Fluence rate is an effector of photodynamic therapy (PDT) outcome. Lower light fluence rates can conserve tumor perfusion during some illumination protocols for PDT, but then treatment times are proportionally longer to deliver equivalent fluence. Likewise, higher fluence rates can shorten treatment time but may compromise treatment efficacy by inducing blood flow stasis during illumination. We developed blood-flow-informed PDT (BFI-PDT) to balance these effects. BFI-PDT uses real-time noninvasive monitoring of tumor blood flow to inform selection of irradiance, i.e., incident fluence rate, on the treated surface. BFI-PDT thus aims to conserve tumor perfusion during PDT while minimizing treatment time. Pre-clinical studies in murine tumors of radiation-induced fibrosarcoma (RIF) and a mesothelioma cell line (AB12) show that BFI-PDT preserves tumor blood flow during illumination better than standard PDT with continuous light delivery at high irradiance. Compared to standard high irradiance PDT, BFI-PDT maintains better tumor oxygenation during illumination and increases direct tumor cell kill in a manner consistent with known oxygen dependencies in PDT-mediated cytotoxicity. BFI-PDT promotes vascular shutdown after PDT, thereby depriving remaining tumor cells of oxygen and nutrients. Collectively, these benefits of BFI-PDT produce a significantly better therapeutic outcome than standard high irradiance PDT. Moreover, BFI-PDT requires ~40% less time on average to achieve outcomes that are modestly better than those with standard low irradiance treatment. This contribution introduces BFI-PDT as a platform for personalized light delivery in PDT, documents the design of a clinically-relevant instrument, and establishes the benefits of BFI-PDT with respect to treatment outcome and duration.

Reactive oxygen species explicit dosimetry to predict local tumor control for Photofrin-mediated photodynamic therapy

Although photodynamic therapy (PDT) is an established modality for cancer treatment, current dosimetric quantities, such as light fluence and PDT dose, do not account for the differences in PDT oxygen consumption for different fluence rates (ϕ). A macroscopic model was adopted to calculate reactive oxygen species concentration ([ROS]_rx) to predict Photofrin-PDT outcome in mice bearing radiation-induced fibrosarcoma (RIF) tumors. Singlet oxygen is the primary cytotoxic species for ROS, which is responsible for cell death in type II PDT, although other type I ROS is included in the parameters used in our model. Using a combination of fluences (50-250 J/cm²) and ϕ (50 - 150 mW/cm²), tumor regrowth rate, k, was determined for each condition by fitting the tumor volume vs. time to V₀*exp(k*t). Treatment was delivered with a collimated laser beam of 1 cm diameter at 630 nm. Explicit dosimetry of initial tissue oxygen concentration, tissue optical properties, and Photofrin concentration was used to calculate [ROS]_rx,cal. ϕ was determined for the treatment volume based on Monte-Carlo simulations and measured tissue optical properties. Tissue oxygenation is measured using an oxylite oxygen probe to throughout the treatment to calculate the measured [ROS]_rx,mea. Cure index, CI = 1-k/k _ctr , for tumor gowth up to 14 days were determined as an endpoint using five dose metrics: light fluence, PDT dose, and [ROS]_rx,cal, and [ROS]_rx,mea. PDT dose was defined as the product of the time-integral of photosensitizer concentration and ϕ at a 3 mm tumor depth. Preliminary studies show that [ROS]_rx,mea best correlates with CI and is an effective dosimetric quantity that can predict treatment outcome.

Reactive oxygen species explicit dosimetry to predict tumor growth for BPD-mediated vascular photodynamic therapy

Photodynamic therapy (PDT) is a well-established treatment modality for cancer and other malignant diseases; however, quantities such as light fluence, and PDT dose do not fully account for all of the dynamic interactions between the key components involved. In particular, fluence rate (ϕ) effects are not accounted for, which has a large effect on the oxygen consumption rate. In this preclinical study, reacted reactive oxygen species ([ROS]_rx) was investigated as a dosimetric quantity for PDT outcome. We studied the ability of [ROS]_rx to predict the cure index (CI) after PDT of murine tumors; CI = 1 - k/k_ctr, where k and k_ctr are the growth rate of PDT-treated and control(untreated) tumor, respectively. Mice bearing radiation induced fibrosarcoma (RIF) tumors were treated with BPD-mediated PDT at different in-air fluences (22.5, 40, 45, 50, 70 and 100 J/cm²) and in-air ϕ (75 and 150 mW/cm²) with a BPD dose of 1 mg/kg and a drug-light interval of 15 mins. Treatment was delivered with a collimated laser beam of 1 cm diameter at 690 nm. Explicit dosimetry of initial tissue oxygen concentration, tissue optical properties, and BPD concentration was used to calculate [ 1 O 2 ] rx . ϕ was calculated for the treatment volume based on Monte-Carlo simulations and measured tissue optical properties. CI was used as an endpoint for four dose metrics: light fluence, PDT dose, and [ROS]_rx. PDT dose was defined as the product of the time-integral of photosensitizer concentration and ϕ at a 3 mm tumor depth. Preliminary studies show that [ROS]_rx best correlates with CI and is an effective dosimetric quantity that can predict treatment outcome. The threshold dose for [ROS]_rx is determined to be 0.23 mM and is about 4.3 times smaller than the corresponding value for conventional BPD-mediated PDT using DLI of 3 hrs.

