It is important to understand that the TTFields frequency is not the treatment dose, and hence increased frequency does not mean increased efficacy. In the case of TTFields, intensity, duration, and usage are the factors that contribute to the “treatment dose”. Nevertheless, we have added to the discussion an explanation on this issue of optimal frequency: “It has been previously shown that maximal effectivity of TTFields occurs at a different frequency for different cancer types, owing to the specific electrical properties of the cells [15, 28]. Hence, the first step in applying TTFields to a new tumor type includes frequency scans.” Regarding the option that the optimal frequency will differ between in vitro and in vivo setting, this is indeed a concern. However, as shown by the in vitro frequency scans, the effect of TTFields is not dichotomic, and effectiveness can be seen at more than one frequency. Therefore, the relatively low expected differences between animals treated with different TTFields frequencies together with the variability inherent to animal studies, makes it technically problematic to perform frequency scans in vivo. As of today, in vitro frequency scans are the common practice for determining the optimal TTFields frequency for delivery to animals and to humans. In fact, in vitro frequency scans were the basis for the clinical studies leading to FDA approval of TTFields at 200 kHz for the treatment of GBM and at 150 kHz for the treatment of MPM. We have added this issue to the discussion as a limitation of the study: “Since the optimal TTFields frequency has been shown to be dependent on the electrical properties of the cells and it is not clear how much effect the tumor microenvironment has on these properties, and because it is technically problematic to perform TTFields frequency scans in vivo, the frequency detected in the cell cultures was also employed for the animal studies.” Point 5: Why the in vitro experiment was performed for 72 hours and in in vivo for 120 hours?
In general, the manuscript is well written and provides novel and interesting data illustrating the possibility to enhance the efficacy of sorafenib in the therapy of hepatocellular carcinoma (HCC).