Pfizer has acquired for $87.5 million a minority equity stake in AM-Pharma and an exclusive option to acquire the remaining equity—an outlay that could balloon to $600 million if the pharma giant decides to buy the Dutch biotech.

Pfizer’s decision to exercise the option will hinge on the results of a Phase II trial of AM-Pharma’s recombinant human Alkaline Phosphatase (recAP) for sepsis-related acute kidney injury (AKI). No drugs are currently approved for AKI, which according to AM-Pharma affects about 3 million people each year in Europe, the U.S. and Japan, and is associated with death in about 700,000 patients. The only treatment option available is dialysis and supportive care.

Results from the Phase II trial are expected in the second half of 2016, the companies said. The trial’s primary objectives are to determine the most effective dose of recAP; establish proof-of-concept in ameliorating AKI through measuring kidney function; and confirm favorable safety data from previous trials.

The trial has two-stages, with AM-Pharma saying in January it will recruit a total of 290 patients. In the first stage, 120 patients will be evaluated to identify and select the most effective dose out of three different doses of recAP. In the second stage, an additional 170 patients will be recruited in two arms of 85 patients each, receiving either the best dose of recAP as identified in stage one, or placebo.

In both stages, the effect on kidney function during the first seven days following therapy will be measured by creatinine clearance rate. The trial will also record the incidence and duration of dialysis over 28 days, the prevention of chronic kidney disease, and non-kidney related clinical parameters such as the duration of intensive care and hospital stay, and patients’ quality of life.

In addition to what it shelled out for the minority stake and option, Pfizer agreed to spend $512.5 million tied to exercising its option and launching any product resulting from the agreement. Other terms of the deal were not disclosed.

The AM-Pharma deal continues a buying spree for Pfizer in the year since it failed to come to terms with AstraZeneca that has included an up-to-$360 million purchase of InnoPharma, a controlling interest in Redvax for an undisclosed price, a $17 billion acquisition of Hospira—and according to unnamed sources cited by Reuters, a deal in the works to buy Swedish Orphan Biovitrum, which has reported a market value of $4.3 billion.

“This agreement is a significant step for AM-Pharma, and we welcome Pfizer as a shareholder and dedicated partner,” AM-Pharma CEO Erik van den Berg said in a statement. “This deal not only provides good shareholder value, but provides the next step in the development of recAP as a potential treatment for patients with acute kidney injury and other inflammatory diseases.”

AM-Pharma is developing recAP as a potential treatment for ulcerative colitis (UC) and hypophosphatasia (HPP), in addition to AKI. Before launching the Phase II trial in January, AM-Pharma developed and successfully tested a bovine form of alkaline phosphatase in three Phase II trials in patients with UC, as well as AKI and sepsis.

Founded in 2001, AM-Pharma is a private company based in Bunnik, the Netherlands. AM-Pharma has raised €67 million (about $75.3 million) from a syndicate of international investors including biopharma giants Abbvie and Shire, as well as Inventages, Forbion Capital Partners, Gilde Healthcare, Ysios Capital, Kurma biofund, IDInvest Partners, and BB Biotech Ventures.

During its most recent financing round in September, AM-Pharma raised €12.2 million ($13.7 million) toward the completion of the Phase II study of recAP in AKI patients, as well as continued development of an oral formulation of recAP for UC patients.