Two D-glucose analogues (compounds 14 and 15, Figure ) were synthesized by condensation of the benzoselenadiazole scaffold 4F with two 2-D-deoxyglucosamine analogues. Both compounds were isolated as the mixture of α-and βanomers of D-glucose (characterization data in Supplemental Information). Compound 15 showed better water solubility and photoreactivity than compound 14, thus we assessed whether it could be actively taken up by GLUT1/3 transporters in glioblastoma cells, the most abundant glucose transporters in human U87 cells. As controls, we also prepared Dglucosamine derivatives of previously reported photosensitizers, such as the commercial Nile Blue and the TPE reported by the group of Bin Liu for metabolic PDT (compounds 16 and 17, respectively, Figure ). First, we compared the uptake for all D-glucose derivatives in U87 cells. As shown in Figure , compound 15 -but not Nile Blue (16) or TPE (17) derivatives-exhibited reduced uptake in cells that had been pre-incubated with the GLUT inhibitor cytochalasin B, suggesting that compound 15 -unlike other photosensitizers-can enter glioblastoma cancer cells through active uptake via GLUT transporters. We also analyzed whether the phototoxicity of compound 15 in U87 cells was dependent on GLUT-mediated transport and observed that its activity was significantly blocked with cytochalasin B (Figure ). Furthermore, compound 15 showed the highest singlet oxygen generation quantum yield among all aminobenzoselenadiazoles (Figure ), with values around 25% -comparable to TPE-and produced effective amounts of singlet oxygen by single-photon (520 nm) as well as two-photon (970 nm) excitation (Figure ). Given the technical complexity of two-photon in vivo experiments and the limited availability of multi-photon illumination in clinical settings, we decided to perform our biological characterization using single-photon excitation. )). Data presented as mean values±SEM (n=3). Phototoxicity in U87 cells after incubation with compound 15 (100 μM) in the presence or absence of cytochalasin B (20 μM). Cells were illuminated (10 mW, 37 J cm -2 ) and viability was assessed 16 h post illumination using a TACSR MTT cell proliferation assay with values normalized to those in cells without cytochalasin B. Data presented as means±SEM (n=8). (d) Excitation wavelengths used for single-photon illumination ( * corresponds to two-photon illumination) and singlet oxygen generation quantum yields determined using DPBF in EtOH (Note: DPBF was found insoluble in water) using Rose Bengal as a reference (68%). † Singlet oxygen generation quantum yield reported for TPE. ¥ Reported values for protoporphyrin IX, the main photosensitizer produced upon metabolism of 5-aminolevulinic acid (5-ALA). P values were obtained from two-tailed unpaired t tests (ns for p >0.05, ** for p <0.01, *** for p <0.001).