Purpose: To (a) identify key expressed genes in the periablational rim after radiofrequency ablation (RFA) and their role in driving the stimulation of distant tumor growth and (b) use adjuvant drug therapies to block key identified mediator(s) to suppress off-target tumorigenic effects of hepatic RFA. Materials and Methods: This institutional animal care and use committee-approved study was performed in C57BL6 mice (n = 20) and F344 rats (n = 124). First, gene expression analysis was performed in mice after hepatic RFA or sham procedure; mice were sacrificed 24 hours to 7 days after treatment. Data were analyzed for differentially expressed genes (greater than twofold change) and their functional annotations. Next, animals were allocated to hepatic RFA or sham treatment with or without STAT3 (signal transducer and activator of transcription 3) inhibitor S3I-201 for periablational phosphorylated STAT3 immunohistochemistry analysis at 24 hours. Finally, animals with subcutaneous R3230 adenocarcinoma tumors were allocated to RFA or sham treatment with or without a STAT3 inhibitor (S3I-201 or micellar curcumin, eight arms). Outcomes included distant tumor growth, proliferation (Ki- 67 percentage), and microvascular density. Results: At 24 hours, 217 genes had altered expression (107 upregulated and 110 downregulated), decreasing to 55 genes (27 upregulated and 28 downregulated) and 18 genes (four upregulated, 14 downregulated) at 72 hours and 7 days, respectively. At 24 hours, STAT3 occurred in four of seven activated pathways associated with pro-oncogenic genes at network analysis. Immunohistochemistry analysis confirmed elevated periablational phosphorylated STAT3 24 hours after RFA, which was suppressed with S3I-201 (percentage of positive cells per field: 31.7% 6 3.4 vs 3.8% 6 1.7; P , .001). Combined RFA plus S3I- 201 reduced systemic distant tumor growth at 7 days (end diameter: 11.8 mm 6 0.5 with RFA plus S3I-201, 19.8 mm 6 0.7 with RFA alone, and 15 mm 6 0.7 with sham procedure; P , .001). STAT3 inhibition with micellar curcumin also suppressed postablation stimulation of distant tumor growth, proliferation, and microvascular density (P , .01). Conclusion: Gene expression analysis identified multiple pathways upregulated in the periablational rim after hepatic RFA, of which STAT3 was active in four of seven. Postablation STAT3 activation is linked to increased distant tumor stimulation and can be suppressed with adjuvant STAT3 inhibitors.
Bibliographical noteFunding Information:
Supported by a Radiological Society of North America Research Seed Grant (grant 1215), the Israel Ministry of Health (no. 3-12063), Israel Science Foundation (grant 1277/15), and the National Cancer Institute (grants 1R01CA197081-01A1 and 1U54CA151881-01).