Studies for head and neck cancer have primarily relied on cell lines or in vivo animal studies. However, a technique that combines the benefits of high-throughput in vitro studies with a complex, physiologically relevant microenvironment would be advantageous for understanding drug effects. Organoids provide a unique platform that fulfills these goals. Organoids are generated from excised and digested tumor tissue and are grown in culture. Fluorescence microscopy provides high-resolution images on a similar spatial scale as organoids. In particular, autofluorescence imaging of the metabolic cofactors NAD(P)H and FAD can provide insight into response to anti-cancer treatment. The optical redox ratio reflects relative amounts of NAD(P)H and FAD, and the fluorescence lifetime reflects enzyme activity of NAD(P)H and FAD. This study optimizes and characterizes the generation and culture of organoids grown from head and neck cancer tissue. Additionally, organoids were treated for 24 hours with a standard chemotherapy, and metabolic response in the organoids was measured using optical metabolic imaging. Ultimately, combining head and neck cancer organoids with optical metabolic imaging could be applied to test drug sensitivity for drug development studies as well as treatment planning for cancer patients.
Standard methods to characterize patient tissue rely on histology. This technique provides only anatomical information, so complementary imaging methods could provide beneficial phenotypic information. Cancer cells exhibit altered metabolism, and metabolic imaging could be applied to better understand cancer tissue. This study applies redox ratio, fluorescence lifetime, and second harmonic generation (SHG) imaging to ex vivo tissue from head and neck cancer patients. This high-resolution imaging technique has unique advantages of utilizing intrinsic tissue contrast, which eliminates the need for sample processing or staining, and multiphoton microscopy, which provides depth sectioning in intact tissue. This study demonstrates feasibility of these measurements in patient tissue from multiple anatomical sites and carcinoma types of head and neck cancer.
There is a need for accurate, high-throughput measures to gauge the efficacy of potential drugs in living cells.
Metabolism is an early marker of drug response in cells, and NADH and FAD are autofluorescent cellular metabolic
coenzymes that can be non-invasively monitored using optical techniques. Relative rates of glycolysis and oxidative
phosphorylation in a cell are quantified by the redox ratio, defined as the autofluorescence intensity of NADH divided by
that of FAD. Microplate readers are high-throughput instruments that can rapidly measure NADH and FAD
autofluorescence intensities for hundreds of wells, and are capable of identifying receptor status and resolving drug
response in breast cancer cell lines.
This study tests the accuracy and repeatability of plate reader experiments measuring the redox ratio in breast
cancer cell lines. NADH and FAD fluorescence levels remained constant over the course of multiple measurements
(p<0.1), ruling out the incidence of photobleaching. The contribution of media to background fluorescence signal was
also investigated. Media fluorescence levels for both coenzymes were significantly lower (p<0.0001) than those from
wells containing cells, and replacing the media with saline resulted in the same redox ratio trends among cell lines as
initial measurements with media. Following treatment with carbonyl cyanide p-fluorodeoxyphenylhydrazone (FCCP), an
oxidative phosphorylation inhibitor, the redox ratio decreased (p<0.05), validating NADH and FAD as the primary
fluorescence sources. These findings verify that autofluorescence measurements taken by microplate readers accurately
and reliably characterize NADH and FAD fluorescence, validating their promise in the areas of metabolic monitoring
and drug development.
There is a need for accurate, high-throughput, functional measures to gauge the efficacy of potential drugs in living cells. As an early marker of drug response in cells, cellular metabolism provides an attractive platform for high-throughput drug testing. Optical techniques can noninvasively monitor NADH and FAD, two autofluorescent metabolic coenzymes. The autofluorescent redox ratio, defined as the autofluorescence intensity of NADH divided by that of FAD, quantifies relative rates of cellular glycolysis and oxidative phosphorylation. However, current microscopy methods for redox ratio quantification are time-intensive and low-throughput, limiting their practicality in drug screening. Alternatively, high-throughput commercial microplate readers quickly measure fluorescence intensities for hundreds of wells. This study found that a commercial microplate reader can differentiate the receptor status of breast cancer cell lines (p<0.05) based on redox ratio measurements without extrinsic contrast agents. Furthermore, microplate reader redox ratio measurements resolve response (p<0.05) and lack of response (p>0.05) in cell lines that are responsive and nonresponsive, respectively, to the breast cancer drug trastuzumab. These studies indicate that the microplate readers can be used to measure the redox ratio in a high-throughput manner and are sensitive enough to detect differences in cellular metabolism that are consistent with microscopy results.
Many studies have found that hypoxia, particularly cycling hypoxia (CH), can lead to enhanced tumor metastasis and resistance to radiation and chemotherapy. It was also reported that tumor total hemoglobin content (THb), which is directly related to tumor angiogenesis, can have significant impact on tumor’s response to radiation and neoadjuvant chemotherapy. There is a growing demand for technologies to measure tumor hypoxia and angiogenesis temporally in vivo. In this paper, a side-firing fiber optic sensor based on a multi-wavelength frequency-domain near infrared spectroscopy (FD-NIRS) instrument was used to quantify tumor oxygenation and hemoglobin concentrations in nude rats bearing human FaDu head and neck (H and N) tumors during normoxia and forced hyperoxia and cyclic hypoxia. Significant increase (with carbogen gas inhalation) or decrease (with reduced O2 supply) in tumor oxygenation was observed. The studies demonstrated the feasibility of the technology for longitudinal monitoring of H and N tumor’s response to therapy.