David M Hwang

University of Toronto, Toronto, Ontario, Canada

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Publications (63)

  • Article · Aug 2016 · Journal of Biomedical Optics
  • Conference Paper · Mar 2016
  • [Show abstract] [Hide abstract] ABSTRACT: Nanoparticles can provide significant improvements in the diagnosis and treatment of cancer. How nanoparticle size, shape, and surface chemistry can affect their accumulation, retention, and penetration in tumors remains heavily investigated, because such findings provide guiding principles for engineering optimal nanosystems for tumor targeting. Currently, the experimental focus has been on particle design and not the biological system. Here, we varied tumor volume to determine whether cancer pathophysiology can influence tumor accumulation and penetration of different sized nanoparticles. Monte Carlo simulations were also used to model the process of nanoparticle accumulation. We discovered that changes in pathophysiology associated with tumor volume can selectively change tumor uptake of nanoparticles of varying size. We further determine that nanoparticle retention within tumors depends on the frequency of interaction of particles with the perivascular extracellular matrix for smaller nanoparticles, whereas transport of larger nanomaterials is dominated by Brownian motion. These results reveal that nanoparticles can potentially be personalized according to a patient's disease state to achieve optimal diagnostic and therapeutic outcomes.
    Article · Feb 2016 · Proceedings of the National Academy of Sciences
  • [Show abstract] [Hide abstract] ABSTRACT: Background: Increasing evidence suggests that interleukin (IL)-17A plays an important role in chronic lung allograft dysfunction (CLAD), characterized by airway and lung parenchymal fibrosis, after lung transplantation. Halofuginone is a plant derivative that has been shown to inhibit Th17 differentiation. The purpose of this study was to examine the effect of halofuginone on CLAD development using a minor alloantigen-mismatched mouse orthotopic lung transplant model. Methods: C57BL/6 recipient mice received an orthotopic left lung transplant from C57BL/10 donors, mismatched for minor antigens. Lung transplant recipients received daily intraperitoneal injections of 2.5 μg halofuginone or vehicle alone. Lung grafts were assessed on Days 7, 14, and 28 post-transplant. Results: Compared with control mice, on Day 28 post-transplant, lung grafts of mice treated with halofuginone showed a significant reduction in the percentage of obliterated airways (6.8 ± 4.7% vs 52.5 ± 13.8%, p < 0.01), as well as significantly reduced parenchymal fibrosis (5.5 ± 2.3% vs 35.9 ± 10.9%, p < 0.05). Immunofluorescent staining for IL-17A demonstrated a decreased number and frequency of IL-17A-positive cells in halofuginone-treated lung grafts on Day 28, as compared with controls. Halofuginone treatment also decreased IL-17A and IL-22 transcripts at Day 14, transforming growth factor-β1 and matrix metalloproteinase-2 transcripts at Days 14 and 28. Conclusion: The beneficial effect of halofuginone on development of airway and lung parenchymal fibrosis in the mouse lung transplant model highlights the important role of IL-17A in CLAD and merits further pre-clinical and clinical studies. © 2016 International Society for Heart and Lung Transplantation.
    Article · Dec 2015 · The Journal of Heart and Lung Transplantation
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    [Show abstract] [Hide abstract] ABSTRACT: The microbiome shapes diverse facets of human biology and disease, with the importance of fungi only beginning to be appreciated. Microbial communities infiltrate diverse anatomical sites as with the respiratory tract of healthy humans and those with diseases such as cystic fibrosis, where chronic colonization and infection lead to clinical decline. Although fungi are frequently recovered from cystic fibrosis patient sputum samples and have been associated with deterioration of lung function, understanding of species and population dynamics remains in its infancy. Here, we coupled high-throughput sequencing of the ribosomal RNA internal transcribed spacer 1 (ITS1) with phenotypic and genotypic analyses of fungi from 89 sputum samples from 28 cystic fibrosis patients. Fungal communities defined by sequencing were concordant with those defined by culture-based analyses of 1,603 isolates from the same samples. Different patients harbored distinct fungal communities. There were detectable trends, however, including colonization with Candida and Aspergillus species, which was not perturbed by clinical exacerbation or treatment. We identified considerable inter- and intra-species phenotypic variation in traits important for host adaptation, including antifungal drug resistance and morphogenesis. While variation in drug resistance was largely between species, striking variation in morphogenesis emerged within Candida species. Filamentation was uncoupled from inducing cues in 28 Candida isolates recovered from six patients. The filamentous isolates were resistant to the filamentation-repressive effects of Pseudomonas aeruginosa, implicating inter-kingdom interactions as the selective force. Genome sequencing revealed that all but one of the filamentous isolates harbored mutations in the transcriptional repressor NRG1; such mutations were necessary and sufficient for the filamentous phenotype. Six independent nrg1 mutations arose in Candida isolates from different patients, providing a poignant example of parallel evolution. Together, this combined clinical-genomic approach provides a high-resolution portrait of the fungal microbiome of cystic fibrosis patient lungs and identifies a genetic basis of pathogen adaptation.
