Optical Redox Imaging of Lonidamine Treatment Response of Melanoma Cells and Xenografts

Use of Optical Redox Imaging to Quantify Alveolar Macrophage Redox State in Infants: Proof of Concept Experiments in a Murine Model and Human Tracheal Aspirates Samples

Emerging data indicate that lung macrophages (LM) may provide a novel biomarker to classify disease endotypes in bronchopulmonary dysplasia (BPD), a form of infant chronic lung disease, and that augmentation of the LM phenotype may be a potential therapeutic target. To contribute to this area of research, we first used Optical Redox Imaging (ORI) to characterize the responses to H2O2-induced oxidative stress and caffeine treatment in an in vitro model of mouse alveolar macrophages (AM). H2O2 caused a dose-dependent decrease in NADH and an increase in FAD-containing flavoproteins (Fp) and the redox ratio Fp/(NADH + Fp). Caffeine treatment did not affect Fp but significantly decreased NADH with doses of ≥50 µM, and 1000 µM caffeine treatment significantly increased the redox ratio and decreased the baseline level of mitochondrial ROS (reactive oxygen species). However, regardless of whether AM were pretreated with caffeine or not, the mitochondrial ROS levels increased to similar levels after H2O2 challenge. We then investigated the feasibility of utilizing ORI to examine macrophage redox status in tracheal aspirate (TA) samples obtained from premature infants receiving invasive ventilation. We observed significant heterogeneity in NADH, Fp, Fp/(NADH + Fp), and mitochondrial ROS of the TA macrophages. We found a possible positive correlation between gestational age and NADH and a negative correlation between mean airway pressure and NADH that provides hypotheses for future testing. Our study demonstrates that ORI is a feasible technique to characterize macrophage redox state in infant TA samples and supports further use of this method to investigate lung macrophage-mediated disease endotypes in BPD.

Quantitative Optical Redox Imaging of Melanoma Xenografts with Different Metastatic Potentials

To develop imaging biomarkers for tumors aggressiveness, our previous optical redox imaging (ORI) studies of the reduced nicotinamide adenine dinucleotide (NADH) and oxidized flavoproteins (Fp, containing flavin adenine dinucleotide, i.e., FAD) in tumor xenografts of human melanoma associated the high optical redox ratio (ORR = Fp/(Fp + NADH)) and its heterogeneity to the high invasive/metastatic potential, without having reported quantitative results for NADH and Fp. Here, we implemented a calibration procedure to facilitate imaging the nominal concentrations of tissue NADH and Fp in the mouse xenografts of two human melanoma lines, an indolent less metastatic A375P and a more metastatic C8161. Images of the redox indices (NADH, Fp, ORR) revealed the existence of more oxidized areas (OAs) and more reduced areas (RAs) within individual tumors. ORR was found to be higher and NADH lower in C8161 compared to that of A375P xenografts, both globally for the whole tumors and locally in OAs. The ORR in the OA can differentiate xenografts with a higher statistical significance than the global averaged ORR. H&E staining of the tumors indicated that the redox differences we identified were more likely due to intrinsically different cell metabolism, rather than variations in cell density.

Development of an Endoscopic Auto-Fluorescent Sensing Device to Aid in the Detection of Breast Cancer and Inform Photodynamic Therapy

Breast cancer is the most diagnosed cancer type in women, with it being the second most deadly cancer in terms of total yearly mortality. Due to the prevalence of this disease, better methods are needed for both detection and treatment. Reduced nicotinamide adenine dinucleotide (NADH) and flavin adenine dinucleotide (FAD) are autofluorescent biomarkers that lend insight into cell and tissue metabolism. As such, we developed an endoscopic device to measure these metabolites in tissue to differentiate between malignant tumors and normal tissue. We performed initial validations in liquid phantoms as well as compared to a previously validated redox imaging system. We also imaged ex vivo tissue samples after modulation with carbonyl cyanide 4-(trifluoromethoxy) phenylhydrazone (FCCP) and a combination of rotenone and antimycin A. We then imaged the rim and the core of MDA-MB-231 breast cancer tumors, with our results showing that the core of a cancerous lesion has a significantly higher optical redox ratio ([FAD]/([FAD] + [NADH])) than the rim, which agrees with previously published results. The mouse muscle tissues exhibited a significantly lower FAD, higher NADH, and lower redox ratio compared to the tumor core or rim. We also used the endoscope to measure NADH and FAD after photodynamic therapy treatment, a light-activated treatment methodology. Our results found that the NADH signal increases in the malignancy rim and core, while the core of cancers demonstrated a significant increase in the FAD signal.

