Optical molecular imaging of lysyl oxidase activity - detection of active fibrogenesis in human lung tissue

Lysyl Oxidases as Targets for Cancer Therapy and Diagnostic Imaging

The understanding of the contribution of the tumour microenvironment to cancer progression and metastasis, in particular the interplay between tumour cells, fibroblasts and the extracellular matrix has grown tremendously over the last years. Lysyl oxidases are increasingly recognised as key players in this context, in addition to their function as drivers of fibrotic diseases. These insights have considerably stimulated drug discovery efforts towards lysyl oxidases as targets over the last decade. This review article summarises the biochemical and structural properties of theses enzymes. Their involvement in tumour progression and metastasis is highlighted from a biochemical point of view, taking into consideration both the extracellular and intracellular action of lysyl oxidases. More recently reported inhibitor compounds are discussed with an emphasis on their discovery, structure-activity relationships and the results of their biological characterisation. Molecular probes developed for imaging of lysyl oxidase activity are reviewed from the perspective of their detection principles, performance and biomedical applications.

A first-in-class pan-lysyl oxidase inhibitor impairs stromal remodeling and enhances gemcitabine response and survival in pancreatic cancer

The lysyl oxidase family represents a promising target in stromal targeting of solid tumors due to the importance of this family in crosslinking and stabilizing fibrillar collagens and its known role in tumor desmoplasia. Using small-molecule drug-design approaches, we generated and validated PXS-5505, a first-in-class highly selective and potent pan-lysyl oxidase inhibitor. We demonstrate in vitro and in vivo that pan-lysyl oxidase inhibition decreases chemotherapy-induced pancreatic tumor desmoplasia and stiffness, reduces cancer cell invasion and metastasis, improves tumor perfusion and enhances the efficacy of chemotherapy in the autochthonous genetically engineered KPC model, while also demonstrating antifibrotic effects in human patient-derived xenograft models of pancreatic cancer. PXS-5505 is orally bioavailable, safe and effective at inhibiting lysyl oxidase activity in tissues. Our findings present the rationale for progression of a pan-lysyl oxidase inhibitor aimed at eliciting a reduction in stromal matrix to potentiate chemotherapy in pancreatic ductal adenocarcinoma.

The challenge of determining lysyl oxidase activity: Old methods and novel approaches

The lysyl oxidase (LOX) family of enzymes catalyze the oxidative deamination of lysine and hydroxylysine residues in collagen and elastin in the initiation step of the formation of covalent cross-linkages, an essential process for extracellular matrix (ECM) maturation. Elevated LOX expression levels leading to increased LOX activity is associated with diverse pathologies including fibrosis, cancer, and cardiovascular diseases. Different protocols have been so far established to detect and quantify LOX activity from tissue samples and cultured cells, all of them showing advantages and drawbacks. This review article presents a critical overview of the main features of currently available methods as well as introduces some recent technologies called to revolutionize our approach to LOX catalysis.

Early Detection Methods for Silicosis in Australia and Internationally: A Review of the Literature

Pneumoconiosis, or occupational lung disease, is one of the world’s most prevalent work-related diseases. Silicosis, a type of pneumoconiosis, is caused by inhaling respirable crystalline silica (RCS) dust. Although silicosis can be fatal, it is completely preventable. Hundreds of thousands of workers globally are at risk of being exposed to RCS at the workplace from various activities in many industries. Currently, in Australia and internationally, there are a range of methods used for the respiratory surveillance of workers exposed to RCS. These methods include health and exposure questionnaires, spirometry, chest X-rays, and HRCT. However, these methods predominantly do not detect the disease until it has significantly progressed. For this reason, there is a growing body of research investigating early detection methods for silicosis, particularly biomarkers. This literature review summarises the research to date on early detection methods for silicosis and makes recommendations for future work in this area. Findings from this review conclude that there is a critical need for an early detection method for silicosis, however, further laboratory- and field-based research is required.

