Uses of Annexin Imaging Updated in Presentations at Society of Nuclear Medicine 50th Annual Meeting.

Business Editors/Health/Medical Writers

CHATSWORTH, Calif.--(BUSINESS WIRE)--June 26, 2003

North American Scientific Inc. (Nasdaq:NASI) today announced that Annexin imaging in cancer and cardiovascular disease was the subject of several peer-reviewed presentations at the 50th Annual Society of Nuclear Medicine Meeting held June 22-25 in New Orleans, La. North American Scientific's lead radiopharmaceutical product candidate is Hynic-Annexin V, which is based upon its Apomate(TM) technology platform and is a kit for the preparation of Technetium Tc-99m labeled Annexin V.

Preclinical studies carried out by Narula, Hartung, Petrov and colleagues at Hahnemann Hospital in Philadelphia provided data supporting the theory that unstable atherosclerotic plaque in coronary blood vessels that may rupture, causing sudden death, is characterized by a large number of scavenger cells called macrophages which are undergoing programmed cell death (apoptosis). These dying macrophages are thought to cause plaque instability by releasing enzymes that degrade its supporting structure. This group showed that radiolabeled annexin localizes preferentially on apoptotic cells in unstable plaque. They were able to use radiolabeled annexin binding to apoptotic cells to show that therapeutic interventions, such as diet or drugs, reduce the numbers of dying macrophages in such atheromas and, therefore, may be useful in treating unstable plaque. (1)

The ability of radiolabeled annexin to image vascular injury in the brain was demonstrated by Drs. Mari, Yenari, Tait, Zhu, Goris and Blankenberg using a dedicated small animal imaging camera. (783)

Tc-99m-annexin imaging was used by physicians from Maastricht, The Netherlands, in the diagnostic workup of abnormal tissue masses found in the heart of patients with cardiac abnormalities. Kietselaer, Boersma, Heidendal, Reutelingsperger, Hofstra and colleagues showed that they were able to image intracardiac masses. They suggested that Tc-99m annexin may be useful in distinguishing benign from malignant masses. (509)

The ability of annexin imaging to define the time course of programmed cell death in tumors was again confirmed in preclinical animal studies by Drs. Tamaki, Takei, Tait, Blankenberg, Strauss and colleagues. (583)

The ability to perform multiple sequential imaging studies with radiolabeled annexin after tumor chemotherapy was confirmed in a new study by Drs. Tamaki, Kuge, Tait, Blankenberg, Dstrauyss and colleagues. (587)

Using a genetically engineered murine lymphoma model in which the tumor had been altered to express the firefly enzyme called luciferase which can emit visible light signals, researchers proved that annexin uptake in dying tumor cells precedes loss of those cells. Drs. Mandl, Mari, Contag, Tait and Blankenberg used this model to confirm the sequence of events in effectively treated tumor in which annexin binding precedes destruction and removal of the dying tumor cells. (582)

Several groups presented data on the preparation of radiolabeled annexin using isotopes suitable for positron emission tomographic (PET) imaging and its feasibility for PET imaging. Drs. Smith-Jones, Afroze, Zanzonico, Tait, Larson and Strauss reported on the use of gallium-68 labeling of annexin. (159) Drs. Murakami, Takamatsu, Nishimura and colleagues reported on their experience preparing F-18 labeled annexin. (1119) Another report on the preparation of F-18 labeled annexin was presented by Drs. Mease, Weinberg, Toretsky and Tait. (1058) Annexin labeled with radioisotopes such as fluorine-18 or gallium-68 which are suitable for PET imaging may be used in the new generation of high resolution PET scanners and PET/CT combination imaging instruments. North American Scientific's Theseus Imaging Corporation subsidiary is currently collaborating on the development of a PET annexin agent and expects to be able to use its current annexin protein produced under good manufacturing practices (GMP) as the basis of a PET annexin agent for human use.

About North American Scientific

North American Scientific develops, produces and sells innovative radioisotopic products, including brachytherapy seeds and radiopharmaceuticals, principally for the treatment and diagnosis of disease. Its lead radiopharmaceutical product candidate is Hynic-Annexin V which is based upon its Apomate(TM) technology platform and is a kit for the preparation of Technetium Tc-99m labeled Annexin V. It is administered intravenously and is intended for the in vivo imaging of apoptosis and necrosis, two common forms of cell death. For more information, please visit the Company's Web site at www.nasi.net .

Statements included in this release that are not historical facts may be considered forward-looking statements that are subject to a variety of risks and uncertainties. There are a number of important factors that could cause actual results to differ materially from those expressed in any forward-looking statements made by the Company including, but not limited to, uncertainties relating to drug discovery and clinical development processes, the impact of competitive products and technological changes, changes in relationships with strategic partners and dependence upon strategic partners for the performance of critical activities under collaborative agreements, the ability of the Company to successfully directly market and sell its brachytherapy products, uncertainties relating to patent protection and regulatory approval, the stable supply of appropriate isotopes, the impact of competitive products and pricing, research and development estimates, market opportunities, risks associated with strategic opportunities or acquisitions the Company may pursue and the risk factors included in the Company's filings with the Securities and Exchange Commission. Any forward-looking statements contained in this news release speak only as of the date of this release, and the Company undertakes no obligation to revise or update any forward-looking statements, whether as a result of new information, future results or otherwise.