Objective: Hepatocellular carcinoma (HCC) is the third cause of cancer related mortality. Sorafenib, an oral multikinase inhibitor, is approved for patients with advanced HCC, however its survival benefit is limited. Tumor Treating Fields (TTFields) therapy is an effective, anti-neoplastic treatment modality delivered via noninvasive application of low intensity, intermediate frequency, alternating electric fields. The aim of this work is to explore the potential use of TTFields alone and in combination with sorafenib as a treatment for HCC.

Methods: HepG2 and Huh-7D12 HCC cells were treated with various TTFields frequencies (100-400 kHz) for 72 hours using the inovitroTM system. Efficacy of the combined treatment of TTFields and sorafenib was tested by applying TTFields at the optimal frequency together with various sorafenib concentrations. Cell counts, induction of apoptosis, and clonogenic potential were determined. Moreover, N1S1 HCC cells were injected into the left lobe of the liver of Sprague Dawley rats. After 1 week, TTFields (1.2 V/cm) and sorafenib (10 mg/kg) were applied for 6 days and tumor growth was evaluated, using MRI. Healthy rats were used to study the safety of TTFields (150 kHz) application to the abdomen.

Results: The optimal frequency of TTFields was 150 kHz for both HCC cell lines. TTFields application (1.0 - 1.7 V/cm, 72 hours) at 150 kHz led to a 53-55% reduction in cell counts and to an additional reduction (65-69%) in clonogenic potential. The combination of TTFields and sorafenib led to a significant reduction in cell count (2-way ANOVA, P <0.05) as compared to either treatment alone. HCC tumor growth was significantly reduced in the combined group compared to the control group (student t-test, P <0.01). On average, the HCC tumor volume (fold-increase) in the combination treatment group (1.6-times) was significantly lower than in the control group (5.9-times, P <0.0001), TTFields alone group (3.3-times, P <0.01), and sorafenib alone group (2.3-times, P <0.05). Histological analysis of the KI67 proliferation marker in HCC tumors showed reduced proliferation in all treated groups. Based on preliminary analysis of autophagy marker (LC3) in tumors, we hypothesized the involvement of autophagy as 1 of the mechanisms underlying increased treatment efficacy. Safety studies did not reveal any adverse events associated with TTFields application to the rat abdomen.

Conclusions: These results demonstrate that TTFields can be a safe and effective in the treatment of HCC, and that the combination with sorafenib leads to further enhancements in treatment effectiveness. Based on these results, a Phase 2 clinical trial evaluating the effects of TTFields and sorafenib treatment in patients with HCC is planned (HEPANOVA; NCT03606590).

Citation Format: Shiri Davidi, Catherine Tempel-Brami, Mijal Munster, Anna Shteingauz, Einav Zeevi, Rosa Schneiderman, Tali Voloshin, Moshe Giladi, Adrian Kinzel, Uri Weinberg, Yoram Palti. In vitro and in vivo evidence for the safety and efficacy of Tumor Treating Fields (TTFields) in combination with sorafenib [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 572.