Imaging and targeting LOX-mediated tissue remodeling with a reactive collagen peptide

Collagens are fibrous proteins that are integral to the strength and stability of connective tissues. During collagen maturation, lysyl oxidases (LOX) initiate the cross-linking of fibers, but abnormal LOX activity is associated with impaired tissue function as seen in fibrotic and malignant diseases. Visualizing and targeting this dynamic process in healthy and diseased tissue is important, but so far not feasible. Here we present a probe for the simultaneous monitoring and targeting of LOX-mediated collagen cross-linking that combines a LOX-activity sensor with a collagen peptide to chemoselectively target endogenous aldehydes generated by LOX. This synergistic probe becomes covalently anchored and lights up in vivo and in situ in response to LOX at the sites where cross-linking occurs, as demonstrated by staining of normal skin and cancer sections. We anticipate that our reactive collagen-based sensor will improve understanding of collagen remodeling and provide opportunities for the diagnosis of fibrotic and malignant diseases.

Small-molecule fluorescence-based probes for interrogating major organ diseases

Chemical tools that allow the real-time monitoring of organ function and the visualisation of organ-related processes at the cellular level are of great importance in biological research. The upregulation/downregulation of specific biomarkers is often associated with the development of organ related diseases. Small-molecule fluorescent probes have the potential to create advances in our understanding of these disorders. Viable probes should be endowed with a number of key features that include high biomarker sensitivity, low limit of detection, fast response times and appropriate in vitro and in vivo biocompatibility. In this tutorial review, we discuss the development of probes that allow the targeting of organ related processes in vitro and in vivo. We highlight the design strategy that underlies the preparation of various promising probes, their optical response to key biomarkers, and proof-of-concept biological studies. The inherent drawbacks and limitations are discussed as are the current challenges and opportunities in the field. The hope is that this tutorial review will inspire the further development of small-molecule fluorescent probes that could aid the study of pathogenic conditions that contribute to organ-related diseases.

Lysyl oxidase inhibition in primary myelofibrosis: A renewed strategy

Primary myelofibrosis (PMF) is a type of myeloproliferative neoplasm (MPN) that portends a poor prognosis and has limited options for treatment. PMF is often driven by clonal mutations in one of three genes that regulate the JAK-STAT signaling pathway, leading to hyperactivation of this signaling pathway and over-proliferation of megakaryocytes (MKs) and their precursors. PMF presents with debilitating symptoms such as splenomegaly and weight loss. The few available treatments for PMF include a JAK2 inhibitor, ruxolitinib, which causes side effects and is not always effective. The extracellular matrix (ECM) and bone marrow (BM) microenvironment may play an important role in the pathogenesis of PMF. Lysyl oxidase (LOX), an enzyme that plays a key role in the ECM by facilitating the cross-linking of collagen and elastin fibers, has been shown to be upregulated in MKs of PMF mice and in PMF patients, suggesting its role in the progression of BM fibrosis. Recently, LOX has been identified as a potential novel therapeutic target for PMF and the development of new small molecule LOX inhibitors, PXS-LOX_1 and PXS-LOX_2, has shown some promise in slowing the progression of PMF in pre-clinical studies. Given that these inhibitors displayed an ability to target the dysregulation of the ECM via LOX inhibition, they show promise as therapeutic agents for an underappreciated aspect of PMF.

Image computing for fibre-bundle endomicroscopy: A review

Endomicroscopy is an emerging imaging modality, that facilitates the acquisition of in vivo, in situ optical biopsies, assisting diagnostic and potentially therapeutic interventions. While there is a diverse and constantly expanding range of commercial and experimental optical biopsy platforms available, fibre-bundle endomicroscopy is currently the most widely used platform and is approved for clinical use in a range of clinical indications. Miniaturised, flexible fibre-bundles, guided through the working channel of endoscopes, needles and catheters, enable high-resolution imaging across a variety of organ systems. Yet, the nature of image acquisition though a fibre-bundle gives rise to several inherent characteristics and limitations necessitating novel and effective image pre- and post-processing algorithms, ranging from image formation, enhancement and mosaicing to pathology detection and quantification. This paper introduces the underlying technology and most prevalent clinical applications of fibre-bundle endomicroscopy, and provides a comprehensive, up-to-date, review of relevant image reconstruction, analysis and understanding/inference methodologies. Furthermore, current limitations as well as future challenges and opportunities in fibre-bundle endomicroscopy computing are identified and discussed.

