Reprogramming of VEGF-mediated extracellular matrix changes through autocrine signaling

Vascular endothelial growth factor (VEGF) plays key roles in angiogenesis, vasculogenesis, and wound healing. In cancers, including triple negative breast cancer (TNBC), VEGF has been associated with increased invasion and metastasis, processes that require cancer cells to traverse through the extracellular matrix (ECM) and establish angiogenesis at distant sites. To further understand the role of VEGF in modifying the ECM, we characterized VEGF-mediated changes in the ECM of tumors derived from TNBC MDA-MB-231 cells engineered to overexpress VEGF. We established that increased VEGF expression by these cells resulted in tumors with reduced collagen 1 (Col1) fibers, fibronectin, and hyaluronan. Molecular characterization of tumors identified an increase of MMP1, uPAR, and LOX, and a decrease of MMP2, and ADAMTS1. α-SMA, a marker of cancer associated fibroblasts (CAFs), increased, and FAP-α, a marker of a subset of CAFs associated with immune suppression, decreased with VEGF overexpression. Analysis of human data from The Cancer Genome Atlas Program confirmed mRNA differences for several molecules when comparing TNBC with high and low VEGF expression. We additionally characterized enzymatic changes induced by VEGF overexpression in three different cancer cell lines that clearly identified autocrine-mediated changes, specifically uPAR, in these enzymes. Unlike the increase of Col1 fibers and fibronectin mediated by VEGF during wound healing, in the TNBC model, VEGF significantly reduced key protein components of the ECM. These results further expand our understanding of the role of VEGF in cancer progression and identify potential ECM-related targets to disrupt this progression.

Water and Collagen Content Are High in Pancreatic Cancer: Implications for Quantitative Metabolic Imaging

In magnetic resonance metabolic imaging, signal from the water content is frequently used for normalization to derive quantitative or semi-quantitative values of metabolites in vivo or ex vivo tumors and tissues. Ex vivo high-resolution metabolic characterization of tumors with magnetic resonance spectroscopy (MRS) provides valuable information that can be used to drive the development of noninvasive MRS biomarkers and to identify metabolic therapeutic targets. Variability in the water content between tumor and normal tissue can result in over or underestimation of metabolite concentrations when assuming a constant water content. Assuming a constant water content can lead to masking of differences between malignant and normal tissues both in vivo and ex vivo. There is a critical need to develop biomarkers to detect pancreatic cancer and to develop novel treatments. Our purpose here was to determine the differences in water content between pancreatic tumors and normal pancreatic tissue as well as other organs to accurately quantify metabolic differences when using the water signal for normalization. Our data identify the importance of factoring the differences in water content between tumors and organs. High-resolution proton spectra of tumors and pancreatic tissue extracts normalized to the water signal, assuming similar water content, did not reflect the significantly increased total choline observed in tumors in vivo without factoring the differences in water content. We identified significant differences in the collagen 1 content between Panc1 and BxPC3 pancreatic tumors and the pancreas that can contribute to the differences in water content that were observed.

Hypoxia theranostics of a human prostate cancer xenograft and the resulting effects on the tumor microenvironment

•

Developed a hypoxia theranostic imaging strategy to eliminate hypoxic cells.

•

Hypoxic cell elimination resulted in fewer cancer associated fibroblasts (CAFs)

•

Collagen 1 fiber patterns were altered with hypoxic cell elimination.

•

cDNA nanoparticles with HRE driven prodrug enzyme expression can target hypoxia.

Hypoxia is frequently observed in human prostate cancer, and is associated with chemoresistance, radioresistance, metastasis, and castrate-resistance. Our purpose in these studies was to perform hypoxia theranostics by combining in vivo hypoxia imaging and hypoxic cancer cell targeting in a human prostate cancer xenograft. This was achieved by engineering PC3 human prostate cancer cells to express luciferase as well as a prodrug enzyme, yeast cytosine deaminase, under control of hypoxic response elements (HREs). Cancer cells display an adaptive response to hypoxia through the activation of several genes mediated by the binding of hypoxia inducible factors (HIFs) to HRE in the promoter region of target gene that results in their increased transcription. HIFs promote key steps in tumorigenesis, including angiogenesis, metabolism, proliferation, metastasis, and differentiation. HRE-driven luciferase expression allowed us to detect hypoxia in vivo to time the administration of the nontoxic prodrug 5-fluorocytosine that was converted by yeast cytosine deaminase, expressed under HRE regulation, to the chemotherapy agent 5-fluorouracil to target hypoxic cells. Conversion of 5-fluorocytosine to 5-fluorouracil was detected in vivo by ¹⁹F magnetic resonance spectroscopy. Morphological and immunohistochemical staining and molecular analyses were performed to characterize tumor microenvironment changes in cancer-associated fibroblasts, cell viability, collagen 1 fiber patterns, and HIF-1α. These studies expand our understanding of the effects of eliminating hypoxic cancer cells on the tumor microenvironment and in reducing stromal cell populations such as cancer-associated fibroblasts.

