P11.25 Assessing electrical properties of cells as predictive marker for patient-specific TTFields response and optimal frequency

BACKGROUND

Tumor treating fields (TTFields) are currently approved for the treatment of glioblastoma multiforme (GBM, using 200 kHz), and being tested in other tumor types such as non-small cell lung cancer and brain metastases occurring in this indication (LUNAR and METIS trials, using 150 kHz). Response to TTFields in cancer cells was empirically shown to be frequency-dependent specific for cell type; however, there are no markers available predicting optimal frequency or response in different cancer types or individual patients to date. There is evidence indicating electrical properties determine the optimal anti-mitotic frequency. This study analyzed the correlation of electrical properties of cells with their optimal TTFields frequency and sensitivity using the 3DEP reader (LabTech) to determine the electrical properties with the help of Dielectrophoresis (DEP) force. With this technique, cell movements within electric fields of different frequencies can by analyzed based on the physical effect of DEP, exercising a force on polarizable particles inside a non-homogeneous electric field.

MATERIAL AND METHODS

We used the 3DEP reader to obtain baseline properties (permittivity and conductivity) of 17 different cell lines of several tumor types. The resulting curves were analyzed by a 2-way ANOVA. Additionally, we determined the optimal frequency for maximum cytotoxic effect for each cell line using the inovitroTM system and eventually compared with the detected electrical properties.

RESULTS

We found cell lines with an optimal TTFields frequency of 150 kHz (corresponding to cells with a membrane capacitance in the lower range of the observed 3DEP curves, n=9) to possess significantly different (p<0.001) electrical properties from cells with an optimal TTFields frequency of 200 kHz (n=8). According to the curve differences in the lower frequency range, the measure of membrane capacitance served as a good predictor for TTFields response.

CONCLUSION

This study showed a correlation of cell membrane capacitance and optimal TTFields frequency and response. Our results provide a substantial rationale for further studies investigating the predictive potential of electrical properties of tumor cells as a measure for the optimal frequency and sensitivity to TTFields in individual patients.

P11.20 Assessing TTFields-response and associated gene expression in various human cancer cell lines

BACKGROUND

Various cancer cell lines were reported to be affected in an inhibitory manner of varying magnitude by tumor treating fields (TTFields). Here, we aimed to detect response markers for TTFields treatment by analyzing specific properties of cell lines according to their response pattern to these alternating electric fields of intermediate frequency and low intensity.

MATERIAL AND METHODS

We treated 45 cell lines of diverse types of human cancer with TTFields at their specific optimal frequency and equal nominal intensity of 1.7 V/cm for 72 h. In addition to investigating cytotoxicity and clonogenic potential, we used the Cancer Cell Line Encyclopedia (CCLE) database for further analysis: First, to functionally examine patterns of differentially expressed genes or mutations associated with response to TTFields; and second, to compare sensitivity to TTFields using pharmacological profiling (CCLE).

RESULTS

TTFields had a cytotoxic effect on tested cell lines of 50 % on average (range: 14–86% reduced cell counts), whereas the clonogenic effect varied between no effect and 88 % reduction in the number of colonies. With regard to differential gene expression and mutation analysis, our analysis detected upregulated pathways associated with migration, DNA damage repair response, oxidative stress, and hypoxia. Further, cells identified as having a better response to TTFields were also more sensitive to lapatinib, PHA-665752 and PLX-4720.

CONCLUSION

In this study, we determined the optimal frequency for maximum response to TTFields in numerous human cancer cell lines. Our results argue strongly for a vast effectiveness of TTFields treatment in cancer cells, and synergistic effects in combination with other therapeutic agents might be revealed in future studies using pharmacological profiling. Beyond that, further research is needed on the role of identified response-associated mutations.