Ipsen has become an active dealmaker as it pursues growth in oncology, and its latest move is the $450 million acquisition of Kartos Therapeutics, a clinical-stage biotech whose lead program could improve the standard of care for a rare type of blood cancer.
Redwood City, California-based Kartos aims to treat cancer by leveraging p53, a protein with tumor-suppressing properties. This protein has eluded many efforts to drug it directly, but Kartos takes another approach. The biotech’s drug, navtemadlin, is an oral small molecule designed to block murine double minute 2 (MDM2), a protein that tags p53 for degradation by a cellular disposal system. Blocking MDM2 is intended to lead to higher levels of p53.
The lead cancer indication for navtemadlin is myelofibrosis, a cancer in which scar tissue in the bone marrow leads to the production of abnormal blood cells. The declining bone marrow function shifts production of blood cells to other organs, such as the spleen. An enlarged spleen is a hallmark characteristic of myelofibrosis. Standard treatment is the Incyte drug Jakafi, a small molecule designed to block JAK1 and JAK2 enzymes whose overactive signaling drives the disease. The problem is some patients don’t respond well enough to Jakafi, leading many of them to discontinue treatment.
In Phase 1b/2 testing in myelofibrosis patients who had an inadequate response to Jakafi, Kartos reported that adding navtemadlin led to clinically meaningful and disease-modifying activity. These results were presented at the European Hematology Association Congress in 2023. Navtemadlin has since advanced to a larger Phase 3 study enrolling more than 600 patients globally. The main goals are measuring spleen volume reduction and disease symptoms at 24 weeks.
In a prepared statement included in Monday’s Kartos acquisition announcement, Dr. Pankit Vachhani, director of clinical research unit at the University of Alabama at Birmingham and global principal investigator of navtemadlin’s Phase 3 study, said this clinical trial is the largest ever conducted in myelofibrosis and is designed to reflect real-world clinical practice.
“I am excited by the prospect of navtemadlin delivering disease modifying benefits, ushering an era of rational combination therapies for those with suboptimal response to standard therapy, and targeting complementary disease pathways beyond JAK inhibition alone in myelofibrosis,” Vachhani said.
Oncology is the largest therapeutic area for Paris-based Ipsen, accounting for more than €2.5 billion (about $2.8 billion) of the company’s €3.6 billion (about $4.1 billion) in 2025 revenue. Ipsen’s top product is Somatuline Depot, whose approval in cancer covers the treatment of gastroenteropancreatic neuroendocrine tumors. Somatuline accounted for €1.1 billion (about $1.2 billion) in revenue last year, but its patents have expired.
Business deals are helping Ipsen build up its oncology pipeline. The company’s newest product is Ojemda, awarded conditional marketing authorization in Europe in April as a treatment for a particular type of pediatric brain cancer. Ojemda was developed by Day One Biopharmaceuticals; in 2024, Ipsen licensed rights to the molecule outside of the U.S. In blood cancer, Ipsen’s IPN60340 is in mid-stage development for acute myeloid leukemia patients who are ineligible for traditional chemotherapy. This drug candidate came from the acquisition of ImCheck Therapeutics last year. Ipsen also has early-stage antibody drug conjugates (ADCs) via deals with China-based biotechs Foreseen Biotechnology and Simcere Zaiming.
Not all of Ipsen’s deals have panned out. Tazverik, a drug for follicular lymphoma and epithelioid sarcoma from the 2022 acquisition of Epizyme, was voluntarily withdrawn from the market in March after post-marketing testing showed a higher risk of secondary hematologic malignancies. Also, Ipsen last year terminated an agreement that gave it rights to clinical-stage ADC from Sutro Biopharma.
The Kartos acquisition is expected to close by the end of the third quarter of this year. Beyond the $450 million upfront payment, the deal terms make Ipsen responsible for paying out up to $1.3 billion more if Kartos’s drug achieves regulatory and sales milestones.
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