Abstract 4299: Collagen 1 fiber content can predict for recurrence in stage 1 non-small cell lung cancer

Introduction: Non-small cell lung carcinoma (NSCLC) comprises 85% of all lung cancers. Since most stage 1 NSCLC can be cured by surgery alone, these patients generally do not receive further cancer treatment. However, 20-30% of them will have their lung cancer progressed and died from it. There is a major unmet need to early identify those individuals who are likely to recur so that they can benefit from current effective cancer treatments. Collagen 1 (Col1) fibers are a major structural component of the extracellular matrix (ECM) of tumors. While increased Col1 fibers have been associated with increased metastasis in breast cancer, the role of Col1 in NSCLC and its relationship to recurrence has not been previously examined.

Method: We performed a blinded second harmonic generation (SHG) microscopy study on surgically resected tumor histology tissue sections obtained from twelve patients with non-recurrent stage 1 NSCLC and fourteen patients with recurrent stage 1 NSCLC from The National Lung Screening Trial (NLST) project conducted by the National Institute of Health (NIH). Col1 fibers were detected with SHG microscopy that detects an intrinsic signal derived from the noncentrosymmetric molecular structure of Col1 fibers. SHG microscopy of tumor regions was performed on the H&E sections to quantify Col1 fiber volume and inter fiber distance in the tumors. At least 10 fields of view were analyzed from 1-2 sections obtained from each patient sample. We additionally performed Haralick feature analyses to further analyze Col1 fiber patterns. We also performed tile scan SHG on four patient samples (two non-recurrent and two recurrent) to acquire the Col1 fiber distribution over the entire tissue sample.

Results: We observed a significant increase of Col1 fiber volume and a significant decrease of inter fiber distance in recurrent NSCLC. Three Haralick features (contrast, energy and homogeneity) were also significantly different in the recurrent tumors compared to the non-recurrent tumors. The tile scan dataset revealed thick long fiber tracks throughout the tumor regions in the recurrent NSCLC compared to short and less dense fiber distribution in the tumor regions of the non-recurrent NSCLC.

Conclusions: Col1 fiber analysis may provide a companion diagnostic test that can be performed rapidly on H&E tumor sections, using a multiphoton microscope, to evaluate the likelihood of tumor recurrence. These studies provide new insights into the role of the tumor microenvironment in NSCLC recurrence, and identify new targets for future therapeutic strategies. This work was supported by NIH R35CA209960.

Citation Format: Samata Kakkad, Peng Huang, Malcom Brock, Balaji Krishnamachary, Zaver M. Bhujwalla. Collagen 1 fiber content can predict for recurrence in stage 1 non-small cell lung cancer [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 4299.

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.

Abstract 3691: Collagen 1 fiber content may predict for recurrence in non-small cell lung cancer

Non-small cell lung carcinoma (NSCLC) comprises 85% of all lung cancers. Approximately 30-50% of NSCLC recur despite curative resection. There is a major unmet need to identify NSCLC that are likely to recur so that these patients may be treated with more aggressive therapies. Collagen 1 (Col1) fibers are a major structural component of the extracellular matrix (ECM) of tumors. While increased Col1 fibers have been associated with increased metastasis in breast cancer, the role of Col1 in NSCLC and its relationship to recurrence has not been previously examined. We performed a blinded second harmonic generation (SHG) microscopy study on tumor tissue obtained from 5 patients with nonrecurrent NSCLC and 5 patients with recurrent NSCLC. Col1 fibers were detected with SHG microscopy that detects an intrinsic signal derived from the noncentrosymmetric molecular structure of Col1 fibers. SHG microscopy of tumor regions was performed on the H&E sections to quantify Col1 fiber volume and inter fiber distance in the tumors. At least 10 fields of view were analyzed from 1-2 sections obtained from each tumor. We additionally performed Haralick feature analyses to further analyze Col1 fiber patterns. Adjacent sections were immunostained for CD44 and α-SMA to identify cancer associated fibroblasts (CAFs) and understand their role in these tumors. We observed a significant increase of Col1 fiber volume and a significant decrease of inter fiber distance in recurrent NSCLC. Four Haralick features (orientation, contrast, energy and homogeneity) were also significantly higher in the recurrent tumors compared to the non recurrent tumors. We are currently analyzing the CAFs in the tumor sections to understand their role in the significant differences observed in Col1 fibers between recurrent and nonrecurrent tumors. If these preliminary data are confirmed in an expanded sample set, Col1 fiber analysis may provide a companion diagnostic test that can be performed rapidly on H&E tumor sections, using a confocal microscope, to evaluate the likelihood of tumor recurrence. These studies provide new insights into the role of the tumor microenvironment in NSCLC recurrence, and identify new targets for future therapeutic strategies. This work was supported in part by NIH R35CA209960.

