Hypoxic tumor environments exhibit disrupted collagen I fibers and low macromolecular transport

SHG Fiberscopy Assessment of Collagen Morphology and Its Potential for Breast Cancer Optical Histology

OBJECTIVE

This study is to investigate the feasibility of our recently developed nonlinear fiberscope for label-free in situ breast tumor detection and lymph node status assessment based on second harmonic generation (SHG) imaging of fibrillar collagen matrix with histological details. The long-term goal is to improve the current biopsy-based cancer paradigm with reduced sampling errors.

METHODS

In this pilot study we undertook retrospective SHG imaging study of ex vivo invasive ductal carcinoma human biopsy tissue samples, and carried out quantitative image analysis to search for collagen structural signatures that are associated with the malignance of breast cancer.

RESULTS

SHG fiberscopy image-based quantitative assessment of collagen fiber morphology reveals that: 1) cancerous tissues contain generally less extracellular collagen fibers compared with tumor-adjacent normal tissues, and 2) collagen fibers in lymph node positive biopsies are more aligned than lymph node negative counterparts.

CONCLUSION/SIGNIFICANCE

The results demonstrate the promising potential of our SHG fiberscope for in situ breast tumor detection and lymph node involvement assessment and for offering real-time guidance during ongoing tissue biopsy.

Diagnostic and prognostic significance of keloid-like collagen remodeling patterns in the extracellular matrix of colorectal cancer

Background

The desmoplastic reaction is considered a promising prognostic parameter for colorectal cancer. However, intermediate desmoplastic reaction is characterized by sizeable stromal heterogeneity, including both small amounts of keloid-like collagen (KC) in the fibrotic stroma and thick tufts of KC circumferentially surrounding cancer nests and occupying most of the fields of view. The present study aimed to evaluate the diagnostic and prognostic significance of KC histophenotyping with a quantitative visual assessment of its presence in the stroma of the invasive margin of TNM (The "tumor-node-metastasis" classification) stage II/III colorectal cancer (CRC).

Methods and results

175 resected tumors from patients with TNM stage II/III CRC were examined. Keloid-like collagen was assessed according to Ueno H. criteria. KC was assessed at the primary tumor invasive margin using Hematoxylin & Eosin and Masson's trichrome staining. The cut-off point for KC was examined using "the best cutoff approach by log-rank test." Using a cutoff point of 30%, we histologically divided fibrous stroma in the invasive area into two groups: "type A"-KC ≤ 0.3 and "type B"-KC>0.3. Type A stroma was observed in 48% of patients, type B-in 52%. The association between collagen amount and 5-year recurrence-free survival (5-RFS) was assessed using Cox regression analysis. Kaplan-Meier analysis and log-rank tests were used to assess the significance of survival analysis. Analysis of categorical variables showed that increased KC in CRC stroma predicted adverse outcomes for 5-RFS (hazard ratio [HR] = 3.143, 95%, confidence interval [CI] = 1.643-6.012, p = 0.001). Moreover, in Kaplan-Meier analysis, the log-rank test showed that type B exhibited worse 5-RFS than type A (p = 0.000).

Conclusion

KC is an independent predictor of 5-year overall and RFS in patients with TNM stage II/III CRC treated with surgery, with worse survival rates when the amount of KC increases by >30%.

PET/MRI and Bioluminescent Imaging Identify Hypoxia as a Cause of Programmed Cell Death Ligand 1 Image Heterogeneity

Purpose To examine the association between hypoxia and programmed cell death ligand 1 (PD-L1) expression using bioluminescence imaging (BLI) and PET/MRI in a syngeneic mouse model of triple-negative breast cancer (TNBC). Materials and Methods PET/MRI and optical imaging were used to determine the role of hypoxia in altering PD-L1 expression using a syngeneic TNBC model engineered to express luciferase under hypoxia. Results Imaging showed a close spatial association between areas of hypoxia and increased PD-L1 expression in the syngeneic murine (4T1) tumor model. Mouse and human TNBC cells exposed to hypoxia exhibited a significant increase in PD-L1 expression, consistent with the in vivo imaging data. The role of hypoxia in increasing PD-L1 expression was further confirmed by using The Cancer Genome Atlas analyses of different human TNBCs. Conclusion These results have identified the potential role of hypoxia in contributing to PD-L1 heterogeneity in tumors by increasing cancer cell PD-L1 expression. Keywords: Hypoxia, PD-L1, Triple-Negative Breast Cancer, PET/MRI, Bioluminescence Imaging Supplemental material is available for this article. © RSNA, 2023.