    Full-text Article · Nov 2015 · PLoS Pathogens
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    [Show abstract] [Hide abstract] ABSTRACT: Pulmonary infections caused by Pseudomonas aeruginosa are a recalcitrant problem in cystic fibrosis (CF) patients. While the clinical implications and long-term evolutionary patterns of these infections are well studied, we know little about the short-term population dynamics that enable this pathogen to persist despite aggressive antimicrobial therapy. Here, we describe a short-term population genomic analysis of 233 P. aeruginosa isolates collected from 12 sputum specimens obtained over a 1-year period from a single patient. Whole-genome sequencing and antimicrobial susceptibility profiling identified the expansion of two clonal lineages. The first lineage originated from the coalescence of the entire sample less than 3 years before the end of the study and gave rise to a high-diversity ancestral population. The second expansion occurred 2 years later and gave rise to a derived population with a strong signal of positive selection. These events show characteristics consistent with recurrent selective sweeps. While we cannot identify the specific mutations responsible for the origins of the clonal lineages, we find that the majority of mutations occur in loci previously associated with virulence and resistance. Additionally, approximately one-third of all mutations occur in loci that are mutated multiple times, highlighting the importance of parallel pathoadaptation. One such locus is the gene encoding penicillin-binding protein 3, which received three independent mutations. Our functional analysis of these alleles shows that they provide differential fitness benefits dependent on the antibiotic under selection. These data reveal that bacterial populations can undergo extensive and dramatic changes that are not revealed by lower-resolution analyses.
    Full-text Article · Sep 2015 · mBio
  • [Show abstract] [Hide abstract] ABSTRACT: The long-term success of lung transplantation is challenged by the development of chronic lung allograft dysfunction (CLAD) and its distinct subtypes of bronchiolitis obliterans syndrome (BOS) and restrictive allograft syndrome (RAS). However, the current diagnostic criteria for CLAD subtypes rely on total lung capacity (TLC), which is not always measured during routine post-transplant assessment. Our aim was to investigate the utility of low-dose 3-dimensional computed tomography (CT) lung volumetry for differentiating RAS from BOS. This study was a retrospective evaluation of 63 patients who had developed CLAD after bilateral lung or heart‒lung transplantation between 2006 and 2011, including 44 BOS and 19 RAS cases. Median post-transplant follow-up was 65 months in BOS and 27 months in RAS. The median interval between baseline and the disease-onset time-point for CT volumetry was 11 months in both BOS and RAS. Chronologic changes and diagnostic accuracy of CT lung volume (measured as percent of baseline) were investigated. RAS showed a significant decrease in CT lung volume at disease onset compared with baseline (mean 3,916 ml vs 3,055 ml when excluding opacities, p < 0.0001), whereas BOS showed no significant post-transplant change (mean 4,318 ml vs 4,396 ml, p = 0.214). The area under the receiver operating characteristic curve of CT lung volume for differentiating RAS from BOS was 0.959 (95% confidence interval 0.912 to 1.01, p < 0.0001) and the calculated accuracy was 0.938 at a threshold of 85%. In bilateral lung or heart‒lung transplant patients with CLAD, low-dose CT volumetry is a useful tool to differentiate patients who develop RAS from those who develop BOS. Copyright © 2015 International Society for Heart and Lung Transplantation. Published by Elsevier Inc. All rights reserved.