Citation Format: Samata Kakkad, Peng Huang, Malcolm Brock, Balaji Krishnamachary, Zaver M. Bhujwalla. Collagen 1 fiber content may predict for recurrence in non-small cell lung cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 3691.

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.

Hypoxia Inducible Factors Modify Collagen I Fibers in MDA-MB-231 Triple Negative Breast Cancer Xenografts

Hypoxia inducible factors (HIFs) are transcription factors that mediate the response of cells to hypoxia. HIFs have wide-ranging effects on metabolism, the tumor microenvironment (TME) and the extracellular matrix (ECM). Here we investigated the silencing effects of two of the three known isoforms, HIF-1α and HIF-2α, on collagen 1 (Col1) fibers, which form a major component of the ECM of tumors. Using a loss-of-function approach for HIF-1α or 2α or both HIF-1α and 2α, we identified a relationship between HIFs and Col1 fibers in MDA-MB-231 tumors. Tumors derived from MDA-MB-231 cells with HIF-1α or 2α or both HIF-1α and 2α silenced contained higher percent fiber volume and lower inter-fiber distance compared to tumors derived from empty vector MDA-MB-231 cells. Depending upon the type of silencing, we observed changes in Col1 degrading enzymes, and enzymes involved in Col1 synthesis and deposition. Additionally, a reduction in lysyl oxidase protein expression in HIF-down-regulated tumors suggests that more non-cross-linked fibers were present. Collectively these results identify the role of HIFs in modifying the ECM and the TME and provide new insights into the effects of hypoxia on the tumor ECM.

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.

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.

Lymphatic endothelial cells actively regulate prostate cancer cell invasion

Lymphatic vessels serve as the primary route for metastatic spread to lymph nodes. However, it is not clear how interactions between cancer cells and lymphatic endothelial cells (LECs), especially within hypoxic microenvironments, affect the invasion of cancer cells. Here, using an MR compatible cell perfusion assay, we investigated the role of LEC-prostate cancer (PCa) cell interaction in the invasion and degradation of the extracellular matrix (ECM) by two human PCa cell lines, PC-3 and DU-145, under normoxia and hypoxia, and determined the metabolic changes that occurred under these conditions. We observed a significant increase in the invasion of ECM by invasive PC-3 cells, but not poorly invasive DU-145 cells when human dermal lymphatic microvascular endothelial cells (HMVEC-dlys) were present. Enhanced degradation of ECM by PC-3 cells in the presence of HMVEC-dlys identified interactions between HMVEC-dlys and PCa cells influencing cancer cell invasion. The enhanced ECM degradation was partly attributed to increased MMP-9 enzymatic activity in PC-3 cells when HMVEC-dlys were in close proximity. Significantly higher uPAR and MMP-9 expression levels observed in PC-3 cells compared to DU-145 cells may be one mechanism for increased invasion and degradation of matrigel by these cells irrespective of the presence of HMVEC-dlys. Hypoxia significantly decreased invasion by PC-3 cells, but this decrease was significantly attenuated when HMVEC-dlys were present. Significantly higher phosphocholine was observed in invasive PC-3 cells, while higher glycerophosphocholine was observed in DU-145 cells. These metabolites were not altered in the presence of HMVEC-dlys. Significantly increased lipid levels and lipid droplets were observed in PC-3 and DU-145 cells under hypoxia reflecting an adaptive survival response to oxidative stress. These results suggest that in vivo, invasive cells in or near lymphatic endothelial cells are likely to be more invasive and degrade the ECM to influence the metastatic cascade. Copyright © 2016 John Wiley & Sons, Ltd.

