Abstract
Photodynamic therapy (PDT) has drawn great interest in recent years mainly due to its low side effects and few drug resistances. Nevertheless, one of the issues of PDT is the need for oxygen to induce a photodynamic effect. Tumours often have low oxygen concentrations, related to the abnormal structure of the microvessels leading to an ineffective blood distribution. Moreover, PDT consumes O2. In order to improve the oxygenation of tumour or decrease hypoxia, different strategies are developed and are described in this review: (1) The use of O2 vehicle; (2) the modification of the tumour microenvironment (TME); (3) combining other therapies with PDT; (4) hypoxia-independent PDT; (5) hypoxia-dependent PDT and (6) fractional PDT.
Highlights
In the case of cancer, tissue hypoxia is a key feature of virtually all solid tumours [1]
Success of Photodynamic therapy (PDT) requires that the PS incorporate preferentially into the tumor cell, that the number of photons be correctly evaluated in order to excite a majority of the PS molecules, and that there be enough O2 to induce the photo-oxidation process [7]
The authors showed that the production of 1O2 was independent of the level of O2 (1 or 21 %) since almost no change was observed between the two conditions contrary to others PS such as verteporfin and methylene blue (MB)
Summary
In the case of cancer, tissue hypoxia is a key feature of virtually all solid tumours [1]. In vivo, reduced oxygenation induces a lack of nutrients and growth factors, increased acidosis and production of products coming from the close necrotic area. This leads to alteration of cells and cell-matrix interaction and even sometimes to cell death. When the oxygen concentration in the medium is not high enough, the photodamage is reduced or even no photodynamic reaction occurs at all [8]. These spare hypoxic cells can induce the regrowth of the tumor. We chose to divide them onto six strategies developed in the literature to fight hypoxia for an enhancement of PDT: (1) The use of O2 vehicles; (2) the modification of the tumour microenvironment (TME); (3) combining other therapies with PDT; (4) hypoxia-independent PDT; (5) hypoxia-dependent PDT and (6) fractional PDT
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