Optical Redox Imaging of Ex Vivo Hippocampal Tissue Reveals Age-Dependent Alterations in the 5XFAD Mouse Model of Alzheimer’s Disease

A substantial decline in nicotinamide adenine dinucleotide (NAD) has been reported in brain tissue homogenates or neurons isolated from Alzheimer’s disease (AD) models. NAD, together with flavin adenine dinucleotide (FAD), critically supports energy metabolism and maintains mitochondrial redox homeostasis. Optical redox imaging (ORI) of the intrinsic fluorescence of reduced NAD (NADH) and oxidized FAD yields cellular redox and metabolic information and provides biomarkers for a variety of pathological conditions. However, its utility in AD has not been characterized at the tissue level. We performed ex vivo ORI of freshly dissected hippocampi from a well-characterized AD mouse model with five familial Alzheimer’s disease mutations (5XFAD) and wild type (WT) control littermates at various ages. We found (1) a significant increase in the redox ratio with age in the hippocampi of both the WT control and the 5XFAD model, with a more prominent redox shift in the AD hippocampi; (2) a higher NADH in the 5XFAD versus WT hippocampi at the pre-symptomatic age of 2 months; and (3) a negative correlation between NADH and Aβ₄₂ level, a positive correlation between Fp and Aβ₄₂ level, and a positive correlation between redox ratio and Aβ₄₂ level in the AD hippocampi. These findings suggest that the ORI can be further optimized to conveniently study the metabolism of freshly dissected brain tissues in animal models and identify early AD biomarkers.

Subcellular analysis of nuclear and cytoplasmic redox indices differentiates breast cancer cell subtypes better than nuclear-to-cytoplasmic area ratio

SIGNIFICANCE

Stratification of malignancy is valuable for cancer treatment. Both optical redox imaging (ORI) indices and nuclear-to-cytoplasmic volume/area ratio (N:C ratio) have been investigated to differentiate between cancers with varying aggressiveness, but these two methods have not been directly compared. The redox status in the cell nucleus has not been studied by ORI, and it remains unknown whether nuclear ORI indices add new biological information.

AIM

We sought to compare the capacity of whole-cell and subcellular ORI indices and N:C ratio to differentiate between breast cancer subtypes with varying aggressiveness and between mitotic and nonmitotic cells.

APPROACH

ORI indices for whole cell, cytoplasm, and nucleus as well as the N:C area ratio were generated for two triple-negative (more aggressive) and two receptor-positive (less aggressive) breast cancer cell lines by fluorescence microscopy.

RESULTS

We found positive correlations between nuclear and cytoplasmic ORI indices within individual cells. On average, a nuclear redox status was found to be more oxidized than cytoplasm in triple-negative cells but not in receptor-positive cells. Whole-cell and subcellular ORI indices distinguished between the receptor statuses better than the N:C ratio. However, N:C ratio was a better differentiator between nonmitotic and mitotic triple-negative cells.

CONCLUSIONS

Subcellular ORI analysis differentiates breast cancer subtypes with varying aggressiveness better than N:C area ratio.

Cu(I) and Cu(II) Complexes Based on Lonidamine-Conjugated Ligands Designed to Promote Synergistic Antitumor Effects

Bis(pyrazol-1-yl)- and bis(3,5-dimethylpyrazol-1-yl)-acetates were conjugated with the 2-hydroxyethylester and 2-aminoethylamide derivatives of the antineoplastic drug lonidamine to prepare Cu(I) and Cu(II) complexes that might act through synergistic mechanisms of action due to the presence of lonidamine and copper in the same chemical entity. Synchrotron radiation-based complementary techniques [X-ray photorlectron spectroscopy and near-edge X-ray absorption fine structure (NEXAFS)] were used to characterize the electronic and molecular structures of the complexes and the local structure around the copper ion (XAFS) in selected complexes. All complexes showed significant antitumor activity, proving to be more effective than the reference drug cisplatin in a panel of human tumor cell lines, and were able to overcome oxaliplatin and multidrug resistance. Noticeably, these Cu complexes appeared much more effective than cisplatin against 3D spheroids of pancreatic PSN-1 cancer cells; among these, PPh₃-containing Cu(I) complex 15 appeared to be the most promising derivative. Mechanistic studies revealed that 15 induced cancer cell death by means of an apoptosis-alternative cell death.

