Understanding the metabolic basis of drug resistance: Therapeutic induction of the Warburg effect kills cancer cells

Previously, we identified a form of epithelial-stromal metabolic coupling, in which cancer cells induce aerobic glycolysis in adjacent stromal fibroblasts, via oxidative stress, driving autophagy and mitophagy. In turn, these cancer-associated fibroblasts provide recycled nutrients to epithelial cancer cells, “fueling” oxidative mitochondrial metabolism and anabolic growth. An additional consequence is that these glycolytic fibroblasts protect cancer cells against apoptosis, by providing a steady nutrient stream to mitochondria in cancer cells. Here, we investigated whether these interactions might be the basis of tamoxifen-resistance in ER(+) breast cancer cells. We show that MCF7 cells alone are Tamoxifen-sensitive, but become resistant when co-cultured with hTERT-immortalized human fibroblasts. Next, we searched for a drug combination (Tamoxifen + Dasatinib) that could over-come fibroblast-induced Tamoxifen-resistance. Importantly, we show that this drug combination acutely induces the Warburg effect (aerobic glycolysis) in MCF7 cancer cells, abruptly cutting off their ability to use their fuel supply, effectively killing these cancer cells. Thus, we believe that the Warburg effect in tumor cells is not the “root cause” of cancer, but rather it may provide the necessary clues to preventing chemoresistance in cancer cells. Finally, we observed that this drug combination (Tamoxifen + Dasatinib) also had a generalized anti-oxidant effect, on both co-cultured fibroblasts and cancer cells alike, potentially reducing tumor-stroma co-evolution. Our results are consistent with the idea that chemo-resistance may be both a metabolic and stromal phenomenon that can be overcome by targeting mitochondrial function in epithelial cancer cells. Thus, simultaneously targeting both (1) the tumor stroma and (2) the epithelial cancer cells, with combination therapies, may be the most successful approach to anti-cancer therapy. This general strategy of combination therapy for overcoming drug resistance could be applicable to many different types of cancer.Key words: drug resistance, tamoxifen, dasatinib, tumor stroma, microenvironment, Warburg effect, aerobic glycolysis, mitochondrial oxidative phosphorylation, glucose uptake, oxidative stress, reactive oxygen species (ROS), cancer-associated fibroblasts     

Understanding the metabolic basis of drug resistance

Previously, we identified a form of epithelial-stromal metabolic coupling, in which cancer cells induce aerobic glycolysis in adjacent stromal fibroblasts, via oxidative stress, driving autophagy and mitophagy. In turn, these cancer-associated fibroblasts provide recycled nutrients to epithelial cancer cells, "fueling" oxidative mitochondrial metabolism and anabolic growth. An additional consequence is that these glycolytic fibroblasts protect cancer cells against apoptosis, by providing a steady nutrient stream of to mitochondria in cancer cells. Here, we investigated whether these interactions might be the basis of tamoxifen-resistance in ER(+) breast cancer cells. We show that MCF7 cells alone are Tamoxifen-sensitive, but become resistant when co-cultured with hTERT-immortalized human fibroblasts. Next, we searched for a drug combination (Tamoxifen + Dasatinib) that could over-come fibroblast-induced Tamoxifen-resistance. Importantly, we show that this drug combination acutely induces the Warburg effect (aerobic glycolysis) in MCF7 cancer cells, abruptly cutting off their ability to use their fuel supply, effectively killing these cancer cells. Thus, we believe that the Warburg effect in tumor cells is not the "root cause" of cancer, but rather it may provide the necessary clues to preventing chemo-resistance in cancer cells. Finally, we observed that this drug combination (Tamoxifen + Dasatinib) also had a generalized anti-oxidant effect, on both co-cultured fibroblasts and cancer cells alike, potentially reducing tumor-stroma co-evolution. Our results are consistent with the idea that chemo-resistance may be both a metabolic and stromal phenomenon that can be overcome by targeting mitochondrial function in epithelial cancer cells. Thus, simultaneously targeting both (1) the tumor stroma and (2) the epithelial cancer cells, with combination therapies, may be the most successful approach to anti-cancer therapy. This general strategy of combination therapy for overcoming drug resistance could be applicable to many different types of cancer.     

