Oxygen distribution in murine tumors: characterization using oxygen-dependent quenching of phosphorescence

Shining New Light on Biological Systems: Luminescent Transition Metal Complexes for Bioimaging and Biosensing Applications

Luminescence imaging is a powerful and versatile technique for investigating cell physiology and pathology in living systems, making significant contributions to life science research and clinical diagnosis. In recent years, luminescent transition metal complexes have gained significant attention for diagnostic and therapeutic applications due to their unique photophysical and photochemical properties. In this Review, we provide a comprehensive overview of the recent development of luminescent transition metal complexes for bioimaging and biosensing applications, with a focus on transition metal centers with a d6, d8, and d10 electronic configuration. We elucidate the structure-property relationships of luminescent transition metal complexes, exploring how their structural characteristics can be manipulated to control their biological behavior such as cellular uptake, localization, biocompatibility, pharmacokinetics, and biodistribution. Furthermore, we introduce the various design strategies that leverage the interesting photophysical properties of luminescent transition metal complexes for a wide variety of biological applications, including autofluorescence-free imaging, multimodal imaging, organelle imaging, biological sensing, microenvironment monitoring, bioorthogonal labeling, bacterial imaging, and cell viability assessment. Finally, we provide insights into the challenges and perspectives of luminescent transition metal complexes for bioimaging and biosensing applications, as well as their use in disease diagnosis and treatment evaluation.

Organic-Inorganic Porphyrinoid Frameworks for Biomolecule Sensing

Porphyrinoids and their analogous compounds play an important role in biosensing applications on account of their unique and versatile catalytic, coordination, photophysical, and electrochemical properties. Their remarkable arrays of properties can be finely tuned by synthetically modifying the porphyrinoid ring and varying the various structural parameters such as peripheral functionalization, metal coordination, and covalent or physical conjugation with other organic or inorganic scaffolds such as nanoparticles, metal-organic frameworks, and polymers. Porphyrinoids and their organic-inorganic conjugates are not only used as responsive materials but also utilized for the immobilization and embedding of biomolecules for applications in wearable devices, fast sensing devices, and other functional materials. The present review delineates the impact of different porphyrinoid conjugates on their physicochemical properties and their specificity as biosensors in a range of applications. The newest porphyrinoid types and their synthesis, modification, and functionalization are presented along with their advantages and performance improvements.

Estimating quantitative physiological and morphological tissue parameters of murine tumor models using hyperspectral imaging and optical profilometry

Understanding tumors and their microenvironment are essential for successful and accurate disease diagnosis. Tissue physiology and morphology are altered in tumors compared to healthy tissues, and there is a need to monitor tumors and their surrounding tissues, including blood vessels, non-invasively. This preliminary study utilizes a multimodal optical imaging system combining hyperspectral imaging (HSI) and three-dimensional (3D) optical profilometry (OP) to capture hyperspectral images and surface shapes of subcutaneously grown murine tumor models. Hyperspectral images are corrected with 3D OP data and analyzed using the inverse-adding doubling (IAD) method to extract tissue properties such as melanin volume fraction and oxygenation. Blood vessels are segmented using the B-COSFIRE algorithm from oxygenation maps. From 3D OP data, tumor volumes are calculated and compared to manual measurements using a vernier caliper. Results show that tumors can be distinguished from healthy tissue based on most extracted tissue parameters ( p < 0.05 ). Furthermore, blood oxygenation is 50% higher within the blood vessels than in the surrounding tissue, and tumor volumes calculated using 3D OP agree within 26% with manual measurements using a vernier caliper. Results suggest that combining HSI and OP could provide relevant quantitative information about tumors and improve the disease diagnosis.

Multiphoton Phosphorescence Quenching Microscopy Reveals Kinetics of Tumor Oxygenation during Antiangiogenesis and Angiotensin Signaling Inhibition

PURPOSE

The abnormal function of tumor blood vessels causes tissue hypoxia, promoting disease progression and treatment resistance. Although tumor microenvironment normalization strategies can alleviate hypoxia globally, how local oxygen levels change is not known because of the inability to longitudinally assess vascular and interstitial oxygen in tumors with sufficient resolution. Understanding the spatial and temporal heterogeneity should help improve the outcome of various normalization strategies.

EXPERIMENTAL DESIGN

We developed a multiphoton phosphorescence quenching microscopy system using a low-molecular-weight palladium porphyrin probe to measure perfused vessels, oxygen tension, and their spatial correlations in vivo in mouse skin, bone marrow, and four different tumor models. Further, we measured the temporal and spatial changes in oxygen and vessel perfusion in tumors in response to an anti-VEGFR2 antibody (DC101) and an angiotensin-receptor blocker (losartan).

RESULTS

We found that vessel function was highly dependent on tumor type. Although some tumors had vessels with greater oxygen-carrying ability than those of normal skin, most tumors had inefficient vessels. Further, intervessel heterogeneity in tumors is associated with heterogeneous response to DC101 and losartan. Using both vascular and stromal normalizing agents, we show that spatial heterogeneity in oxygen levels persists, even with reductions in mean extravascular hypoxia.

CONCLUSIONS

High-resolution spatial and temporal responses of tumor vessels to two agents known to improve vascular perfusion globally reveal spatially heterogeneous changes in vessel structure and function. These dynamic vascular changes should be considered in optimizing the dose and schedule of vascular and stromal normalizing strategies to improve the therapeutic outcome.

