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According to the World Health Organization (WHO), cancer is one of main causes of death worldwide, with 8.2 million people dying from this disease in 2012. Because of this, new forms of treatments or improvement of current treatments are crucial. In this regard, Photodynamic therapy (PDT) has been used to successfully treat cancers that can be easily accessed externally or by fibre-optic endoscopes, such as skin, bladder and esophagus cancers. In addition, this therapy can used alongside radiotherapy and chemotherapy in order to kill cancer cells. The main problem in implementing PDT is penetration of visible light deeper than 10 mm in tissues, due to scattering and absorption by tissue chromophores. Unfortunately, this excludes several internal organs affected by cancer. Another issue in this regard is the use of a selective cancer cell-photosensitizing compound. Nevertheless, several groups have recently developed scintillation nanoparticles, which can be stimulated by X-rays, thereby making this a possible solution for light production in deeper tissues. Alternative approaches have also been developed, such as photosensitizer structure modifications and cell membrane permeabilizing agents. In this context, certain channels lead to transitory plasma membrane permeability changes, such as pannexin, connexin hemmichannels, TRPV1-4 and P2×7, which allow for the non-selective passage of molecules up to 1,000 Da. Herein, we discuss the particular case of the P2×7 receptor-associated pore as a drug delivery system for hydrophilic substances to be applied in PDT, which could also be carried out with other channels. Methylene blue (MB) is a low cost dye used as a prototype photosensitizer, approved for clinical use in several other clinical conditions, as well as photodynamic therapy for fungi infections.

The second-generation photosensitizer methylene blue (MB) exhibits photochemical and photophysical properties suitable for photodynamic therapy (PDT)-based cancer treatment. However, the clinical application of MB is limited because of its high hydrophilicity, which hinders its penetration into tumor tissues. Therefore, new methods to improve the entry of MB into the cytoplasm of target cells are necessary. Because MB has a mass of 319 Da, transient pores on the plasma membrane, such as the pore induced by the P2X7 receptor (P2X7R) that allows the passage of molecules up to 900 Da, could be used. Using MTT viability assays, flow cytometry experiments, and fluorescence microscopy, we evaluated the toxicity and phototoxicity of MB and potentiation effects of ATP and MB on cell death processes in the J774 cell line (via a P2X7-associated pore). We observed that treatment with 5 μM MB for 15 min promoted the rate of entry of MB into the cytoplasm to 4.7 %. However, treatment with 5 μM MB and 1 mM ATP for the same amount of time increased this rate to 90.2 %. However, this effect was inhibited by pretreatment with a P2X7 antagonist. We used peritoneal macrophages and a cell line that does not express P2X7R as controls. These cells were more resistant to PDT with MB under the same experimental conditions. Taken together, these results suggest the use of the pore associated with P2X7R as a drug delivery system to increase the passage of hydrophilic drugs into cells that express this receptor, thus facilitating PDT.

Human pregnancy poses an immunological paradox: at the fetal-maternal interface, semi-allogeneic fetal extravillous trophoblasts (EVT) invade the uterine mucosa without being rejected by the maternal immune system. HLA-G is a nonclassical MHC class I molecule specifically expressed on the surface of EVT and is believed to be a key to fetus-induced immune tolerance. However, the EVT-specific expression of HLA-G is still poorly understood. A novel enhancer more than 10 kb upstream of HLA-G, Enhancer L, was discovered via dissection of the HLA-G locus using a Massively Parallel Reporter Assay (MPRA). DNase I Hypersensitive Site (DHS) mapping, Chromosome Conformation Capture (3C) and reporter gene assays established Enhancer L as a cell type-specific enhancer that loops into the HLA-G classical promoter. Strikingly, deletion of Enhancer L using a CRISPR/Cas9 dual guide approach results in complete ablation of HLA-G expression. Saturation mutagenesis of Enhancer L revealed the existence of motifs for transcription factors paramount in trophoblast development. Two of them, GATA2 and CEBPB, associate with Enhancer L and the HLA-G classical promoter, and are absolutely required for HLA-G expression. Interestingly, progesterone upregulates HLA-G, as well as GATA2, via a nonclassical membrane progesterone receptor complex in trophoblasts. These findings shed light on the mechanism by which HLA-G is specifically expressed in invasive trophoblasts during pregnancy.

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