Enzon Pharmaceuticals, Inc. (Nasdaq: ENZN) today announced the publication of preclinical data demonstrating that PEG-SN38 (EZN-2208), the Company’s novel PEGylated DNA topoisomerase I inhibitor, led to significantly greater tumor regression as compared to CPT-11 (irinotecan) in both in vitro and in vivo models of pediatric neuroblastoma. The data were published in the October 1, 2010 issue of Clinical Cancer Research (Pastorino, F. et al, volume 16, number 9, pp. 4809-4821). “PEG-SN38 demonstrated complete and durable tumor regression in a series of experimental models that were designed to reflect the clinical progression of neuroblastoma in pediatric patients,” said Ivan Horak, M.D., Enzon’s President of Research and Development and Chief Scientific Officer, and one of the study’s authors. “Neuroblastoma is the second-most common pediatric solid tumor, with a five year-survival rate of only 25 percent. The limited efficacy and significant toxicities associated with currently available treatment options underscore the need for new and better therapies. The present findings form the basis for our ongoing Phase I study of PEG-SN38 in pediatric patients with solid tumors which may include patients with neuroblastoma.” The preclinical study was designed to assess the antitumor activity of PEG-SN38 relative to CPT-11, a chemotherapeutic drug that is currently used in the clinical treatment of neuroblastoma and other solid tumors. CPT-11 has shown activity against neuroblastoma that has become resistant to standard treatments, and its non-hematological toxicities are considered transient and manageable. However, its limitations include the inconvenience of current daily schedule and gastrointestinal side effects. While direct administration of SN38 may overcome these limitations, its low solubility does not allow formulation in conventional pharmaceutical vehicles that would permit administration to patients. Enzon’s proprietary customized linker-enhanced PEGylation technology allows a soluble, more potent, and longer-lasting version of the drug, which may be administered weekly or once every three weeks.