Data Supports Broad Anti-Cancer Potential Of Peregrine's Anti-PS Technology Platform

Peregrine Pharmaceuticals's fusion protein combining interleukin-2 (IL-2) and 2aG4, an anti-phosphatidylserine (anti-PS) antibody similar to Peregrine's bavituximab, was effective in stimulating a strong protective immune response when added to a cancer vaccine. The combination was effective in protecting animals against a lethal challenge with a highly aggressive form of breast cancer. The new data is being presented by Dr. Philip Thorpe, professor of pharmacology at UT Southwestern Medical Center in Dallas and a member of the Peregrine Scientific Resource Board.

In the study reported today, breast cancer cells were irradiated to inactivate them and to expose the anti-PS target on their surface. Their radiated cancer cells were then treated with the 2aG4-IL-2 fusion protein to increase their immunogenicity before being used to vaccinate the study animals. Eighty percent of the immunized mice survived a subsequent lethal challenge with live versions of these aggressive breast cancer cells. In contrast, no animals immunized with untreated irradiated breast cancer cells survived the subsequent lethal challenge.

"We are encouraged by the results of this study in a very challenging model of breast cancer that further support the broad potential of our anti-PS targeting platform," said Dr. Thorpe. "In view of these results, we are eager to learn more about the anti-cancer utility of these immunocytokine fusion proteins in combination with vaccines and as direct therapeutic agents."

The results of this study also suggest that anti-PS antibodies may be stimulating the immune system by a second mechanism. Phosphatidylserine that has become exposed on the external surface of cells has been shown to dampen the body's natural immune response. Researchers have demonstrated that anti-PS antibodies can block this immune-suppressing signal by binding to and neutralizing the exposed phosphatidylserine, allowing the immune system to mount a more vigorous response.

"This data further supports the broad potential of our anti-PS platform, building on earlier data demonstrating that anti-PS antibodies have the ability to recognize tumors and then initiate a robust immune response," said Steven W. King, president and CEO of Peregrine. "Previously we reported that our fusion proteins demonstrated excellent anti-tumor activity in a number of cancer models as a therapeutic agent. This new research shows that these same agents also have the potential to enhance cancer vaccines, priming the body's immune system to prevent the development of cancer in animals challenged with a normally lethal dose of cancer cells by enhancing the immune response to the tumor."

The new class of immunocytokine fusion protein agents is part of Peregrine's Vascular Targeting Agent (VTA) technology platform for cancer therapy that includes over 200 patents and patent applications covering broad concepts of tumor therapy using agents that target tumor blood vessels.