Live-Cell Imaging Quantifies Changes in Function and Metabolic NADH Autofluorescence During Macrophage-Mediated Phagocytosis of Tumor Cells

BACKGROUND

The immune system has evolved to detect foreign antigens and deliver coordinated responses, while minimizing "friendly fire." Until recently, studies investigating the behavior of immune cells were limited to static in vitro measurements. Although static measurements allow for real-time imaging, results are often difficult to translate to an in vivo setting. Multiphoton microscopy is an emerging method to capture spatial information on subcellular events and characterize the local microenvironment. Previous studies have shown that multiphoton microscopy can monitor changes in single-cell macrophage heterogeneity during differentiation. Therefore, there is a need to use multiphoton microscopy to monitor molecular interactions during immunological activities like phagocytosis. Here we investigate the correlation between phagocytic function and changes in endogenous optical reporters during phagocytosis.

METHODS

In vitro autofluorescence imaging of nicotinamide adenine dinucleotide (NADH) and flavin adenine dinucleotide (FAD) was used to detect metabolic changes in macrophages during phagocytosis. More specifically, optical redox ratio, mean NADH fluorescence lifetime and ratio of free to protein-bound NADH were used to quantify changes in metabolism.

RESULTS

Results show that IFN-γ (M1) macrophages showed decreased optical redox ratios and mean NADH lifetime while phagocytosing immunogenic cancer cells compared to metastatic cells. To validate phagocytic function, a fluorescence microscopy-based protocol using a pH-sensitive fluorescent probe was used. Results indicate that M0 and M1 macrophages show similar trends in phagocytic potential.

CONCLUSION

Overall, this work demonstrates that in vitro multiphoton imaging can be used to longitudinally track changes in phagocytosis and endogenous metabolic cofactors.

Autofluorescence imaging of endogenous metabolic cofactors in response to cytokine stimulation of classically activated macrophages

BACKGROUND

Macrophages are one of the most prevalent subsets of immune cells within the tumor microenvironment and perform a range of functions depending on the cytokines and chemokines released by surrounding cells and tissues. Recent research has revealed that macrophages can exhibit a spectrum of phenotypes, making them highly plastic due to their ability to alter their physiology in response to environmental cues. Recent advances in examining heterogeneous macrophage populations include optical metabolic imaging, such as fluorescence lifetime imaging (FLIM), and multiphoton microscopy. However, the method of detection for these systems is reliant upon the coenzymes NAD(P)H and FAD, which can be affected by factors other than cytoplasmic metabolic changes. In this study, we seek to validate these optical measures of metabolism by comparing optical results to more standard methods of evaluating cellular metabolism, such as extracellular flux assays and the presence of metabolic intermediates.

METHODS

Here, we used autofluorescence imaging of endogenous metabolic co-factors via multiphoton microscopy and FLIM in conjunction with oxygen consumption rate and extracellular acidification rate through Seahorse extracellular flux assays to detect changes in cellular metabolism in quiescent and classically activated macrophages in response to cytokine stimulation.

RESULTS

Based on our Seahorse XFP flux analysis, M0 and M1 macrophages exhibit comparable trends in oxygen consumption rate (OCR) and extracellular acidification rate (ECAR). Autofluorescence imaging of M0 and M1 macrophages was not only able to show acute changes in the optical redox ratio from pre-differentiation (0 hours) to 72 hours post-cytokine differentiation (M0: 0.320 to 0.258 and M1: 0.316 to 0.386), mean NADH lifetime (M0: 1.272 ns to 1.379 ns and M1: 1.265 ns to 1.206 ns), and A1/A2 ratio (M0: 3.452 to ~ 4 and M1: 3.537 to 4.529) but could also detect heterogeneity within each macrophage population.

CONCLUSIONS

Overall, the findings of this study suggest that autofluorescence metabolic imaging could be a reliable technique for longitudinal tracking of immune cell metabolism during activation post-cytokine stimulation.