Novel lysyl oxidase inhibitors attenuate hallmarks of primary myelofibrosis in mice

Primary myelofibrosis (PMF) is a chronic myeloproliferative neoplasm (MPN) that usually portends a poor prognosis with limited therapeutic options available. Currently, only allogeneic stem cell transplantation is curative in those who are candidates, while administration of the JAK1/2 inhibitor ruxolitinib carries a risk of worsening cytopenia. The limited therapeutic options available highlight the need for the development of novel treatments for PMF. Lysyl oxidase (LOX), an enzyme vital for collagen cross-linking and extracellular matrix stiffening, has been found to be upregulated in PMF. Herein, we evaluate two novel LOX inhibitors, PXS-LOX_1 and PXS-LOX_2, in two animal models of PMF (GATA1low and JAK2V617F-mutated mice). Specifically, PXS-LOX_1 or vehicle was given to 15- to 16-week-old GATA1low mice via intraperitoneal injection at a dose of 15 mg/kg four times a week for 9 weeks. PXS-LOX_1 was found to significantly decrease the bone marrow fibrotic burden and megakaryocyte number compared to vehicle in both male and female GATA1low mice. Given these results, PXS-LOX_1 was then tested in 15- to 17-week-old JAK2V617F-mutated mice at a dose of 30 mg/kg four times a week for 8 weeks. Again, we observed a significant decrease in bone marrow fibrotic burden. PXS-LOX_2, a LOX inhibitor with improved oral bioavailability, was next evaluated in 15- to 17-week-old JAK2V617F-mutated mice at a dose of 5 mg/kg p.o. four times a week for 8 weeks. This inhibitor also resulted in a significant decrease in bone marrow fibrosis, albeit with a more pronounced amelioration in female mice. Taking these results together, PXS-LOX_1 and PXS-LOX_2 appear to be promising new candidates for the treatment of fibrosis in PMF.

In Vivo Endomicroscopy of Lung Injury and Repair in ARDS: Potential Added Value to Current Imaging

BACKGROUND

Standard clinical imaging of the acute respiratory distress syndrome (ARDS) lung lacks resolution and offers limited possibilities in the exploration of the structure-function relationship, and therefore cannot provide an early and clear discrimination of patients with unexpected diagnosis and unrepair profile. The current gold standard is open lung biopsy (OLB). However, despite being able to reveal precise information about the tissue collected, OLB cannot provide real-time information on treatment response and is accompanied with a complication risk rate up to 25%, making longitudinal monitoring a dangerous endeavor. Intravital probe-based confocal laser endomicroscopy (pCLE) is a developing and innovative high-resolution imaging technology. pCLE offers the possibility to leverage multiple and specific imaging probes to enable multiplex screening of several proteases and pathogenic microorganisms, simultaneously and longitudinally, in the lung. This bedside method will ultimately enable physicians to rapidly, noninvasively, and accurately diagnose degrading lung and/or fibrosis without the need of OLBs.

OBJECTIVES AND METHODS

To extend the information provided by standard imaging of the ARDS lung with a bedside, high-resolution, miniaturized pCLE through the detailed molecular imaging of a carefully selected region-of-interest (ROI). To validate and quantify real-time imaging to validate pCLE against OLB.

RESULTS

Developments in lung pCLE using fluorescent affinity- or activity-based probes at both preclinical and clinical (first-in-man) stages are ongoing-the results are promising, revealing correlations with OLBs in problematic ARDS.

CONCLUSION

It can be envisaged that safe, high-resolution, noninvasive pCLE with activatable fluorescence probes will provide a "virtual optical biopsy" and will provide decisive information in selected ARDS patients at the bedside.

