Enzon Pharmaceuticals’ PEG-SN38 (EZN-2208) has demonstrated positive results in a Phase II open-label study involving patients previously treated with metastatic breast cancer.

PEG-SN38, a PEGylated conjugate of SN38, is designed to provide therapeutic advantages over unmodified SN38 and current therapies.

The Phase II study investigated the efficacy of single-agent PEG-SN38 in 164 2 women who had previously been treated for metastatic breast cancer with either anthracycline and taxane, or anthracycline, taxane and capecitabine.

The primary endpoint was to determine overall response and secondary objectives including` duration of response, progression-free survival, overall survival and safety.

The trial demonstrated median duration of response of 4.2 and 5.2 months, median PFS values of 3.8 and 3.4 months for the anthracycline and taxane cohort, and median overall survival values of 10.5 and eight months anthracycline, taxane and capecitabine cohort.

Overall response was found to be meaningful, with both groups demonstrating clinical benefit rates, and PEG-SN38 was also found to be safe and well-tolerated in the pre-treated patients with neutropenia, diarrhoea and leukopenia.

Principal investigator Joyce O’Shaughnessy said that PEG-SN38 demonstrated an improvement in overall response rate in previously treated patients.

”PEG-SN38 further demonstrated similar activity in both hormone-expressing and non-hormone-expressing tumours, suggesting it may be effective in ‘triple-negative’ forms of breast cancer," O’Shaughnessy said.

Enzon Pharmaceuticals vice-president Aby Buchbinder said that the findings support the earlier findings demonstrating PEG-SN38’s anti-tumour activity in breast cancer, including triple-negative models.

”Furthermore, they contribute to the substantial clinical evidence indicating the potential of PEG-SN38 to deliver meaningful therapeutic benefit in multiple oncology indications in which the full benefit of irinotecan cannot be realised due to toxicity," Buchbinder added.

The company is currently looking for a strategic partner to further develop and commercialise PEG-SN38, to treat breast cancer as well as for other malignancies, including paediatric neuroblastoma.