Merrimack Pharmaceuticals Expands Phase II Lung Cancer Study

Merrimack Pharmaceuticals Inc. saw a slight uptick in pre-market trading this morning after the company announced it is expanding enrollment in a Phase II lung cancer study.

Cambridge, Mass.-based Merrimack said it has seen a "tremendous interest" in its open-label Phase II SHERLOC study assessing progression-free survival in patients who have received MM-121 in combination with docetaxel. The trial is comparing the combination treatment with docetaxel as a stand-alone therapy in patients with heregulin-positive non-small cell lung cancer who have progressed after a platinum-containing regimen.

In its announcement, Merrimack said it will expand trial enrollment from 80 patients to 100. The trial patients must have received a prior platinum-based therapy, as well as prior immunotherapy where available and clinically indicated, the company said.

The trial expansion followed a year in which Merrimack reset its focus on its 10 wholly-owned clinical and preclinical programs that target biomarker-defined cancers. Merrimack began its internally-developed focus in early January after the company sold some assets, including FDA-approved pancreatic cancer treatment Onivde to Ipsen for $575 million. That placed the company’s futures on its wholly-owned assets, including MM-121.

Investors have not been too happy with Merrimack since the Ipsen deal. Over the course of 2017, the company saw its share prices drop by 63 percent. Shares of Merrimack closed at $11.58 on March 9.

Merrimack’s MM-121 (seribantumab) is a fully human anti-HER3 (ErbB3) monoclonal antibody. The drug is designed to target phenotypically distinct heregulin positive cancer cells within solid tumors. Typically heregulin positive cancer cells have been able to "escape the effects" of targeted, cytotoxic and anti-endocrine therapies, Merrimack said. That ability provides the potential for the rapid progression of the disease. When MM-121 is used in combination with the chemotherapy drug docetaxel, the company believes the dual treatment will block the heregulin/HER3 signaling axis, which will make tumor cells more sensitive to the effects of the combination therapy.

In October 2017 the U.S. Food and Drug Administration granted orphan drug designation to MM-121 in this setting. The orphan drug designation is granted to drugs that are being developed to treat a patient population of fewer than 200,000 people in the United States.

Sergio Santillana, Merrimack’s chief medical officer, said enrollment in the SHERLOC study has been faster than the company expected. Calling that an encouraging sign, Santillana said the interest reflects what the company believes is "the significant unmet medical need among this patient population."

"This expansion enables us to maximize this opportunity to gain meaningful insight, by strengthening the statistical design of the study, and emerge with a clear path forward," Santillana said in a statement.

Even with the additional patients added to the trial, Merrimack said it anticipates rolling out top-line data for the study in the second half of 2018.

In addition to heregulin-positive non-small cell lung cancer, Merrimack is also testing MM-121 in patients with heregulin-positive, hormone receptor-positive and HER2-negative post-menopausal metastatic breast cancer. In February the company dosed its first patient in a randomized Phase II trial. The mid-stage study, called SHERBOC, is testing the combination of MM-121 with chemotherapy treatment fulvestrant against placebo.

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