Optical Redox Imaging of Treatment Responses to Nampt Inhibition and Combination Therapy in Triple-Negative Breast Cancer Cells

We evaluated the utility of optical redox imaging (ORI) to identify the therapeutic response of triple-negative breast cancers (TNBC) under various drug treatments. Cultured HCC1806 and MDA-MB-231 cells treated with FK866 (nicotinamide phosphoribosyltransferase (Nampt) inhibitor), FX11 (lactate dehydrogenase A inhibitor), paclitaxel, and their combinations were subjected to ORI, followed by imaging fluorescently labeled reactive oxygen species (ROS). Cell growth inhibition was measured by a cell viability assay. We found that both cell lines experienced significant NADH decrease and redox ratio (Fp/(NADH+Fp)) increase due to FK866 treatment; however, HCC1806 was much more responsive than MDA-MB-231. We further studied HCC1806 with the main findings: (i) nicotinamide riboside (NR) partially restored NADH in FK866-treated cells; (ii) FX11 induced an over 3-fold NADH increase in FK866 or FK866+NR pretreated cells; (iii) FK866 combined with paclitaxel caused synergistic increases in both Fp and the redox ratio; (iv) FK866 sensitized cells to paclitaxel treatments, which agrees with the redox changes detected by ORI; (v) Fp and the redox ratio positively correlated with cell growth inhibition; and (vi) Fp and NADH positively correlated with ROS level. Our study supports the utility of ORI for detecting the treatment responses of TNBC to Nampt inhibition and the sensitization effects on standard chemotherapeutics.

Imaging NAD(H) Redox Alterations in Cryopreserved Alveolar Macrophages from Ozone-Exposed Mice and the Impact of Nutrient Starvation during Long Lag Times

Employing the optical redox imaging technique, we previously identified a significant redox shift of nicotinamide adenine dinucleotide (NAD and the reduced form NADH) in freshly isolated alveolar macrophages (AM) from ozone-exposed mice. The goal here was twofold: (a) to determine the NAD(H) redox shift in cryopreserved AM isolated from ozone-exposed mice and (b) to investigate whether there is a difference in the redox status between cryopreserved and freshly isolated AM. We found: (i) AM from ozone-exposed mice were in a more oxidized redox state compared to that from filtered air (FA)-exposed mice, consistent with the results obtained from freshly isolated mouse AM; (ii) under FA exposure, there was no significant NAD(H) redox difference between fresh AM that had been placed on ice for 2.5 h and cryopreserved AM; however, under ozone exposure, fresh AM were more oxidized than cryopreserved AM; (iii) via the use of nutrient starvation and replenishment and H₂O₂-induced oxidative stress of an AM cell line, we showed that this redox difference between cryopreserved and freshly isolated AM is likely the result of the double “hit”, i.e., the ozone-induced oxidative stress plus nutrient starvation that prevented freshly isolated AM from a full recovery after being on ice for a prolonged time period. The cryopreservation technique we developed eliminates/minimizes the effects of oxidative stress and nutrient starvation on cells. This method can be adopted to preserve lung macrophages from animal models or clinical patients for further investigations.

Optical Redox Imaging Differentiates Triple-Negative Breast Cancer Subtypes

Triple-negative breast cancer (TNBC) is a highly diverse group of cancers with limited treatment options, responsible for about 15% of all breast cancers. TNBC cells differ from each other in many ways such as gene expression, metabolic activity, tumorigenicity, and invasiveness. Recently, many research and clinical efforts have focused on metabolically targeted therapy for TNBC. Metabolic characterization of TNBC cell lines can facilitate the assessment of therapeutic effects and assist in metabolic drug development. Herein, we used optical redox imaging (ORI) techniques to characterize TNBC subtypes metabolically. We found that various TNBC cell lines had differing redox statuses (levels of reduced nicotinamide adenine dinucleotide (NADH), oxidized flavin adenine dinucleotide (FAD), and the redox ratio (FAD/(NADH+FAD)). We then metabolically perturbed the cells with mitochondrial inhibitors and an uncoupler and performed ORI accordingly. As expected, we observed that these TNBC cell lines had similar response patterns to the metabolic perturbations. However, they exhibited differing redox plasticity. These results suggest that subtypes of TNBC cells are different metabolically and that ORI can serve as a sensitive technique for the metabolic profiling of TNBC cells.