Phase 2 trial of hypoxia activated evofosfamide (TH302) for treatment of recurrent bevacizumab-refractory glioblastoma

Evofosfamide (Evo or TH302) is a hypoxia-activated prodrug which is reduced leading to the release of alkylating agent bromo-isophosphoramide mustard, which has shown safety and signals of efficacy in a prior phase 1 study in recurrent glioblastoma. We performed a dual center single-arm Phase II study to expand on the safety and efficacy of Evo plus bevacizumab in bevacizumab refractory glioblastoma. 33 patients with bevacizumab refractory GBM received Evo 670 mg/m2 in combination with Bevacizumab 10 mg/kg IV every 2 weeks. Assessments included adverse events, response, and survival. Median age of patients was 47 (range 19-76) and 24 (69%) were male. At the time of study entry, 9 (26%) had ongoing corticosteroid use. ECOG performance status was 0 or 1 in 83% of patients. Patients were mostly heavily pretreated with 77% have three or more prior regimens. A total of 12 patients (36%) suffered grade 3-4 drug associated adverse event (AE); no grade 5 AE were reported. Of the 33 evaluable patients, best response was PR in 3 (9%), SD in 14 (43%), and PD in 16 (48%) with responses confirmed by a second reviewer. Median time to progression of disease was 53 days (95% CI 42-113) and Median time to death was 129 days (95% CI 86-199 days). Progression free survival at 4 months (PFS-4) on Evo-Bev was 31%, which was a statistically significant improvement over the historical rate of 3%. The median overall survival of patients receiving Evo-Bevacizumab was 4.6 months (95% CI 2.9-6.6). The progression free survival of patients on Evo-Bevacizumab met the primary endpoint of progression free survival at 4 months of 31%, although the clinical significance of this may be limited. Given the patient population and Phase II design, these clinical outcomes will need further validation.

Hypoxia-activated evofosfamide for treatment of recurrent bevacizumab-refractory glioblastoma: a phase I surgical study

Background

Anti-angiogenic therapy is known to induce a greater degree of hypoxia, including in glioblastoma (GBM). Evofosfamide (Evo) is a hypoxia-activated prodrug which is reduced, leading to the release of the alkylating agent bromo-isophosphoramide mustard. We assessed the safety, tolerability, preliminary efficacy, and biomarkers of Evo plus bevacizumab (Bev) in Bev-refractory GBM.

Methods

Twenty-eight patients with Bev-refractory GBM were enrolled in a dose escalation study receiving from 240 mg/m2 (cohort 1) to 670 mg/m2 (cohort 4) of Evo every 2 weeks in combination with Bev. Patients deemed surgical candidates underwent a single dose of Evo or placebo with pimonidazole immediately prior to surgery for biomarker evaluation, followed by dose escalation upon recovery. Assessments included adverse events, response, and survival.

Results

Evo plus Bev was well tolerated up to and including the maximum dose of 670 mg/m2, which was determined to be the recommended phase II dose. Overall response rate was 17.4%, with disease control (complete response, partial response, and stable disease) observed in 14 (60.9%) of the 23 patients. The ratio of enhancement to non-enhancement was significant on log-rank analysis with time to progression (P = 0.023), with patients having a ratio of less than 0.37 showing a median progression-free survival of 98 days versus 56 days for those with more enhancement.

Conclusions

Evo plus Bev was well tolerated in patients with Bev-refractory GBM, with preliminary evidence of activity that merits further investigation.

Synthesis and in Vitro Evaluation of Monodisperse Amino-Functional Polyester Dendrimers with Rapid Degradability and Antibacterial Properties

Amine functional polymers, especially cationically charged, are interesting biomacromolecules for several reasons, including easy cell membrane entrance, their ability to escape endosomes through the proton sponge effect, spontaneous complexation and delivery of drugs and siRNA, and simple functionalization in aqueous solutions. Dendrimers, a subclass of precision polymers, are monodisperse and exhibit a large and exact number of peripheral end groups in relation to their size and have shown promise in drug delivery, biomedical imaging and as antiviral agents. In this work, hydroxyl functional dendrimers of generation 1 to 5 based on 2,2-bis(methylol)propionic acid (bis-MPA) were modified to bear 6 to 96 peripheral amino groups through esterification reactions with beta-alanine. All dendrimers were isolated in high yields and with remarkable monodispersity. This was successfully accomplished utilizing the present advantages of fluoride-promoted esterification (FPE) with imidazole-activated monomers. Straightforward postfunctionalization was conducted on a second generation amino-functional dendrimer with tetraethylene glycol through NHS-amidation and carbonyl diimidazole (CDI) activation to full conversion with short reaction times. Fast biodegradation of the dendrimers through loss of peripheral beta-alanine groups was observed and generational- and dose-dependent cytotoxicity was evaluated with a set of cell lines. An increase in neurotoxicity compared to hydroxyl-functional dendrimers was shown in neuronal cells, however, the dendrimers were slightly less neurotoxic than commercially available poly(amidoamine) dendrimers (PAMAMs). Additionally, their effect on bacteria was evaluated and the second generation dendrimer was found unique inhibiting the growth of Escherichia coli at physiological conditions while being nontoxic toward human cells. Finally, these results cement a robust and sustainable synthetic route to amino-functional polyester dendrimers with interesting chemical and biological properties.

Oxygenation measurement by multi-wavelength oxygen-dependent phosphorescence and delayed fluorescence: catchment depth and application in intact heart

Oxygen delivery and metabolism represent key factors for organ function in health and disease. We describe the optical key characteristics of a technique to comprehensively measure oxygen tension (PO(2)) in myocardium, using oxygen-dependent quenching of phosphorescence and delayed fluorescence of porphyrins, by means of Monte Carlo simulations and ex vivo experiments. Oxyphor G2 (microvascular PO(2)) was excited at 442 nm and 632 nm and protoporphyrin IX (mitochondrial PO(2)) at 510 nm. This resulted in catchment depths of 161 (86) µm, 350 (307) µm and 262 (255) µm respectively, as estimated by Monte Carlo simulations and ex vivo experiments (brackets). The feasibility to detect changes in oxygenation within separate anatomical compartments is demonstrated in rat heart in vivo. Schematic of ex vivo measurements.

