Grant: Alternative Radiopharmaceuticals for Medical Imaging

The aim of this proposal is to replace the current agent of choice for lung perfusion imaging, macroaggregated albumin radiolabelled with Tc-99m, with small microspheres radiolabelled with Ga-68. Such a new radioactive PET agent (positron emitting tomography agent) has 3 important advantages. First, the PET isotope Ga-68 is more easily obtained than the gamma emitting isotope Tc-99m. Second, our microspheres avoid the risk of contamination posed by the blood product albumin, as they are made from poly(lactic acid), a biodegradable polymer which is approved by Health Canada. Third, our microspheres can be made to be of uniform size thereby guaranteeing that only capillaries will be clogged and toxic effects can thus be prevented even in patients with severe pulmonary disease. Our approach is to synthesize a Ga-68-binding biodegradable polymer, to prepare uniformly sized microspheres from it, and to test the biodistribution, toxicity and radiation dosimetry of the radiolabelled microspheres in animals and in a first clinical trial with healthy volunteers. Lung perfusion imaging with our uniform Ga-68-labelled microspheres is expected to substantially reduce the use of reactor-produced radioisotopes and to help in overcoming the current shortage of medical isotopes, while simultaneously improving on the currently used procedure.