Functional Investigation of NCI-H460-Inducible Myofibroblasts on the Chemoresistance to VP-16 with a Microfluidic 3D Co-Culture Device

Fibroblasts, the major cell type in tumor stroma, are essential for tumor growth and survival, and represent an important therapeutic target for cancers. Here we presented a microfluidic co-culture device in which the three-dimensional (3D) matrix was employed to reconstruct an in vivo-like fibroblast-tumor cell microenvironment for investigation of the role of myofibroblasts induced by lung cancer cells in the chemoresistance to VP-16. Composed of a double-layer chip and an injection pump, the device houses fibroblasts and lung cancer cells co-cultured in 3D matrix and 2D mode to induce fibroblasts to become myofibroblasts with the supplement of the medium continuously. With this device, we verified that the cytokines secreted by lung cancer cells could effectively transform the fibroblasts into myofibroblasts. Moreover, compared to fibroblasts, the myofibroblasts showed higher resistance to anticancer drug VP-16. We also demonstrated that this kind of acquired resistance in myofibroblasts was associated with the expression of Glucose-regulated protein 78 (GP78). We concluded that this device allows for the assay to characterize various cellular events in a single device sequentially, facilitating a better understanding of the interactions among heterotypic cells in a sophisticated microenvironment.     

Carcinoma‐associated fibroblasts: Non‐neoplastic tumour‐promoting mesenchymal cells

Cancerous stroma coevolves alongside tumour progression, thereby promoting the malignant conversion of epithelial carcinoma cells. To date, an abundance of data have supported crucial roles of the tumour microenvironment (TME) in providing cancer cells with proliferative, migratory, survival and invasive propensities favouring the processes of tumourigenesis. The cancerous reactive stroma is frequently populated by a large number of myofibroblasts (MFs), which are activated, non‐transformed fibroblasts expressing α‐smooth muscle actin (α‐SMA). MFs together with non‐MF cells present in the tumour‐associated stroma are collectively referred to as carcinoma‐associated fibroblasts (CAFs), one of the major stromal cell types recognised in various human carcinomas. Recruitment of fibroblasts and/or their progenitors to a tumour mass and their subsequent transdifferentiation into MFs, as well as ongoing maintenance of their activated state, are believed to be essential processes facilitating tumour progression. However, the complex networks of signalling pathways mediating the phenotypic conversion into CAFs, as well as those underlying their tumour‐promoting interactions with other tumour‐constituting cells, have yet to be fully explored. Histopathological confirmation of the presence of large numbers of CAF MFs within TME and their altered gene expression profiles are known to be associated with disease progression and to serve as independent negative prognostic factors for a wide range of tumour types. In this review, we examine the current evidence shedding light on the emerging roles of tumour‐promoting CAFs, cells that are pivotal for epithelial cancer development and progression, and discuss the therapeutic potential of targeting these cells. J. Cell. Physiol. 228: 1651–1657, 2013. © 2013 Wiley Periodicals, Inc.     

Bidirectional cross talk between patient‐derived melanoma and cancer‐associated fibroblasts promotes invasion and proliferation

Tumor–stroma interactions are critical for epithelial‐derived tumors, and among the stromal cell types, cancer‐associated fibroblasts (CAFs) exhibit multiple functions that fuel growth, dissemination, and drug resistance. However, these interactions remain insufficiently characterized in non‐epithelial tumors such as malignant melanoma. We generated monocultures of melanoma cells and matching CAFs from patients’ metastatic lesions, distinguished by oncogenic drivers and immunoblotting of characteristic markers. RNA sequencing of CAFs revealed a homogenous epigenetic program that strongly resembled the signatures from epithelial cancers, including enrichment for an epithelial‐to‐mesenchymal transition (EMT). Melanoma CAFs in monoculture displayed robust invasive behavior while patient‐derived melanoma monocultures showed very little invasiveness. Instead, melanoma cells showed increased invasion when co‐cultured with CAFs. In turn, CAFs showed increased proliferation when exposed to melanoma conditioned media (CM), mediated in part by melanoma‐secreted transforming growth factor‐alpha that acted on CAFs via the epidermal growth factor receptor. This study provides evidence that bidirectional interactions between melanoma and CAFs regulate progression of metastatic melanoma.     

