Radiation Promptly Alters Cancer Live Cell Metabolic Fluxes: An In Vitro Demonstration

Optical Imaging Approaches to Investigating Radiation Resistance

Radiation therapy is frequently the first line of treatment for over 50% of cancer patients. While great advances have been made in improving treatment response rates and reducing damage to normal tissue, radiation resistance remains a persistent clinical problem. While hypoxia or a lack of tumor oxygenation has long been considered a key factor in causing treatment failure, recent evidence points to metabolic reprogramming under well-oxygenated conditions as a potential route to promoting radiation resistance. In this review, we present recent studies from our lab and others that use high-resolution optical imaging as well as clinical translational optical spectroscopy to shine light on the biological basis of radiation resistance. Two-photon microscopy of endogenous cellular metabolism has identified key changes in both mitochondrial structure and function that are specific to radiation-resistant cells and help promote cell survival in response to radiation. Optical spectroscopic approaches, such as diffuse reflectance and Raman spectroscopy have demonstrated functional and molecular differences between radiation-resistant and sensitive tumors in response to radiation. These studies have uncovered key changes in metabolic pathways and present a viable route to clinical translation of optical technologies to determine radiation resistance at a very early stage in the clinic.

A novel bioreactor for combined magnetic resonance spectroscopy and optical imaging of metabolism in 3D cell cultures

PURPOSE

Fluorescence lifetime imaging microscopy (FLIM) of endogenous fluorescent metabolites permits the measurement of cellular metabolism in cell, tissue and animal models. In parallel, magnetic resonance spectroscopy (MRS) of dynamic nuclear (hyper)polarized (DNP) ¹³ C-pyruvate enables measurement of metabolism at larger in vivo scales. Presented here are the design and initial application of a bioreactor that connects these 2 metabolic imaging modalities in vitro, using 3D cell cultures.

METHODS

The model fitting for FLIM data analysis and the theory behind a model for the diffusion of pyruvate into a collagen gel are detailed. The device is MRI-compatible, including an optical window, a temperature control system and an injection port for the introduction of contrast agents. Three-dimensional printing, computer numerical control machining and laser cutting were used to fabricate custom parts.

RESULTS

Performance of the bioreactor is demonstrated for 4 T1 murine breast cancer cells under glucose deprivation. Mean nicotinamide adenine dinucleotide (NADH) fluorescence lifetimes were 10% longer and hyperpolarized ¹³ C lactate:pyruvate (Lac:Pyr) ratios were 60% lower for glucose-deprived 4 T1 cells compared to 4 T1 cells in normal medium. Looking at the individual components of the NADH fluorescent lifetime, τ₁ (free NADH) showed no significant change, while τ₂ (bound NADH) showed a significant increase, suggesting that the increase in mean lifetime was due to a change in bound NADH.

CONCLUSION

A novel bioreactor that is compatible with, and can exploit the benefits of, both FLIM and ¹³ C MRS in 3D cell cultures for studies of cell metabolism has been designed and applied.

Autofluorescence lifetime imaging of cellular metabolism: Sensitivity toward cell density, pH, intracellular, and intercellular heterogeneity

Autofluorescence imaging (AFI) has greatly accelerated in the last decade, way past its origins in detecting endogenous signals in biological tissues to identify differences between samples. There are many endogenous fluorescence sources of contrast but the most robust and widely utilized have been those associated with metabolism. The intrinsically fluorescent metabolic cofactors nicotinamide adenine dinucleotide (NAD+ /NADH) and flavin adenine dinucleotide (FAD/FADH2 ) have been utilized in a number of AFI applications including basic research, clinical, and pharmaceutical studies. Fluorescence lifetime imaging microscopy (FLIM) has emerged as one of the more powerful AFI tools for NADH and FAD characterization due to its unique ability to noninvasively detect metabolite bound and free states and quantitate cellular redox ratio. However, despite this widespread biological use, many standardization methods are still needed to extend FLIM-based AFI into a fully robust research and clinical diagnostic tools. FLIM is sensitive to a wide range of factors in the fluorophore microenvironment, and there are a number of analysis variables as well. To this end, there has been an emphasis on developing imaging standards and ways to make the image acquisition and analysis more consistent. However, biological conditions during FLIM-based AFI imaging are rarely considered as key sources of FLIM variability. Here, we present several experimental factors with supporting data of the cellular microenvironment such as confluency, pH, inter-/intracellular heterogeneity, and choice of cell line that need to be considered for accurate quantitative FLIM-based AFI measurement of cellular metabolism. © 2018 International Society for Advancement of Cytometry.

Phase I/II Study of Preoperative Chemoradiotherapy With TEGAFIRI for Locally Advanced Rectal Cancer

INTRODUCTION

Chemoradiotherapy (CRT) is the standard treatment for locally advanced rectal cancer; however, the optimal chemotherapy sequence to administer simultaneously with radiotherapy remains unclear. We conducted a phase I/II study to test a new regimen, TEGAFIRI (combination tegafur, uracil [UFT], leucovorin [LV], irinotecan), for patients with locally advanced rectal cancer.

PATIENTS AND METHODS

A total of 22 patients with locally advanced lower rectal adenocarcinoma were enrolled in the present study. The radiation dose was 50.4 Gy in 28 fractions. UFT (300 mg/m²/d) and LV (75 mg/body weight/d) were administered orally 3 times daily. Irinotecan was administered as an intravenous infusion at 3 escalating dose levels. The initial dose was 50 mg/m² (level 1; n = 7), the intermediate was 70 mg/m² (level 2; n = 8), and the maximum was 80 mg/m² (level 3; n = 7). The drug was administered on days 1, 15, 29, and 43.

RESULTS

Dose-limiting toxicity was not observed at any dosing level. The most frequent adverse event was leukopenia (50%), followed by diarrhea (45.5%), anal pain (31.8%), and neutropenia (27.3%). All were well-managed with the appropriate drugs. The total pathologic complete response rate was 22.7%, and the proportion of good responders was 28.6%, 50%, and 71.4% at levels 1, 2, and 3, respectively. None of the patients experienced local recurrence. The 5-year relapse-free and overall survival rates were 80.4% and 80.8%, respectively.

CONCLUSION

TEGAFIRI is a promising CRT regimen that results in marked tumor regression and good local control. Moreover, its adverse events are well-tolerated.

Optical imaging of radiation-induced metabolic changes in radiation-sensitive and resistant cancer cells

Radiation resistance remains a significant problem for cancer patients, especially due to the time required to definitively determine treatment outcome. For fractionated radiation therapy, nearly 7 to 8 weeks can elapse before a tumor is deemed to be radiation-resistant. We used the optical redox ratio of FAD / ( FAD + NADH ) to identify early metabolic changes in radiation-resistant lung cancer cells. These radiation-resistant human A549 lung cancer cells were developed by exposing the parental A549 cells to repeated doses of radiation (2 Gy). Although there were no significant differences in the optical redox ratio between the parental and resistant cell lines prior to radiation, there was a significant decrease in the optical redox ratio of the radiation-resistant cells 24 h after a single radiation exposure ( p = 0.01 ). This change in the redox ratio was indicative of increased catabolism of glucose in the resistant cells after radiation and was associated with significantly greater protein content of hypoxia-inducible factor 1 ( HIF - 1 ? ), a key promoter of glycolytic metabolism. Our results demonstrate that the optical redox ratio could provide a rapid method of determining radiation resistance status based on early metabolic changes in cancer cells.