Hypoxic Cancer Stem Cells Research Articles

Lactate promotes metastasis of normoxic colorectal cancer stem cells through PGC-1α-mediated oxidative phosphorylation

Uneven oxygen supply in solid tumors leads to hypoxic and normoxic regions. Hypoxic cells exhibit increased secretion of lactate, which creates an acidic tumor microenvironment (TME). This acidic TME is positively associated with tumor metastasis. Despite the increased metastatic capacity of hypoxic cells, they are located relatively further away from the blood vessels and have limited access to the circulatory system. Studies have shown that cancer stem cells (CSCs) are enriched for tumor metastasis-initiating cells and generally undergo aerobic respiration, which could be enhanced by lactate. We therefore hypothesized that TME-derived lactate may promote the metastasis of normoxic CSCs. In the present study, the abundance of hypoxic and normoxic CSCs was analyzed in primary CRC tumors. It was found that the proportion of normoxic CSCs was positively associated with tumor stage. Using two human CRC cell lines, LoVo and SW480, and a patient-derived xenograft (XhCRC), it was found that treatment with lactate promoted normoxic CSC metastasis. Metabolism analysis indicated that, upon treatment with lactate, oxidative phosphorylation (OXPHOS) activity in normoxic CSCs was enhanced, whereas hypoxic CSCs were rarely altered. At the molecular level, the expression of peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α), a master regulator of lactate oxidation, was found to be elevated in normoxic CSCs. Furthermore, PGC-1α knockdown markedly reduced the metastatic potential of normoxic CSCs. Notably, both the PGC-1α-mediated OXPHOS activity and metastatic potential were impaired when hypoxia-inducible factor-1α (HIF-1α) was activated in normoxic CSCs. Together, these findings provide a therapeutic strategy against tumor metastasis through the targeting of PGC-1α and, thus, the suppression of lactate-feeding OXPHOS in normoxic CSCs may improve the therapeutic benefit of patients with cancer, particularly CRC.

Abstract 5539: Mesenchymal stem cell altruism mediates a novel HMGB1/NKG2D immune response in oral cancer

Abstract Background: Although cancer immunotherapy is now becoming a standard treatment method in oral cancer, but only about 20% cases respond to checkpoint inhibitors [1]. For example, Pembrolizumab a PDL1 inhibitor has not been showing good results to target hypoxic cancer stem cells (CSC). It may be attributed to the fact that immune editing mechanism is suppressed in cancer due to deficient function of immune cells like NK cells, T cells[2]. Thus, immune privileged tumor microenvironment may pose a major challenge to immunotherapyagainst CSCs. In the hypoxic tumor microenvironment (TME), CSCs interacts withmesenchymal stem cells (MSCs)and reprogram these cells to pro-tumorigenic cells. The interaction between CSC and BM-MSC may confer a stemness state to BM-MSCs, called Altruistic stemness; a mechanism where individual fitness is sacrificed for group fitness [3]. We speculate thatBCG internalized MSC may exploit the CSC-MSC interaction to target CSCs in the hypoxic niche. Methods: 1. ABCG2+ CSCs were infected with BM-MSC+BCG. 2. Acid-fast bacilli staining demonstrated the presence of BCG intracellular to BM-MSCs. The cells were lysed, and then subjected to CFU assay to quantify BCG colonies to confirm BCG internaliztion. 3. In vitro, in a Boyden chamber assay, BCG-MSCs and SCC-25 oral cancer cell line derived ABCG2+ CSCs were grown. Also, NK cells, T reg cells and macrophages were grown in the bottom chamber of Bodyen chamber assay. In this manner, NKG2D+mediated immune response can be evaluated. 4. After a week of culture, ABCG2+ cells were recovered from the bottom chamber, and ELISA was performed to detect HMGB1 and p53. The number of NKG2D+ NK cells, F/80 macrophages and CD8+ T cells were detected by flow cytometry. Results: We found that BCG+BM-MSC delivery to ABCG2+oral CSCs led to a marked immune response characterized by increase NKG2D+NK cells, F4/80 macrophages and CD8+ T cells and decrease in T-regcells(CD4+/FoxP3/CD25-) in the Boyden chamber assay. We also found that BCG-infected MSCs underwent stem cell altruism, and secreted HMGB1. Inhibition of HMGB1 led to marked reduction in NKG2D+ NK cells. Conclusions: These results indicate the potential activation of the NKG2D-mediated immune response by MSC derived altruistic stem cells. Overall our findings suggest that mesenchymal stem cell altruism mediated HMGB1/NKGD2 immune response in oral cancer can serve as a novel immunotherapeutic technique.

