Heat response of HT29 cells depends strongly on perfusion—A31P NMR spectroscopy, HPLC and cell survival analysis

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Abstract
A model system of perfused human colon adenocarcinoma cells (HT29) encapsulated in alginate was used to examine metabolic response to heat therapy with 31P NMR spectroscopy, HPLC and cell survival analysis. The presented data show, that perfused (medium flow during hyperthermia) and non-perfused (no medium flow during hyperthermia) cells are very difficult in their sensitivity to hyperthermia. Under equivalent experimental conditions with respect to medium pH, oxygen and nutrient concentration, encapsulated perfused HT 29 cells display a significantly lower thermal sensitivity than non-perfused cells. This reduced sensitivity of perfused cells is characterized by an increased cell survival and relative ATP concentration, and reduced drop of the NTP/Pi ratio in the long-term follow up towards zero. The relative ATP concentration determined by HPLC after hyperthermia is correlated with the clonogenic survival fraction. There is a direct relationship, depending on the specific experimental conditions (perfused, non-perfused). For perfused cells only a slight dependency of survival and relative ATP concentration on heat dose is observed. In consequence, the correlation between survival and relative ATP concentration is weak, described by log(SFperf) = 0.7*[ATP-12.4, R2 = 0.79, p < 0.04. For non-perfused cells the correlation is stronger resulting in a relationship of log(SFno perf) = 0.6*[ATP]-9.0, R2 = 0.98, p < 0.0002. Altogether, the presented data suggest that the relative ATP concentration measured by HPLC after hyperthermia might be predictive for cell survival. On the other hand, a dependence between cell survival and long-term changes of NTP/Pi has been found. The results confirm the importance of tumour perfusion for hyperthermia-induced metabolic changes and cytotoxicity and therefore, for the therapeutic outcome.