Characterization of Pancreatic Cancer Cell Thermal Response to Heat Ablation or Cryoablation

Abstract

One of the most lethal carcinomas is pancreatic cancer. As standard treatment using chemotherapy and radiation has shown limited success, thermal regimens (cryotherapy or heat ablation) are emerging as viable alternatives. Although promising, our understanding of pancreatic cancer response to thermal ablation remains limited. In this study, we investigated the thermal responses of 2 pancreatic cancer cell lines in an effort to identify the minimum lethal temperature needed for complete cell death to provide guidance for in vivo applications. PANC-1 and BxPC-3 were frozen (À10 C to À25 C) or heated (45 C-50 C) in single and repeated exposure regimes. Posttreatment survival and recovery were analyzed using alamarBlue assay over a 7-day interval. Modes of cell death were assessed using fluorescence microscopy (calcein acetoxymethyl ester/propidium iodide) and flow cytometry (YO-PRO-1/propidium iodide). Freezing to À10C resulted in minimal cell death. Exposure to À15 C had a mild impact on PANC-1 survival (93%), whereas BxPC-3 was more severely damaged (33%). Exposure to À20 C caused a significant reduction in viability (PANC-1 ¼ 23%; BxPC-3 ¼ 2%) whereas À25 C yielded complete death. Double freezing exposure was more effective than single exposure. Repeat exposure to À15 C resulted in complete death of BxPC-3, whereas À20 C severely impacted PANC-1 (7%). Heating to 45 C resulted in minimum cell death. Exposure to 48 C yielded a slight increase in cell loss (PANC-1 ¼ 85%; BxPC-3 ¼ 98%). Exposure to 50 C caused a significant decline (PANC-1 ¼ 70%; BxPC-3 ¼ 9%) with continued deterioration to 0%. Double heating to 45 C resulted in similar effects observed in single exposures, whereas repeated 48 C resulted in significant increases in cell death (PANC-1 ¼ 68%; BxPC-3 ¼ 29%). In conclusion, we observed that pancreatic cancer cells were completely destroyed at temperatures <À25 C or >50 C using single thermal exposures. Repeated exposures resulted in increased cell death at less extreme temperatures. Our data suggest that thermal ablation strategies (heat or cryoablation) may represent a viable technique for the treatment of pancreatic cancer.

Dual thermal ablation of pancreatic cancer cells as an improved combinatorial treatment strategy

“…Comparison of heating versus freezing from our previous study [37] indicated that apoptosis was Liver Pancreat Sci, 2017 doi: 10.15761/LPS.1000115 more prominent following freeze exposure and almost completely absent after heating. Even in the case of BxPC-3 samples that possessed an apoptotic peak, once DTA was performed, the levels of apoptosis declined dramatically.…”

“…Studies using PaCa cells previously revealed that temperatures below -20 or -25°C were necessary for complete ablation of BxPC-3 and PANC-1 samples, respectively [37]. When PANC-1 cells were exposed to -15°C there was an initial drop in viability; however, samples recovered over the seven-day assessment interval.…”

“…BxPC-3 samples exhibited a larger decrease in cell viability compared to controls (21%(±1) ( Figure 1B). At -20°C, viability further declined in both cell lines (PANC-1=15%(±1); BxPC-3=2%(±0.1) [37]) with reduced recovery observed ( Figure 1). As previously reported, following exposure to -25°C, minimal survival (<2%) and no repopulation was observed in both cells lines [37].…”

“…At -20°C, viability further declined in both cell lines (PANC-1=15%(±1); BxPC-3=2%(±0.1) [37]) with reduced recovery observed ( Figure 1). As previously reported, following exposure to -25°C, minimal survival (<2%) and no repopulation was observed in both cells lines [37]. Assessment of cell proliferation and recovery post-treatment indicated that following exposure to temperatures of -15°C or warmer, both PANC-1 and BxPC-3 cells were capable of repopulating.…”

Cryoablation: physical and molecular basis with putative immunological consequences

“…The pro-inflammatory cytokine TNF-a in combination with freezing elevates the lethal temperature to À0.5 C [32]. Similarly, RF ablation [36], radiation with CA [37] and heat plus freezing [38] also enhance tumor cell death. One benefit reported on the use of CA in combination with chemotherapy is the potential to use lower, sub-lethal, doses of chemotherapeutic agents in combination with CA to obtain the desired outcome [4,30,31].…”