Two-photon fluorescent probe for hypoxic cancer stem cells by responding to endogenous nitroreductase

A two-photon fluorescent probe to detect the NTR in 3D cultured-cancer stem cells and monitor the hypoxic microenvironment in vitro. This novel probe was hoped to apply for disease-relevant hypoxia detection in the biomedical research fields.

Targeting hypoxic cancer stem cells (CSCs) with Doxycycline: Implications for optimizing anti-angiogenic therapy.

Here, we report new mechanistic insight into how chronic hypoxia increases ‘stemness’ in cancer cells. Using chemical inhibitors, we provide direct experimental evidence that ROS production and mitochondrial biogenesis are both required for the hypoxia-induced propagation of CSCs. More specifically, we show that hypoxic CSCs can be effectively targeted with i) simple mitochondrial anti-oxidants (Mito-TEMPO) and/or ii) inhibitors of mitochondrial biogenesis (Doxycycline). In this context, we discuss the idea that mitochondrial biogenesis itself may be a primary driver of “stemness” in hypoxic cancer cells, with metabolic links to fatty acid oxidation (FAO). As Doxycycline is an FDA-approved drug, we propose that it could be re-purposed to target hypoxic CSCs, either alone or in combination with chemotherapy, i.e., Paclitaxel. For example, we demonstrate that Doxycycline effectively targets the sub-population of hypoxia-induced CSCs that are Paclitaxel-resistant, overcoming hypoxia-induced drug-resistance. Finally, anti-angiogenic therapy often induces tumor hypoxia, allowing CSCs to survive and propagate, ultimately driving tumor progression. Therefore, we suggest that Doxycycline could be used in combination with anti-angiogenic agents, to actively prevent or minimize hypoxia-induced treatment failure. In direct support of this assertion, Paclitaxel is already known to behave as an angiogenesis inhibitor.

Serine Synthesis Helps Hypoxic Cancer Stem Cells Regulate Redox.

Phosphoglycerate dehydrogenase (PHGDH) is the metabolic enzyme responsible for shunting the glycolytic intermediate 3-phosphoglycerate to the serine synthesis pathway. In breast cancer and several other types of cancer, increased PHGDH expression is associated with patient mortality. Early studies focused on the role of PHGDH in promoting cell proliferation in the small percentage of breast cancers with PHGDH gene amplification. However, recent studies have revealed a critical role for PHGDH and downstream enzymes of the serine synthesis pathway and one carbon metabolism in NADPH production and the maintenance of redox homeostasis, which are required for enrichment of breast cancer stem cells in response to hypoxia or chemotherapy. These results provide a mechanism for PHGDH overexpression in breast cancers in which PHGDH is not amplified and have implications for improving the response of triple-negative breast cancers to cytotoxic chemotherapy. Cancer Res; 76(22); 6458-62. ©2016 AACR.

Synergistic role of three dimensional niche and hypoxia on conservation of cancer stem cell phenotype

Hypoxia is a pathalogical condition in which tissues are deprived of adequate oxygen supply. The hypoxia effect on tumors has a critically important role on maintenance of cancer stem cell phenotype. The aim of this study is to investigate the effects of hypoxia on cancer stem cells on three dimensional (3D) in vitro culture models. Osteosarcoma stem cells characterized by CD133 surface protein were isolated from osteosarcoma cell line (SaOS-2) by magnetic-activated cell sorting (MACS) technique. Isolated CD133+ and CD133− cells were cultivated under hypoxic (1% O2) and normoxic conditions (21% O2) for 3 days. For the 3D model, bacterial cellulose scaffold was used as the culture substrate. 3D morphologies of cells were examined by scanning electron microscopy (SEM); RT-PCR and immunocytochemistry staining were used to demonstrate conservation of the cancer stem cell phenotype in 3D environment under hypoxic conditions. Cell viability was shown by MTT assay on 3. and 7. culture days. This study is seen as an introduction to develop a 3D hypoxic cancer stem cell based tumor model to study CSC behavior and tumor genesis in vitro.

