BAE Graduate Student Exit Seminar
Friday, August 29, 2014
2-3 pm, 2045 BAINER HALL
Topic: "Optical Molecular Imaging for Cancer Detection and Therapy Evaluation"
Presenter: Zhen Luo
PhD degree candidate
Department of Biological & Agricultural Engineering
University of California, Davis
Abstract:
Cancer is a leading cause of death worldwide. It remains the second most common cause of death in the US, accounting for nearly 1 out of every 4 deaths. Improved fundamental understanding of molecular processes and pathways resulting in cancer development and its response to diverse therapies has catalyzed a shift towards molecular analysis of cancer using imaging technologies. It is expected that the non-invasive or minimally invasive molecular imaging analysis of cancer can significantly aid in improving the early detection of cancer, improved selection of personalized therapy and will result in reduced mortality and morbidity associated with the disease. The central hypothesis of the proposed research is that non-invasive imaging of changes in metabolic activity of individual cells, and extracellular pH within a tissue will improve early stage detection of cancer and enable non-invasive evaluation of response to cancer therapy. The specific goals of this research project were to: (a) develop novel optical imaging probes to image changes in choline metabolism and tissue pH as a function of progression of cancer using clinically isolated tissue biopsies; (b) correlate changes in tissue extracellular pH and metabolic activity of tissues as a function of disease state using clinically isolated tissue biopsies; and (c) evaluate the potential of optical molecular imaging approaches metabolic tracers to detect drug response of cancer cells to chemo and molecular targeted therapies and detect presence of drug resistant cells using model systems.
Three novel molecular imaging probes were developed to detect changes in choline and glucose metabolism and extracellular pH in model systems and clinically isolated cells and biopsies. Glucose uptake and metabolism was measured using a fluorescence analog of glucose, 2-NBDG (2-[N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino]-2-deoxy-D-glucose), while choline metabolism was measured using a click chemistry analog of choline, propargyl choline, which can be in-situ labeled with a fluorophore Alexa-488 azide via a click chemistry reaction. Extracellular pH in tissue were measured by Alexa-647 labeled pHLIP (pH low insertion peptide), which can selectively target plasma membrane of cells based on lower extracellular pH. 20 pairs of clinically normal and abnormal biopsies were obtained from consenting patients at UCDMC. Fluorescence intensity of tissue biopsies before and after topical delivery of 2-NBDG and Alexa 647-pHLIP was measured non-invasively by widefield imaging and confocal microscope. Uptake of proparcyl choline was measured after topical delivery using confocal microscope. The results of all three molecular imagine probes were further correlated with pathological diagnosis.
The imaging results of clinical biopsies demonstrated that 2-NBDG, propargyl choline and pHLIP peptide can accurately distinguish the pathologically normal and abnormal biopsies. Topical application of the contrast agents generated significantly higher fluorescence signal intensity in all neoplastic tissues as compared to clinically normal biopsies irrespective of the anatomic location or patient. This unpaired comparison across all the cancer patients in this study highlights the specificity of the imaging approach. Furthermore, the results indicated that changes in intracellular glucose, choline metabolism and cancer acidosis are initiated in the early stages of cancer and these changes are correlated with the progression of the disease. In conclusion, these novel optical molecular imaging approaches to measure multiple biomarkers in cancer have significant potential to be a useful tool for improving early detection and prognostic evaluation of oral neoplasia.
These novel optical molecular imaging approaches were further validated for monitoring cancer therapy response. Current evaluation approaches have limited ability to predict response to cancer therapy prior to treatment rapidly and detect heterogeneity within tumor including detection of small fraction of drug resistance cells. In response to this need, the second part of our study was aim at developing optical molecular imaging approaches with single cell resolution to complement current in-vivo imaging methods and in-vitro drug responses assays.
Two optical molecular imaging probes 2-NBDG and propargyl choline were used to measure changes in glucose and choline metabolic activity of cancer cells upon treatment. It was based on the understanding that the successful cancer therapies result in downregulation of glucose and choline metabolism. To demonstrate potential of this approach, cancer cells in 2-d culture and 3-d spheroid models were treated with chemotherapy agents and selected molecular targeted drug that are widely used in clinical practice. The results demonstrate that this imaging approach has higher sensitivity as compared to conventional cell viability assay to detect early drug responses in cancer cells. These results indicate that changes in metabolic activity of cancer cells may precede loss of viability and can provide a sensitive measure of response of cancer tissue to treatment. The ability of these imaging approaches to differentiate drug resistant cells from sensitive cells for the selected therapies were also demonstrated in this dissertation. In conclusion, compared to cell viability assay and cell growth curve, the molecular imaging approaches based on changes in the uptake of 2-NBDG and propargyl choline could detect and differentiate response of cancer cells to both molecular targeted drug and chemo drug at lower concentration levels and with higher sensitivity.
We further integrated microwell arrays and molecular imaging approaches to provide a rapid, sensitive and high-throughput platform for therapy response measurement. The microwell array allowed for a high throughput analysis of individual cell response, and the drug response was quantified based on reduction of glucose metabolic activity. This microarray molecular imaging approach has a great potential as a research tool to improve the understanding of drug resistance in cancer cells, and as a point-of-care platform for a more personalized treatment of cancer.
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