Targeted Delivery of Radioprotectants

Description of projects available to graduate students:
One focus of our laboratory is the study of irradiation-induced damage and the development of targeted radioprotectants. Irradiation damage is mainly mediated by reactive oxygen and nitrogen species (ROS and RNS). Hence, scavengers of free radicals (e.g., superoxide (O2-) and hydroxyl (OH) radicals) form the principal group of radioprotectors. Findings from our lab suggest that that the principal origin of radiation-induced free radical generation is the mitochondria and that another group of very effective radioprotectors are nitric oxide synthase (NOS) antagonists.
One tissue that we work with is the urinary bladder, because the urothelial cells lining the bladder lumen are among the most sensitive to irradiation damage. Radiation cystitis of the bladder is a major consequence of irradiation therapy for various pelvic tumors. Our group was the first to show that NOS antagonists present in the bladder lumen at the time of irradiation are more protective than ROS scavengers or manganese superoxide dismutase (MnSOD) mimetics. We have evidence that NOS antagonists may prevent both NO and O2- production, whereas scavenging or dismutation of O2- results in H2O2 formation which may be toxic if not converted into water by the antioxidants glutathione peroxidase (GPX) or catalase.
To evaluate the effectiveness of newly developed/synthesized radioprotectors we utilize radiosensitive hemopoietic cells. Cell are irradiated using a linear accelerator and NO, O2- and peroxinitrite (ONOO-) levels are measured using fluorescent dyes or our unique NO/ONOO- microsensors. The most effective radioprotectors are then used in vivo in mice to evaluate potency and selectivity. In these experiments, mice are irradiated with different radioprotectors instilled into the bladder. Following irradiation at different time points cystometry is performed to evaluate the physiological activity of the bladder. After cystometry, the bladders are excised for transepithelial resistance measurements using Ussing chambers.
Systemic administration of free radical scavengers and NOS antagonists are contraindicated because of their often poor ability to penetrate cellular and mitochondrial membranes or undesirable side effects. Our studies are directed to targeting these compounds to the mitochondria and accumulating them in close proximity to ROS and RNS generation sites. The approach is to drag the radioprotectors with peptides based on the naturally occurring membrane-active antibiotic gramicidin S. Moreover, we are developing “dual-action compounds” containing a NOS antagonist to radioprotect normal tissues and a MnSOD mimetics to radiosensitize tumors since they have low levels of GPX and catalase.

Techniques graduate student will learn:
See above.