Effect of tumor treating fields or DD fields on DNA damage and the Fanconia anemia BRCA DNA repair pathway in mesothelioma. Malignant plural mesothelioma or in short MPM is an aggressive thoracic cancer. Combination chemotherapy with Bemetrex and platinum base agent or immunotherapy with nivolumab plus ipilimumab are used for treatment of MPM. Still, the prognosis of patients diagnosed with MPM is dismal and better treatment options are required. Tumor treating fields or in short DD fields are low intensity intermediate frequency alternating electron fields. DD field therapy is an anti-cancer treatment modality with antimyotic effects on cancerous cells. DD fields in combination with Bemetrex and a platinum base agent are FDA and CEA approved for treatment and of MPM. The current research aim to examine the mechanism of action of DD fields for MPM treatment. DD fields at a frequency of 150 kilohertz were applied to MSTO and H2052 human MPM cell lines and to a mouse subcutaneous MPM model. Cytotoxic effects, DNA damage, protein expression levels, and tumor volumes were measured. Levels of the histone variant gamma H2AX were measured by fluorescent microscopy and may be seen in the green staining. Blue DAPI staining was employed for cellular visualization. Higher gamma H2AX levels indicative of elevated DNA damage may clearly be seen in cells treated with DD fields for 72 hours relative to control cells. Cell lysates were examined for changes in expression levels of DNA damage induced cell cycle inhibitors. In line with the increased DNA damage, P21 and P27 were found to be elevated in cells treated with DD fields. The cell lysates were also examined for changes in expression levels of DNA repair proteins. Significant reductions in the levels of FUNC A, FUNC D2, FUNC J, and BRCA1 were evident for cells treated with DD fields relative to control cells. All these proteins are part of the FUNCONI anemia BRCA pathway that is involved in the repair of DNA double strand breaks. The combined efficacy of DD fields with cisplatin or pemetrex was examined. The figure shows the overall effect which is the product of the cytotoxic and corresponding clonogenic effects. Each chemotherapy agent displays dose response in both cell lines and co-application of DD fields augmented the effects. To evaluate the type of interaction between DD fields and each chemotherapy agent, we calculated the expected additive response from the values of the individual treatments. The calculations are shown as a red dashed line. In the case of DD fields with cisplatin, the cyan line for the measured results is below the calculated one, indicating a synergistic interaction. The overlap of the calculation line with the blue line of the actual results for the DD fields pemetrex combination indicate additivity. The efficacy of DD fields together with cisplatin and pemetrex was examined in a mouse model. DD fields were continuously applied for seven days and chemotherapy injected intraperitoneally according to the depicted timeline. Tumor volume was significantly lower for the DD fields chemocombination group relative to control. Levels of gamma H2AX were elevated in this treatment group relative to control and to each modality alone. In conclusion, this research provide insights on the mechanism of action of DD fields for treatment of MPM. The results demonstrate that the efficacy is associated with increased DNA damage and reduced expression of proteins from the Fanconia anemia BRCA DNA repair pathway. This mechanism is further supported by the synergistic interaction of DD fields with cisplatin. As DNA damage induced by cisplatin is known to be repaired by the Fanconia anemia BRCA pathway.

tumor treating fields

DD fields

DNA damage

Fanconia anemia BRCA DNA repair pathway

mesothelioma