The clinical importance of assessing tumor hypoxia: relationship of tumor hypoxia to prognosis and therapeutic opportunities

Tumor hypoxia is a well-established biological phenomenon that affects the curability of solid tumors, regardless of treatment modality. Especially for head and neck cancer patients, tumor hypoxia is linked to poor patient outcomes. Given the biological problems associated with tumor hypoxia, the goal for clinicians has been to identify moderately to severely hypoxic tumors for differential treatment strategies. The "gold standard" for detecting and characterizing of tumor hypoxia are the invasive polarographic electrodes. Several less invasive hypoxia assessment techniques have also shown promise for hypoxia assessment. The widespread incorporation of hypoxia information in clinical tumor assessment is severely impeded by several factors, including regulatory hurdles and unclear correlation with potential treatment decisions. There is now an acute need for approved diagnostic technologies for determining the hypoxia status of cancer lesions, as it would enable clinical development of personalized, hypoxia-based therapies, which will ultimately improve outcomes. A number of different techniques for assessing tumor hypoxia have evolved to replace polarographic pO2 measurements for assessing tumor hypoxia. Several of these modalities, either individually or in combination with other imaging techniques, provide functional and physiological information of tumor hypoxia that can significantly improve the course of treatment. The assessment of tumor hypoxia will be valuable to radiation oncologists, surgeons, and biotechnology and pharmaceutical companies who are engaged in developing hypoxia-based therapies or treatment strategies.

Cherenkov excited phosphorescence-based pO2 estimation during multi-beam radiation therapy: phantom and simulation studies

Megavoltage radiation beams used in External Beam Radiotherapy (EBRT) generate Cherenkov light emission in tissues and equivalent phantoms. This optical emission was utilized to excite an oxygen-sensitive phosphorescent probe, PtG4, which has been developed specifically for NIR lifetime-based sensing of the partial pressure of oxygen (pO2). Phosphorescence emission, at different time points with respect to the excitation pulse, was acquired by an intensifier-gated CCD camera synchronized with radiation pulses delivered by a medical linear accelerator. The pO2 distribution was tomographically recovered in a tissue-equivalent phantom during EBRT with multiple beams targeted from different angles at a tumor-like anomaly. The reconstructions were tested in two different phantoms that have fully oxygenated background, to compare a fully oxygenated and a fully deoxygenated inclusion. To simulate a realistic situation of EBRT, where the size and location of the tumor is well known, spatial information of a prescribed region was utilized in the recovery estimation. The phantom results show that region-averaged pO2 values were recovered successfully, differentiating aerated and deoxygenated inclusions. Finally, a simulation study was performed showing that pO2 in human brain tumors can be measured to within 15 mmHg for edge depths less than 10-20 mm using the Cherenkov Excited Phosphorescence Oxygen imaging (CEPhOx) method and PtG4 as a probe. This technique could allow non-invasive monitoring of pO2 in tumors during the normal process of EBRT, where beams are generally delivered from multiple angles or arcs during each treatment fraction.

Pd-porphyrin-cross-linked implantable hydrogels with oxygen-responsive phosphorescence

Development of long-term implantable luminescent biosensors for subcutaneous oxygen has proved challenging due to difficulties in immobilizing a biocompatible matrix that prevents sensor aggregation yet maintains sufficient concentration for transdermal optical detection. Here, Pd-porphyrins can be used as PEG cross-linkers to generate a polyamide hydrogel with extreme porphyrin density (≈5 × 10(-3) m). Dye aggregation is avoided due to the spatially constraining 3D mesh formed by the porphyrins themselves. The hydrogel exhibits oxygen-responsive phosphorescence and can be stably implanted subcutaneously in mice for weeks without degradation, bleaching, or host rejection. To further facilitate oxygen detection using steady-state techniques, an oxygen-non-responsive companion hydrogel is developed by blending copper and free base porphyrins to yield intensity-matched luminescence for ratiometric detection.

Optical methods for sensing and imaging oxygen: materials, spectroscopies and applications

We review the current state of optical methods for sensing oxygen. These have become powerful alternatives to electrochemical detection and in the process of replacing the Clark electrode in many fields. The article (with 694 references) is divided into main sections on direct spectroscopic sensing of oxygen, on absorptiometric and luminescent probes, on polymeric matrices and supports, on additives and related materials, on spectroscopic schemes for read-out and imaging, and on sensing formats (such as waveguide sensing, sensor arrays, multiple sensors and nanosensors). We finally discuss future trends and applications and summarize the properties of the most often used indicator probes and polymers. The ESI† (with 385 references) gives a selection of specific applications of such sensors in medicine, biology, marine and geosciences, intracellular sensing, aerodynamics, industry and biotechnology, among others.

In vivo photoacoustic lifetime imaging of tumor hypoxia in small animals

Tumor hypoxia is an important factor in assessment of both cancer progression and cancer treatment efficacy. This has driven a substantial effort toward development of imaging modalities that can directly measure oxygen distribution and therefore hypoxia in tissue. Although several approaches to measure hypoxia exist, direct measurement of tissue oxygen through an imaging approach is still an unmet need. To address this, we present a new approach based on in vivo application of photoacoustic lifetime imaging (PALI) to map the distribution of oxygen partial pressure (pO2) in tissue. This method utilizes methylene blue, a dye widely used in clinical applications, as an oxygen-sensitive imaging agent. PALI measurement of oxygen relies upon pO2-dependent excitation lifetime of the dye. A multimodal imaging system was designed and built to achieve ultrasound (US), photoacoustic, and PALI imaging within the same system. Nude mice bearing LNCaP xenograft hindlimb tumors were used as the target tissue. Hypoxic regions were identified within the tumor in a combined US/PALI image. Finally, the statistical distributions of pO2 in tumor, normal, and control tissues were compared with measurements by a needle-mounted oxygen probe. A statistically significant drop in mean pO2 was consistently detected by both methods in tumors.

The acute effects of exercise on the microvascular volume of Achilles tendons in healthy young subjects

BACKGROUND

Real-time harmonic contrast-enhanced ultrasound (CEU) is used in several diseases to visualize the microvascularization in various tissues, due to its high sensitivity.