Choline kinase-α protein and phosphatidylcholine but not phosphocholine are required for breast cancer cell survival

High levels of total choline and phosphocholine (PC) are consistently observed in aggressive cancers. Choline kinase (Chk) catalyzes choline phosphorylation to produce PC in phosphatidylcholine (PtdCho) biosynthesis. PtdCho is the most abundant phospholipid in eukaryotic cell membranes and plays a dual role as the structural component of membranes and as a substrate to produce lipid second messengers such as phosphatidic acid and diacylglycerol. Chk-α, but not Chk-β, is overexpressed in various cancers, and is closely associated with tumor progression and invasiveness. We have previously shown that downregulation of mRNA using small interfering RNA (siRNA) against Chk-α (siRNA-Chk) or Chk short hairpin RNA, and the resultant decrease of Chk-α protein levels, significantly reduced proliferation in breast cancer cells and tumors. A novel potent and selective small-molecule Chk-α inhibitor, V-11-0711, that inhibits the catalytic activity of Chk has recently been developed. Here, we used triple negative MDA-MB-231 and SUM149 breast cancer cells to further investigate the role of Chk-α in cancer, by examining Chk-α protein levels, cell viability/proliferation, choline phospholipid and lipid metabolism, lipid droplet formation, and apoptosis, following treatment with V-11-0711. Under the conditions used in this study, treatment with V-11-0711 significantly decreased PC levels but did not reduce cell viability as long as Chk-α protein and PtdCho levels were not reduced, suggesting that Chk-α protein and PtdCho, but not PC, may be crucial for breast cancer cell survival. These data also support the approach of antitumor strategies that destabilize Chk-α protein or downregulate PtdCho in breast cancer treatment.

Combining Optical Reporter Proteins with Different Half-lives to Detect Temporal Evolution of Hypoxia and Reoxygenation in Tumors

Here we have developed a hypoxia response element driven imaging strategy that combined the hypoxia-driven expression of two optical reporters with different half-lives to detect temporal changes in hypoxia and hypoxia inducible factor (HIF) activity. For this purpose, human prostate cancer PC3 cells were transfected with the luciferase gene fused with an oxygen-dependent degradation domain (ODD-luc) and a variant of the enhanced green fluorescent protein (EGFP). Both ODD-luciferase and EGFP were under the promotion of a poly-hypoxia-response element sequence (5xHRE). The cells constitutively expressed tdTomato red fluorescent protein. For validating the imaging strategy, cells were incubated under hypoxia (1% O2) for 48 hours and then reoxygenated. The luciferase activity of PC3-HRE-EGFP/HRE-ODD-luc/tdtomato cells detected by bioluminescent imaging rapidly decreased after reoxygenation, whereas EGFP levels in these cells remained stable for several hours. After in vitro validation, PC3-HRE-EGFP/HRE-ODD-luc/tdtomato tumors were implanted subcutaneously and orthotopically in nude male mice and imaged in vivo and ex vivo using optical imaging in proof-of-principle studies to demonstrate differences in optical patterns between EGFP expression and bioluminescence. This novel "timer" imaging strategy of combining the short-lived ODD-luciferase and the long-lived EGFP can provide a time frame of HRE activation in PC3 prostate cancer cells and will be useful to understand the temporal changes in hypoxia and HIF activity during cancer progression and following treatments including HIF targeting strategies.

Synthesis and Evaluation of Gd(III) -Based Magnetic Resonance Contrast Agents for Molecular Imaging of Prostate-Specific Membrane Antigen

Magnetic resonance (MR) imaging is advantageous because it concurrently provides anatomic, functional, and molecular information. MR molecular imaging can combine the high spatial resolution of this established clinical modality with molecular profiling in vivo. However, as a result of the intrinsically low sensitivity of MR imaging, high local concentrations of biological targets are required to generate discernable MR contrast. We hypothesize that the prostate-specific membrane antigen (PSMA), an attractive target for imaging and therapy of prostate cancer, could serve as a suitable biomarker for MR-based molecular imaging. We have synthesized three new high-affinity, low-molecular-weight Gd(III) -based PSMA-targeted contrast agents containing one to three Gd(III)  chelates per molecule. We evaluated the relaxometric properties of these agents in solution, in prostate cancer cells, and in an in vivo experimental model to demonstrate the feasibility of PSMA-based MR molecular imaging.