Cleavage of Type I Collagen by Fibroblast Activation Protein-α Enhances Class A Scavenger Receptor Mediated Macrophage Adhesion

Pathophysiological conditions such as fibrosis, inflammation, and tumor progression are associated with modification of the extracellular matrix (ECM). These modifications create ligands that differentially interact with cells to promote responses that drive pathological processes. Within the tumor stroma, fibroblasts are activated and increase the expression of type I collagen. In addition, activated fibroblasts specifically express fibroblast activation protein-α (FAP), a post-prolyl peptidase. Although FAP reportedly cleaves type I collagen and contributes to tumor progression, the specific pathophysiologic role of FAP is not clear. In this study, the possibility that FAP-mediated cleavage of type I collagen modulates macrophage interaction with collagen was examined using macrophage adhesion assays. Our results demonstrate that FAP selectively cleaves type I collagen resulting in increased macrophage adhesion. Increased macrophage adhesion to FAP-cleaved collagen was not affected by inhibiting integrin-mediated interactions, but was abolished in macrophages lacking the class A scavenger receptor (SR-A/CD204). Further, SR-A expressing macrophages localize with activated fibroblasts in breast tumors of MMTV-PyMT mice. Together, these results demonstrate that FAP-cleaved collagen is a substrate for SR-A-dependent macrophage adhesion, and suggest that by modifying the ECM, FAP plays a novel role in mediating communication between activated fibroblasts and macrophages.     

Oncogenes and inflammation rewire host energy metabolism in the tumor microenvironment

Here, we developed a model system to evaluate the metabolic effects of oncogene(s) on the host microenvironment. A matched set of “normal” and oncogenically transformed epithelial cell lines were co-cultured with human fibroblasts, to determine the “bystander” effects of oncogenes on stromal cells. ROS production and glucose uptake were measured by FACS analysis. In addition, expression of a panel of metabolic protein biomarkers (Caveolin-1, MCT1, and MCT4) was analyzed in parallel. Interestingly, oncogene activation in cancer cells was sufficient to induce the metabolic reprogramming of cancer-associated fibroblasts toward glycolysis, via oxidative stress. Evidence for “metabolic symbiosis” between oxidative cancer cells and glycolytic fibroblasts was provided by MCT1/4 immunostaining. As such, oncogenes drive the establishment of a stromal-epithelial “lactate-shuttle”, to fuel the anabolic growth of cancer cells. Similar results were obtained with two divergent oncogenes (RAS and NFκB), indicating that ROS production and inflammation metabolically converge on the tumor stroma, driving glycolysis and upregulation of MCT4. These findings make stromal MCT4 an attractive target for new drug discovery, as MCT4 is a shared endpoint for the metabolic effects of many oncogenic stimuli. Thus, diverse oncogenes stimulate a common metabolic response in the tumor stroma. Conversely, we also show that fibroblasts protect cancer cells against oncogenic stress and senescence by reducing ROS production in tumor cells. Ras-transformed cells were also able to metabolically reprogram normal adjacent epithelia, indicating that cancer cells can use either fibroblasts or epithelial cells as “partners” for metabolic symbiosis. The antioxidant N-acetyl-cysteine (NAC) selectively halted mitochondrial biogenesis in Ras-transformed cells, but not in normal epithelia. NAC also blocked stromal induction of MCT4, indicating that NAC effectively functions as an “MCT4 inhibitor”. Taken together, our data provide new strategies for achieving more effective anticancer therapy. We conclude that oncogenes enable cancer cells to behave as selfish “metabolic parasites”, like foreign organisms (bacteria, fungi, viruses). Thus, we should consider treating cancer like an infectious disease, with new classes of metabolically targeted “antibiotics” to selectively starve cancer cells. Our results provide new support for the “seed and soil” hypothesis, which was first proposed in 1889 by the English surgeon, Stephen Paget.     