AIM

The aim of the present study was to investigate whether CEU could be used to detect an increase in the microvascular volume (MV) in healthy tendon tissue in response to exercise comprising a 1-h run.

METHODS

After a bolus injection of the ultrasound contrast SonoVue(®), CEU measurements of (MV) in the Achilles tendon were taken prior to exercise, immediately after a 1-h run, and 24 h after exercise in nine healthy young subjects (seven men and two women) mean age 31 ± 4 years. In addition, the effect of 15 min of arm cycling exercise on the flow within the Achilles tendon was tested in four athletes (mean age 33 ± 6 years) using the CEU method before and after exercise.

RESULTS

The present data show a significant increase in the (MV) of the Achilles tendon for all subjects following the run compared with before exercise. No significant change in (MV) was seen in the Achilles tendon after 15-min arm cycling exercise (P = 0·96). This indicates that the increase in microvascular blood volume within the Achilles tendon in response to running is a local response.

CONCLUSION

The present data reveal that real-time harmonic CEU can be used to determine the MV of healthy Achilles tendons both at rest and after 1 h of running exercise.

Modelling tumour oxygenation, reoxygenation and implications on treatment outcome

Oxygenation is an important component of the tumour microenvironment, having a significant impact on the progression and management of cancer. Theoretical determination of tissue oxygenation through simulations of the oxygen transport process is a powerful tool to characterise the spatial distribution of oxygen on the microscopic scale and its dynamics and to study its impact on the response to radiation. Accurate modelling of tumour oxygenation must take into account important aspects that are specific to tumours, making the quantitative characterisation of oxygenation rather difficult. This paper aims to discuss the important aspects of modelling tumour oxygenation, reoxygenation, and implications for treatment.

3D-resolved fluorescence and phosphorescence lifetime imaging using temporal focusing wide-field two-photon excitation

Fluorescence and phosphorescence lifetime imaging are powerful techniques for studying intracellular protein interactions and for diagnosing tissue pathophysiology. While lifetime-resolved microscopy has long been in the repertoire of the biophotonics community, current implementations fall short in terms of simultaneously providing 3D resolution, high throughput, and good tissue penetration. This report describes a new highly efficient lifetime-resolved imaging method that combines temporal focusing wide-field multiphoton excitation and simultaneous acquisition of lifetime information in frequency domain using a nanosecond gated imager from a 3D-resolved plane. This approach is scalable allowing fast volumetric imaging limited only by the available laser peak power. The accuracy and performance of the proposed method is demonstrated in several imaging studies important for understanding peripheral nerve regeneration processes. Most importantly, the parallelism of this approach may enhance the imaging speed of long lifetime processes such as phosphorescence by several orders of magnitude.

Čerenkov radiation emission and excited luminescence (CREL) sensitivity during external beam radiation therapy: Monte Carlo and tissue oxygenation phantom studies

Radiotherapy generates Čerenkov radiation emission in tissue, and spectral absorption features appearing in the emission spectrum can be used to quantify blood oxygen saturation (S(t)O(2)) from the known absorptions of hemoglobin. Additionally, the Čerenkov light can be used to excite oxygen-sensitive phosphorescence of probe PtG4, whose emission lifetime directly reports on tissue oxygen partial pressure (pO(2)). Thus, it is feasible to probe both hemoglobin S(t)O(2) and pO(2) using external radiation therapy beam to create as an internal light source in tumor tissue. In this study, the sensitivity and spatial origins of these two signals were examined. Emission was detected using a fiber-optic coupled intensifier-gated CCD camera interfaced to a spectrometer. The phosphorescence lifetimes were quantified and compared with S(t)O(2) changes previously measured. Monte Carlo simulations of the linear accelerator beam were used together with tracking of the optical signals, to predict the spatial distribution and zone sensitivity within the phantom. As the fiber-to-beam distance (FBD) varied from 0 to 30 mm, i.e. the distance from the fiber tip to the nearest side of the radiotherapy beam, the effective sampling depth for CR emission changed from 4 to 29 mm for the wavelengths in the range of 600-1000 nm. For the secondary emission (phosphorescence) the effective sampling depth was determined to be in the range of 9 to 19 mm. These results indicate that sampling of S(t)O(2) and pO(2) in tissue should be feasible during radiation therapy, and that the radiation beam and fiber sampling geometry can be set up to acquire signals that originate as deep as a few centimeters in the tissue.

Lifetime-based photoacoustic oxygen sensing in vivo

The determination of oxygen levels in blood and other tissues in vivo is critical for ensuring proper body functioning, for monitoring the status of many diseases, such as cancer, and for predicting the efficacy of therapy. Here we demonstrate, for the first time, a lifetime-based photoacoustic technique for the measurement of oxygen in vivo, using an oxygen sensitive dye, enabling real time quantification of blood oxygenation. The results from the main artery in the rat tail indicated that the lifetime of the dye, quantified by the photoacoustic technique, showed a linear relationship with the blood oxygenation levels in the targeted artery.

Microvascular and mitochondrial PO(2) simultaneously measured by oxygen-dependent delayed luminescence

Measurement of tissue oxygenation is a complex task and various techniques have led to a wide range of tissue PO(2) values and contradictory results. Tissue is compartmentalized in microcirculation, interstitium and intracellular space and current techniques are biased towards a certain compartment. Simultaneous oxygen measurements in various compartments might be of great benefit for our understanding of determinants of tissue oxygenation. Here we report simultaneous measurement of microvascular PO(2) (μPO(2) ) and mitochondrial PO(2) (mitoPO(2) ) in rats. The μPO(2) measurements are based on oxygen-dependent quenching of phosphorescence of the near-infrared phosphor Oxyphor G2. The mitoPO(2) measurements are based on oxygen-dependent quenching of delayed fluorescence of protoporphyrin IX (PpIX). Favorable spectral properties of these porphyrins allow simultaneous measurement of the delayed luminescence lifetimes. A dedicated fiber-based time-domain setup consisting of a tunable pulsed laser, 2 red-sensitive gated photomultiplier tubes and a simultaneous sampling data-acquisition system is described in detail. The absence of cross talk between the channels is shown and the feasibility of simultaneous μPO(2) and mitoPO(2) measurements is demonstrated in rat liver in vivo. It is anticipated that this novel approach will greatly contribute to our understanding of tissue oxygenation in physiological and pathological circumstances.

