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An Introduction to Bone Marrow Transplantation and Processing
Published in Adrian P. Gee, BONE MARROW PROCESSING and PURGING, 2020
Numerous animal experiments demonstrate that the possibility of eliminating an experimentally induced tumor relates directly to the total dose of radiation administered. According to this concept, the chance of eradicating disease depends upon the initial tumor mass and the number of log kill of tumor cells achieved by a given dose of radiation or chemotherapy. It is therefore advantageous to start with a reduced tumor size, in order to achieve a log kill of a greater number of tumor cells than existed at the start of treatment. Limitations to these theoretical models are the nonhemopoietic organ damage sustained with high-dose chemoor radiotherapy, repair by sublethally damaged tumor cells, and protection of tumor cells from lethal damage due to the oxygen effect. The oxygen effect describes the protection by anoxia of poorly vascularized tumor cells from the normal radiosensitization conferred by oxygen.10 The principles of radiobiology as applied to BMT have been reviewed elsewhere.11
Modifications of Cellular Radiation Damage
Published in Kedar N. Prasad, Handbook of RADIOBIOLOGY, 2020
One of the most general and best-known modifying agents of radiation damage is molecular oxygen. Its ability to potentiate radiation response is called the oxygen effect, which is expressed in terms of the oxygen enhancement ratio (OER):
Relative Radiosensitivities of Cells, Tissues, and Organs
Published in George W. Casarett, Radiation Histopathology, 2019
Many of the concepts concerning the nature of radiation action on cells and the radiation sensitivity of cells are derived from experimental studies in vivo and in vitro that involve variable environmental conditions which change or influence the relative radiosensitivity of cells. It is important therefore to distinguish between the essential radiosensitivity of a cell which is based on its inherent constitution and normal environment, and the conditional radiosensitivity of a cell in which changes in environmental or other factors from the normal may alter the relative sensitivity to limited degrees. For example, a cell that has a high essential radiosensitivity may be made somewhat more sensitive or less sensitive to a given amount of radiation, in terms of lethal effect, chromosome damage, mutagenic effect, and some biochemical effects, if it is irradiated, respectively, under conditions of abnormally high oxygen tension or abnormally low oxygen tension. In any case, the cell may be much more sensitive than a cell with high essential radioresistance. This kind of change in conditional radiosensitivity also depends upon the specific ionization of the radiations used or LET. An almost threefold elevation of response has been demonstrated under conditions of high oxygen tension as compared with anoxic conditions, when radiations of low LET have been used, for example, X-rays, gamma rays, or electrons. This oxygen effect is much smaller in the case of radiation of high LET, such as alpha particles or neutrons. The oxygen effect has been observed in both in vivo and in vitro systems.
A preliminary approach in the prediction of orthodontic bone remodeling by coupling experiments, theory and numerical models
Published in Computer Methods in Biomechanics and Biomedical Engineering, 2019
Daniel George, Delphine Wagner, Yves Bolender, Pascal Laheurte, Boris Piotrowski, Paul Didier, Morad Bensidhoum, Valentin Herbert, Camille Spingarn, Yves Rémond
The mechanical force system applied onto the teeth induces a deformation of the PDL. In the compression area, the PDL vascularization is partially occluded causing a decrease in oxygen concentration which is known to increase the proliferation of osteoclasts (Utting et al. 2006). On the other hand, in the tensile zone, the oxygen concentration will increase due to PDL stretching, which is the cause of proliferation of osteoblasts (Arnett et al. 2003). These key factors are assumed to be at the origin of the bone remodeling phenomena in orthodontics. With this understanding of the PDL physiological behavior, the impact of the oxygen effect on the cells’ evolutions is highlighted (George et al. 2018). The phenomena are integrated within a second FE model (FE2) (Spingarn et al. 2018), accounting for the mechanobiological coupling between mechanical forces and cellular activation, in order to determine the initiation of the bone remodeling phenomena and tooth movements.
Hyperthermia with photon radiotherapy is thermoradiobiologically analogous to neutrons for tumors without enhanced normal tissue toxicity
Published in International Journal of Hyperthermia, 2019
Niloy Ranjan Datta, Stephan Bodis
The presence of hypoxic cells within solid tumors is a known limiting factor with low LET radiation (photons and protons). These are best treated with high LET radiation whereby the OER falls to 1.2 at around 200 keV/µm compared with 2.8–3.0 for protons or photons [13,27,35]. However, the lack of oxygen effect with HT offers additional thermoradiobiological advantages in clinical situations with low LET radiation similar to high LET radiation [29]. Thus as proposed by Robinson et al [14], adding HT to low LET radiation provides potentially a viable alternative to heavy particle therapy.
Phage display technology for target determination of small-molecule therapeutics: an update
Published in Expert Opinion on Drug Discovery, 2020
Yoichi Takakusagi, Kaori Takakusagi, Kengo Sakaguchi, Fumio Sugawara
Recently, it has been reported that SQAP has a radiosensitization effect; intravenously administered SQAP increases tumor oxygenation by enhancing oxygen release from the hemoglobin in erythrocytes and tumor perfusion, thereby potentiating the oxygen effect upon ionizing irradiation therapy [47]. Further experiments using the T7 PD and characterizing the target candidates may elucidate the molecular mechanisms underlying the pharmacological effects of SQAP.