Abstract LB-160: Collagen I fiber signatures in breast cancer predict lymph node metastasis

The extracellular matrix (ECM) in breast cancers is altered and provides new biomarkers for cancer diagnosis [1] and prognosis [2,3]. Collagen I (Col1) fibers are the major ECM component in breast tumors, and increased Col1 has been found to facilitate breast tumor formation, invasion, and metastasis [2,3]. We tested the relationship between occurrence of lymph node (LN) and Col1 fibers in primary tumors on a tissue microarray by using second harmonic generation (SHG) imaging and image analyses.

A breast tissue microarray that had 50 LN positive (LN+) and 50 LN negative (LN-) status patient's primary breast tumor biopsy samples was used in this study. Z-stacks of SHG tile images were acquired on a Zeiss 710 multiphoton microscope. We analyzed the SHG images from all breast biopsies for geometric features such as fiber volume, inter-fiber distance [4], and both 2D and 3D Haralick features such as energy, entropy, and correlation, among others. K-mean clustering of a case-controlled subset (19 LN+ and 16 LN- cases with grade 2, Stage II, T2) was performed. Principal component analysis (PCA) was performed to reduce data dimensions. Supervised nonlinear support vector machine (SVM) classification of 50 LN+ and 50 LN- samples with cross validation was performed on the 3D Haralick features.

The detection errors of LN+ and LN- samples based on individual geometric, Haralick texture features and their combinations, which were obtained from the analysis of the Col 1 fiber patterns of 35 case-controlled samples, were calculated. The features that best differentiate LN+ and LN- samples were 3D entropy and 3D energy in the analysis of 35 case-controlled samples. A receiver operating characteristic (ROC) curve of SVM was generated to classify 3D Haralick features of 50 LN+ and 50 LN- samples, in which a Gaussian kernel with a sigma of 2.9 was the best model and gave a false negative rate of 0.13, a false positive rate of 0.31, and an area under the ROC curve of 0.81. In this larger statistical analysis from 100 breast cancer samples, we performed supervised SVM classification with cross validation to ensure the robustness and obtained a best false positive rate of 0.3. This could be because some LN- cases may have turned out as LN+ cases later on, and no follow-up data were available to us. A larger number of breast cancer samples with patient follow-up information is currently being imaged in our lab to train a more robust statistical SVM model. SHG imaging of Col1 fibers in primary breast tumors followed by image analyses can serve as a predictive biomarker to assess LN status and thereby predict outcome of breast cancer.

[1]. A. Bergamaschi et al., J. Pathol. (2008). [2] P. P. Provenzano et al., BMC Med. (2008). [3] M. W. Conklin et al., Am. J. Pathol. (2011). [4] S. Kakkad et al., J. Biomed Optics (2012). This work was supported by NIH P50 CA103175.

Citation Format: Jiang Lu, Samata Kakkad, Tiffany Greenwood, Meiyappan Solaiyappan, Zaver M. Bhujwalla, Xingde Li, Kristine Glunde. Collagen I fiber signatures in breast cancer predict lymph node metastasis. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr LB-160. doi:10.1158/1538-7445.AM2014-LB-160

Phospholipase D1 and choline kinase-α are interactive targets in breast cancer

A consistent metabolic hallmark observed in multiple cancers is the increase of cellular phosphocholine (PC) and total choline-containing compounds (tCho), which is closely related to malignant transformation, invasion, and metastasis. Enzymes in choline phospholipid metabolism present attractive targets to exploit for treatment, but require a clear understanding of the mechanisms underlying the altered choline phospholipid metabolism observed in cancer. Choline kinase-α (Chk-α) is an enzyme in the Kennedy pathway that phosphorylates free choline (Cho) to PC, and its upregulation in several cancers is a major contributor to increased PC levels. Similarly, increased expression and activity of phospholipase D1 (PLD1), which converts phosphatidylcholine (PtdCho) to phosphatidic acid (PA) and Cho, has been well documented in gastric, ovarian and breast cancer. Here we report a strong correlation between expression of Chk-α and PLD1 with breast cancer malignancy. Data from patient samples established an association between estrogen receptor (ER) status and Chk-α and PLD1 expression. In addition, these two enzymes were found to be interactive. Downregulation of Chk-α with siRNA increased PLD1 expression, and downregulation of PLD1 increased Chk-α expression. Simultaneous silencing of PLD1 and Chk-α in MDA-MB-231 cells increased apoptosis as detected by the TUNEL assay. These data provide new insights into choline phospholipid metabolism of breast cancer, and support multiple targeting of enzymes in choline phospholipid metabolism as a strategy for treatment.