Early assessment of tumor response to photodynamic therapy using combined diffuse optical and diffuse correlation spectroscopy to predict treatment outcome

Photodynamic therapy (PDT) of cancer involves the use of a photosensitizer that can be light-activated to eradicate tumors via direct cytotoxicity, damage to tumor vasculature and stimulating the body's immune system. Treatment outcome may vary between individuals even under the same regime; therefore a non-invasive tumor response monitoring system will be useful for personalization of the treatment protocol. We present the combined use of diffuse optical spectroscopy (DOS) and diffuse correlation spectroscopy (DCS) to provide early assessment of tumor response. The relative tissue oxygen saturation (rStO2) and relative blood flow (rBF) in tumors were measured using DOS and DCS respectively before and after PDT with reference to baseline values in a mouse model. In complete responders, PDT-induced decreases in both rStO2 and rBF levels were observed at 3 h post-PDT and the rBF remained low until 48 h post-PDT. Recovery of these parameters to baseline values was observed around 2 weeks after PDT. In partial responders, the rStO2 and rBF levels also decreased at 3 h post PDT, however the rBF values returned toward baseline values earlier at 24 h post-PDT. In contrast, the rStO2 and rBF readings in control tumors showed fluctuations above the baseline values within the first 48 h. Therefore tumor response can be predicted at 3 to 48 h post-PDT. Recovery or sustained decreases in the rBF at 48 h post-PDT corresponded to long-term tumor control. Diffuse optical measurements can thus facilitate early assessment of tumor response. This approach can enable physicians to personalize PDT treatment regimens for best outcomes.

Pre-clinical longitudinal monitoring of hemodynamic response to anti-vascular chemotherapy by hybrid diffuse optics

The longitudinal effect of an anti-vascular endothelial growth factor receptor 2 (VEGFR-2) antibody (DC 101) therapy on a xenografted renal cell carcinoma (RCC) mouse model was monitored using hybrid diffuse optics. Two groups of immunosuppressed male nude mice (seven treated, seven controls) were measured. Tumor microvascular blood flow, total hemoglobin concentration and blood oxygenation were investigated as potential biomarkers for the monitoring of the therapy effect twice a week and were related to the final treatment outcome. These hemodynamic biomarkers have shown a clear differentiation between two groups by day four. Moreover, we have observed that pre-treatment values and early changes in hemodynamics are highly correlated with the therapeutic outcome demonstrating the potential of diffuse optics to predict the therapy response at an early time point.

Macroscopic singlet oxygen modeling for dosimetry of Photofrin-mediated photodynamic therapy: an in-vivo study

Although photodynamic therapy (PDT) is an established modality for cancer treatment, current dosimetric quantities, such as light fluence and PDT dose, do not account for the differences in PDT oxygen consumption for different fluence rates ( ? ). A macroscopic model was adopted to evaluate using calculated reacted singlet oxygen concentration ( [ O 2 1 ] rx ) to predict Photofrin-PDT outcome in mice bearing radiation-induced fibrosarcoma tumors, as singlet oxygen is the primary cytotoxic species responsible for cell death in type II PDT. Using a combination of fluences (50, 135, 200, and 250 ?? J / cm 2 ) and ? (50, 75, and 150 ?? mW / cm 2 ), tumor regrowth rate, k , was determined for each condition. A tumor cure index, CI = 1 ? k / k control , was calculated based on the k between PDT-treated groups and that of the control, Available on the SPIE Digital Library.

Intraoperative monitoring of blood perfusion in port wine stains by laser Doppler imaging during vascular targeted photodynamic therapy: A preliminary study

OBJECTIVE

The objective of this study was to monitor blood perfusion dynamics of port wine stains (PWS) during vascular targeted photodynamic therapy (V-PDT) with laser Doppler imaging (LDI).

METHODS

The PWS lesions of 30 facial PWS patients received V-PDT, while the normal skins on the forearm of 5 healthy subjects were treated as light-only controls for comparison. Furthermore, two different PWS lesions in the same individual from each of 3 PWS patients successively received laser irradiation only and V-PDT, respectively. LDI was used to monitor intraoperative blood perfusion dynamics.