Quantitative intravital imaging for real-time monitoring of pancreatic tumor cell hypoxia and stroma in an orthotopic mouse model

Pancreatic cancer is a lethal disease with few successful treatment options. Recent evidence demonstrates that tumor hypoxia promotes pancreatic tumor invasion, metastasis, and therapy resistance. However, little is known about the complex relationship between hypoxia and the pancreatic tumor microenvironment (TME). In this study, we developed a novel intravital fluorescence microscopy platform with an orthotopic mouse model of pancreatic cancer to study tumor cell hypoxia within the TME in vivo, at cellular resolution, over time. Using a fluorescent BxPC3-DsRed tumor cell line with a hypoxia-response element (HRE)/green fluorescent protein (GFP) reporter, we showed that HRE/GFP is a reliable biomarker of pancreatic tumor hypoxia, responding dynamically and reversibly to changing oxygen concentrations within the TME. We also characterized the spatial relationships between tumor hypoxia, microvasculature, and tumor-associated collagen structures using in vivo second harmonic generation microscopy. This quantitative multimodal imaging platform enables the unprecedented study of hypoxia within the pancreatic TME in vivo.

Molecular and functional imaging insights into the role of hypoxia in cancer aggression

Hypoxia in cancers has evoked significant interest since 1955 when Thomlinson and Gray postulated the presence of hypoxia in human lung cancers, based on the observation of necrosis occurring at the diffusion limit of oxygen from the nearest blood vessel, and identified the implication of these observations for radiation therapy. Coupled with discoveries in 1953 by Gray and others that anoxic cells were resistant to radiation damage, these observations have led to an entire field of research focused on exploiting oxygenation and hypoxia to improve the outcome of radiation therapy. Almost 65 years later, tumor heterogeneity of nearly every parameter measured including tumor oxygenation, and the dynamic landscape of cancers and their microenvironments are clearly evident, providing a strong rationale for cancer personalized medicine. Since hypoxia is a major cause of extracellular acidosis in tumors, here, we have focused on the applications of imaging to understand the effects of hypoxia in tumors and to target hypoxia in theranostic strategies. Molecular and functional imaging have critically important roles to play in personalized medicine through the detection of hypoxia, both spatially and temporally, and by providing new understanding of the role of hypoxia in cancer aggressiveness. With the discovery of the hypoxia-inducible factor (HIF), the intervening years have also seen significant progress in understanding the transcriptional regulation of hypoxia-induced genes. These advances have provided the ability to silence HIF and understand the associated molecular and functional consequences to expand our understanding of hypoxia and its role in cancer aggressiveness. Most recently, the development of hypoxia-based theranostic strategies that combine detection and therapy are further establishing imaging-based treatment strategies for precision medicine of cancer.

MRI and MRS of intact perfused cancer cell metabolism, invasion, and stromal cell interactions

Because of the spatial and temporal heterogeneities of cancers, technologies to investigate cancer cells and the consequences of their interactions with abnormal physiological environments, such as hypoxia and acidic extracellular pH, with stromal cells, and with the extracellular matrix, under controlled conditions, are valuable to gain insights into the functioning of cancers. These insights can lead to an understanding of why cancers invade and metastasize, and identify effective treatment strategies. Here we have provided an overview of the applications of MRI/MRS/MRSI to investigate intact perfused cancer cells, their metabolism and invasion, and their interactions with stromal cells and the extracellular matrix.

