OXi4503's Tumor Cell-Killing Mechanism Explored in Peer-Reviewed International Journal of Cancer.

Business Editors/Health/Medical Writers

WALTHAM, Mass.--(BUSINESS WIRE)--May 6, 2004

New Research Highlights OXiGENE's Lead Pre-Clinical

Vascular Targeting Agent

OXiGENE, Inc. (NASDAQ: OXGN, XSSE: OXGN) today announced the publication of a research paper exploring the mechanism by which its lead pre-clinical compound, OXi4503, triggers the collapse of the chaotic network of blood vessels within a solid tumor. The paper, "Combretastatin family member OXi4503 induces tumor vascular collapse through the induction of endothelial apoptosis," appears in the "Early View" online edition of the peer-reviewed International Journal of Cancer (http://www3.interscience.wiley.com/cgi-bin/jissue/76502439). Findings will be published in the journal's print edition in issue 111 (4). The study, conducted in conjunction with scientists from the University of Lund in Sweden and Baylor University in Texas, is important in understanding the sequence of events thought to make tumor vessels vulnerable to this new vascular targeting agent.

The effects of a single dose of OXi4503 (100 mg/kg) on tumor blood flow were studied in a mouse model bearing MHEC5-T hemangioendothelioma. Blood flow in the tumor tissue was reduced to 50 percent one hour after drug administration and to less than 10 percent at six hours. Even at extended periods up to 72 hours, after a single treatment, blood flow had recovered to just 35 percent.

"The time course of the tumor vascular response observed with OXi4503 treatment supports this drug for development as a stand-alone therapy, and also lends support for the use of the drug in combination with other cancer therapies," researchers reported.

"These findings further validate the body of pre-clinical data suggesting that OXi4503 holds significant promise as an anti-tumor compound," said Dai Chaplin, Ph.D., OXiGENE's chief scientific officer and head of research and development. "While it is still very early in the evolution of this compound, the insight we have gained into how OXi4503 works will be important as we prepare to embark on its clinical development."

OXi4503 and OXiGENE's investigational drug, Combretastatin A4 Prodrug (CA4P), are small molecule vascular targeting agents designed to cut off blood supply to tumors by changing the shape of the vasculature's endothelial cells.

The International Journal of Cancer research produced several key findings in addition to evidence of blood flow shutdown. For example, researchers said that, compared with the reduction in tumor tissue, blood flow in normal tissue was not significantly affected by OXi4503. This suggests the potential of OXi4503 to selectively target tumor blood vessels.

In addition, researchers noted that the compound increased the permeability of tumor blood vessels, potentially ignited by a sudden release of a substance known as vascular endothelial growth factor (VEGF). Under normal conditions, VEGF causes new tumor blood vessels to sprout and tumors to spread. But when coupled with blood flow shutdown, researchers hypothesized that VEGF-induced changes in vessel permeability following treatment with OXi4503 might actually contribute to the collapse of the tumor vasculature.

Cancer Research UK, the world's largest volunteer-sponsored cancer research organization, is completing pre-clinical toxicology testing on OXi4503 and plans to advance the compound into a Phase I clinical trial in late 2004.

About OXiGENE

OXiGENE is the world leader in the development of vascular targeting agents (VTAs), novel biopharmaceutical compounds designed to selectively target and destroy new blood vessels. The Company's lead compound, Combretastatin A4 Prodrug (CA4P), is in clinical development in patients with solid tumor cancers and wet age-related macular degeneration. Three other OXiGENE VTAs, OXi4503, OXi6197 and OXi8007, are in pre-clinical development. For more information about OXiGENE, visit www.oxigene.com.

Safe Harbor Statement

Statements in this news release are considered "forward-looking statements" within the meaning of the Private Securities Litigation Reform Act of 1995. These statements include, but are not limited to the potential effects of OXi4503 and the expectation that OXi4503 will enter clinical trials in late 2004. Any or all of the forward-looking statements in this press release may turn out to be wrong. They can be affected by inaccurate assumptions OXiGENE might make or by known or unknown risks and uncertainties, including, but not limited to: the early stage of product development; the ability to secure necessary patents; uncertainties as to the future success of ongoing and planned clinical trials; and the unproven safety and efficacy of products under development. Consequently, no forward-looking statement can be guaranteed, and actual results may vary materially. Additional information concerning factors that could cause actual results to materially differ from those in the forward-looking statements are contained in OXiGENE's reports to the Securities and Exchange Commission, including OXiGENE's 10-Q, 8-K and 10-K reports. However, OXiGENE undertakes no obligation to publicly update forward-looking statements, whether because of new information, future events or otherwise.