Abstract 3745: Validation of the co-expression of breast cancer stem cell markers with HIF-1α in tumors

Stem-like breast cancer cells (SBCCs) are drug resistant, invasive, and likely to lead to tumor recurrence and repopulation. High expression of the adhesion molecule CD44, the drug transporter ABCG2, and of the enzyme ALDH1A1 are well-established markers associated with SBCC-enriched tumor populations [1]. Hypoxic tumor microenvironments are frequently associated with increased aggressiveness and resistance to chemo and radiation therapy. Hypoxia results in the stabilization of the hypoxia inducible factor -1 (HIF-1), a transcription factor that activates a battery of genes, including those associated with SBCCs, that help cancer cells to survive, repopulate and finally metastasize to distant location. Recently, we reported the role of hypoxia and HIF-1α in regulating the expression of CD44 and its variant isoforms in triple negative breast cancer [2]. Here we have validated the association between hypoxia and CD44 expression in these tumors. We used tumors derived from MDA-MB-231 cells genetically engineered to express red fluorescent protein (tdtomato) under the control of hypoxia response element (231-HRE-RFP). Optical imaging (Nikon fluorescence microscope) was performed to detect hypoxia in fresh tissue slices, followed by immunohistochemistry (IHC) staining for HIF-1α, CD44 and ABCG2 expression in 5μm thickness adjacent sections from paraffin embedded 231-HRE-RFP tumors. Slides were scanned on an Image Scope digital scanner. Analysis for HIF-1 α nuclear staining was performed by drawing regions of interest (ROI) on scanned images using manufacturer supplied macro (Aperio Technologies Inc. CA, USA). For co-registration and quantification studies, ROI drawn images of HIF-1α and CD44 were co-registered to the bright field and fluorescent optical images using an in-house program developed in MATLAB (Mathworks Inc.). Statistical analysis (t-test) was performed using Microsoft Excel 2010 (Microsoft Inc. Seattle, USA). Following co-registration, intensely fluorescing regions of 231-HRE-RFP tumors were found to be associated with elevated nuclear HIF-1α expression and higher CD44 membrane expression. A trend of increased optical intensity (p≤0.09) and significantly increased CD44 pixel intensity (p≤0.05) was observed in the high HIF-1α ROI compared to the low HIF-1α ROI. Work is under way to co-register other breast cancer stem cell markers such as ABCG2 and ALDH1A1 in these tumors. These data further highlight the role of hypoxia in engendering a stem-like phenotype, and the potential importance of targeting hypoxia to minimize the burden of cells with stem-like characteristics in tumors. All animal protocols were approved by the JHU animal care and use committee.

This work was supported by NIH R01CA136576 and P50 CA103175.

1. Al-Hajj, M et al., Proc Natl Acad Sci U S A, 2003.

2. Krishnamachary.B. et al., PLoS One 2012;7(8)e44078-

Citation Format: Balaji Krishnamachary, Samata Kakkad, Marie-France Penet, Keve Zoltani, Venu Raman, Mayur Gadiya, Yelena Mironchik, Flonne Wildes, Zaver M. Bhujwalla. Validation of the co-expression of breast cancer stem cell markers with HIF-1α in tumors. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 3745. doi:10.1158/1538-7445.AM2013-3745

Noninvasive imaging identifies new roles for cyclooxygenase-2 in choline and lipid metabolism of human breast cancer cells

The expression of cyclooxygenase-2 (COX-2) is observed in approximately 40% of breast cancers. A major product of the COX-2-catalyzed reaction, prostaglandin E(2), is an inflammatory mediator that participates in several biological processes, and influences invasion, vascularization and metastasis. Using noninvasive MRI and MRS, we determined the effect of COX-2 downregulation on the metabolism and invasion of intact poorly differentiated MDA-MB-231 human breast cancer cells stably expressing COX-2 short hairpin RNA. Dynamic tracking of invasion, extracellular matrix degradation and metabolism was performed with an MRI- and MRS-compatible cell perfusion assay under controlled conditions of pH, temperature and oxygenation over the course of 48  h. COX-2-silenced cells exhibited a significant decrease in invasion relative to parental cells that was consistent with the reduced expression of invasion-associated matrix metalloproteinase genes and an increased level of the tissue inhibitor of metalloproteinase-1. We identified, for the first time, a role for COX-2 in mediating changes in choline phospholipid metabolism, and established that choline kinase expression is partly dependent on COX-2 function. COX-2 silencing resulted in a significant decrease in phosphocholine and total choline that was detected by MRS. In addition, a significant increase in lipids, as well as lipid droplet formation, was observed. COX-2 silencing transformed parental cell metabolite patterns to those characteristic of less aggressive cancer cells. These new functional roles of COX-2 may identify new biomarkers and new targets for use in combination with COX-2 targeting to prevent invasion and metastasis.

