Academic Collaborator of Theseus Imaging Corporation Receives Award for Apomate Research.

Business Editors

CHATSWORTH, Calif.--(BUSINESS WIRE)--June 8, 2000

North American Scientific Inc. (Nasdaq:NASI) and Theseus Imaging Corp. announced today that for the third time in the last two years, a scientific study related to Theseus Imaging Corporation's Apomate(TM) imaging agent for the in-vivo detection of cell death has been recognized as the most outstanding original work presented at a peer-reviewed scientific meeting.

Dr. Ali Zarrinkhameh of Hahnemann Hospital, Philadelphia, received the award for his study entitled "Tc 99m Annexin-V Imaging Study for the Noninvasive Detection of Apoptosis in Patients with Cardiac Allografts," presented at the Fourth International Meeting of Nuclear Cardiology Today in Cesena, Italy. The meeting was sponsored by seven international medical societies including the American Society of Nuclear Cardiology, the European Society of Nuclear Medicine and the Working Group on Nuclear Cardiology of the European Society of Cardiology.

Dr. Zarrinkhameh concluded that the study had demonstrated "the clinical feasibility and safety of annexin imaging." He also noted that, if confirmed in larger pivotal trials, "the techniques may allow reduction in the number of surveillance biopsies in cardiac allograft recipients."

Dr. Zarrinkhameh's comments refer to the working hypothesis that has guided development of Apomate(TM), centering on the possible therapeutic benefits of imaging apoptosis, or programmed cell death. The process of apoptosis typically accompanies at least two medical processes of immediate interest to researchers: the early phases of rejection of a transplanted heart, and the attack of chemotherapeutic agents on cancerous cells.

Within both the undesired transplant rejection scenario and the desired chemotherapy effects, a protein called annexin binds to cells undergoing apoptosis. By incorporating a radioactive marker into annexin administered to the patient, Apomate(TM) allows real-time imaging of the tissues undergoing apoptosis, using conventional imaging systems.

In heart transplant cases, researchers hope to find an alternative for the frequent, invasive post-transplant biopsies of heart tissue that have been required to monitor the recipient's acceptance or rejection of the transplanted organ. Used as an adjunct to chemotherapy, it is hoped that Apomate(TM) will allow physicians to gain quicker, more accurate confirmation of the cancer-killing effects of the chosen chemotherapeutic agent, potentially allowing more effective treatment to be selected for each individual patient.

This confirmation of the importance of the Apomate(TM) imaging research follows the earlier receipt of the Caffey Award from the Society of Pediatric Radiology in 1998 to Dr. Francis Blankenberg of Stanford University for his pioneering work with Tc-99m Annexin V for imaging apoptosis. Dr. Blankenberg also received the 1999 Fleischner Society Memorial Award for his work on imaging of apoptosis with Tc-99m annexin V, the active component of the Theseus Apomate(TM) kit.

This recognition of the importance of in vivo imaging of cell death by multiple professional societies continues to confirm the belief that Apomate(TM) will be an important new clinical technique in the management of therapy of cancer and heart disease.

"We are pleased to see further confirmation of the potential applications of Apomate(TM), whose promise has been validated on a preliminary basis by a series of successful studies suggesting that it may become a new standard of care," commented L. Michael Cutrer, President and CEO of North American Scientific.

North American Scientific and Theseus Imaging announced the signing of a definitive merger agreement on Oct. 21, 1999. The acquisition of Theseus is contingent upon final due diligence, receipt of a financial fairness opinion from a qualified independent third party and satisfactory initial clinical results.

North American Scientific manufactures and markets a broad line of products for medical therapeutic and diagnostic, environmental, and research applications. For more information, 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, uncertainties relating to patent protection and regulatory approval, the stable supply of appropriate isotopes, whether produced by the company or purchased from third-party vendors, the impact of competitive products and pricing, 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.