Irina N. Druzhkova

Intracellular pH imaging in cancer cells in vitro and tumors in vivo using the new genetically encoded sensor SypHer2.

BACKGROUND Measuring intracellular pH (pHi) in tumors is essential for the monitoring of cancer progression and the response of cancer cells to various treatments. The purpose of the study was to develop a method for pHi mapping in living cancer cells in vitro and in tumors in vivo, using the novel genetically encoded indicator, SypHer2. METHODS A HeLa Kyoto cell line stably expressing SypHer2 in the cytoplasm was used, to perform ratiometric (dual excitation) imaging of the probe in cell culture, in 3D tumor spheroids and in tumor xenografts in living mice. RESULTS Using SypHer2, pHi was demonstrated to be 7.34±0.11 in monolayer HeLa cells in vitro under standard cultivation conditions. An increasing pHi gradient from the center to the periphery of the spheroids was displayed. We obtained fluorescence ratio maps for HeLa tumors in vivo and ex vivo. Comparison of the map with the pathomorphology and with hypoxia staining of the tumors revealed a correspondence of the zones with higher pHi to the necrotic and hypoxic areas. CONCLUSIONS Our results demonstrate that pHi imaging with the genetically encoded pHi indicator, SypHer2, can be a valuable tool for evaluating tumor progression in xenograft models. GENERAL SIGNIFICANCE We have demonstrated, for the first time, the possibility of using the genetically encoded sensor SypHer2 for ratiometric pH imaging in cancer cells in vitro and in tumors in vivo. SypHer2 shows great promise as an instrument for pHi monitoring able to provide high accuracy and spatiotemporal resolution.

The metabolic interaction of cancer cells and fibroblasts – coupling between NAD(P)H and FAD, intracellular pH and hydrogen peroxide

ABSTRACT Alteration in the cellular energy metabolism is a principal feature of tumors. An important role in modifying cancer cell metabolism belongs to the cancer-associated fibroblasts. However, the regulation of their interaction has been poorly studied to date. In this study we monitored the metabolic status of both cell types by using the optical redox ratio and the fluorescence lifetimes of the metabolic co-factors NAD(P)H and FAD, in addition to the intracellular pH and the hydrogen peroxide levels in the cancer cells, using genetically encoded sensors. In the co-culture of human cervical carcinoma cells HeLa and human fibroblasts we observed a metabolic shift from oxidative phosphorylation toward glycolysis in cancer cells, and from glycolysis toward OXPHOS in fibroblasts, starting from Day 2 of co-culturing. The metabolic switch was accompanied by hydrogen peroxide production and slight acidification of the cytosol in the cancer cells in comparison with that of the corresponding monoculture. Therefore, our HeLa-huFb system demonstrated metabolic behavior similar to Warburg type tumors. To our knowledge, this is the first time that these 3 parameters have been investigated together in a model of tumor-stroma co-evolution. We propose that determination of the start-point of the metabolic alterations and understanding of the mechanisms of their realization can open a new ways for cancer treatment.

Chemotherapy with cisplatin: insights into intracellular pH and metabolic landscape of cancer cells in vitro and in vivo

Although cisplatin plays a central role in cancer chemotherapy, the mechanisms of cell response to this drug have been unexplored. The present study demonstrates the relationships between the intracellular pH (pHi), cell bioenergetics and the response of cervical cancer to cisplatin. pHi was measured using genetically encoded sensor SypHer2 and metabolic state was accessed by fluorescence intensities and lifetimes of endogenous cofactors NAD(P)H and FAD. Our data support the notion that cisplatin induces acidification of the cytoplasm early after the treatment. We revealed in vitro that a capacity of cells to recover and maintain alkaline pHi after the initial acidification is the crucial factor in mediating the cellular decision to survive and proliferate at a vastly reduced rate or to undergo cell death. Additionally, we showed for the first time that pHi acidification occurs after prolonged therapy in vitro and in vivo, and this, likely, favors metabolic reorganization of cells. A metabolic shift from glycolysis towards oxidative metabolism accompanied the cisplatin-induced inhibition of cancer cell growth in vitro and in vivo. Overall, these findings contribute to an understanding of the mechanisms underlying the responsiveness of an individual cell and tumor to therapy and are valuable for developing new therapeutic strategies.

