Hypoxic cells in tumors as a target for cancer therapy.

Hypoxic cells that are found in solid tumors are resistant to anticancer drugs and radiation therapy. Thus, for effective anticancer chemotherapy, it is important to identify drugs with selective toxicity towards hypoxic cells. The recent development of new drugs that are toxic only when activated in the hypoxic cell opens a new era of cancer treatment. Recently, we evaluated the hypoxia-selective toxicity of four differently substituted quinoxaline 1,4-dioxides (QdNOs) in human cancer cells. These compounds were synthesized by the Beirut Reaction. The various QdNOs were found to exert potent hypoxic cytotoxic activities against human colon cancer cells (T-84) and to possess a 50-100 fold greater cytotoxicity under hypoxia compared to oxia. Interestingly, the hypoxia cytotoxicity ratio (HCR: ratio between drug concentration in air and in hypoxia to give 10% cell survival) of these compounds was found to depend on the nature of the substituents on the quinoxaline 1,4-dioxide heterocycle. Because of their differential hypoxic cytotoxicity, these drugs could provide useful therapeutic agents against solid tumors. Presently we are investigating the selective cytotoxicity of QdNOs for hypoxic cells in tumors in vivo and their ability to potentiate radiation-induced tumor cell killing. We will also study their in vitro anti-angiogenic activity and their mechanism of action at the molecular level. The deciphering of the mechanism of action of QdNOs may allow us to ultimately recommend their use as therapeutic agents against human tumors.