Abstract 1327: Macromolecular transport, collagen fiber morphology, and metastasis are influenced by the tumor growth location

Metastasis and malignant ascites are major causes of poor prognosis in prostate cancer patients. Cancer cells metastasize more readily from orthotopic sites than from heterotopic sites (1). Here we have focused on characterizing the role of the extracellular matrix (ECM) in facilitating metastatic dissemination from metastasis-permissive environments and on understanding the role of hypoxia in these environments using noninvasive MRI and optical imaging of orthotopic and subcutaneous PC3 tumor xenografts. MRI of a macromolecular contrast agent was used to characterize interstitial fluid transport, second harmonic generation (SHG) microscopy to determine collagen I fiber distribution, and enhanced green fluorescent protein (EGFP) expression to detect hypoxia. These studies will provide insights into the dynamics of interstitial transport, and the influence of collagen I fibers within these metastasis-permissive environments. PC3-HRE-EGFP cells were engineered to express EGFP under hypoxia (1). For the orthotopic implantation, we used a microsurgical method that avoids disseminating cancer cells during inoculation in the prostate. By implanting PC3 tumor tissues rather than injecting cells, the stromal tissue and the three dimensional cytoarchitecture, believed to play a critical role in tumor progression and metastasis, were maintained. Interstitial fluid transport parameters were measured on a Bruker Biospec 4.7T spectrometer as previously described (2). SHG microscopy of freshly excised xenograft slices was performed on a Zeiss 710 LSM NLO microscope system. Collagen fiber morphology was characterized in terms of the inter-fiber distance and fiber volume (3). A significantly higher number of interstitial fluid pooling voxels, and lower efflux and influx rates were observed in orthotopic tumors compared to the subcutaneous ones. SHG imaging demonstrated significantly higher fiber density and volume in orthotopic tumors. Metastases to lymph nodes, lungs and several other organs were routinely observed following orthotopic implantation, but rarely occurred after subcutaneous implantation. Overall, orthotopic prostate tumors were characterized by a higher density of collagen fibers, a higher number of interstitial fluid pooling voxels, and lower efflux and influx rates compared to subcutaneous tumors. Characterization of hypoxia in orthotopic and subcutaneous environments and its relationship to interstitial transport and collagen fiber distribution is ongoing. These data demonstrate the profound impact of the location of tumor growth on the ECM and macromolecular transport, and provide additional insights into environments that are permissive for metastasis and the accumulation of malignant ascites. (1) Raman et al, Cancer Res, 66:9929-9936, 2006. (2) Pathak et al, Cancer Res, 65:1425-32, 2005. (3) Kakkad et al, Neoplasia 12:608-17, 2010.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 1327. doi:1538-7445.AM2012-1327

Abstract 2970: Cyclooxygenase-2 mediates significant changes in the extracellular matrix in triple negative breast cancer

