gms | German Medical Science

Objective: Optical imaging that exploits invisible fluorescent light offers several advantages for image-guided surgery, including highly sensitive and specific detection of tumors in tissue and real-time imaging. We are developing fluorophores targeted specifically to human cancer and normal structures. If translated to the clinic, these targeted fluorescent contrast agents would widen the spectrum to resect malignant tumors under direct visualization while avoiding healthy brain tissue.

Methods: Fourteen substances were synthesized with chemical structure similar to 4’6-diamidino-2-phenylindole (DAPI), as a fluorescent dye, used in fluorescence microscopy for labeling of DNA. Solvents were phosphate buffered saline (PBS), methanol, ethanol and dimethyl sulfoxide (DMSO). Glioblastoma cell lines were grown for three days, to achieve an 80% occupancy of the slide. For fixation of the cells we used 4% paraformaldehyde (PFA) with fixation time of 12.5 minutes. Incubation time for staining of the cells was 15 minutes. The cells were then washed three times for 5 minutes each with PBS. Subsequently, cell lines were observed under microscope with DAPI filter and photographed for fluorescence.

Results: Three substances were not dissolved in the used solvents. They appeared extracellularly as fluorescent crystals. The remaining substances diffused into the nucleus, bound to AT-rich regions and led to fluorescence on chromatin. Maximum fluorescence was reached for the corresponding substances in different concentrations. Fluorescence of chromatin was strongest with 1-benzyl-2-(4-bromophenyl)-1H-indole, 2-(4-benzylphenyl)-1H-indole, ethyl-5-chloro-3-formyl-1H-indole-2-carboxylate, 5-bromo-2-(4-bromophenyl)-1H-indole, 2-(4-bromophenyl)-5-methyl-1H-indole und 3,3'-dicianomethyl-2,2'-diethoxycarbonyl-bis-(1H-indole-5-yl)-methane.

Conclusion: Eleven of the manufactured and investigated fourteen substances show good diffusion through the cell and nuclear membrane. Six compounds showed strong fluorescence properties upon binding to DNA in the nucleus. These substances will now be further developed.