Direct measurement of doxorubicin concentration in the intact, living single cancer cell during hyperthermia.

BACKGROUND

It is well known that the effect of doxorubicin on cancer cells is enhanced by hyperthermia. The mechanism of this phenomenon is not fully understood.

METHODS

Two esophageal squamous cell carcinoma cell lines, TE-2 and TE-6, were used; these cell lines have different sensitivities for doxorubicin. The cells were exposed to 1 microgram/mL of doxorubicin for 30 minutes. With a confocal laser scanning microscope and a transparent warming plate, doxorubicin concentration was measured continuously in the intact, living single cancer cells, and the two-dimensional distribution of the drug during hyperthermia (43 degrees C) was analyzed.

RESULTS

A doxorubicin sensitivity difference was confirmed between TE-2 and TE-6 cells by colonogenic assay (P < 0.05). Hyperthermia increased the sensitivity of both cell lines to the drug (P < 0.05) and eliminated the sensitivity difference. Doxorubicin accumulated in the nuclei in both cell lines 30 minutes after exposure to the drug in a time-dependent manner (P < 0.05). Without hyperthermia, the doxorubicin concentration in the nuclei of the TE-2 cells (4.8 +/- 0.3 micrograms/mL) was higher than in the nuclei of the TE-6 cells (2.3 +/- 0.5 micrograms/mL) (P < 0.05). With hyperthermia, there was no significant difference in doxorubicin concentration between the nuclei of the TE-2 cells (20.8 +/- 1.3 micrograms/mL) and the nuclei of the TE-6 cells (16.5 +/- 3.9 micrograms/mL).

CONCLUSIONS

Hyperthermia increased the uptake of doxorubicin in the nuclei of cancer cells. Thus, the authors concluded that hyperthermia increases the cells' sensitivity to the drug.