Radiofrequency ablation (RFA)-induced systemic tumor growth can be reduced by suppression of resultant heat shock proteins

Purpose: To determine the role of hepatic radiofrequency ablation (RFA) heating parameters and their activation of heat shock proteins (HSPs) in modulating distant tumor growth.Methods and materials: First, to study the effects of RFA dose on distant tumor growth, rats with subcutaneous R3230 adenocarcinoma (101mm) were assigned to 3 different hepatic RF doses (60 degrees Cx10min, 70 degrees Cx5min or 90 degrees Cx2min) that induced identical sized ablation or sham (n=6/arm). Post-RFA tumor growth rates, cellular proliferation (Ki-67) and microvascular density (MVD) were compared at 7d. Next, the effect of low and high power doses on local HSP70 expression and cellular infiltration (-SMA +myofibroblasts and CD68+macrophages), cytokine (IL-6) and growth factor (HGF and VEGF) expression was assessed. Finally, 60 degrees Cx10min and 90 degrees Cx2min RFA were combined with anti-HSP micellar quercetin (MicQ, 2mg/ml). A total of 150 animals were used.Results: Lower RF heating (70 degrees Cx5min and 60 degrees Cx10min) resulted in larger distant tumors at 7d (19.2 +/- 0.8mm for both) while higher RF heating (90 degrees Cx2) led to less distant tumor growth (16.7 +/- 1.5mm, p<.01 for both), though increased over sham (13.5 +/- 0.5mm, p<.01). Ki-67 and MVD correlated with tumor growth (p<.01 for all). Additionally, lower dose 60 degrees Cx10min hepatic RFA had more periablational HSP70 compared to 90 degrees Cx2min (rim: 1.106 +/- 163 mu m vs. 360 +/- 18 mu m, p<.001), with similar trends for periablational -SMA, CD68 and CDC47 (p<.01 for all). Anti-HSP70 MicQ blocked distant tumor growth for lower dose (60 degrees Cx10: RF/MicQ 14.6 +/- 0.4mm vs. RF alone: 18.1 +/- 0.4mm, p<.01) and higher dose RFA (90 degrees Cx2min: RF/MicQ 14.6 +/- 0.5mm vs. RF alone: 16.4 +/- 0.7mm, p<.01).Conclusion: Hepatic RF heating parameters alter periablational HSP70, which can influence and stimulate distant tumor growth. Modulation of RF heating parameters alone or in combination with adjuvant HSP inhibition can reduce unwanted, off-target systemic tumorigenic effects.