Minimally invasive in vivo endoscopic monitoring of dextran sulfate sodium-induced murine colitis

Ulcerative colitis (UC) is a gastrointestinal, autoimmune disease that causes ulceration and inflammation of the colon with an incidence of 10 out of every 100,000 people in North America and Western Europe. Though the specific cause is unknown, several studies have demonstrated that inflammatory cells as well as environmental variables, genetics, and lifestyle behaviors can play a role in the long-term inflammatory response. Researchers have commonly used immunohistochemistry, western blotting and gene sequencing to establish the cellular processes behind UC relapse and remission. However, because these destructive methods necessitate the removal of a sample, they can only be used on non-living tissues. The use of minimally invasive approaches to evaluate the in vivo, longitudinal effects of UC on the mucosa in the colon is gaining popularity among clinicians and researchers. We have created a dextran sulfate sodium-induced model of UC in C57 mice based on the work of Wirtz et al., and a minimally invasive imaging modality to explore the changes in mucosal tissue during "active" and "in remission" UC. Briefly, C57 mice were given dextran sulfate sodium (DSS) dissolved in water in 5-day cycles with a remission/recovery period of 10 days. After 7 days post-DSS treatment and 7 days post-recovery, mice were anesthetized and exploratory endoscopies were performed to assess the mucosal changes that occur during the "active" and "remission" periods of UC. Value of protocol:•Minimally invasive induction of ulcerative colitis in a murine mouse model.•Minimally invasive longitudinal monitoring of "active" and "in remission" ulcerative colitis.•Our endoscopic based imaging modality can be used to validate the induction of ulcerative colitis and the potential treatment response for pre-clinical trials.

Macrophage-targeted anti-CCL2 immunotherapy enhances tumor sensitivity to 5-fluorouracil in a Balb/c-CT26 murine colon carcinoma model measured using diffuse reflectance spectroscopy

Background

Immunotherapy in colorectal cancer (CRC) regulates specific immune checkpoints and, when used in combination with chemotherapy, can improve patient prognosis. One specific immune checkpoint is the recruitment of circulating monocytes that differentiate into tumor-associated macrophages (TAMs) and promote tumor angiogenesis. Changes in vascularization can be non-invasively assessed via diffuse reflectance spectroscopy using hemoglobin concentrations and oxygenation in a localized tumor volume. In this study, we examine whether blockade of monocyte recruitment via CCL2 (macrophage chemoattractant protein-1) leads to enhanced sensitivity of 5-fluorouracil (5-FU) in a CT26-Balb/c mouse model of CRC. It was hypothesized that the blockade of TAMs will alter tumor perfusion, increasing chemotherapy response. A subcutaneous tumor model using Balb/c mice injected with CT26 colon carcinoma cells received either a saline or isotype control, anti-CCL2, 5-FU, or a combination of anti-CCL2 and 5-FU.

Results

Findings show that 12 days post-treatment, monocyte recruitment was significantly reduced by approximately 61% in the combination group. This shows that the addition of anti-CCL2 to 5-FU slowed the fold-change (change from the original measurement to the final measurement) in tumor volume from Day 0 to Day 12 (~ 5 fold). Modest improvements in oxygen saturation (~ 30%) were observed in the combination group.

Conclusion

The findings in this work suggest that the blockade of CCL2 is sufficient in the reduction of TAMs that are recruited into the tumor microenvironment and has the ability to modestly alter tumor perfusion during early-tumor response to treatment even though the overall benefit is relatively modest.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12865-022-00493-5.

