Hyperthermia in combination with chemotherapy has been widely used in cancer treatment. Our previous study has
shown that rapid rate hyperthermia in combination with chemotherapy can synergistically kill cancer cells whereas a
sub-additive effect was found when a slow rate hyperthermia was applied. In this study, we explored the basis of this
difference. For this purpose, in vitro cell culture experiments with a uterine cancer cell line (MES-SA) and its multidrug
resistant (MDR) variant MES-SA/Dx5 were conducted. P-glycoprotein
(P-gp) expression, Caspase 3 activity, and heat
shock protein 70 (HSP 70) expression following the two different modes of heating were measured. Doxorubicin (DOX)
was used as the chemotherapy drug. Indocyanine green (ICG), which absorbs near infrared light at 808nm (ideal for
tissue penetration), was chosen for achieving rapid rate hyperthermia. Slow rate hyperthermia was provided by a cell
culture incubator. Two sets of thermal doses were delivered by either slow rate or rapid rate hyperthermia. HSP70
expression was highly elevated under low dose slow rate incubator hyperthermia while maintained at the baseline level
under the other three treatments. Caspase3 level slightly increased after low dose slow rate incubator hyperthermia while
necrotic cell death was found in the other three types of heat treatment. In conclusion, when given at the same thermal
dose, slow rate hyperthermia is more likely to induce thermotolerance. Meanwhile, hyperthermia showed a dose
dependent capability in reversing P-gp mediated MDR; when MDR is reversed, the combinational treatment induced
extensive necrotic cell death. During this process, the rate of heating also played a very important role; necrosis was
more dramatic in rapid rate hyperthermia than in slow rate hyperthermia even though they were given at the same dose.
Doxorubicin (DOX), widely used in cancer chemotherapy, is limited by drug resistance and cardiac toxicity.
Hyperthermia can aid the functionality of DOX, but current external heat delivery methods are hard to apply selectively
and locally. Indocyanine green (ICG) absorbs near infrared light at 808nm (ideal for tissue penetration) and emits the
energy as heat. These properties make it an ideal agent for rapid and localized hyperthermia. The purpose of this study
was to investigate the in vitro cytotoxic effect of combined chemotherapy and hyperthermia to a DOX resistant ovarian
cancer cell line (SKOV-3). The effects of laser-ICG photothermotherapy, which induces localized rapid heating, and an
incubator, which induces a slow rate of heating, were compared. Cells were subjected to different concentrations of DOX
and either 60 minutes in a 43°C incubator or to one minute at 43°C using 5μM of ICG and 808nm laser. SRB assay was
used to measure cell growth. ICG itself without laser irradiation was not toxic to the cells. DOX by itself was cytotoxic
with an IC50 about 5μM. Both incubator and laser-ICG Hyperthermia in combination with DOX achieved significantly
greater growth inhibition at all DOX concentrations compared to DOX alone. DOX combined with 60 minutes 43°C
incubation lowered DOX IC50 to about 1μM. The DOX IC50 value with one minute laser-ICG was even lower (0.1μM)
suggesting a synergistic effect between DOX and laser-ICG photothermotherapy. In conclusion, the combination of
localized heating and chemotherapy may provide a valuable tool for cancer treatment with minimized toxic effect.
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