gms | German Medical Science

Objective: Glioblastoma (GBM) is still the most common and aggressive primary brain cancer and is largely incurable.Despite radical surgical resection coupled with chemo- and radiotherapy, no other treatment alternatives are established. It is thought that glioma stem cells (GSCs) are the main cause of therapeutic resistance and recurrence of GBM since they exhibit high self-renewing and tumorigenic capacity. In an effort to identify potential genetic vulnerabilities in GBMs and their GSCs the Yes-Associated-Protein (YAP) network, a developmentally relevant transcription factor, was targeted. Verteporfin (VP) has been identified as a potent inhibitor of YAP-driven signaling by disrupting YAP's interaction with its cognate transcription factor, TEAD. As a second-generation photosensitizing drug for photodynamic therapy (PDT) VP is already used in the treatment of the wet form of macular degeneration. We now want to elucidate whether human glioma cell lines are susceptible to PDT using VP, too.

Methods: Human glioma cell lines LN229 and HSR-GBM1 were treated with variable concentrations of VP for 24 h, followed by a photodynamic activation at 689 nm using a diode laser light. 24 h and 48 h after laser irradiation, cell viability was measured using the MTT assay and VP uptake was measured using a desktop cytometer. Protein expression of YAP was measured after 24 h VP treatment.

Results: We observed significant cell death following PDT in all cell models (HSR-GBM1, LN229). In LN229 an EC50 of 0.64 µM (30 sec laser) or 0.25 µM (60 sec laser) could be determined 24 h post PDT. VP treatment with subsequent PDT in HSR-GBM1 cell revealed an EC50 of 0.77 µM (30 sec laser) or 0.08 µM (60 sec laser) 24 hours post radiation. Flowcytometric measurements revealed a cellular uptake of VP after 24 h incubation in LN229 with 1 µM or 10 µM of 17.7% or 99.6%, respectively. For HSR-GBM1 we could detect a VP uptake of 60% or 100% after 1 µM or 10 µM treatment. Furthermore, we could demonstrate a suppression of YAP protein expression after 48 h of VP-treatment [7 µM].

Conclusion: PDT with VP causes cell death in human glioma cells at marginal concentrations. Additionally, we could measure fluorescence emission around 680 nm, validating the cellular uptake. VP therefore is not only a potential drug in targeting GSCs pharmacologically but can be used as an optical imaging dye in glioma surgery and photosensitizer to make GBM susceptible for PDT.