Two new "protected" oxyphors for biological oximetry: properties and application in tumor imaging

We report the synthesis, calibration, and examples of application of two new phosphorescent probes, Oxyphor R4 and Oxyphor G4, optimized specifically for in vivo oxygen imaging by phosphorescence quenching. These "protected" dendritic probes can operate in either albumin-rich (blood plasma) or albumin-free (interstitial space) environments at all physiological oxygen concentrations, from normoxic to deep hypoxic conditions. Oxyphors R4 and G4 are derived from phosphorescent Pd-meso-tetra-(3,5-dicarboxyphenyl)-porphyrin (PdP) or Pd-meso-tetra-(3,5-dicarboxyphenyl)-tetrabenzoporphyrin (PdTBP), respectively, and possess features common for protected dendritic probes, i.e., hydrophobic dendritic encapsulation of phosphorescent metalloporphyrins and hydrophilic PEGylated periphery. The new Oxyphors are highly soluble in aqueous environments and do not permeate biological membranes. The probes were calibrated under physiological conditions (pH 6.4-7.8) and temperatures (22-38 °C), showing high stability, reproducibility of signals, and lack of interactions with biological solutes. Oxyphor G4 was used to dynamically image intravascular and interstitial oxygenation in murine tumors in vivo. The physiological relevance of the measurements was demonstrated by dynamically recording changes in tissue oxygenation during application of anesthesia (isofluorane). These experiments revealed that changes in isofluorane concentration significantly affect tissue oxygenation.

Structurally Diverse Nitric Oxide-Releasing Poly(propylene Imine) Dendrimers

Structurally diverse secondary amine-functionalized poly(propylene imine) (PPI) dendrimers capable of tunable nitric oxide (NO) release were synthesized in a straightforward, one-step manner using ring-opening or conjugate-addition reactions with propylene oxide (PO), styrene oxide (SO), acrylonitrile (ACN), poly(ethylene glycol) methyl ether acrylate (average Mn = 480) (PEG) or 1,2-epoxy-9-decene (ED). N-Diazeniumdiolate nitric oxide donors were formed on the resulting secondary amine-functionalized G2-G5 PPI dendrimers by reaction with NO gas in basic solution. The NO storage and release kinetics for the resulting dendritic scaffolds were diverse (0.9-3.8 μmol NO/mg totals and 0.3 to 4.9 h half lives), illustrating the importance of the exterior chemical modification (e.g., steric environments, hydrophobicity, etc.) on diazeniumdiolate stability/decomposition. Tunable NO release was demonstrated by combining two donor systems on the exterior of one macromolecular scaffold. Additionally, a mathematical model was developed that allows for the simulation of dual NO release kinetics using the NO release data from the two single NO donor systems. The approaches described herein extend the range and scope of NO-releasing macromolecular scaffolds by unlocking a series of materials for use as dopants in biomedical polymers or stand-alone therapeutics depending on the exterior modification.

Effects of sepiapterin infusion on renal oxygenation and early acute renal injury after suprarenal aortic clamping in rats

Acute kidney injury (AKI) can occur after aortic clamping due to microvascular dysfunction leading to renal hypoxia. In this rat study, we have tested the hypothesis that the administration of the precursor of the nitric oxide synthase essential cofactor tetrahydrobiopterin (BH4) could restore renal oxygenation after ischemia reperfusion (I/R) and prevent AKI. We randomly distributed rats into 4 groups: sham group; ischemia-reperfusion group; I/R + sepiapterin, the precursor of BH4; and I/R + sepiapterin + methotrexate, an inhibitor of the pathway generating BH4 from sepiapterin. Cortical and outer medullary microvascular oxygen pressure, renal oxygen delivery, renal oxygen consumption were measured using dual-wavelength oxygen-dependent quenching phosphorescence techniques during ischemia and throughout 3 hours of reperfusion. Kidney injury was assessed using myeloperoxidase staining for leukocyte infiltration and urine neutrophil gelatinase-associated lipocalin levels. Ischemia reperfusion induced a drop in microvascular PO2 (P < 0.01 vs. Sham, both), which was prevented by the infusion of sepiapterin. Sepiapterin partially prevented the rise in renal oxygen extraction (P < 0.001 vs. I/R). Finally, treatment with sepiapterin prevented renal infiltration by inflammatory cells and decreased urine neutrophil gelatinase-associated lipocalin levels indicating a decrease of renal injury. These effects were blunted when adding methotrexate, except for myeloperoxidase. In conclusion, the administration of sepiapterin can prevent renal hypoxia and AKI after suprarenal aortic clamping in rats.

Near infrared luminescent oxygen nanosensors with nanoparticle matrix tailored sensitivity

The development of sensors for noninvasive determination of oxygen levels in live cells and tissues is critical for the understanding of cellular functions, as well as for monitoring the status of disease, such as cancer, and for predicting the efficacy of therapy. We describe such nontoxic, targeted, and ratiometric 30 nm oxygen nanosensors made of polyacrylamide hydrogel, near-infrared (NIR) luminescent dyes, and surface-conjugated tumor-specific peptides. They enabled noninvasive real-time monitoring of oxygen levels in live cancer cells under normal and hypoxic conditions. The required sensitivity, brightness, selectivity, and stability were achieved by tailoring the interaction between the nanomatrix and indicator dyes. The developed nanosensors may become useful for in vivo oxygen measurements.