Theranostics and metabolotheranostics for precision medicine in oncology

Most diseases, especially cancer, would significantly benefit from precision medicine where treatment is shaped for the individual. The concept of theragnostics or theranostics emerged around 2002 to describe the incorporation of diagnostic assays into the selection of therapy for this purpose. Increasingly, theranostics has been used for strategies that combine noninvasive imaging-based diagnostics with therapy. Within the past decade theranostic imaging has transformed into a rapidly expanding field that is located at the interface of diagnosis and therapy. A critical need in cancer treatment is to minimize damage to normal tissue. Molecular imaging can be applied to identify targets specific to cancer with imaging, design agents against these targets to visualize their delivery, and monitor response to treatment, with the overall purpose of minimizing collateral damage. Genomic and proteomic profiling can provide an extensive 'fingerprint' of each tumor. With this cancer fingerprint, theranostic agents can be designed to personalize treatment for precision medicine of cancer, and minimize damage to normal tissue. Here, for the first time, we have introduced the term 'metabolotheranostics' to describe strategies where disease-based alterations in metabolic pathways detected by MRS are specifically targeted with image-guided delivery platforms to achieve disease-specific therapy. The versatility of MRI and MRS in molecular and functional imaging makes these technologies especially important in theranostic MRI and 'metabolotheranostics'. Our purpose here is to provide insights into the capabilities and applications of this exciting new field in cancer treatment with a focus on MRI and MRS.

Breast cancer cell cyclooxygenase-2 expression alters extracellular matrix structure and function and numbers of cancer associated fibroblasts

Cyclooxygenase-2 (COX-2) is a critically important mediator of inflammation that significantly influences tumor angiogenesis, invasion, and metastasis. We investigated the role of COX-2 expressed by triple negative breast cancer cells in altering the structure and function of the extracellular matrix (ECM). COX-2 downregulation effects on ECM structure and function were investigated using magnetic resonance imaging (MRI) and second harmonic generation (SHG) microscopy of tumors derived from triple negative MDA-MB-231 breast cancer cells, and a derived clone stably expressing a short hairpin (shRNA) molecule downregulating COX-2. MRI of albumin-GdDTPA was used to characterize macromolecular fluid transport in vivo and SHG microscopy was used to quantify collagen 1 (Col1) fiber morphology. COX-2 downregulation decreased Col1 fiber density and altered macromolecular fluid transport. Immunohistochemistry identified significantly fewer activated cancer associated fibroblasts (CAFs) in low COX-2 expressing tumors. Metastatic lung nodules established by COX-2 downregulated cells were infrequent, smaller, and contained fewer Col1 fibers.COX-2 overexpression studies were performed with tumors derived from triple negative SUM-149 breast cancer cells lentivirally transduced to overexpress COX-2. SHG microscopy identified significantly higher Col1 fiber density in COX-2 overexpressing tumors with an increase of CAFs. These data expand upon the roles of COX-2 in shaping the structure and function of the ECM in primary and metastatic tumors, and identify the potential role of COX-2 in modifying the number of CAFs in tumors that may have contributed to the altered ECM.

Transglutaminase-2 is Involved in Cell Apoptosis of Osteosarcoma Cell Line U2OS Under Hypoxia Condition

Osteosarcoma is the most common type of solid bone cancer, which is the second leading cause of cancer-related death. Hypoxia is an ordinary phenomenon in solid tumor tissues and can induce cell apoptosis but the specific molecular mechanism remains unclear. In this study, we explored the effect and the molecular mechanism of Transglutaminase 2 (TG2) on cell apoptosis in osteosarcoma U2OS cells under hypoxia. We found the enzymatic activity of TG2 is significantly increased and the expression of TG2 is remarkably up-regulated under hypoxia condition. Cell apoptotic rate is markedly increased upon knockdown of TG2 by siRNA under hypoxia. We further investigated the mechanism of cell apoptosis and found Bax protein is significantly increased after depletion of TG2 under hypoxia. Moreover, our data also show that cytochrome C (Cyt C) is significantly increased in cytoplasm and markedly decreased in mitochondria of U2OS cells after depletion of TG2 under hypoxia. Our results suggest that TG2 can inhibit tumor cell apoptosis through down-regulation of Bax and prevention of release Cyt C from mitochondria into cytoplasm.