SU‐E‐J‐95: Predicting Treatment Outcomes for Prostate Cancer: Irradiation Responses of Prostate Cancer Stem Cells

Purpose:Most prostate cancers are slow‐growing diseases but normally require much higher doses (80Gy) with conventional fractionation radiotherapy, comparing to other more aggressive cancers. This study is to disclose the radiobiological basis of this discrepancy by proposing the concept of prostate cancer stem cells (CSCs) and examining their specific irradiation responses.Methods:There are overwhelming evidences that CSC may keep their stemness, e.g. the competency of cell differentiation, in hypoxic microenvironments and hence become radiation resistive, though the probability is tiny for aggressiveness cancers. Tumor hypoxia used to be considered as an independent reason for poor treatment outcomes, and recent evidences showed that even prostate cancers were also hypoxic though they are very slow‐growing. In addition, to achieve comparable outcomes to other much more aggressive cancers, much higher doses (rather than lower doses) are always needed for prostate cancers, regardless of its non‐aggressiveness. All these abnormal facts can only be possibly interpreted by the irradiation responses characteristics of prostate CSCs.Results:Both normal cancer cells (NCCs) and CSCs exiting in tumors, in which NCCs are mainly for symptoms whereas killing all CSCs achieves disease‐free. Since prostate cancers are slow‐growing, the hypoxia in prostate cancers cannot possibly from NCCs, thus it is caused by hypoxic CSCs. However, single hypoxic cell cannot be imaged due to limitation of imaging techniques, unless a large group of hypoxic cells exist together, thus most of CSCs in prostate cancers are virtually hypoxic, i.e. not in working mode because CSCs in proliferating mode have to be normoxic, and this explains why prostate cancers are unaggressive.Conclusion:The fractional dose in conventional radiotherapy (∼2Gy) could only kill NCCs and CSCs in proliferating modes, whereas most CSCs survived fractional treatments since they were hypoxic, thus to eliminate all CSCs and achieve disease‐free, much more fractionations are needed.

Are cancer stem cells concentrated in more alkaline hypoxic regions of tumors?

We wonder if the most viable hypoxic cancer stem cells concentrate in more alkaline regions of tumors, favoring their survival and evolution. Alternately, or in addition, do some cancer stem cells themselves maintain a more alkaline internal environment, achieving the same result. Based upon the response of cultured cells, including stem cells, to a certain degree of hypoxia and of most if not all proliferating cells to a somewhat more alkaline ambient and especially endogenous pH, their survival and proliferation should be favored. The broad outline of the argument, abstracted from a number of the available examples is developed: that the survival of cancer stem cells is favored by these conditions, contributing to their limited response to various therapies and their subsequent development of more malignant properties.

Hypoxic Tumor Microenvironment and Cancer Cell Differentiation

Hypoxia or oxygen deficiency is a salient feature of solid tumors. Hypoxic tumors are often resistant to conventional cancer therapies, and tumor hypoxia correlates with advanced stages of malignancy. Hypoxic tumors appear to be poorly differentiated. Increasing evidence suggests that hypoxia has the potential to inhibit tumor cell differentiation and thus plays a direct role in the maintenance of cancer stem cells. Studies have also shown that hypoxia blocks differentiation of mesenchymal stem/progenitor cells, a potential source of tumor-associated stromal cells. It is therefore likely that hypoxia may have a profound impact on the evolution of the tumor stromal microenvironment. These observations have led to the emergence of a novel paradigm for a role of hypoxia in facilitating tumor progression. Hypoxia may help create a microenvironment enriched in poorly differentiated tumor cells and undifferentiated stromal cells. Such an undifferentiated hypoxic microenvironment may provide essential cellular interactions and environmental signals for the preferential maintenance of cancer stem cells. This hypothesis suggests that effectively targeting hypoxic cancer stem cells is a key to successful tumor control.