Ketone bodies and two-compartment tumor metabolism: Stromal ketone production fuels mitochondrial biogenesis in epithelial cancer cells

We have previously suggested that ketone body metabolism is critical for tumor progression and metastasis. Here, using a co-culture system employing human breast cancer cells (MCF7) and hTERT-immortalized fibroblasts, we provide new evidence to directly support this hypothesis. More specifically, we show that the enzymes required for ketone body production are highly upregulated within cancer-associated fibroblasts. This appears to be mechanistically controlled by the stromal expression of caveolin-1 (Cav-1) and/or serum starvation. In addition, treatment with ketone bodies (such as 3-hydroxy-butyrate, and/or butanediol) is sufficient to drive mitochondrial biogenesis in human breast cancer cells. This observation was also validated by unbiased proteomic analysis. Interestingly, an MCT1 inhibitor was sufficient to block the onset of mitochondrial biogenesis in human breast cancer cells, suggesting a possible avenue for anticancer therapy. Finally, using human breast cancer tumor samples, we directly confirmed that the enzymes associated with ketone body production (HMGCS2, HMGCL and BDH1) were preferentially expressed in the tumor stroma. Conversely, enzymes associated with ketone re-utilization (ACAT1) and mitochondrial biogenesis (HSP60) were selectively associated with the epithelial tumor cell compartment. Our current findings are consistent with the “two-compartment tumor metabolism” model. Furthermore, they suggest that we should target ketone body metabolism as a new area for drug discovery, for the prevention and treatment of human cancers.     

Ketone bodies and two-compartment tumor metabolism: Stromal ketone production fuels mitochondrial biogenesis in epithelial cancer cells

We have previously suggested that ketone body metabolism is critical for tumor progression and metastasis. Here, using a co-culture system employing human breast cancer cells (MCF7) and hTERT-immortalized fibroblasts, we provide new evidence to directly support this hypothesis. More specifically, we show that the enzymes required for ketone body production are highly upregulated within cancer-associated fibroblasts. This appears to be mechanistically controlled by the stromal expression of caveolin-1 (Cav-1) and/or serum starvation. In addition, treatment with ketone bodies (such as 3-hydroxy-butyrate, and/or butanediol) is sufficient to drive mitochondrial biogenesis in human breast cancer cells. This observation was also validated by unbiased proteomic analysis. Interestingly, an MCT1 inhibitor was sufficient to block the onset of mitochondrial biogenesis in human breast cancer cells, suggesting a possible avenue for anticancer therapy. Finally, using human breast cancer tumor samples, we directly confirmed that the enzymes associated with ketone body production (HMGCS2, HMGCL and BDH1) were preferentially expressed in the tumor stroma. Conversely, enzymes associated with ketone re-utilization (ACAT1) and mitochondrial biogenesis (HSP60) were selectively associated with the epithelial tumor cell compartment. Our current findings are consistent with the “two-compartment tumor metabolism” model. Furthermore, they suggest that we should target ketone body metabolism as a new area for drug discovery, for the prevention and treatment of human cancers.     

Understanding the Impact of 2D and 3D Fibroblast Cultures on In Vitro Breast Cancer Models

The utilization of 3D, physiologically relevant in vitro cancer models to investigate complex interactions between tumor and stroma has been increasing. Prior work has generally focused on the cancer cells and, the role of fibroblast culture conditions on tumor-stromal cell interactions is still largely unknown. Here, we focus on the stroma by comparing functional behaviors of human mammary fibroblasts (HMFs) cultured in 2D and 3D and their effects on the invasive progression of breast cancer cells (MCF10DCIS.com). We identified increased levels of several paracrine factors from HMFs cultured in 3D conditions that drive the invasive transition. Using a microscale co-culture model with improved compartmentalization and sensitivity, we demonstrated that HMFs cultured in 3D intensify the promotion of the invasive progression through the HGF/c-Met interaction. This study highlights the importance of the 3D stromal microenvironment in the development of multiple cell type in vitro cancer models.     