Potential Biomarker for Triple-Negative Breast Cancer Invasiveness by Optical Redox Imaging

Predicting tumor metastatic potential remains a challenge in cancer research and in clinical diagnosis. Cancer invasion to neighboring tissues is a significant event in cancer progression to metastasis. Optical redox imaging (ORI) is based on detecting the endogenous fluorescence signals of reduced nicotinamide adenine dinucleotide (NADH) and oxidized flavin adenine dinucleotide (FAD). Previously, we found that ORI can discriminate between cancer and normal tissue specimens from clinical breast cancer patients and can differentiate the relative invasiveness of melanoma and breast tumors. In this study, we aimed to identify ORI biomarkers to differentiate the invasiveness of four triple-negative breast cancer cell lines (TNBC). Using a fluorescence microscope, we acquired NADH and FAD fluorescent signals from cultured MDA-MB-231, MDA-MB-436, HCC1806, and MDA-MB-468 cells. We found that (1) the redox ratio, FAD/(NADH+FAD), differentiated the four TNBC lines; (2) there was a significant difference of invasive potential between MDA-MB-231 and the other three TNBC lines measured by the transwell invasion assay; and (3) there was a positive logarithmic correlation between the redox ratio and the invasive potential, where the most invasive MDA-MB-231 cells had the highest redox ratio and the least invasive MDA-MB-468 cells had the lowest redox ratio. These results suggest that the redox ratio can potentially be used as a biomarker for TNBC invasiveness and prognosis.

Sex and SP-A2 Dependent NAD(H) Redox Alterations in Mouse Alveolar Macrophages in Response to Ozone Exposure: Potential Implications for COVID-19

Co-enzyme nicotinamide adenine dinucleotide (NAD(H)) redox plays a key role in macrophage function. Surfactant protein (SP-) A modulates the functions of alveolar macrophages (AM) and ozone (O₃) exposure in the presence or absence of SP-A and reduces mouse survival in a sex-dependent manner. It is unclear whether and how NAD(H) redox status plays a role in the innate immune response in a sex-dependent manner. We investigated the NAD(H) redox status of AM from SP-A2 and SP-A knockout (KO) mice in response to O₃ or filtered air (control) exposure using optical redox imaging technique. We found: (i) In SP-A2 mice, the redox alteration of AM in response to O₃ showed sex-dependence with AM from males being significantly more oxidized and having a higher level of mitochondrial reactive oxygen species than females; (ii) AM from KO mice were more oxidized after O₃ exposure and showed no sex differences; (iii) AM from female KO mice were more oxidized than female SP-A2 mice; and (iv) Two distinct subpopulations characterized by size and redox status were observed in a mouse AM sample. In conclusions, the NAD(H) redox balance in AM responds to O₃ in a sex-dependent manner and the innate immune molecule, SP-A2, contributes to this observed sex-specific redox response.

Rapamycin maintains NAD+/NADH redox homeostasis in muscle cells

Rapamycin delays multiple age-related conditions and extends lifespan in organisms ranging from yeast to mice. However, the mechanisms by which rapamycin influences longevity are incompletely understood. The objective of this study was to investigate the effect of rapamycin on NAD⁺/NADH redox balance. We report that the NAD⁺/NADH ratio of C2C12 myoblasts or differentiated myotubes significantly decreases over time in culture, and that rapamycin prevents this effect. Despite lowering the NADH available to support ATP generation, rapamycin increases ATP availability, consistent with lowering energetic demand. Although rapamycin did not change the NAD⁺/NADH ratio or steady-state ATP concentration in the livers, kidneys, or muscles of young mice, optical redox imaging revealed that rapamycin caused a substantial decline in the NADH content and an increase in the optical redox ratio (a surrogate of NAD⁺/NADH redox ratio) in muscles from aged mice. Collectively, these data suggest that rapamycin favors a more oxidized NAD⁺/NADH ratio in aged muscle, which may influence metabolism and the activity of NAD⁺-dependent enzymes. This study provides new insight into the mechanisms by which rapamycin might influence the aging process to improve health and longevity among the aging population.

Relationship between Optical Redox Status and Reactive Oxygen Species in Cancer Cells