    Article · Aug 2015 · The Journal of heart and lung transplantation: the official publication of the International Society for Heart Transplantation
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    Shawn T. Clark · Julio Diaz Caballero · Mary Cheang · [...] · David M. Hwang
    [Show abstract] [Hide abstract] ABSTRACT: Chronic airway infections caused by Pseudomonas aeruginosa contribute to the progression of pulmonary disease in individuals with cystic fibrosis (CF). In the setting of CF, within-patient adaptation of a P. aeruginosa strain generates phenotypic diversity that can complicate microbiological analysis of patient samples. We investigated within- and between- sample diversity of 34 phenotypes among 235 P. aeruginosa isolates cultured from sputum samples collected from a single CF patient over the span of one year, and assessed colony morphology as a screening tool for predicting phenotypes, including antimicrobial susceptibilities. We identified 15 distinct colony morphotypes that varied significantly in abundance both within and between sputum samples. Substantial within sample phenotypic heterogeneity was also noted in other phenotypes, with morphotypes being unreliable predictors of antimicrobial susceptibility and other phenotypes. Emergence of isolates with reduced susceptibility to β-lactams was observed during periods of clinical therapy with aztreonam. Our findings confirm that the P. aeruginosa population in chronic CF lung infections is highly dynamic, and that intra-sample phenotypic diversity is underestimated if only one or few colonies are analyzed per sample.
    Full-text Article · Jun 2015 · Scientific Reports
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    [Show abstract] [Hide abstract] ABSTRACT: Understanding the significance of bacterial species that colonize and persist in cystic fibrosis (CF) airways requires a detailed examination of bacterial community structure across a broad range of age and disease stage. We used 16S ribosomal RNA sequencing to characterize the lung microbiota in 269 CF patients spanning a 60 year age range, including 76 pediatric samples from patients of age 4-17, and a broad cross-section of disease status to identify features of bacterial community structure and their relationship to disease stage and age. The CF lung microbiota shows significant inter-individual variability in community structure, composition and diversity. The core microbiota consists of five genera - Streptococcus, Prevotella, Rothia, Veillonella and Actinomyces. CF-associated pathogens such as Pseudomonas, Burkholderia, Stenotrophomonas and Achromobacter are less prevalent than core genera, but have a strong tendency to dominate the bacterial community when present. Community diversity and lung function are greatest in patients less than 10 years of age and lower in older age groups, plateauing at approximately age 25. Lower community diversity correlates with worse lung function in a multivariate regression model. Infection by Pseudomonas correlates with age-associated trends in community diversity and lung function.
    Full-text Article · May 2015 · Scientific Reports
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    [Show abstract] [Hide abstract] ABSTRACT: Background: It is estimated that millions of North Americans would qualify for lung cancer screening and that billions of dollars of national health expenditures would be required to support population-based computed tomography lung cancer screening programs. The decision to implement such programs should be informed by data on resource utilization and costs. Methods: Resource utilization data were collected prospectively from 2059 participants in the Pan-Canadian Early Detection of Lung Cancer Study using low-dose computed tomography (LDCT). Participants who had 2% or greater lung cancer risk over 3 years using a risk prediction tool were recruited from seven major cities across Canada. A cost analysis was conducted from the Canadian public payer's perspective for resources that were used for the screening and treatment of lung cancer in the initial years of the study. Results: The average per-person cost for screening individuals with LDCT was $453 (95% confidence interval [CI], $400-$505) for the initial 18-months of screening following a baseline scan. The screening costs were highly dependent on the detected lung nodule size, presence of cancer, screening intervention, and the screening center. The mean per-person cost of treating lung cancer with curative surgery was $33,344 (95% CI, $31,553-$34,935) over 2 years. This was lower than the cost of treating advanced-stage lung cancer with chemotherapy, radiotherapy, or supportive care alone, ($47,792; 95% CI, $43,254-$52,200; p = 0.061). Conclusion: In the Pan-Canadian study, the average cost to screen individuals with a high risk for developing lung cancer using LDCT and the average initial cost of curative intent treatment were lower than the average per-person cost of treating advanced stage lung cancer which infrequently results in a cure.