Oxygen-dependent quenching of phosphorescence used to characterize improved myocardial oxygenation resulting from vasculogenic cytokine therapy

This study evaluates a therapy for infarct modulation and acute myocardial rescue and utilizes a novel technique to measure local myocardial oxygenation in vivo. Bone marrow-derived endothelial progenitor cells (EPCs) were targeted to the heart with peri-infarct intramyocardial injection of the potent EPC chemokine stromal cell-derived factor 1α (SDF). Myocardial oxygen pressure was assessed using a noninvasive, real-time optical technique for measuring oxygen pressures within microvasculature based on the oxygen-dependent quenching of the phosphorescence of Oxyphor G3. Myocardial infarction was induced in male Wistar rats (n = 15) through left anterior descending coronary artery ligation. At the time of infarction, animals were randomized into two groups: saline control (n = 8) and treatment with SDF (n = 7). After 48 h, the animals underwent repeat thoracotomy and 20 μl of the phosphor Oxyphor G3 was injected into three areas (peri-infarct myocardium, myocardial scar, and remote left hindlimb muscle). Measurements of the oxygen distribution within the tissue were then made in vivo by applying the end of a light guide to the beating heart. Compared with controls, animals in the SDF group exhibited a significantly decreased percentage of hypoxic (defined as oxygen pressure ≤ 15.0 Torr) peri-infarct myocardium (9.7 ± 6.7% vs. 21.8 ± 11.9%, P = 0.017). The peak oxygen pressures in the peri-infarct region of the animals in the SDF group were significantly higher than the saline controls (39.5 ± 36.7 vs. 9.2 ± 8.6 Torr, P = 0.02). This strategy for targeting EPCs to vulnerable peri-infarct myocardium via the potent chemokine SDF-1α significantly decreased the degree of hypoxia in peri-infarct myocardium as measured in vivo by phosphorescence quenching. This effect could potentially mitigate the vicious cycle of myocyte death, myocardial fibrosis, progressive ventricular dilatation, and eventual heart failure seen after acute myocardial infarction.

Imaging tumor hypoxia by magnetic resonance methods

Tumor hypoxia results from the negative balance between the oxygen demands of the tissue and the capacity of the neovasculature to deliver sufficient oxygen. The resulting oxygen deficit has important consequences with regard to the aggressiveness and malignancy of tumors, as well as their resistance to therapy, endowing the imaging of hypoxia with vital repercussions in tumor prognosis and therapy design. The molecular and cellular events underlying hypoxia are mediated mainly through hypoxia-inducible factor, a transcription factor with pleiotropic effects over a variety of cellular processes, including oncologic transformation, invasion and metastasis. However, few methodologies have been able to monitor noninvasively the oxygen tensions in vivo. MRI and MRS are often used for this purpose. Most MRI approaches are based on the effects of the local oxygen tension on: (i) the relaxation times of (19)F or (1)H indicators, such as perfluorocarbons or their (1)H analogs; (ii) the hemodynamics and magnetic susceptibility effects of oxy- and deoxyhemoglobin; and (iii) the effects of paramagnetic oxygen on the relaxation times of tissue water. (19)F MRS approaches monitor tumor hypoxia through the selective accumulation of reduced nitroimidazole derivatives in hypoxic zones, whereas electron spin resonance methods determine the oxygen level through its influence on the linewidths of appropriate paramagnetic probes in vivo. Finally, Overhauser-enhanced MRI combines the sensitivity of EPR methodology with the resolution of MRI, providing a window into the future use of hyperpolarized oxygen probes.

Evaluation of multi-exponential curve fitting analysis of oxygen-quenched phosphorescence decay traces for recovering microvascular oxygen tension histograms

Although it is generally accepted that oxygen-quenched phosphorescence decay traces can be analyzed using the exponential series method (ESM), its application until now has been limited to a few (patho)physiological studies, probably because the reliability of the recovered oxygen tension (pO(2)) histograms has never been extensively evaluated and lacks documentation. The aim of this study was, therefore, to evaluate the use of the ESM to adequately determine pO(2) histograms from phosphorescence decay traces. For this purpose we simulated decay traces corresponding to uni- and bimodal pO(2) distributions and recovered the pO(2) histograms at different signal-to-noise ratios (SNRs). Ultimately, we recovered microvascular pO(2) histograms measured in the rat kidney in a model of endotoxemic shock and fluid resuscitation and showed that the mean microvascular oxygen tension, [Symbol: see text]pO(2)[Symbol: see text], decreased after induction of endotoxemia and that after 2 h of fluid resuscitation, [Symbol: see text]pO(2)[Symbol: see text] remained low, but the hypoxic peak that had arisen during endotoxemia was reduced. This finding illustrates the importance of recovering pO(2) histograms under (patho)physiological conditions. In conclusion, this study has characterized how noise affects the recovery of pO(2) histograms using the ESM and documented the reliability of the ESM for recovering both low- and high-pO(2) distributions for SNRs typically found in experiments. This study might therefore serve as a frame of reference for investigations focused on oxygen (re)distribution during health and disease and encourage researchers to (re-)analyze data obtained in (earlier) studies possibly revealing new insights into complex disease states and treatment strategies.

Optical oxygen sensors for applications in microfluidic cell culture

The presence and concentration of oxygen in biological systems has a large impact on the behavior and viability of many types of cells, including the differentiation of stem cells or the growth of tumor cells. As a result, the integration of oxygen sensors within cell culture environments presents a powerful tool for quantifying the effects of oxygen concentrations on cell behavior, cell viability, and drug effectiveness. Because microfluidic cell culture environments are a promising alternative to traditional cell culture platforms, there is recent interest in integrating oxygen-sensing mechanisms with microfluidics for cell culture applications. Optical, luminescence-based oxygen sensors, in particular, show great promise in their ability to be integrated with microfluidics and cell culture systems. These sensors can be highly sensitive and do not consume oxygen or generate toxic byproducts in their sensing process. This paper presents a review of previously proposed optical oxygen sensor types, materials and formats most applicable to microfluidic cell culture, and analyzes their suitability for this and other in vitro applications.

