Merrimack Pharmaceuticals, Inc, a biopharmaceutical company discovering, developing and preparing to commercialize innovative medicines, announced the initiation of clinical imaging assessing the use of a potential marker for delivery of MM-398 (irinotecan liposome injection), also known as "nal-IRI," to metastatic breast cancer.

This study is an expansion of a phase 1 pilot study which assessed the feasibility of using ferumoxytol, an iron oxide nanoparticle, to act as a marker for MM-398 tumor response prediction. The study will now enroll patients who have metastatic breast cancer which is either hormone receptor-positive, triple-negative, or where active brain metastases are present.

"We were encouraged by the results of the initial pilot phase of the study, particularly the data that suggest a relationship between high levels of ferumoxytol uptake and shrinkage of tumor lesions after MM-398 treatment," said Dr. Jasgit Sachdev, MD, Virginia G Piper Cancer Center. "We are excited to continue to evaluate the activity of MM-398 and the predictive value of this imaging approach in additional patients with metastatic breast cancer."

The data from the initial pilot study (n=31 lesions comprising 9 patients) showed a relationship between ferumoxytol levels in individual tumor lesions, as measured using magnetic resonance imaging, and corresponding change in individual tumor lesion size following treatment with MM-398. Results observed in several patients with metastatic breast cancer in the pilot study warranted further expansion of the study to additional patients in this population. Adverse events from MM-398 therapy were consistent with previous studies. Reported grade 3 and above adverse events related to MM-398 treatment included diarrhea, hypokalemia, abdominal pain, anemia, nausea and neutropenia.

"We look forward to expanding this study and aim to use it to support our biomarker hypothesis and further our strategy to use diagnostic imaging to identify the patients who are most likely to derive benefit from treatment with MM-398," said Bart Hendriks, Ph.D., director of imaging diagnostics at Merrimack.

As part of this expansion, 30 patients with metastatic breast cancer will be imaged with ferumoxytol followed by treatment with MM-398. Ten patients will be enrolled in each of three cohorts as follows: ER and/or PR-positive metastatic breast cancer, triple-negative metastatic breast cancer or metastatic breast cancer with active brain metastases.

Eligible patients for the trial must have received less than four prior lines of chemotherapy for the treatment of metastatic disease. The primary objectives of this study are to investigate the feasibility of ferumoxytol quantitation in tumor lesions and to characterize the relationship between ferumoxytol uptake in the tumor and tumor response to MM-398 in patients with advanced metastatic breast cancer. Merrimack plans to conduct the trial at multiple sites in the United States. The Virginia G Piper Cancer Center in Scottsdale, Arizona is now open to screen patients.

MM-398 (irinotecan liposome injection), is an encapsulation of irinotecan in a long-circulating liposomal formulation. The activated form of irinotecan is SN-38, which functions by inhibiting topoisomerase I (an essential enzyme involved in DNA transcription and replication) and promoting cell death. Merrimack and Baxter International's biopharmaceutical business (NYSE: BAX) have an exclusive licensing agreement to develop and commercialize MM-398 outside of the United States. PharmaEngine, Inc. (Taipei, Taiwan) holds the rights to commercialize MM-398 in Taiwan.

Ferumoxytol, commercially available as Feraheme (AMAG Pharmaceuticals), is an iron-oxide, super-paramagnetic nanoparticle, known to be taken up by macrophages and for exhibiting magnetic resonance imaging properties. The US Food and Drug Administration has approved ferumoxytol for intravenous use as an iron replacement product for the treatment of iron deficiency anemia in adult patients with chronic kidney disease (CKD).