Synthesis and photophysical properties of side-chain chlorinated benzo[a]phenoxazinium chlorides

Novel Benzo[a]phenoxazinium Chlorides Functionalized with Sulfonamide Groups as NIR Fluorescent Probes for Vacuole, Endoplasmic Reticulum, and Plasma Membrane Staining

The demand for new fluorophores for different biological target imaging is increasing. Benzo[a]phenoxazine derivatives are fluorochromophores that show promising optical properties for bioimaging, namely fluorescent emission at the NIR of the visible region, where biological samples have minimal fluorescence emission. In this study, six new benzo[a]phenoxazinium chlorides possessing sulfonamide groups at 5-amino-positions were synthesized and their optical and biological properties were tested. Compared with previous probes evaluated using fluorescence microscopy, using different S. cerevisiae strains, these probes, with sulfonamide groups, stained the vacuole membrane and/or the perinuclear membrane of the endoplasmic reticulum with great specificity, with some fluorochromophores capable of even staining the plasma membrane. Thus, the addition of a sulfonamide group to the benzo[a]phenoxazinium core increases their specificity and attributes for the fluorescent labeling of cell applications and fractions, highlighting them as quite valid alternatives to commercially available dyes.

Targeting Lysosomes in Colorectal Cancer: Exploring the Anticancer Activity of a New Benzo[a]phenoxazine Derivative

Colorectal cancer (CRC) has been ranked as one of the cancer types with a higher incidence and one of the most mortal. There are limited therapies available for CRC, which urges the finding of intracellular targets and the discovery of new drugs for innovative therapeutic approaches. In addition to the limited number of effective anticancer agents approved for use in humans, CRC resistance and secondary effects stemming from classical chemotherapy remain a major clinical problem, reinforcing the need for the development of novel drugs. In the recent years, the phenoxazines derivatives, Nile Blue analogues, have been shown to possess anticancer activity, which has created interest in exploring the potential of these compounds as anticancer drugs. In this context, we have synthetized and evaluated the anticancer activity of different benzo[a]phenoxazine derivatives for CRC therapy. Our results revealed that one particular compound, BaP1, displayed promising anticancer activity against CRC cells. We found that BaP1 is selective for CRC cells and reduces cell proliferation, cell survival, and cell migration. We observed that the compound is associated with reactive oxygen species (ROS) generation, accumulates in the lysosomes, and leads to lysosomal membrane permeabilization, cytosolic acidification, and apoptotic cell death. In vivo results using a chicken embryo choriollantoic membrane (CAM) assay showed that BaP1 inhibits tumor growth, angiogenesis, and tumor proliferation. These observations highlight that BaP1 as a very interesting agent to disturb and counteract the important roles of lysosomes in cancer and suggests BaP1 as a promising candidate to be exploited as new anticancer lysosomal-targeted agent, which uses lysosome membrane permeabilization (LMP) as a therapeutic approach in CRC.

Novel Nile Blue Analogue Stains Yeast Vacuolar Membrane, Endoplasmic Reticulum, and Lipid Droplets, Inducing Cell Death through Vacuole Membrane Permeabilization

Phenoxazine derivatives such as Nile Blue analogues are assumed to be increasingly relevant in cell biology due to their fluorescence staining capabilities and antifungal and anticancer activities. However, the mechanisms underlying their effects remain poorly elucidated. Using S. cerevisiae as a eukaryotic model, we found that BaP1, a novel 5- and 9-N-substituted benzo[a]phenoxazine synthesized in our laboratory, when used in low concentrations, accumulates and stains the vacuolar membrane and the endoplasmic reticulum. In contrast, at higher concentrations, BaP1 stains lipid droplets and induces a regulated cell death process mediated by vacuolar membrane permeabilization. BaP1 also induced mitochondrial fragmentation and depolarization but did not lead to ROS accumulation, changes in intracellular Ca²⁺, or loss of plasma membrane integrity. Additionally, our results show that the cell death process is dependent on the vacuolar protease Pep4p and that the vacuole permeabilization results in its translocation from the vacuole to the cytosol. In addition, although nucleic acids are commonly described as targets of benzo[a]phenoxazines, we did not find any alterations at the DNA level. Our observations highlight BaP1 as a promising molecule for pharmacological application, using vacuole membrane permeabilization as a targeted approach.