Exploiting evolutionary principles to prolong tumor control in preclinical models of breast cancer

Conventional cancer treatment strategies assume that maximum patient benefit is achieved through maximum killing of tumor cells. However, by eliminating the therapy-sensitive population, this strategy accelerates emergence of resistant clones that proliferate unopposed by competitors-an evolutionary phenomenon termed "competitive release." We present an evolution-guided treatment strategy designed to maintain a stable population of chemosensitive cells that limit proliferation of resistant clones by exploiting the fitness cost of the resistant phenotype. We treated MDA-MB-231/luc triple-negative and MCF7 estrogen receptor-positive (ER(+)) breast cancers growing orthotopically in a mouse mammary fat pad with paclitaxel, using algorithms linked to tumor response monitored by magnetic resonance imaging. We found that initial control required more intensive therapy with regular application of drug to deflect the exponential tumor growth curve onto a plateau. Dose-skipping algorithms during this phase were less successful than variable dosing algorithms. However, once initial tumor control was achieved, it was maintained with progressively smaller drug doses. In 60 to 80% of animals, continued decline in tumor size permitted intervals as long as several weeks in which no treatment was necessary. Magnetic resonance images and histological analysis of tumors controlled by adaptive therapy demonstrated increased vascular density and less necrosis, suggesting that vascular normalization resulting from enforced stabilization of tumor volume may contribute to ongoing tumor control with lower drug doses. Our study demonstrates that an evolution-based therapeutic strategy using an available chemotherapeutic drug and conventional clinical imaging can prolong the progression-free survival in different preclinical models of breast cancer.

Structure and Function of a Prostate Cancer Dissemination-Permissive Extracellular Matrix

Purpose: The poor prognosis of metastatic prostate cancer continues to present a major challenge in prostate cancer treatment. The tumor extracellular matrix (ECM) plays an important role in facilitating metastasis. Here, we investigated the structure and function of an ECM that facilitates prostate cancer metastasis by comparing orthotopic tumors that frequently metastasize to poorly metastatic subcutaneous tumors.Experimental Design: Both tumors were derived from a human prostate cancer PC3 cell line engineered to fluoresce under hypoxia. Second harmonic generation (SHG) microscopy was used to characterize collagen 1 (Col1) fiber patterns in the xenografts as well as in human samples. MRI was used to determine albumin-Gd-diethylenetriaminepenta-acetate (alb-GdDTPA) transport through the ECM using a saturation recovery MR method combined with fast T₁ SNAPSHOT-FLASH imaging. Cancer-associated fibroblasts (CAF) were also quantified in these tumors.Results: Significant structural and functional differences were identified in the prometastatic orthotopic tumor ECM compared to the less metastatic subcutaneous tumor ECM. The significantly higher number of CAFs in orthotopic tumors may explain the higher Col1 fiber volumes in these tumors. In vivo, alb-GdDTPA pooling was significantly elevated in metastatic orthotopic tumors, consistent with the increased Col1 fibers.Conclusions: Developing noninvasive MRI indices of macromolecular transport, together with characterization of Col1 fiber patterns and CAFs can assist in stratifying prostate cancers for aggressive treatments or active surveillance. These results highlight the role of CAFs in supporting or creating aggressive cancers, and the importance of depleting CAFs to prevent metastatic dissemination in prostate cancer. Clin Cancer Res; 23(9); 2245-54. ©2016 AACR.

