Oxygen supply and diffusion into tissues are necessary for survival. The oxygen partial pressure (pO2), which is a key component of the physiological state of an organ, results from the balance between oxygen delivery and its consumption. In mammals, oxygen is transported by red blood cells circulating in a well-organized vasculature. Oxygen delivery is dependent on the metabolic requirements and functional status of each organ. Consequently, in a physiological condition, organ and tissue are characterized by their own unique ‘tissue normoxia’ or ‘physioxia’ status. Tissue oxygenation is severely disturbed during pathological conditions such as cancer, diabetes, coronary heart disease, stroke, etc., which are associated with decrease in pO2, i.e. ‘hypoxia’. In this review, we present an array of methods currently used for assessing tissue oxygenation. We show that hypoxia is marked during tumour development and has strong consequences for oxygenation and its influence upon chemotherapy efficiency. Then we compare this to physiological pO2 values of human organs. Finally we evaluate consequences of physioxia on cell activity and its molecular modulations. More importantly we emphasize the discrepancy between in vivo and in vitro tissue and cells oxygen status which can have detrimental effects on experimental outcome. It appears that the values corresponding to the physioxia are ranging between 11% and 1% O2 whereas current in vitro experimentations are usually performed in 19.95% O2, an artificial context as far as oxygen balance is concerned. It is important to realize that most of the experiments performed in so-called normoxia might be dangerously misleading.

Non-thermal plasma (NTP) is generated by ionizing neutral gas molecules/atoms leading to a highly reactive gas at ambient temperature containing excited molecules, reactive species and generating transient electric fields. Given its potential to interact with tissue or cells without a significant temperature increase, NTP appears as a promising approach for the treatment of various diseases including cancer. The aim of our study was to evaluate the interest of NTP both in vitro and in vivo. To this end, we evaluated the antitumor activity of NTP in vitro on two human cancer cell lines (glioblastoma U87MG and colorectal carcinoma HCT-116). Our data showed that NTP generated a large amount of reactive oxygen species (ROS), leading to the formation of DNA damages. This resulted in a multiphase cell cycle arrest and a subsequent apoptosis induction. In addition, in vivo experiments on U87MG bearing mice showed that NTP induced a reduction of bioluminescence and tumor volume as compared to nontreated mice. An induction of apoptosis was also observed together with an accumulation of cells in S phase of the cell cycle suggesting an arrest of tumor proliferation. In conclusion, we demonstrated here that the potential of NTP to generate ROS renders this strategy particularly promising in the context of tumor treatment.Plasma, considered as the fourth state of the matter, has already a broad range of applications in industry 1 and in medicine.2,3 Recently, the development of a new kind of plasma devices generating non-thermal plasma (NTP) has extended their potential applications especially in biology and medicine.4-6 NTP with a temperature less than 40 C at the point of treatment is a partially ionized media generated by excitation of a gas mixture in a discharge reactor. It contains electrons, positive/negative ions, radicals, various excited molecules, energetic photons (UV) and generates transient electric field. Given these interesting properties, potential applications are blood coagulation, 7 skin decontamination without significant skin damages, 8 wound healing, 9 and tumor treatment. 10The dose of NTP delivered is an important parameter to induce biological responses in tissue and cells.8 Indeed, low dose of plasma (<1 J cm À2) is able to induce inactivation of bacteria and proliferation of cells, 11,12 while higher dose (>7 J cm À2) can induce apoptosis of tumor cells including melanoma, breast cancer cells and hepatocellular carcinoma. [13][14][15][16][17] Sensenig et al. and Kim et al. have suggested that DNA damages and reactive species generated by plasma could be the main causes of this effect.14,18 In a recent work, Kalghatgi et al. showed that a low dose of NTP enhances endothelial cell proliferation due to the reactive oxygen species (ROS) generated by NTP mediated FGF-2 release.11 On non-tumorigenic breast epithelial cell line, NTP was also recently described to induce DNA damage leading to apoptosis due to the formation of intracellular ROS.19 ROS are potentially harmful on cellular metabolism by affec...

-The tumor microenvironment is a complex system, playing an important role in tumor development and progression. Besides cellular stromal components, extracellular matrix fibers, cytokines, and other metabolic mediators are also involved. In this review we outline the potential role of hypoxia, a major feature of most solid tumors, within the tumor microenvironment and how it contributes to immune resistance and immune suppression/tolerance and can be detrimental to antitumor effector cell functions. We also outline how hypoxic stress influences immunosuppressive pathways involving macrophages, myeloid-derived suppressor cells, T regulatory cells, and immune checkpoints and how it may confer tumor resistance. Finally, we discuss how microenvironmental hypoxia poses both obstacles and opportunities for new therapeutic immune interventions.hypoxia; hypoxia-inducible factor; tumor microenvironment; myeloid cells; lymphoid cells; immune suppression; cancer stem cells; programmed death-ligand 1; epithelial-mesenchymal transition; circulating tumor cells; autophagy and antitumor immune response IT HAS BECOME INCREASINGLY apparent that malignant cells exist in a complex cellular and extracellular microenvironment that plays key roles in the initiation and maintenance of the malignant phenotype. Among the microenvironmental factors that play a dominant role in neoplasia, hypoxia is believed to be one of the most relevant in the neoplastic response of tumor cells. It is widely appreciated that the majority of malignancies create a hostile hypoxic microenvironment that can hamper cellmediated immunity and dampen the efficacy of the immune response. Poorly vascularized and hypoxic zones inside solid tumors contribute to immune tolerance of tumor cells by impeding the homing of immunocompetent cells into tumors and inhibiting their antitumor efficacy. Several regulatory mechanisms can occur concurrently within the hypoxic tumor microenvironment, resulting in multiple redundant levels of immune cell plasticity and suppression, tumor plasticity, and functional heterogeneity. Hypoxic stress clearly plays a crucial role in tumor promotion and immune escape by controlling angiogenesis and favoring immune suppression and tumor resistance. Like other therapeutic attempts, immunotherapy is heavily hampered by the morphologically aberrant tumor microvasculature, preventing migration of immune effector cells into established tumors. Many strategies are emerging for changing the immunosuppressive nature of the tumor to a microenvironment able to support antitumor immunity. The identification of ways to induce a permissive and less hostile tumor microenvironment to avoid tumor resistance and immune suppression is of major interest and pertinence. Hypoxia as an Integral Component of the Tumor MicroenvironmentAll life on Earth depends on O 2 , and all physiological and pathological processes of a living cell rely principally on O 2 (103). Hypoxia is characterized by lack of O 2 , and hypoxic tissues are inadequately oxygenated (107). A p...