Enzon Pharmaceuticals, Inc. announced that several patients have been enrolled in two phase 1 studies of PEG-SN38 (EZN-2208), Enzon's PEGylated form of SN38, the active metabolite of the cancer drug Camptosar (irinotecan HCl injection). These studies are designed to evaluate the safety, tolerability, and pharmacokinetics of PEG-SN38 in different dosing schedules for patients with advanced solid tumours or lymphoma.

At the April 2007 American Association for Cancer Research (AACR) annual meeting, researchers presented positive preclinical data for PEG-SN38. The data showed that treatment with the PEGylated SN38 resulted in significant tumour growth inhibition in mice resistant to Camptosar and outperformed Camptosar in mice when given as a second round therapy. Additionally, PEG-SN38 demonstrated long-lasting anti-tumour activity in mouse models of human breast, colorectal and pancreatic cancers.

"The positive preclinical data showing tumour growth inhibition in Camptosar-resistant mice generated a lot of excitement around this product candidate in the oncology field," said Jeffrey H. Buchalter, Enzon's chairman and chief executive officer. "Resistant tumours are very difficult to treat. We look forward to evaluating PEG-SN38 in patients with cancer and hope to develop a product that can help these people."

SN38 is the active metabolite of the widely used cancer drug irinotecan, marketed as Camptosar in the US. Although unmodified SN38 is 1,000 times more potent than Camptosar, it has not been converted into a viable drug candidate because it is insoluble. Using Enzon's new PEGylation technology, the company developed PEG-SN38 (EZN-2208), which results in a compound with excellent pharmaceutical properties as shown in animal models: increased solubility, higher exposure, and longer half-life than unmodified SN38. Preclinical data presented at the 18th annual EORTC-NCI-AACR (European Organization for Research and Treatment of Cancer-National Cancer Institute-American Association for Cancer Research) meeting showed that these features led to greater efficacy over Camptosar in breast, colorectal and pancreatic cancer models.

Enzon Pharmaceuticals, Inc. is a biopharmaceutical company dedicated to the development, manufacturing, commercialization of important medicines for patients with cancer and other life-threatening conditions.