Collagen fibers mediate MRI-detected water diffusion and anisotropy in breast cancers

Collagen 1 (Col1) fibers play an important role in tumor interstitial macromolecular transport and cancer cell dissemination. Our goal was to understand the influence of Col1 fibers on water diffusion, and to examine the potential of using noninvasive diffusion tensor imaging (DTI) to indirectly detect Col1 fibers in breast lesions. We previously observed, in human MDA-MB-231 breast cancer xenografts engineered to fluoresce under hypoxia, relatively low amounts of Col1 fibers in fluorescent hypoxic regions. These xenograft tumors together with human breast cancer samples were used here to investigate the relationship between Col1 fibers, water diffusion and anisotropy, and hypoxia. Hypoxic low Col1 fiber containing regions showed decreased apparent diffusion coefficient (ADC) and fractional anisotropy (FA) compared to normoxic high Col1 fiber containing regions. Necrotic high Col1 fiber containing regions showed increased ADC with decreased FA values compared to normoxic viable high Col1 fiber regions that had increased ADC with increased FA values. A good agreement of ADC and FA patterns was observed between in vivo and ex vivo images. In human breast cancer specimens, ADC and FA decreased in low Col1 containing regions. Our data suggest that a decrease in ADC and FA values observed within a lesion could predict hypoxia, and a pattern of high ADC with low FA values could predict necrosis. Collectively the data identify the role of Col1 fibers in directed water movement and support expanding the evaluation of DTI parameters as surrogates for Col1 fiber patterns associated with specific tumor microenvironments as companion diagnostics and for staging.

Molecular imaging of the tumor microenvironment for precision medicine and theranostics

Morbidity and mortality from cancer and their associated conditions and treatments continue to extract a heavy social and economic global burden despite the transformative advances in science and technology in the twenty-first century. In fact, cancer incidence and mortality are expected to reach pandemic proportions by 2025, and costs of managing cancer will escalate to trillions of dollars. The inability to establish effective cancer treatments arises from the complexity of conditions that exist within tumors, the plasticity and adaptability of cancer cells coupled with their ability to escape immune surveillance, and the co-opted stromal cells and microenvironment that assist cancer cells in survival. Stromal cells, although destroyed together with cancer cells, have an ever-replenishing source that can assist in resurrecting tumors from any residual cancer cells that may survive treatment. The tumor microenvironment landscape is a continually changing landscape, with spatial and temporal heterogeneities that impact and influence cancer treatment outcome. Importantly, the changing landscape of the tumor microenvironment can be exploited for precision medicine and theranostics. Molecular and functional imaging can play important roles in shaping and selecting treatments to match this landscape. Our purpose in this review is to examine the roles of molecular and functional imaging, within the context of the tumor microenvironment, and the feasibility of their applications for precision medicine and theranostics in humans.

Metabolism and its sequelae in cancer evolution and therapy

Cancers progress through a series of events that can be characterized as "somatic evolution." A central premise of Darwinian evolutionary theory is that the environment imparts pressure to select for species that are most fit within that particular microenvironmental context. Furthermore, the rate of evolution is proportional to both (1) the strength of the environmental selection and (2) the phenotypic variance of the selected population. It is notable that, during the progression of cancers from carcinogenesis to local invasion to metastasis, the selective landscape continuously changes, and throughout this process, there is increased selection for cells that have altered metabolic phenotypes: implying that these phenotypes impart a selective advantage during the process of environmental selection. One of the most prevalent selected phenotypes is that of aerobic glycolysis, that is, the continued fermentation of glucose even in the presence of adequate oxygen. The mechanisms of this so-called "Warburg effect" have been well studied, and there are multiple models to explain how this occurs at the molecular level. Herein, we propose that unifying insights can be gained by evaluating the environmental context within which this phenotype arises. In other words, we focus not on the "how" but the "why" do cancer cells exhibit high aerobic glycolysis. This is best approached by examining the sequelae of aerobic glycolysis that may impart a selective advantage. Many of these have been considered, including generation of anabolic substrates, response rates of glycolysis vis-à-vis respiration, and generation of antioxidants. A further sequeala considered here is that aerobic glycolysis results in a high rate of lactic acid production; resulting in acidification of the extracellular space. Indeed, it has been shown that a low extracellular pH promotes local invasion, promotes metastasis, and inhibits antitumor immunity. In naturally occurring cancers, low extracellular pH is a strong negative prognostic indicator of metastasis-free survival. Furthermore, it has been shown that inhibition of extracellular acidosis can inhibit metastasis and promote antitumor immunity. Hence, we propose that excess acid production confers a selective advantage for cells during the somatic evolution of cancers.