Metabolic cofactors NAD(P)H and FAD as potential indicators of cancer cell response to chemotherapy with paclitaxel

Paclitaxel, a widely used antimicrotubular agent, predominantly eliminates rapidly proliferating cancer cells, while slowly proliferating and quiescent cells can survive the treatment, which is one of the main reasons for tumor recurrence and non-responsiveness to the drug. To improve the efficacy of chemotherapy, biomarkers need to be developed to enable monitoring of tumor responses. In this study we considered the auto-fluorescent metabolic cofactors NAD(P)H and FAD as possible indicators of cancer cell response to therapy with paclitaxel. It was found that, among the tested parameters (the fluorescence intensity-based redox ratio FAD/NAD(P)H, and the fluorescence lifetimes of NAD(P)H and FAD), the fluorescence lifetime of NAD(P)H is the most sensitive in tracking the drug response, and is capable of indicating heterogeneous cellular responses both in cell monolayers and in multicellular tumor spheroids. We observed that metabolic reorganization to a more oxidative state preceded the morphological manifestation of cell death and developed faster in cells that were more responsive to the drug. Our results suggest that noninvasive, label-free monitoring of the drug-induced metabolic changes by noting the NAD(P)H fluorescence lifetime is a valuable approach to characterize the responses of cancer cells to anti-cancer treatments and, therefore, to predict the effectiveness of chemotherapy.

Soluble OX40L favors tumor rejection in CT26 colon carcinoma model.

OX40 receptor-expressing regulatory T cells (Tregs) populate tumors and suppress a variety of immune cells, posing a major obstacle for cancer immunotherapy. Different ways to functionally inactivate Tregs by triggering OX40 receptor have been suggested, including anti-OX40 antibodies and Fc:OX40L fusion proteins. To investigate whether the soluble extracellular domain of OX40L (OX40Lexo) is sufficient to enhance antitumor immune response, we generated an OX40Lexo-expressing CT26 colon carcinoma cell line and studied its tumorigenicity in immunocompetent BALB/c and T cell deficient nu/nu mice. We found that soluble OX40L expressed in CT26 colon carcinoma favors the induction of an antitumor response which is not limited just to cells co-expressing EGFP as an antigenic determinant, but also eliminates CT26 cells expressing another fluorescent protein, KillerRed. Tumor rejection required the presence of T lymphocytes, as indicated by the unhampered tumor growth in nu/nu mice. Subsequent re-challenge of tumor-free BALB/c mice with CT26 EGFP cells resulted in no tumor growth, which is indicative of the formation of immunological memory. Adoptive transfer of splenocytes from mice that successfully rejected CT26 OX40Lexo EGFP tumors to naïve mice conferred 100% resistance to subsequent challenge with the CT26 EGFP tumor.

Two-dimensional OCT-relaxography of collagenous tissues

Collageneus tissues manifest strongly pronounced viscoelastic behavior. Namely, viscosity leads to time-dependence of the deformation processes. This concerns both compression (loading) and unloading of the tissue. Both processes can be characterized by a relaxation time - the time during which the strain changes e-times. We demonstrate the applicability of the OCT-based 2D relaxography to characterize local relaxation time of collageneous tissues. The developed technique can be used for further investigation of the viscoelastic properties of healthy and pathological collageneous tissues.

