Bifunctionalised long-wavelength fluorescent probes for biological applications

Anticancer Activity of Benzo[a]phenoxazine Compounds Promoting Lysosomal Dysfunction

Specific cancer therapy remains a problem to be solved. Breast and colorectal cancer are among the cancers with the highest prevalence and mortality rates. Although there are some therapeutic options, there are still few effective agents for those cancers, which constitutes a clinical problem that requires further research efforts. Lysosomes play an important role in cancer cells' survival, and targeting lysosomes has gained increased interest. In recent years, our team has been synthetizing and testing novel benzo[a]phenoxazine derivatives, as they have been shown to possess potent pharmacological activities. Here, we investigated the anticancer activity of three of the most potent derivatives from our library, C9, A36, and A42, on colorectal- and breast-cancer-derived cell lines, and compared this with the effect on non-neoplastic cell lines. We observed that the three compounds were selective for the cancer cells, namely the RKO colorectal cancer cell line and the MCF7 breast cancer cell line. In both models, the compounds reduced cell proliferation, cell survival, and cell migration, accumulated on the lysosome, and induced cell death accompanied by lysosomal membrane permeabilization (LMP), increasing the intracellular pH and ROS accumulation. Our results demonstrated that these compounds specifically target lysosomes from cancer cells, making them promising candidates as LMP inducers for cancer therapy.

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.

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.

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.

Tuning the solution phase photophysics of two de novo designed hydrogen bond sensitive 9-methyl-2,3,4,9-tetrahydro-1H-carbazol-1-one derivatives

Two new fluorophores, 6,7-dimethoxy-9-methyl-2,3,4,9-tetrahydro-1H-carbazol-1-one (DMTCO) and 5-methyl-8,9-dihydro-5H-[1,3]dioxolo[4,5-b]carbazol-6(7H)-one (MDDCO), first of their kind, have been synthesized from the corresponding methoxy and methylenedioxy derivatives of 2,3,4,9-tetrahydro-1H-carbazol-1-one respectively. Comprehensive photophysical characterization of these compounds has been carried out in sixteen different homogeneous solvents and binary solvent mixtures. Both of these compounds are sensitive to solvent polarity, but the sensitivity is much higher in electronic excited state observed by steady-state and time-resolved fluorescence experiments than in ground state studied by UV-vis absorption spectroscopy. The fluorescence spectral shifts are linearly correlated with the empirical parameters of the protic solvents and also the quantitative influence of the empirical solvent parameters on the emission maxima of the compounds has been calculated. The change in dipole moment of the compounds in their excited state has been calculated from the shifts in corresponding emission maxima in pure solvents. A higher dipole moment change of both DMTCO and MDDCO in protic solvents is due to intermolecular hydrogen bonding which is further confirmed by the comparison of their behaviour in toluene-acetonitrile and toluene-methanol solvent mixtures. From structural features, MDDCO is more planar compared to DMTCO, which is reflected better in fluorescence quenching of the former with organic bases, N,N-dimethylaniline and N,N-diethylaniline. Laser flash photolysis experiments prove that the quenching interaction originates from photoinduced electron transfer from the bases to the compounds.