N-(5-Amino-9H-benzo[a]phenoxazin-9-ylidene)propan-1-aminium chlorides as antifungal agents and NIR fluorescent probes

New benzo[a]phenoxazinium chlorides (λ_emi ≤ 683 nm, Φ_F ≤ 0.24, at pH = 7.4), best MIC 6.25 μM in Saccharomyces cerevisiae, stain vacuolar/perinuclear membranes of cells.

Benzo[a]phenoxazinium chlorides: Synthesis, antifungal activity, in silico studies and evaluation as fluorescent probes

Four new benzo[a]phenoxazinium chlorides with combinations of chloride, ethyl ester and methyl as terminals of the amino substituents were synthesized. These compounds were characterized and their optical properties were studied in absolute dry ethanol and water. Their antiproliferative activity was tested against Saccharomyces cerevisiae in a broth microdilution assay, along with an array of 36 other benzo[a]phenoxazinium chlorides. Minimum Inhibitory Concentration (MIC) values between 1.56 and >200 µM were observed. Fluorescence microscopy studies, used to assess the intracellular distribution of the dyes, showed that these benzo[a]phenoxazinium chlorides function as efficient and site specific probes for the detection of the vacuole membrane. The added advantage of some of the compounds, that displayed the lower MIC values, was the simultaneous staining of both the vacuole membrane and the perinuclear membrane of endoplasmic reticulum (ER). Molecular docking studies were performed on the human membrane protein oxidosqualene cyclase (OSC), using the crystal structure available on PDB (code 1W6K). The results showed that these most active compounds accommodated better in the active sites of ER enzyme OSC suggesting this enzyme as a potential target. As a whole, the results demonstrate that the benzo[a]phenoxazinium chlorides are interesting alternatives to the available commercial dyes. Changes in the substituents of these compounds can tailor both their staining specificity and antimicrobial activity.

Fluorescent probes based on side-chain chlorinated benzo[a]phenoxazinium chlorides: Studies of interaction with DNA

The interaction of DNA with six water soluble benzo[a]phenoxazinium chlorides mono- or di-substituted with 3-chloropropyl groups at the O and N of 2- and 9-positions, along with methyl, hydroxyl and amine terminal groups at 5-positions, was investigated by photophysical techniques. The results indicated that almost all compounds intercalated in DNA base pairs at phosphate to dye ratio higher than 5. At lower values of this ratio, electrostatic binding mode with DNA was observed. Groove binding was detected mainly for the benzo[a]phenoxazinium dye with NH₂·HBr terminal. The set of six benzo[a]phenoxazinium chlorides proved successful to label the migrating DNA in agarose gel electrophoresis assays. These finding proves the ability of these benzo[a]phenoxazinium dyes to strongly interact with DNA.

A comparative study of lysosome-targetable pH probes based on phenoxazinium attached with aliphatic and aromatic amines

Phenoxazinium was used as a fluorophore for the design of pH probes by the photoinduced electron transfer (PET) mechanism.

Benzo[α]phenoxazines and benzo[α]phenothiazine from vitamin K3: synthesis, molecular structures, DFT studies and cytotoxic activity

Novel benzo[α]phenoxazines and benzo[α]phenothiazine from vitamin K3 are cytotoxic against HeLa, MCF-7 cell lines and potential topoisomerase II inhibitors.

Ultrasound promoted synthesis of Nile Blue derivatives

Ultrasound irradiation was used for the first time towards the synthesis of new Nile Blue related benzo[a]phenoxazinium chlorides possessing isopentylamino, (2-cyclohexylethyl)amino and phenethylamino groups at 5-position of the heterocyclic system. The efficacy of sonochemistry was investigated with some of our earlier reported synthesis of benzo[a]phenoxazinium chlorides. This newer protocol proved competent in terms of reaction times and enhanced yields. Photophysical studies carried out in ethanol, water and simulated physiological conditions, revealed that emission maxima occurred in the range 644-656 nm, with high fluorescent quantum yields. Other attractive feature exhibited by these materials includes good thermal stability. These properties might be useful in the development of fluorescent probes for biotechnology.