Bayesian bacterial detection using irregularly sampled optical endomicroscopy images

Pneumonia is a major cause of morbidity and mortality of patients in intensive care. Rapid determination of the presence and gram status of the pathogenic bacteria in the distal lung may enable a more tailored treatment regime. Optical Endomicroscopy (OEM) is an emerging medical imaging platform with preclinical and clinical utility. Pulmonary OEM via multi-core fibre bundles has the potential to provide in vivo, in situ, fluorescent molecular signatures of the causes of infection and inflammation. This paper presents a Bayesian approach for bacterial detection in OEM images. The model considered assumes that the observed pixel fluorescence is a linear combination of the actual intensity value associated with tissues or background, corrupted by additive Gaussian noise and potentially by an additional sparse outlier term modelling anomalies (bacteria). The bacteria detection problem is formulated in a Bayesian framework and prior distributions are assigned to the unknown model parameters. A Markov chain Monte Carlo algorithm based on a partially collapsed Gibbs sampler is used to sample the posterior distribution of the unknown parameters. The proposed algorithm is first validated by simulations conducted using synthetic datasets for which good performance is obtained. Analysis is then conducted using two ex vivo lung datasets in which fluorescently labelled bacteria are present in the distal lung. A good correlation between bacteria counts identified by a trained clinician and those of the proposed method, which detects most of the manually annotated regions, is observed.

Novel Imaging Approaches in Systemic Sclerosis-Associated Interstitial Lung Disease

PURPOSE OF THE REVIEW

Novel imaging approaches, such as quantitative computed tomography (CT), magnetic resonance imaging (MRI), and molecular imaging, are being applied to interstitial lung diseases to provide prognostic, functional, and molecular information. Here, we review such imaging approaches and their applicability to systemic sclerosis-associated interstitial lung disease (SSc-ILD).

RECENT FINDINGS

Quantitative CT can be used to quantify the radiographic response to SSc-ILD therapy. Due to advances in MRI sequence development, MRI can detect the presence of SSc-ILD with high accuracy. MRI can also be utilized to provide functional information as to SSc-ILD and paired with molecular probes to provide non-invasive molecular information. MRI and ultrasound have promising test characteristics for diagnosing ILD in SSc without the use of ionizing radiation. Novel imaging approaches can detect SSc-ILD without the use of ionizing radiation, provide non-invasive functional and molecular information, and quantify treatment response in SSc-ILD. These techniques hold promise for translation into clinical care and clinical trials.

Fibre-based spectral ratio endomicroscopy for contrast enhancement of bacterial imaging and pulmonary autofluorescence

Fibre-based optical endomicroscopy (OEM) permits high resolution fluorescence microscopy in endoscopically accessible tissues. Fibred OEM has the potential to visualise pathologies targeted with fluorescent imaging probes and provide an in vivo in situ molecular pathology platform to augment disease understanding, diagnosis and stratification. Here we present an inexpensive widefield ratiometric fibred OEM system capable of enhancing the contrast between similar spectra of pathologically relevant fluorescent signals without the burden of complex spectral unmixing. As an exemplar, we demonstrate the potential of the platform to detect fluorescently labelled Gram-negative bacteria in the challenging environment of highly autofluorescent lung tissue in whole ex vivo human lungs.

Fluorogenic probes for disease-relevant enzymes

Traditional biochemical methods for enzyme detection are mainly based on antibody-based immunoassays, which lack the ability to monitor the spatiotemporal distribution and, in particular, the in situ activity of enzymes in live cells and in vivo. In this review, we comprehensively summarize recent progress that has been made in the development of small-molecule as well as material-based fluorogenic probes for sensitive detection of the activities of enzymes that are related to a number of human diseases. The principles utilized to design these probes as well as their applications are reviewed. Specific attention is given to fluorogenic probes that have been developed for analysis of the activities of enzymes including oxidases and reductases, those that act on biomacromolecules including DNAs, proteins/peptides/amino acids, carbohydrates and lipids, and those that are responsible for translational modifications. We envision that this review will serve as an ideal reference for practitioners as well as beginners in relevant research fields.

