Abstract:
Despite multimodal treatment, consisting of surgery, radio-, chemo- and electrotherapy, the prognosis of glioblastoma patients remains poor. In this work, we evaluated TRAM-34 as a new potential drug candidate against glioblastoma. TRAM-34 inhibits the intermediate-conductance calcium-activated potassium channel KCa3.1 and was previously shown to inhibit glioma cell migration or invasion. In addition, it increased the efficacy of radiation and temozolomide treatment. More recent findings indicate that KCa3.1 may act as a rhythm generator within communication networks of glioma cells, ultimately boosting tumor growth. In our attempts to generalize these findings to more glioma cell lines, we found varying effects of TRAM-34 treatment in vitro. Our findings indicate that TRAM-34 exerts little radiosensitizing effects in the glioma cell lines used in our studies. Similarly, among the cell lines tested, only one was sensitized to temozolomide treatment by TRAM-34. Last, direct proliferation-inhibiting effects of TRAM-34 were detected for two out of five glioma cell lines. Interestingly, findings indicating efficacy of TRAM-34, were only present when stem-cell-enriching cell culture conditions were used, hence, in a cell population most commonly associated with therapy resistance. Nevertheless, our in vitro findings point towards modest effects of TRAM-34 treatment on glioma cell viability, both on its own or as an add-on therapy. On the contrary, the results of our in vivo experiments suggest a synergistic effect of radiation and TRAM-34 in the syngeneic glioma model SMA-560/VM/Dk. As such, we found a prolonged survival of mice co-treated with radiation and TRAM-34. We hypothesize that TRAM-34 inhibits the radiation-induced hypermigration of glioma cells, as shown by our histological analyses. Mechanistically, irradiation led to an increased secretion of TGF-beta and expression of MMP-9, which was blunted by TRAM-34. We found no detrimental effects of the treatment on the infiltration of reactive macrophages, cytotoxic, or regulatory T cells into the tumor tissue. Last, weight changes or blood counts of the mice indicated few treatment-specific adverse events, pointing towards a well-tolerated treatment strategy. In conclusion, we found modest effects of TRAM-34 in vitro, and synergistic effects of TRAM-34 to radiation treatment in a glioma mouse model. Further research is necessary to expand these findings to other animal models and gain more confidence in the veracity of our results.