RESULTS

During V-PDT, the blood perfusion (278±96 PU) in PWS lesions for 31 of 33 PWS patients significantly increased after the initiation of V-PDT treatment, then reached a peak (638±105 PU) within 10min, followed by a slow decrease to a relatively lower level (515±100 PU). Furthermore, the time for reaching peak and the subsequent magnitude of decrease in blood perfusion varied with different patients. For light-only controls, an initial perfusion peak at 3min followed by a nadir and a secondary increase were found not only in normal skin, but also in PWS lesions.

CONCLUSION

The preliminary results showed that the LDI permits non-invasive monitoring blood perfusion changes of PWS lesions during V-PDT. There was a clear trend in blood perfusion responses during V-PDT and laser irradiation. The blood perfusion changes during treatment were due to V-PDT effects as well as local temperature increase induced by laser irradiation.

Scanning, non-contact, hybrid broadband diffuse optical spectroscopy and diffuse correlation spectroscopy system

A scanning system for small animal imaging using non-contact, hybrid broadband diffuse optical spectroscopy (ncDOS) and diffuse correlation spectroscopy (ncDCS) is presented. The ncDOS uses a two-dimensional spectrophotometer retrieving broadband (610-900 nm) spectral information from up to fifty-seven source-detector distances between 2 and 5 mm. The ncDCS data is simultaneously acquired from four source-detector pairs. The sample is scanned in two dimensions while tracking variations in height. The system has been validated with liquid phantoms, demonstrated in vivo on a human fingertip during an arm cuff occlusion and on a group of mice with xenoimplanted renal cell carcinoma.

An Efficient Operator for the Change Point Estimation in Partial Spline Model

In bio-informatics application, the estimation of the starting and ending points of drop-down in the longitudinal data is important. One possible approach to estimate such change times is to use the partial spline model with change points. In order to use estimate change time, the minimum operator in terms of a smoothing parameter has been widely used, but we showed that the minimum operator causes large MSE of change point estimates. In this paper, we proposed the summation operator in terms of a smoothing parameter, and our simulation study showed that the summation operator gives smaller MSE for estimated change points than the minimum one. We also applied the proposed approach to the experiment data, blood flow during photodynamic cancer therapy.

Intracellular carbonic anhydrase activity sensitizes cancer cell pH signaling to dynamic changes in CO2 partial pressure

Carbonic anhydrase (CA) enzymes catalyze the chemical equilibration among CO2, HCO3(-) and H(+). Intracellular CA (CAi) isoforms are present in certain types of cancer, and growing evidence suggests that low levels correlate with disease severity. However, their physiological role remains unclear. Cancer cell CAi activity, measured as cytoplasmic CO2 hydration rate (kf), ranged from high in colorectal HCT116 (∼2 s(-1)), bladder RT112 and colorectal HT29, moderate in fibrosarcoma HT1080 to negligible (i.e. spontaneous kf = 0.18 s(-1)) in cervical HeLa and breast MDA-MB-468 cells. CAi activity in cells correlated with CAII immunoreactivity and enzymatic activity in membrane-free lysates, suggesting that soluble CAII is an important intracellular isoform. CAi catalysis was not obligatory for supporting acid extrusion by H(+) efflux or HCO3(-) influx, nor for maintaining intracellular pH (pHi) uniformity. However, in the absence of CAi activity, acid loading from a highly alkaline pHi was rate-limited by HCO3(-) supply from spontaneous CO2 hydration. In solid tumors, time-dependence of blood flow can result in fluctuations of CO2 partial pressure (pCO2) that disturb cytoplasmic CO2-HCO3(-)-H(+) equilibrium. In cancer cells with high CAi activity, extracellular pCO2 fluctuations evoked faster and larger pHi oscillations. Functionally, these resulted in larger pH-dependent intracellular [Ca(2+)] oscillations and stronger inhibition of the mTORC1 pathway reported by S6 kinase phosphorylation. In contrast, the pHi of cells with low CAi activity was less responsive to pCO2 fluctuations. Such low pass filtering would "buffer" cancer cell pHi from non-steady-state extracellular pCO2. Thus, CAi activity determines the coupling between pCO2 (a function of tumor perfusion) and pHi (a potent modulator of cancer cell physiology).

A Method for Choosing the Smoothing Parameter in a Semi-parametric Model for Detecting Change-points in Blood Flow

In a smoothing spline model with unknown change-points, the choice of the smoothing parameter strongly influences the estimation of the change-point locations, and the function at the change-points. In a tumor biology example, where change-points in blood flow in response to treatment were of interest, choosing the smoothing parameter based on minimizing generalized cross validation, GCV, gave unsatisfactory estimates of the change-points. We propose a new method, aGCV, that re-weights the residual sum of squares and generalized degrees of freedom terms from GCV. The weight is chosen to maximize the decrease in the generalized degrees of freedom as a function of the weight value, while simultaneously minimizing aGCV as a function of the smoothing parameter and the change-points. Compared to GCV, simulation studies suggest that the aGCV method yields improved estimates of the change-point and the value of the function at the change-point.

