Hypoxic tumor cells are usually resistant to radiotherapy and chemotherapy because oxygen is essential for the cytotoxic activity of these therapies. Nevertheless, hypoxic tumors can be made more susceptible to treatment by increasing the amount of oxygen inside (4). Hyperbaric oxygen therapy (HBO) is one of the modalities to temporarily alleviate or eliminate hypoxic status in growing tumor cells. By providing 100% oxygen at elevated atmospheric pressure, HBO increases the partial pressure of the oxygen gas and thus forces more oxygen to be dissolved in the plasma, which allows the extra oxygen to be diffused or transported to the body tissues. HBO has been documented by The Undersea and Hyperbaric Medicine Society to be beneficial in 13 different diseases (5).
In summary, HBO-alone was found to have no effects on apoptosis of pancreatic tumor cells in vitro. HBO did not enhance gemcitabine-induced apoptosis of pancreatic tumor cells when administered before or after chemotherapy. HBO significantly enhanced gemcitabine-induced apoptosis of pancreatic tumor cells when administered concomitantly with chemotherapy. Our study suggests that the time window of therapy is critical for effectively using HBO as adjuvant to chemotherapy.