Life ins't flat: Taking cancer biology to the next dimension

Classically, most cell culture experiments have been performed under adherent 2D conditions. Cells in the human body grow within an organized 3D matrix, surrounded by other cells. The behavior of individual cells is controlled through their interactions with their immediate neighbors and the extracellular matrix. The complex summation of these multiple signals determines whether a given cell undergoes differentiation, apoptosis, proliferation, or invasion. In 2D culture many of these complex interactions are lost. As a result, there are a growing number of studies which report differences in phenotype, cellular signaling, cell migration, and drug responses when the same cells are grown under 2D or 3D culture conditions. One potential application of these techniques is to anticancer drug discovery, which has long been hampered by the lack of good preclinical models. Compounds with good antitumor activity in 2D cell culture models often fail to translate into the clinic. Here we suggest that the response of cancer cells to drugs is determined in part by the 3D tumor microenvironment and discuss models to re-create the 3D tumor microenvironment in vitro. It is likely that the adoption of these and other 3D models will allow us to more closely re-create the behavior of the tumor in vivo which may lead to identifying better anticancer drug candidates at an earlier stage of development.     

Tumor-associated fibroblasts (part I): Active stromal participants in tumor development and progression?

Phenotypic and functional characteristics of tumor associated fibroblasts (TAF) in contrast to normal fibroblasts are reviewed in this first synopsis (part I). Terms as tumor stroma, desmo-plasia, TAF, myofibroblast, and fetal-type fibroblast are defined, and experimental systems to study heterologous cell interactions are presented. While we only start to gather information on the genotype of TAF, a broad range of data deals with the expression profile of these cells, covering e.g. ECM and ECM-modulating molecules, growth factors and cytokines. Summarizing the recent state of knowledge indicates that TAF provide sources for tumor diagnosis and therapy, that have to be further defined in an organ-specific approach in terms of the functional impact on the tumor cell and its environment (see part II).     

Regulation of IL-6 and IL-8 production by reciprocal cell-to-cell interactions between tumor cells and stromal fibroblasts through IL-1α in ameloblastoma

Ameloblastoma is an odontogenic benign tumor that occurs in the jawbone, which invades bone and reoccurs locally. This tumor is treated by wide surgical excision and causes various problems, including changes in facial countenance and mastication disorders. Ameloblastomas have abundant tumor stroma, including fibroblasts and immune cells. Although cell-to-cell interactions are considered to be involved in the pathogenesis of many diseases, intercellular communications in ameloblastoma have not been fully investigated. In this study, we examined interactions between tumor cells and stromal fibroblasts via soluble factors in ameloblastoma.     

Carcinoma-associated fibroblasts are a rate-limiting determinant for tumour progression

Tumours are highly complex tissues composed of carcinoma cells and surrounding stroma, which is constructed by various different types of mesenchymal cells and an extracellular matrix (ECM). Carcinoma-associated fibroblasts (CAFs), which consist of both fibroblasts and myofibroblasts, are frequently observed in the stroma of human carcinomas, and their presence in large numbers is often associated with the development of high-grade malignancies and poor prognoses. Moreover, in human tumour xenograft models, CAFs extracted from the tumour are more capable of promoting tumour growth through their interactions with carcinoma cells when compared to those isolated from non-cancerous stroma. Taken together, these observations strongly suggest that CAFs actively contribute to tumour progression. In this review we highlight the emerging roles of these cells in promoting tumourigenesis, and we discuss the molecular mechanisms underlying their tumour-promoting capabilities and their cellular origin.     

Components of the hepatocellular carcinoma microenvironment and their role in tumor progression

This review summarizes recently published data on the mechanisms of tumor cell interaction with the tumor microenvironment. Tumor stroma influences the processes of hepatocarcinogenesis, epithelial-to-mesenchymal transition, invasion, and metastasis. The tumor microenvironment includes both cellular and noncellular components. Main cellular components of hepatocellular carcinoma (HCC) stroma are tumor-associated fibroblasts, hepatic stellate cells, immune cells, and endothelial cells that produce extracellular components of tumor microenvironment such as extracellular matrix, various proteins, proteolytic enzymes, growth factors, and cytokines. The noncellular components of the stroma modulate signaling pathways in tumor cells and stimulate invasion and metastasis. The tumor microenvironment composition and organization can serve as prognostic factors in HCC pathogenesis. Current approaches in HCC targeted therapy are aimed at creating efficient strategies for interrupting tumor interactions with the stroma. Recent data on the composition and role of the microenvironment in HCC pathogenesis, as well as new developments in antitumor drug design are discussed.