CAMBRIDGE, Mass., April 8, 2014 (GLOBE NEWSWIRE) -- Merrimack Pharmaceuticals, Inc. (Nasdaq:MACK) today announced Phase 1 results from a clinical pilot study demonstrating that ferumoxytol*, an iron oxide nanoparticle, was well tolerated when used as a tumor contrast agent prior to MM-398 treatment. Data from the first cohort of patients in this study were presented at the American Association of Cancer Research Annual Meeting, April 5-9, 2014, in San Diego, California. "This application of ferumoxytol magnetic resonance imaging has the potential to become a minimally invasive predictive biomarker for liposomal therapies. We hope that the continuation and expansion of this approach will allow us to identify patients most likely to benefit from MM-398 treatment," said Jonathan Fitzgerald, Ph.D., Senior Director of Discovery at Merrimack. "Though our initial data are from a small sample of a diverse patient population, we are encouraged to see that almost all of the tumor lesions that shrank after MM-398 treatment were associated with higher levels of ferumoxytol, as seen on the MRI." Ferumoxytol's propensity for uptake by tumor associated macrophages and similar distribution patterns to MM-398 in preclinical models led to the clinical feasibility study. The ability to image and analyze the levels of ferumoxytol in tumors may be correlated to estimating the MM-398 tumor concentration. These data are also supported by Merrimack's proprietary Systems Biology approach, as computational modeling of ferumoxytol MRI was used to calculate parameters describing its behavior in tumor tissue. This modeling platform, coupled with the imaging approach with ferumoxytol MRI, may be useful as a predictive biomarker of nanotherapeutics such as MM-398. Primary objectives of this study are to evaluate the feasibility of ferumoxytol to identify tumor-associated macrophages, which may positively correlate with MM-398 activity, and to measure tumor levels of irinotecan and SN-38. The ongoing study has shown that there were no safety-related interactions between ferumoxytol and MM-398 in this preliminary patient population.