Angiotensin II-induced hypertension enhanced therapeutic efficacy of liposomal doxorubicin in tumor-bearing mice

In this study, we investigated whether the therapeutic efficacy of liposomal doxorubicin (DXR-SL) could be enhanced by angiotensin II (AT)-induced hypertension. AT-induced hypertension increased the volume of tumor blood flow in mice bearing a poorly vascularized Lewis lung carcinoma (LLC) tumor, but only slightly in mice bearing a well-vascularized colon carcinoma Colon 26 (C26) tumor. In therapeutic efficacy, AT-induced hypertension enhanced the antitumor activity of DXR-SL in mice bearing LLC and C26 tumors. Localization of DXR-SL after injection by AT-induced hypertension was observed outside tumor blood vessels in LLC and C26 tumors, but within them under the normotension. From these findings, AT-induced hypertension had potential to improve the delivery of DXR-SL to both well- and poorly vascularized solid tumors.

Neutrophil alpha-defensins cause lung injury by disrupting the capillary-epithelial barrier

RATIONALE

The involvement of neutrophil activation in the sentinel, potentially reversible, events in the pathogenesis of acute lung injury (ALI) is only partially understood. alpha-Defensins are the most abundant proteins secreted by activated human neutrophils, but their contribution to ALI in mouse models is hindered by their absence from murine neutrophils and the inability to study their effects in isolation in other species.

OBJECTIVES

To study the role of alpha-defensins in the pathogenesis of ALI in a clinically relevant setting using mice transgenic for polymorphonuclear leukocyte expression of alpha-defensins.

METHODS

Transgenic mice expressing polymorphonuclear leukocyte alpha-defensins were generated. ALI was induced by acid aspiration. Pulmonary vascular permeability was studied in vivo using labeled dextran and fibrin deposition. The role of the low-density lipoprotein-related receptor (LRP) in permeability was examined.

MEASUREMENTS AND MAIN RESULTS

Acid aspiration induced neutrophil migration and release of alpha-defensins into lung parenchyma and airways. ALI was more severe in alpha-defensin-expressing mice than in wild-type mice, as determined by inspection, influx of neutrophils into the interstitial space and airways, histological evidence of epithelial injury, interstitial edema, extravascular fibrin deposition, impaired oxygenation, and reduced survival. Within 4 hours of insult, alpha-defensin-expressing mice showed greater disruption of capillary-epithelial barrier function and ALI that was attenuated by systemic or intratracheal administration of specific inhibitors of the LRP.

CONCLUSIONS

alpha-Defensins mediate ALI through LRP-mediated loss of capillary-epithelial barrier function, suggesting a potential new approach to intervention.

Investigation of hypoxia and carbonic anhydrase IX expression in a renal cell carcinoma xenograft model with oxygen tension measurements and ¹²⁴I-cG250 PET/CT

OBJECTIVES

In tumors, hypoxia stimulates angiogenesis and correlates with treatment resistance and poor prognosis. We have previously demonstrated hypoxia in human renal cell carcinoma (RCC) via direct oxygen probe measurements. Carbonic anhydrase IX (CA IX) is a protein stimulated by hypoxia and involved in angiogenesis, and is a potential tumor target for imaging and therapies using cG250, a monoclonal antibody that recognizes CAIX. Our objectives were to characterize intratumoral hypoxia in a human RCC xenograft model using oxygen probe measurements; investigate if (124)I-cG250 targets RCC correlating uptake on noninvasive positron emission tomography-computerized tomography (PET-CT) against traditional biodistribution studies, and investigate CAIX expression in this RCC model.

METHODS

BALB/c nude mice had human RCC (SK-RC-52) subcutaneously xenografted with oxygen levels measured by probe. Positron emission tomography (PET/CT) and biodistribution studies ((124)I-cG250) were correlated with oxygen measurements. Immunohistochemistry and autoradiography were performed on selected tumors to confirm CAIX expression.

RESULTS

Oxygen tension in normal tissue (muscle) was 35.08 ± 2.41 mmHg (mean ± 95% CI), significantly greater compared to xenograft SK-RC-52 tumors at 5.02 ± 1.12 mmHg. Biodistribution studies of (124)I-cG250 demonstrated isotope uptake in SK-RC-52 xenografts peaking at 23.45 ± 5.07% ID/g (mean ± SD) 48 hours after antibody injection, which was maintained for a further 2 days (19.43 ± 4.31 and 10.64 ± 5.64 % ID/g, respectively). PET studies demonstrated excellent localization of (124)I-cG250 in tumor, and a significant correlation between SUVmean, SUVmax, and %/ID (124)I-cG250. CAIX expression was present in all groups studied but there was no significant correlation between it and any oxygen parameter studied.

CONCLUSION

Intratumoral hypoxia does exist within a human RCC xenograft model using invasive oxygen probe measurements. (124)I-cG250 targets RCC with correlation between uptake on noninvasive PET-CT studies and traditional biodistribution studies opening the possibility of using PET/CT in future studies. Finally, CAIX expression was not related to hypoxia in this model, supporting the hypothesis that cell lines may subvert known hypoxia mechanisms in hypoxic environments.

Multimodal optical imaging of microvessel network convective oxygen transport dynamics

Convective oxygen transport by microvessels depends on several parameters, including red blood cell flux and oxygen saturation. We demonstrate the use of intravital microscopy techniques to measure hemoglobin saturations, red blood cell fluxes and velocities, and microvessel cross-sectional areas in regions of microvascular networks containing multiple vessels. With these methods, data can be obtained at high spatial and temporal resolution and correlations between oxygen transport and hemodynamic parameters can be assessed. In vivo data are presented for a mouse mammary adenocarcinoma grown in a dorsal skinfold window chamber model.