Shifted NAD(H) redox status and enhanced reactive oxygen species (ROS) scavenging systems have been observed in cancers. However, how such redox shift is related to the ROS level in cancer cells is less clear. Based on collecting the intrinsic fluorescence of oxidized flavoproteins (Fp containing flavin adenine dinucleotide) and reduced nicotinamide adenine dinucleotide (NADH), optical redox imaging (ORI) provides a quantitative measure of the mitochondrial redox state by the optical redox ratio, Fp/(NADH+Fp), a surrogate marker of the NAD⁺-coupled redox state NAD⁺/NADH. Our study aims to explore the relationship between NAD(H) redox status and ROS by imaging NADH, Fp, and ROS levels using cultured breast cancer cell models. By manipulating either ROS levels via application of exogenous H₂O₂ or redox status via metabolic perturbation compounds, we found that: (1) oxidation of NAD(H) redox status correlates with ROS levels at lower H₂O₂ concentrations (up to ~700 μM), but not necessarily at higher concentrations; (2) an elevated ROS level diminishes NADH and reduces redox ratio plasticity; (3) either more oxidized or more reduced status can correlate to an increased ROS level; and (4) sometimes, a more oxidized status can correlate to a decreased ROS level depending on cell lines. These observations indicated that cellular NAD(H) redox state and ROS are intricately related but can also change separately. This study can benefit cancer research as both NAD(H) redox status and ROS have been implicated in cancer transformation and progression.

Optical Redox Imaging of Fixed Unstained Muscle Slides Reveals Useful Biological Information

PURPOSE

Optical redox imaging (ORI) technique images cellular autofluorescence of nicotinamide adenine dinucleotide (NADH) and oxidized flavoproteins (Fp containing FAD, i.e., flavin adenine dinucleotide). ORI has found wide applications in the study of cellular energetics and metabolism and may potentially assist in disease diagnosis and prognosis. Fixed tissues have been reported to exhibit autofluorescence with similar spectral characteristics to those of NADH and Fp. However, few studies report on quantitative ORI of formalin-fixed paraffin-embedded (FFPE) unstained tissue slides for disease biomarkers. We investigate whether ORI of FFPE unstained skeletal muscle slides may provide relevant quantitative biological information.

PROCEDURES

Living mouse muscle fibers and frozen and FFPE mouse muscle slides were subjected to ORI. Living mouse muscle fibers were imaged ex vivo before and after paraformaldehyde fixation. FFPE muscle slides of three mouse groups (young, mid-age, and muscle-specific overexpression of nicotinamide phosphoribosyltransferase (Nampt) transgenic mid-age) were imaged and compared to detect age-related redox differences.

RESULTS

We observed that living muscle fiber and frozen and FFPE slides all had strong autofluorescence signals in the NADH and Fp channels. Paraformaldehyde fixation resulted in a significant increase in the redox ratio Fp/(NADH + Fp) of muscle fibers. Quantitative image analysis on FFPE unstained slides showed that mid-age gastrocnemius muscles had stronger NADH and Fp signals than young muscles. Gastrocnemius muscles from mid-age Nampt mice had lower NADH compared to age-matched controls, but had higher Fp than young controls. Soleus muscles had the same trend of change and appeared to be more oxidative than gastrocnemius muscles. Differential NADH and Fp signals were found between gastrocnemius and soleus muscles within both mid-aged control and Nampt groups.

CONCLUSION

Aging effect on redox status quantified by ORI of FFPE unstained muscle slides was reported for the first time. Quantitative information from ORI of FFPE unstained slides may be useful for biomedical applications.

Effect of Differences in Metabolic Activity of Melanoma Models on Response to Lonidamine plus Doxorubicin

Lonidamine (LND), a metabolic modulator, sensitizes DB-1 human melanoma to doxorubicin (DOX) chemotherapy by acidifying and de-energizing the tumor. This report compares the effects of LND on two human melanoma lines, DB-1 and WM983B, which exhibit different metabolic properties. Using liquid chromatography mass spectrometry and Seahorse analysis, we show that DB-1 was more glycolytic than WM983B in vitro. ³¹P magnetic resonance spectroscopy (MRS) indicates that LND (100 mg/kg, i.p.) induces similar selective acidification and de-energization of WM983B xenografts in immunosuppressed mice. Over three hours, intracellular pH (pHi) of WM983B decreased from 6.91 ± 0.03 to 6.59 ± 0.10 (p = 0.03), whereas extracellular pH (pHe) of this tumor changed from 7.03 ± 0.05 to 6.89 ± 0.06 (p = 0.19). A decline in bioenergetics (β-NTP/Pi) of 55 ± 5.0% (p = 0.03) accompanied the decline in pHi of WM983B. Using ¹H MRS with a selective multiquantum pulse sequence and Hadamard localization, we show that LND induced a significant increase in tumor lactate levels (p < 0.01). LND pre-treatment followed by DOX (10 mg/kg, i.v.) produced a growth delay of 13.7 days in WM983B (p < 0.01 versus control), a growth delay significantly smaller than the 25.4 days that occurred with DB-1 (p = 0.03 versus WM983B). Differences in relative levels of glycolysis may produce differential therapeutic responses of DB-1 and WM983B melanomas.