E-cadherin in colorectal cancer: the relation to chemosensitivity

Micro‐Abstract We analyzed colorectal cancer chemosensitivity according to expression of the main epithelial–mesenchymal transition (EMT) marker, E‐cadherin. Human colon adenocarcinoma cell lines HT29 and HCT116 and 14 primary short‐term cultures from patient tumors were used. Increased chemosensitivity of the cell line with EMT phenotype, HCT116, was demonstrated; this may serve as a predictive marker of chemotherapy efficacy. Background: The conventional chemotherapy of colorectal cancer with irinotecan, 5‐fluorouracil, and oxaliplatin remains one of the front‐line treatments worldwide. However, its efficacy is quite low. Recently studies of the epithelial–mesenchymal transition (EMT) have become the focus of investigations into the cause of chemoresistance in several types of cancer, including colorectal cancer. The data about the role of EMT in chemosensitivity are controversial. Materials and Methods: Human colon adenocarcinoma cell lines HT29 and HCT116 and 14 primary short‐term cultures established from patient tumors were used. The chemosensitivity to irinotecan, 5‐fluorouracil, and oxaliplatin was assessed using the (4,5‐dimethylthiazol‐2‐yl)‐2,5‐diphenyltetrazolium bromide (MTT) test. Immunocytochemistry, immunohistochemistry, and Western blot test were used to investigate the E‐cadherin expression, the loss of which is a major hallmark of EMT. Results: Elevated chemosensitivity of the cell line with EMT phenotype, HCT116, was demonstrated. Increased chemosensitivity was revealed in HT29 cell line upon EMT induction. E‐cadherin–positive short‐term cultures were more resistant to all the drugs tested, whereas each of E‐cadherin–negative cultures showed sensitivity to at least one drug. The statistically significant dependency of cells viability on the E‐cadherin expression (P < .04) was demonstrated on the short‐term cultures using 2 concentrations of each drug. Conclusion: The data obtained may serve as a basis for the analysis of colon cancer chemosensitivity using short‐term cultures and the assay of E‐cadherin expression.

Insight into microenvironment of tumor on the microscopic level with a focus on cancer-associated fibroblasts

Cancer-associated fibroblasts (CAFs) are one of the key determinants in the malignant progression of cancer. The subject of this research was metabolic reorganization of CAFs and their participation in collagen cross-linking process. The metabolic differences between normal fibroblasts and CAFs were elucidated using two-photon fluorescence lifetime imaging microscopy (FLIM). Collagen structure in 3D model was assessed using second harmonic generation (SHG) microscopy. We show increased metabolic activity of fibroblasts derived from patient’s colon tumor with a shift to more oxidative metabolism compare to dermal fibroblasts. The results of the study of collagen suggest that CAFs may contribute to the tumor progression through the facilitation of collagen alignment. In general, our findings support the idea of the strong association between cancer cells and fibroblasts and extensive involvement of CAFs in modulation of tumor microenvironment.

Quasistatic in-depth local strain relaxation/creep rate mapping using phase-sensitive optical coherence tomography

OCT-based local strain relaxation/creep evaluation is an emerging tool for tissue viscoelasticity characterization. We present a tool for 2D visualization of local strain relaxation and creep time/rate inside the tissue.

Analysis of energy metabolism of HeLa cancer cells in vitro and in vivo using fluorescence lifetime microscopy

The aim of the present work was to study energy metabolism in human cervical carcinoma (HeLa) cells in vitro and in vivo using two-photon FLIM. Cellular metabolism was examined by monitoring of the fluorescence lifetimes of free and protein-bound forms of NAD(P)H and FAD and their relative contributions. Two-photon fluorescence and second harmonic generation microscopy as well as standard histopathology with hematoxylin and eosin were used to characterize tissue structure. Cellular metabolism was analyzed in cancer cells co-cultured with human fibroblasts and in tumor xenografts transplanted to nude mice. In the HeLa-huFB co-culture we observed a metabolic shift from OXPHOS toward glycolysis in cancer cells, and from glycolysis to OXPHOS in fibroblasts, starting from Day 2 of co-culturing. In the tumor tissue we detected metabolic heterogeneity with more glycolytic metabolism of cancer cells in the stroma-rich zones. The results of the study are of a great importance for understanding metabolic behavior of tumors and for development of anticancer drugs targeted to metabolic pathways.