Heat stress and hepatic laser thermal ablation induce hepatocellular carcinoma growth: Role of PI3K/mTOR/AKT Signaling

Purpose: To determine if heat stress and hepatic laser thermal ablation induce hepatocellular carcinoma (HCC) growth and to identify growth factors induced by heat stress. Materials and Methods: Non-heat-stressed HCC cells were cocultured with HCC cells or hepatocytes that were heat stressed at 37°C (physiologic), 45°C (moderate), or 50°C (severe) for 10 minutes and proliferation monitored with bioluminescence imaging for up to 6 days after heat stress (three experiments). Rats bearing orthotopic N1S1 HCC were randomly assigned to undergo immediate sham or laser thermal (3 W for 60 or 90 seconds; hereafter, 3W360s and 3W390s, respectively) ablation of the median (local) or left (distant) hepatic lobe, and tumor growth was monitored with magnetic resonance imaging for up to 18 days after ablation (six or more rats per group). Experiments were repeated with rats randomly assigned to receive either the adjuvant phosphoinositide 3-kinase (PI3K)/mammalian target of rapamycin (mTOR) inhibitor (NVP-BEZ235) or the vehicle control. Heat-stressed HCC cells and hepatocytes were analyzed by using microarray or quantitative real-time polymerase chain reaction analysis for growth factor expression (three or more experiments). Groups were compared by using one- or two-way analysis of variance, and post hoc pairwise comparison was performed with the Dunnett test. Results: There were more non-heat-stressed HCC cells when cells were cocultured with cells subjected to moderate but not physiologic or severe heat stress (P , .001 for both). Local intrahepatic N1S1 tumors were larger at day 18 in the 3W360s (mean, 3102 mm³ 6 463 [standard error]; P = .004) and 3W390s (mean, 3538 mm³ 6 667; P , .001) groups than in the sham group (mean, 1363 mm³ 6 361) but not in distant intrahepatic tumors (P = .31). Adjuvant BEZ235 resulted in smaller N1S1 tumors in the BEZ235 and laser thermal ablation group than in the vehicle control and laser thermal ablation group (mean, 1731 mm³ 6 1457 vs 3844 mm³ 6 2400, P , .001). Moderate heat stress induced expression of growth factors in HCC cells and hepatocytes, including heparin-binding growth factor, fibroblast growth factor 21, and nerve growth factor (range, 2.9-66.9-fold; P , .05). Conclusion: Moderate heat stress and laser thermal ablation induce hepatocellular carcinoma growth, which is prevented with adjuvant PI3K/mTOR/protein kinase B inhibition.