Abstract P009: Correlation between immune modulation of macrophage recruitment and new blood vessel formation in a subcutaneous murine mouse model of colorectal cancer

Purpose: Colorectal cancer is the fourth most common cancer in the United States, accounting for more than 50,000 deaths annually1. The standard treatment is 5-fluorouracil (5-FU)-based chemotherapy, but emerging methods of immunotherapy have gained the attention of investigators and clinicians. A specific cytokine-based strategy for immunotherapy is the blockade of CCL2/MCP-1 (monocyte chemoattractant protein-1)2. CCL2 is a chemotactic cytokine that recruits circulating monocytes to the tumor microenvironment2. These monocytes differentiate into tumor-associated macrophages (TAMs), which promote pro-tumor functions including tumor growth, immunosuppression, and angiogenesis. CCL2 blockade in certain mouse models of cancer has been shown to reduce tumor burden but had not been studied in colorectal cancer. In this study, we examine how cytokine-targeted anti-CCL2 immunotherapy affects tumor-associated macrophage recruitment as well as the promotion of angiogenesis as a standalone and in combination with 5-FU.

Methods: Nine-week-old Balb/c mice (n=13) were acclimated for a week in the Small Animal Facility at the University of Arkansas. CT26 cells, a murine colon carcinoma cell line, were cultured in RPMI-1640 media, supplemented with 10% bovine serum, 0.2% amphotericin B/gentamicin, and 1% antibiotic antimycotic solution. 1 × 106 CT26 cells were subcutaneously injected into the left flank of Balb/c mice (10 weeks old). The tumors grew to 75 mm3, upon which Balb/c mice were randomly divided into saline control, immunotherapy, chemotherapy, and combination (immunotherapy + chemotherapy) groups. The immunotherapy and chemotherapy groups were intraperitoneally injected with a 28G insulin syringe with anti-CCL2 and 5-FU at a concentration of 5.0 mg/kg/dose and 15mg/kg/dose, respectively. The control group was injected with an equal volume of sterile saline on days while the combination group received a dose of anti-CCL2 and 5-FU. Tumor-associated macrophages were quantified via immunohistochemistry using anti-CD68 and tumor vasculature was quantified using anti-CD31. Correlation plots were also created to determine a relationship between macrophage recruitment and new blood vessel formation.

Results: There was a decrease in the total number of tumor-associated macrophages from Day 3 to 7 (33% decrease) when tumors were treated with anti-CCL2 and 5-FU. The area of vasculature in the combination group showed a slight decrease from Day 3 to Day 7 (29% decrease). There was a slight positive correlation between total macrophage recruitment and new blood vessel formation (R2 = 0.3041).

Conclusion: Overall, we have demonstrated that anti-CCL2 in combination with 5-FU has modestly slowed tumor growth, reduced the area of vasculature, and decreased the number of recruited tumor-associated macrophages in a murine model of colorectal cancer.

Acknowledgments: This material is based on work supported by the National Institutes of Health (1R15CA202662- 01), National Science Foundation CAREER award (CBET 1751554), and the Arkansas Biosciences Institute.

Citation Format: Shelby N. Bess, Timothy J. Muldoon. Correlation between immune modulation of macrophage recruitment and new blood vessel formation in a subcutaneous murine mouse model of colorectal cancer [abstract]. In: Abstracts: AACR Virtual Special Conference: Tumor Immunology and Immunotherapy; 2021 Oct 5-6. Philadelphia (PA): AACR; Cancer Immunol Res 2022;10(1 Suppl):Abstract nr P009.

Efficacy and clinical monitoring strategies for immune checkpoint inhibitors and targeted cytokine immunotherapy for locally advanced and metastatic colorectal cancer

Colorectal cancer (CRC) is the fourth most common cancer type and is the second leading cause of cancer deaths annually in the United States. Conventional treatment options include postoperative (adjuvant) and preoperative (neoadjuvant) chemotherapy and radiotherapy. Although these treatment modalities have shown to decrease tumor burden, a major limitation to chemothearpy/radiotherapy is the high recurrence rate in patients. Immune-modulation strategies have emerged as a promising new therapeutic avenue to reduce this recurrence rate while minimizing undesirable systemic side effects. This review will focus specifically on the mechanisms of monoclonal antibodies: immune checkpoint inhibitors and cytokines, as well as current drugs approved by the Food and Drug Administration (FDA) and new clinical/pre-clinical trials. Finally, this review will investigate emerging methods used to monitor tumor response post-treatment.