Antisoma announces that results from its phase I biodistribution study of AS1403 (formerly TheraFab) will be presenting at the European Association of Nuclear Medicine meeting in Amsterdam by Dr Michael Garkavij, a leading investigator in the trial.

AS1403 is a fragment of the monoclonal antibody HMFG1 linked to a radioactive isotope with cell-killing ability. The biodistribution study examined the ability of AS1403 to deliver a targeted dose of radiation to tumours in patients with non-small cell lung cancer. For this study, the therapeutic isotope in AS1403 was replaced by an imaging isotope, allowing the investigators to evaluate the distribution of radioactivity in the body. Imaging showed that radioactivity accumulated in tumours after administration of AS1403. This confirms the targeting ability of the antibody fragment, in line with earlier studies using HMFG1 antibody fragments.

However, dosimetry findings suggested that quantities of radioactivity delivered to other tissues such as the kidneys could be such that they would produce unacceptable levels of toxicity if a therapeutic isotope were used. Significant targeting of the kidneys is a well-documented property of antibody fragments that is not shared by whole antibodies. Work to overcome this issue would require significant investment, and Antisoma has therefore decided not to continue the development of AS1403 at this time.

Glyn Edwards, CEO of Antisoma, said, "We have many promising drug candidates in our pipeline and can therefore move quickly to discontinue programmes when trial results show that resources would be more usefully allocated elsewhere."