Chelating principles in Menkes and Wilson diseases: Choosing the right compounds in the right combinations at the right time

Dysregulation of copper homeostasis in humans is primarily found in two genetic diseases of copper transport, Menkes and Wilson diseases, which show symptoms of copper deficiency or overload, respectively. However, both diseases are copper storage disorders despite completely opposite clinical pictures. Clinically, Menkes disease is characterized by copper deficiency secondary to poor loading of copper-requiring enzymes although sufficient body copper. Copper accumulates in non-hepatic tissues, but is deficient in blood, liver, and brain. In contrast, Wilson disease is characterized by symptoms of copper toxicity secondary to accumulation of copper in several organs most notably brain and liver, and a saturated blood copper pool. It is a challenge to correct copper dyshomeostasis in either disease though copper depletion in Menkes disease is most challenging. Both diseases are caused by defective copper export from distinct cells, and we seek to give new angles and guidelines to improve treatment of these two complementary diseases. Therapy of Menkes disease with copper-histidine, thiocarbamate, nitrilotriacetate or lipoic acid is discussed. In Wilson disease combination of a hydrophilic chelator e.g. trientine or dimercaptosuccinate with a brain shuttle e.g. thiomolybdate or lipoate, is discussed. New chelating principles for copper removal or delivery are outlined.

Development of an alveolar transbronchial catheter for concurrent fiber optics based imaging and fluid delivery

Optical molecular imaging is an emerging field and high resolution optical imaging of the distal lung parenchyma has been made possible with the advent of clinically approved fiber based imaging modalities. However, currently, there is no single method of allowing the simultaneous imaging and delivery of targeted molecular imaging agents. The objective of this research is to create a catheterized device capable of fulfilling this need. We describe the rationale, development, and validation in ex vivo ovine lung to near clinical readiness of a triple lumen bronchoscopy catheter that allows concurrent imaging and fluid delivery, with the aim of clinical use to deliver multiple fluorescent compounds to image alveolar pathology. Using this device, we were able to produce high-quality images of bacterial infiltrates in ex-vivo ovine lung within 60 seconds of instilling a single microdose of (<100 mcgs) imaging agent. This has many advantages for future clinical usage over the current state of the art.

Characterization and modelling of inter-core coupling in coherent fiber bundles

Recent developments in optical endomicroscopy (OEM) and associated fluorescent SmartProbes present a need for sensitive imaging with high detection performance. Inter-core coupling within coherent fiber bundles is a well recognized limitation, affecting the technology's imaging capabilities. Fiber cross coupling has been studied both experimentally and within a theoretical framework (coupled mode theory), providing (i) insights on the factors affecting cross talk, and (ii) recommendations for optimal fiber bundle design. However, due to physical limitations, such as the tradeoff between cross coupling and core density, cross coupling can be suppressed yet not eliminated through optimal fiber design. This study introduces a novel approach for measuring, analyzing and quantifying cross coupling within coherent fiber bundles, in a format that can be integrated into a linear model, which in turn can enable computational compensation of the associated blurring introduced to OEM images.

Low index contrast imaging fibers

We present high-resolution imaging fibers made from low-cost commercially available fiber preforms manufactured for the telecommunications industry. Our fabrication method involves multi-stacking arrays of different sized cores in order to suppress core-to-core crosstalk whilst building up a large array of cores. One of the fibers, based on a square array of cores, has comparable imaging performance to commercial imaging fibers but without the need for exceptionally high refractive index contrasts, and will enable the development of economically viable single-use disposable imaging fibers.

Automated Detection of Uninformative Frames in Pulmonary Optical Endomicroscopy

SIGNIFICANCE

Optical endomicroscopy (OEM) is a novel real-time imaging technology that provides endoscopic images at a microscopic level. The nature of OEM data, as acquired in clinical use, gives rise to the presence of uninformative frames (i.e., pure-noise and motion-artefacts). Uninformative frames can comprise a considerable proportion (up to > 25%) of a dataset, increasing the resources required for analyzing the data (both manually and automatically), as well as diluting the results of any automated quantification analysis.

