Ipsen announced on June 29 that it will acquire California-based Kartos Therapeutics in a deal valued at up to $1.75 billion, aiming to secure a late-stage drug candidate for a rare blood cancer.
The agreement includes an upfront payment of $450 million from Ipsen, with the potential for up to $1.3 billion in additional payments tied to regulatory approval milestones and sales-based commitments. Both companies expect the transaction to close in the third quarter.
At the center of the acquisition is navtemadlin, an orally available MDM2 inhibitor designed to restore expression of the tumor suppressor protein p53. Kartos is evaluating navtemadlin as an add-on therapy with ruxolitinib, a JAK inhibitor, for patients with high-risk myelofibrosis who have responded suboptimally to standard treatment. According to Ipsen’s release, prognosis after discontinuation of ruxolitinib remains poor, with median overall survival ranging from one to two years.
Data from Phase 1b/2 trials released in 2023 showed that 44% of patients experienced at least a 25% reduction in spleen volume after 24 weeks on navtemadlin, while 31% saw reductions of at least 35%. The treatment also reduced disease-causing genetic variants and improved bone marrow fibrosis—effects described by Ipsen as indicative of “potential disease modification activity.”
Navtemadlin is currently being studied in the Phase 3 POIESIS trial involving more than 600 patients across over 250 sites worldwide. The study targets high-risk individuals who previously responded inadequately to ruxolitinib and lack pathologic mutations affecting p53.
Ipsen CEO David Loew said in a prepared statement on Monday that navtemadlin has the potential “to define a new treatment paradigm for patients with myelofibrosis,” adding that it could be available “as early as 2028.”
This acquisition follows Ipsen’s March withdrawal of its lymphoma and sarcoma therapy Tazverik due to increased risk of secondary cancers observed during clinical trials.