    Full-text Article · Aug 2014 · Journal of thoracic oncology: official publication of the International Association for the Study of Lung Cancer
  • [Show abstract] [Hide abstract] ABSTRACT: QUESTION What types of specimens suspected to be or diagnosed as lung cancer should or should not have routine secondary pathology review? Available from Cancer Care Ontario at: https://www.cancercare.on.ca/common/pages/UserFile.aspx?fileId=311334
    Technical Report · Jun 2014
  • [Show abstract] [Hide abstract] ABSTRACT: Introduction: Epidermal growth factor receptor (EGFR) mutation testing has become critical in the treatment of patients with advanced non-small-cell lung cancer. This study involves a large cohort and epidemiologically unselected series of EGFR mutation testing for patients with nonsquamous non-small-cell lung cancer in a North American population to determine sample-related factors that influence success in clinical EGFR testing. Methods: Data from consecutive cases of Canadian province-wide testing at a centralized diagnostic laboratory for a 24-month period were reviewed. Samples were tested for exon-19 deletion and exon-21 L858R mutations using a validated polymerase chain reaction method with 1% to 5% detection sensitivity. Results: From 2651 samples submitted, 2404 samples were tested with 2293 samples eligible for analysis (1780 histology and 513 cytology specimens). The overall test-failure rate was 5.4% with overall mutation rate of 20.6%. No significant differences in the failure rate, mutation rate, or mutation type were found between histology and cytology samples. Although tumor cellularity was significantly associated with test-success or mutation rates in histology and cytology specimens, respectively, mutations could be detected in all specimen types. Significant rates of EGFR mutation were detected in cases with thyroid transcription factor (TTF)-1-negative immunohistochemistry (6.7%) and mucinous component (9.0%). Conclusions: EGFR mutation testing should be attempted in any specimen, whether histologic or cytologic. Samples should not be excluded from testing based on TTF-1 status or histologic features. Pathologists should report the amount of available tumor for testing. However, suboptimal samples with a negative EGFR mutation result should be considered for repeat testing with an alternate sample.
    Article · Jun 2014 · Journal of thoracic oncology: official publication of the International Association for the Study of Lung Cancer
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    [Show abstract] [Hide abstract] ABSTRACT: Supplementary information available for this article at http://www.nature.com/ncomms/2014/140513/ncomms4796/suppinfo/ncomms4796_S1.html
    Full-text Article · May 2014
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    [Show abstract] [Hide abstract] ABSTRACT: The increasing use of nanomaterials raises concerns about the long-term effects of chronic nanoparticle exposure on human health. However, nanoparticle exposure is difficult to evaluate non-invasively using current measurement techniques. Here we show that the skin is an important site of nanoparticle accumulation following systemic administration. Mice injected with high doses of gold nanoparticles have visibly blue skin while quantum dottreated animals fluoresce under ultraviolet excitation. More importantly, elemental analysis of excised skin correlates with the injected dose and nanoparticle accumulation in the liver and spleen. We propose that skin analysis may be a simple strategy to quantify systemic nanoparticle exposure and predict nanoparticle fate in vivo. Our results suggest that in the future, dermal accumulation may also be exploited to trigger the release of ultraviolet and visible light-sensitive therapeutics that are currently impractical in vivo due to limits in optical penetration of tissues at these wavelengths.
    Full-text Article · May 2014 · Nature Communications
  • [Show abstract] [Hide abstract] ABSTRACT: The aim of this work was to establish a novel orthotopic human non-small cell lung cancer (NSCLC) murine xenograft model by a nonsurgical, transbronchial approach. Male athymic nude mice and human NSCLC cell lines, including A549, H460, and H520 were used. Under direct visualization of the vocal cords, a 23-gauge blunt-tip slightly curved metal catheter was introduced into the trachea to the bronchus, and 2.5 × 10(5) tumor cells mixed with Matrigel (BD Biosciences, Mississauga, Ontario, Canada) were administered into the lung. Mice were monitored using weekly microcomputed tomography scans for tumor formation. When the tumor size reached more than 4 mm in diameter, the animals were euthanized, and the tumor tissue was evaluated histopathologically. Of 37 mice studied, 34 were confirmed to have tumor formation: 29 developed solitary tumors and 5 had multifocal lesions. There was no evidence of extrapleural dissemination or effusion. Transbronchial delivery of tumor cells enabled the establishment of a novel orthotopic human NSCLC murine xenograft model. This clinically relevant preclinical model bearing a solitary nodule is of value for a variety of in vivo research studies.