Assessment of cerebral perfusion in post-traumatic brain injury patients with the use of ICG-bolus tracking method

The aim of this study was to verify the usefulness of the time-resolved optical method utilizing diffusely reflected photons and fluorescence signals combined with intravenous injection of indocyanine green (ICG) in the assessment of brain perfusion in post-traumatic brain injury patients. The distributions of times of flight (DTOFs) of diffusely reflected photons were acquired together with the distributions of times of arrival (DTAs) of fluorescence photons. The data analysis methodology was based on the observation of delays between the signals of statistical moments (number of photons, mean time of flight and variance) of DTOFs and DTAs related to the inflow of ICG to the extra- and intracerebral tissue compartments. Eleven patients with brain hematoma, 15 patients with brain edema and a group of 9 healthy subjects were included in this study. Statistically significant differences between parameters obtained in healthy subjects and patients with brain hematoma and brain edema were observed. The best optical parameter to differentiate patients and control group was variance of the DTOFs or DTAs. Results of the study suggest that time-resolved optical monitoring of inflow of the ICG seems to be a promising tool for detecting cerebral perfusion insufficiencies in critically ill patients.

Influence of probe pressure on the diffuse correlation spectroscopy blood flow signal: extra-cerebral contributions

A pilot study explores relative contributions of extra-cerebral (scalp/skull) versus brain (cerebral) tissues to the blood flow index determined by diffuse correlation spectroscopy (DCS). Microvascular DCS flow measurements were made on the head during baseline and breath-holding/hyperventilation tasks, both with and without pressure. Baseline (resting) data enabled estimation of extra-cerebral flow signals and their pressure dependencies. A simple two-component model was used to derive baseline and activated cerebral blood flow (CBF) signals, and the DCS flow indices were also cross-correlated with concurrent Transcranial Doppler Ultrasound (TCD) blood velocity measurements. The study suggests new pressure-dependent experimental paradigms for elucidation of blood flow contributions from extra-cerebral and cerebral tissues.

Nanoparticle clearance is governed by Th1/Th2 immunity and strain background

Extended circulation of nanoparticles in blood is essential for most clinical applications. Nanoparticles are rapidly cleared by cells of the mononuclear phagocyte system (MPS). Approaches such as grafting polyethylene glycol onto particles (PEGylation) extend circulation times; however, these particles are still cleared, and the processes involved in this clearance remain poorly understood. Here, we present an intravital microscopy-based assay for the quantification of nanoparticle clearance, allowing us to determine the effect of mouse strain and immune system function on particle clearance. We demonstrate that mouse strains that are prone to Th1 immune responses clear nanoparticles at a slower rate than Th2-prone mice. Using depletion strategies, we show that both granulocytes and macrophages participate in the enhanced clearance observed in Th2-prone mice. Macrophages isolated from Th1 strains took up fewer particles in vitro than macrophages from Th2 strains. Treating macrophages from Th1 strains with cytokines to differentiate them into M2 macrophages increased the amount of particle uptake. Conversely, treating macrophages from Th2 strains with cytokines to differentiate them into M1 macrophages decreased their particle uptake. Moreover, these results were confirmed in human monocyte-derived macrophages, suggesting that global immune regulation has a significant impact on nanoparticle clearance in humans.

Diffuse optical characterization of an exercising patient group with peripheral artery disease

Peripheral artery disease (PAD) is a common condition with high morbidity. While measurement of tissue oxygen saturation (S(t)O(2)) has been demonstrated, this is the first study to assess both S(t)O(2) and relative blood flow (rBF) in the extremities of PAD patients. Diffuse optics is employed to measure hemodynamic response to treadmill and pedal exercises in 31 healthy controls and 26 patients. For S(t)O(2), mild and moderate/severe PAD groups show pronounced differences compared with controls. Pre-exercise mean S(t)O(2) is lower in PAD groups by 9.3% to 10.6% compared with means of 63.5% to 66.2% in controls. For pedal, relative rate of return of S(t)O(2) to baseline is more rapid in controls (p < 0.05). Patterns of rBF also differ among groups. After both exercises, rBF tend to occur at depressed levels among severe PAD patients compared with healthy (p < 0.05); post-treadmill, rBF tend to occur at elevated levels among healthy compared with severe PAD patients (p < 0.05). Additionally, relative rate of return to baseline S(t)O(2) is more rapid among subjects with reduced levels of depression in rBF (p = 0.041), even after adjustment for ankle brachial index. This suggests a physiologic connection between rBF and oxygenation that can be measured using diffuse optics, and potentially employed as an evaluative tool in further studies.