Triple (ER/PR/HER2) negative breast cancer (TNBC) accounts for approximately 20% of all breast cancer diagnoses and is characterized by metastasis that is refractory to treatment. We and others have demonstrated that cyclooxygenase-2 (COX-2) products are important mediators of increased invasion and metastasis in the MDA-MB-231 human xenograft model of TNBC. Increasing evidence suggest that high density of collagen I fibers in the extracellular matrix (ECM) is predictive of increased metastasis and cancer cells have been observed to migrate along these fibers during the metastatic journey. We previously observed that downregulation of COX-2 significantly reduced the expression of degradative enzymes such as matrix metalloproteinase 1 and altered the expression of ECM components such as hyaluronan and lumican that play a role in intra-fibrillar collagen spacing. Tumor growth of MDA-MB-231 and Clone 13 (a MDA-MB-231-derived COX-2 shRNA-expressing clone secreting less than 10% of PGE2 compared to parental) xenografts, studied following Matrigel-supported orthotopic implantation in SCID mice, showed a 3-week delay in tumor growth. Here, we have used non-Matrigel tumors derived from Clone 13 cells were used to investigate the relationship between COX-2 expression, interstitial fluid transport using MRI and collagen fiber density and volume using second harmonic generation (SHG) microscopy. MRI was performed once tumor volumes were approximately 400-500 mm3. Interstitial fluid transport parameters were measured from quantitative T1 maps obtained before and following intravenous administration of the contrast agent albumin-GdDTPA. Interstitial fluid transport parameters calculated included number of draining and pooling voxels, draining and pooling rates, and volumes. SHG microscopy of tissue slices was performed using a 25x lens on a Zeiss 710 LSM NLO confocal microscope. Collagen I fiber distribution was characterized using an in-house 3D analysis software developed to quantify fiber distance distributions and fiber volumes. Significant differences in the ECM structure and function were evident between high COX-2 expressing MDA-MB-231 tumors compared to Clone 13 tumors with low COX-2 expression. Tumors arising from Clone 13 cells demonstrated an increase in vascular volume, a decrease of draining voxels, an increase of pooling voxels, and a decrease of collagen fiber density. Collectively, these data provide direct evidence for COX-2-mediated changes in the ECM. Here, for the first time, we have shown that dowregulating COX-2 in TNBC cells profoundly impacts collagen I fiber density and volume and alters macromolecular transport. Understanding the role of COX-2 in TNBC and its impact on the ECM and macromolecular transport may provide new insights into preventing relapse and metastasis.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 2970. doi:1538-7445.AM2012-2970

Exploiting the tumor microenvironment for theranostic imaging

The integration of chemistry and molecular biology with imaging is providing some of the most exciting opportunities in the treatment of cancer. The field of theranostic imaging, where diagnosis is combined with therapy, is particularly suitable for a disease as complex as cancer, especially now that genomic and proteomic profiling can provide an extensive 'fingerprint' of each tumor. Using this information, theranostic agents can be shaped for personalized treatment to target specific compartments, such as the tumor microenvironment (TME), whilst minimizing damage to normal tissue. These theranostic agents can also be used to target multiple pathways or networks by incorporating multiple small interfering RNAs (siRNAs) within a single agent. A decade ago genetic alterations were the primary focus in cancer research. Now it is apparent that the tumor physiological microenvironment, interactions between cancer cells and stromal cells, such as endothelial cells, fibroblasts and macrophages, the extracellular matrix (ECM), and a host of secreted factors and cytokines, influence progression to metastatic disease, aggressiveness and the response of the disease to treatment. In this review, we outline some of the characteristics of the TME, describe the theranostic agents currently available to target the TME and discuss the unique opportunities the TME provides for the design of novel theranostic agents for cancer therapy.

Choline kinase overexpression increases invasiveness and drug resistance of human breast cancer cells

A direct correlation exists between increased choline kinase (Chk) expression, and the resulting increase of phosphocholine levels, and histological tumor grade. To better understand the function of Chk and choline phospholipid metabolism in breast cancer we have stably overexpressed one of the two isoforms of Chk-alpha known to be upregulated in malignant cells, in non-invasive MCF-7 human breast cancer cells. Dynamic tracking of cell invasion and cell metabolism were studied with a magnetic resonance (MR) compatible cell perfusion assay. The MR based invasion assay demonstrated that MCF-7 cells overexpressing Chk-alpha (MCF-7-Chk) exhibited an increase of invasion relative to control MCF-7 cells (0.84 vs 0.3). Proton MR spectroscopy studies showed significantly higher phosphocholine and elevated triglyceride signals in Chk overexpressing clones compared to control cells. A test of drug resistance in MCF-7-Chk cells revealed that these cells had an increased resistance to 5-fluorouracil and higher expression of thymidylate synthase compared to control MCF-7 cells. To further characterize increased drug resistance in these cells, we performed rhodamine-123 efflux studies to evaluate drug efflux pumps. MCF-7-Chk cells effluxed twice as much rhodamine-123 compared to MCF-7 cells. Chk-alpha overexpression resulted in MCF-7 human breast cancer cells acquiring an increasingly aggressive phenotype, supporting the role of Chk-alpha in mediating invasion and drug resistance, and the use of phosphocholine as a biomarker of aggressive breast cancers.