    Article · May 2014 · The Annals of thoracic surgery
  • [Show abstract] [Hide abstract] ABSTRACT: We developed an innovative approach for malignant pleural mesothelioma (MPM) with a short accelerated course of high-dose hemithoracic intensity-modulated radiation therapy (IMRT) followed by extrapleural pneumonectomy (EPP). This phase I/II study assessed the feasibility of Surgery for Mesothelioma After Radiation Therapy (SMART). All resectable clinical T1-3N0M0 histologically proven, previously untreated MPMs were eligible. Patients received 25 Gy in five daily fractions during 1 week to the entire ipsilateral hemithorax with concomitant 5 Gy boost to areas at risk followed by EPP within 1 week of completing neoadjuvant IMRT. Adjuvant chemotherapy was offered to ypN2 patients on final pathologic findings. The primary end point was treatment-related mortality and secondary end points were overall survival, disease-free survival, treatment-related morbidity, and patterns of failure. Targeted accrual of 25 patients was completed between November 2008 and October 2012. All patients completed SMART. IMRT was well tolerated with no grade 3+ toxicities. EPP was performed 6 ± 2 days after completing IMRT without any perioperative mortality. Thirteen patients developed grade 3+ surgical complications. One patient (4%) died from treatment-related toxicity (empyema) during follow-up. All but one patient had stage III or IV disease on final pathologic findings. Five of 13 ypN2 patients received adjuvant chemotherapy. After a median follow-up of 23 months (range, 6-51), the cumulative 3-year survival reached 84% in epithelial subtypes compared with 13% in biphasic subtypes (p = 0.0002). SMART is feasible in resectable MPM patients. This innovative protocol presents encouraging results and supports future studies looking at long-term outcome in patients with epithelial subtypes.
    Article · Jan 2014 · Journal of thoracic oncology: official publication of the International Association for the Study of Lung Cancer
  • [Show abstract] [Hide abstract] ABSTRACT: The past decade has seen a dramatic revolution in the treatment of lung cancer, resulting in large part from the discovery of specific molecular alterations that render tumors with these abnormalities amenable to specific targeted therapies. Many of the alterations affect intracellular signaling pathways that promote growth and survival of tumor cells and inhibit apoptosis. As a result, pathologists must be aware of the increasing number of molecular alterations and tests now being implemented as part of routine diagnostic algorithms for personalizing the treatment of lung cancers. Here, we review the molecular alterations that are commonly present in lung cancers and discuss tests for these alterations currently in clinical use, with an emphasis on epidermal growth factor receptor mutations and anaplastic lymphoma kinase-1 (ALK) rearrangements in non-small cell lung cancer. Other emerging, potentially targetable molecular aberrations are also discussed, including those in small cell carcinoma. © 2014 Springer Science+Business Media New York. All rights are reserved.
    Chapter · Jan 2014
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    [Show abstract] [Hide abstract] ABSTRACT: Context.-Surgical removal and pathologic handling of lung tissue has a compressive effect upon its architecture. The effect of surgical atelectasis on morphology has not been examined in depth, especially with respect to lung adenocarcinomas. Objective.-To examine the influence of surgical atelectasis on morphologic lepidic growth pattern, mimicking papillary adenocarcinoma pattern. Design.-In 2 cases serial sections of resected pulmonary adenocarcinoma were used, as was a 3-dimensional reconstruction. Elastin stains were performed on primary and metastatic adenocarcinomas. Results.-Perfusion fixation of another case showed marked morphologic differences of less compressed peripheral lung tissue, emphasizing the preexisting alveolar structure. An elastic stain may help identify true lesional architecture. Conclusions.-We demonstrate that microscopic sections of adenocarcinoma in situ in compressed/collapsed tissue may give rise to a pseudopapillary pattern mimicking invasive adenocarcinoma. Accurate appreciation of different tumor architecture in lung adenocarcinoma has important biologic and clinical implications. Pathologists should be aware of the possibility of misclassification of adenocarcinoma pattern due to tissue artifacts caused by lung tissue handling.
    Full-text Article · Dec 2013 · Archives of pathology & laboratory medicine
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    Full-text Article · Oct 2013 · American Journal of Respiratory and Critical Care Medicine
  • [Show abstract] [Hide abstract] ABSTRACT: Context.-The International Collaboration on Cancer Reporting (ICCR) is a quadripartite alliance formed by the Royal College of Pathologists of Australasia, the Royal College of Pathologists of the United Kingdom, the College of American Pathologists, and the Canadian Partnership Against Cancer. The ICCR was formed with a view to reducing the global burden of cancer data set development and reduplication of effort by different international institutions that commission, publish, and maintain standardized cancer-reporting data sets. The resultant standardization of cancer reporting would be expected to benefit not only those countries directly involved in the collaboration but also others not in a position to develop their own data sets. Objectives.-To develop an evidence-based reporting data set for each cancer site. Design.-A project to develop data sets for prostate, endometrium, and lung cancers and malignant melanoma was piloted by the quadripartite group. Results.-A set of required and recommended data elements and appropriate responses for each element were agreed upon for the reporting of lung cancer. Conclusions.-This review describes the process of development of the lung cancer data set.
    Article · Aug 2013 · Archives of pathology & laboratory medicine