POTENTIAL ANTI-CANCER AGENT INVESTIGATED AT NIST.

NIST researchers are investigating liposome-encapsulated, alpha-emitting radionuclides for potential use in combating liver cancer. The American Cancer Society estimates that there are about 15 300 new cases of liver cancer each year in the United States, with a mortality rate of 90 %. One of the difficulties in treating this disease is the small number of treatment modalities available to physicians. The most widely used treatment schemes, for example, irradiation with external beams, have the disadvantage of exposing healthy liver tissue in the vicinity of the tumors to high radiation fields causing damage to one of the bodys most fragile organs. An alternative approach being investigated by the Radioactivity Group uses radionuclides such as [k.sup.211]At, [Bi.sup.212], and [Bi.sup.213] that emit alpha particles. Alpha particles deposit a much higher amount of energy over a very short distance (2 to 3 cell diameters), thereby killing the tumor cells while sparing healthy liver tissue.

The method being pursued involves encapsulating these radionuclides with liposomes, which are spherical lipid vesicles that can mimic cellular membranes. Because lipids tend to be taken up by the liver, liposomes are an attractive candidate as a potential delivery mechanism for these radionucides. Using a protocol previously developed for the encapsulation of the imaging nuclide [Tc.sup.99m], the researchers have successfully encapsulated [At.sup.211] At [Bi.sub.212] [Bi.sub.211]using cyclotron-produced material from NIH in Bethesda. Further studies will focus on development of a quantitative analysis procedure, along with characterization of in vitro stability and radio-sensitivity. Long-term plans include expansion of the studies to other alpha-emitting radionuclides, such as the aforementioned [Bi.sup.212] and [Bi.213]Bi.