The relationship between vascular oxygen distribution and tissue oxygenation

Tumour oxygenation could be investigated through several methods that use various measuring principles and can therefore highlight its different aspects. The results have to be subsequently correlated, but this might not be straightforward due to intrinsic limitations of the measurement methods. This study describes an analysis of the relationship between vascular and tissue oxygenations that may help the interpretation of results. Simulations have been performed with a mathematical model that calculates the tissue oxygenation for complex vascular arrangements by taking into consideration the oxygen diffusion into the tissue and its consumption at the cells. The results showed that while vascular and tissue oxygenations are deterministically related, the relationship between them is not unequivocal and this could lead to uncertainties when attempting to correlate them. However, theoretical simulation could bridge the gap between the results obtained with various methods.

Vascular oxygen content and the tissue oxygenation--a theoretical analysis

Several methods exist for evaluating tumor oxygenation as hypoxia is an important prognostic factor for cancer patients. They use different measuring principles that highlight various aspects of oxygenation. The results could be empirically correlated, but it has been suspected that there could be discordances in some cases. This study describes an analysis of the relationship between vascular and tissue oxygenations. Theoretical simulation has been employed to characterize tissue oxygenations for a broad range of distributions of intervessel distances and vascular oxygenations. The results were evaluated with respect to the implications for practical measurements of tissue oxygenations. The findings showed that although the tissue oxygenation is deterministically related to vascular oxygenation, the relationship between them is not unequivocal. Variability also exists between the fractions of values below the sensitivity thresholds of various measurement methods which in turn could be reflected in the power of correlations between results from different methods or in the selection of patients for prognostic studies. The study has also identified potential difficulties that may be encountered at the quantitative evaluation of the results from oxygenation measurements. These could improve the understanding of oxygenation measurements and the interpretation of comparisons between results from various measurement methods.

Oxygen pressures in the interstitial space of skeletal muscle and tumors in vivo

A new Oxyphor (Oxyphor G3) has been used to selectively determine the oxygen pressure in interstitial (pericellular) spaces. Oxyphor G3 is a Pd-tetrabenzoporphyrin, encapsulated inside generation 2 poly-arylglycine (AG) dendrimer, and therefore is a true near infrared oxygen sensor, having a strong absorption band at 636nm and emission near 800nm. The periphery of the dendrimer is modified with oligoethylene glycol residues (Av. MW 350) to make the probe water soluble and biologically inert. Oxyphor G3 was injected along "tracks" in the tissue using a small needle (30gage or less) and remained in the pericellular space, allowing oxygen measurements for several hours with a single injection. The oxygen pressure distributions (histograms) were compared with those for Oxyphor G2 in the intravascular (blood plasma) space. In normal muscle, in the lower oxygen pressure region of the histograms (capillary bed) the oxygen pressure difference was small. At higher oxygen pressures in the histograms there were differences consistent with the presence of high flow vessels with oxygen pressures substantially above those of the surrounding interstitial space. In tumors, the oxygen pressures in the two spaces were similar but with large differences among tumors. In mice, anesthesia with ketamine plus xylazine markedly decreased oxygen pressures in the interstitial and intravascular spaces compared to awake or isoflurane anesthetized mice.

Dose-response relationship of ultrasound contrast agent in an in vivo murine melanoma model

Many factors affect the sensitivity and reliability of tumor vasculature assessment at the small doses of contrast agent necessary for imaging mice. In this study we investigate the dose-response relationship of ultrasound contrast agent for a minimal exposure power Doppler technique (minexPD) in a murine melanoma model. K1735 murine melanomas grown in 25 C3H/HeN mice were imaged by power Doppler ultrasound using different doses of contrast agents, Optison(R) and Definity(R). Six mice were treated with an antivascular agent, combretastatin A4-phosphate (CA4P), and imaged before and after treatment. The color-weighted fractional area (CWFA) of the peak-enhanced image was measured to assess tumor perfusion on a relative scale of 0 to 100. CWFA increased logarithmically with dose (R(2)=0.97). Treatment with CA4P resulted in pronounced reduction in tumor perfusion 2 h after contrast injection, but perfusion recovered in the tumor periphery after 2 days. CWFA was significantly different between pre- and post-treatment for all doses at 2 h and 2 days (p < 0.05, respectively). There was no significant difference detectable between the two contrast agents, Optison(R) and Definity(R) (p = 0.46). In vivo tumor enhancement in mice increases as logarithmic function with dose. Although the extent of enhancement is dose dependent, the difference between pre- and post-therapy enhancement is relatively unchanged and uniform at varying doses. The two contrast agents tested in this study performed equally well. These results suggest that quantitative contrast-enhanced power Doppler imaging is an effective method for monitoring therapy response of tumors in mice.

Sensing intracellular oxygen using near-infrared phosphorescent probes and live-cell fluorescence imaging

The development and application of a methodology for measurement of oxygen within single mammalian cells are presented, which employ novel macromolecular near infrared (NIR) oxygen probes based on new metalloporphyrin dyes. The probes, which display optimal spectral characteristics and sensitivity to oxygen, excellent photostability, and low cytotoxicity and phototoxicity, are loaded into cells by simple transfection procedures and subsequently analyzed by high-resolution fluorescence microscopy. The methodology is demonstrated by sensing intracellular oxygen in different mammalian cell lines, including A549, Jurkat, and HeLa, and monitoring rapid and transient changes in response to mitochondrial uncoupling by valinomycin and inhibition by antimycin A. Furthermore, the effect of ryanodine receptor-mediated Ca2+ influx on cellular oxygen uptake is shown by substantial changes in the level of intracellular oxygen. The results demonstrate the ability of this technique to measure small, rapid, and transient changes in intracellular oxygen in response to different biological effectors. Moreover, this technique has wide ranging applicability in cell biology and is particularly useful in the study of low oxygen environments (cellular hypoxia), mitochondrial and cellular (dys)function, and for therapeutic areas, such as cardiovascular and neurological research, metabolic diseases, and cancer.