A synthetic metallotexaphyrin with radiosensitizing and chemosensitizing properties. Motexafin gadolinium accumulates in tumor cells preferentially due to their increased rates of metabolism, generating reactive oxygen species (ROS) intracellularly and lowering the tumor cell apoptotic threshold to ionizing radiation and chemotherapy. Check foractive clinical trials using this agent. or A substance being studied in the treatment and diagnosis of some types of cancer. It builds up in some cancer cells, which may make them easier to kill with radiation therapy and chemotherapy. Motexafin gadolinium is also used in magnetic resonance imaging (MRI) to help find cancer cells in the body. It is a type of radiosensitizing agent, a type of chemosensitizing agent, and a type of contrast agent. Also called gadolinium texaphyrin.