OBJECTIVE

There is, therefore, a need to automatically detect and remove as many of these uninformative frames as possible while keeping frames with structural information intact.

METHODS

This paper employs Gray Level Cooccurrence Matrix texture measures and detection theory to identify and remove such frames. The detection of pure-noise and motion-artefacts frames is treated as two independent problems.

RESULTS

Pulmonary OEM frame sequences of the distal lung are employed for the development and assessment of the approach. The proposed approach identifies and removes uninformative frames with a sensitivity of 93% and a specificity of 92.6%.

CONCLUSION

The detection algorithm is accurate and robust in pulmonary OEM frame sequences. Conditional to appropriate model refinement, the algorithms can become applicable in other organs.

Highly selective and rapidly activatable fluorogenic Thrombin sensors and application in human lung tissue

A fast and selective fluorogenic probe for Thrombin is reported and applied in ex vivo fibrotic human lung tissue.

Assessing the utility of autofluorescence-based pulmonary optical endomicroscopy to predict the malignant potential of solitary pulmonary nodules in humans

Solitary pulmonary nodules are common, often incidental findings on chest CT scans. The investigation of pulmonary nodules is time-consuming and often leads to protracted follow-up with ongoing radiological surveillance, however, clinical calculators that assess the risk of the nodule being malignant exist to help in the stratification of patients. Furthermore recent advances in interventional pulmonology include the ability to both navigate to nodules and also to perform autofluorescence endomicroscopy. In this study we assessed the efficacy of incorporating additional information from label-free fibre-based optical endomicrosopy of the nodule on assessing risk of malignancy. Using image analysis and machine learning approaches, we find that this information does not yield any gain in predictive performance in a cohort of patients. Further advances with pulmonary endomicroscopy will require the addition of molecular tracers to improve information from this procedure.

Two-color widefield fluorescence microendoscopy enables multiplexed molecular imaging in the alveolar space of human lung tissue

We demonstrate a fast two-color widefield fluorescence microendoscopy system capable of simultaneously detecting several disease targets in intact human ex vivo lung tissue. We characterize the system for light throughput from the excitation light emitting diodes, fluorescence collection efficiency, and chromatic focal shifts. We demonstrate the effectiveness of the instrument by imaging bacteria (Pseudomonas aeruginosa) in ex vivo human lung tissue. We describe a mechanism of bacterial detection through the fiber bundle that uses blinking effects of bacteria as they move in front of the fiber core providing detection of objects smaller than the fiber core and cladding (∼3  μm ∼3  μm ). This effectively increases the measured spatial resolution of 4  μm 4  μm . We show simultaneous imaging of neutrophils, monocytes, and fungus (Aspergillus fumigatus) in ex vivo human lung tissue. The instrument has 10 nM and 50 nM sensitivity for fluorescein and Cy5 solutions, respectively. Lung tissue autofluorescence remains visible at up to 200 fps camera acquisition rate. The optical system lends itself to clinical translation due to high-fluorescence sensitivity, simplicity, and the ability to multiplex several pathological molecular imaging targets simultaneously.

Engineering approaches to study fibrosis in 3-D in vitro systems

Fibrotic diseases occur in virtually every tissue of the body and are a major cause of mortality, yet they remain largely untreatable and poorly understood on a mechanistic level. The development of anti-fibrotic agents has been hampered, in part, by the insufficient fibrosis biomimicry provided by traditional in vitro platforms. This review focuses on recent advancements toward creating 3-D platforms that mimic key features of fibrosis, as well as the application of novel imaging and sensor techniques to analyze dynamic extracellular matrix remodeling. Several opportunities are highlighted to apply new tools from the fields of biomaterials, imaging, and systems biology to yield pathophysiologically relevant in vitro platforms that improve our understanding of fibrosis and may enable identification of potential treatment targets.