SignificanceEmerging evidence that aggressive breast tumors rely on various substrates including lipids and glucose to proliferate and recur necessitates the development of tools to track multiple metabolic and vascular endpoints concurrently in vivo.AimOur quantitative spectroscopy technique provides time-matched measurements of the three major axes of breast cancer metabolism as well as tissue vascular properties in vivo.ApproachWe leverage exogenous fluorophores to quantify oxidative phosphorylation, glucose uptake, and fatty acid oxidation, and endogenous contrast for measurements of hemoglobin and oxygen saturation. An inverse Monte Carlo algorithm corrects for aberrations resulting from tissue optical properties, allowing the unmixing of spectrally overlapping fluorophores.ResultsImplementation of our inverse Monte Carlo resulted in a linear relationship of fluorophore intensity with concentration (R2<0.99) in tissue-mimicking phantom validation studies. We next sequenced fluorophore delivery to faithfully recapitulate independent measurement of each fluorophore. The ratio of Bodipy FL C16/2-NBDG administered to a single animal is not different from that in paired animals receiving individual fluorophores (p=n.s.). Clustering of five variables was effective in distinguishing tumor from mammary tissue (sensitivity = 0.75, specificity = 0.83, and accuracy = 0.79).ConclusionsOur system can measure major axes of metabolism and associated vascular endpoints, allowing for future study of tumor metabolic flexibility.
We developed an approach to quantify intra-tumoral metabolic heterogeneity of in vivo tumor models by leveraging a computationally designed multi-scale microscope and a suite of exogenous fluorescent contrast agents to provide functional and structural information.
Commercial imaging systems such as mobile phones are suitable for fluorescence detection of in vivo and ex vivo tissue samples. To leverage this potential, a uniform plane of excitation light is necessary to make quantitative measurements of regions within an image. We have developed a computational model to simulate the illumination of an arbitrary number of sources. Using a pattern search algorithm, the position of these sources can be determined to generate a uniform plane of excitation light. Initial studies demonstrate that 4 fiber optic sources can be used to generate uniform illumination for biopsy samples with different geometries.
Despite improvements in surgical resection, 20-40% of patients undergoing breast conserving surgery require at least one additional re-excision. Leveraging the unique surface expression of heat shock protein 90 (Hsp90), a chaperone protein involved in several key hallmarks of cancer, in breast cancer provides an exciting opportunity to identify residual disease during surgery. We developed a completely non-destructive strategy using HS-27, a fluorescently-tethered Hsp90 inhibitor, to assay surface Hsp90 expression on intact tissue specimens using a fluorescence microendoscope with a field of view of 750 μm and subcellular resolution of 4 μm. HS-27 consists of an FDA approved Hsp90 inhibitor tethered to fluorescein isothiocyanate (EX 488nm, EM 525nm).
Here, we optimized ex vivo HS-27 administration in pre-clinical breast cancer models and validated our approach on 21 patients undergoing standard of care ultrasound guided core needle biopsy. HS-27 administration time was fixed at 1- minute to minimize imaging impact on clinical workflow. HS-27 and HS-217 (non-specific control) doses were modulated from 1 μM up to 100 μM to identify the dose maximizing the ratio of specific uptake (HS-27 fluorescence) to non-specific uptake (HS-217 fluorescence). The specificity ratio was maximized at 100 μM and was significantly greater than all other doses (p<0.05). We applied our optimized imaging protocol to clinical samples and demonstrated significantly greater uptake of HS-27 by tumor than non-tumor tissue (p<0.05). The ubiquitous nature of HS-27 binding to all subtypes of breast cancer makes this technology attractive for assessing tumor margins, as one agent can be used for all subtypes.
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