Drug Development

Seattle Genetics stock tumbles after 4 deaths force the FDA to slap a clinical hold on AML drug

Seven months after Seattle Genetics $SGEN launched a registration study for an armed antibody dubbed SGN-CD33A (vadastuximab talirine), the FDA slapped a full or partial hold on a slate of its early-stage efforts in acute myeloid leukemia after four patients died of liver toxicity.

Seattle Genetics’ stock tumbled 15% on the news, wiping out more than a billion dollars in market cap.

The full hold was placed on a Phase I/II trial in pre- and post-allogeneic transplant AML patients while the FDA ordered new recruitment stopped for two Phase I studies. Researchers say that the tracked 6 cases of hepatotoxicity, or liver toxicity, including cases of veno-occlusive disease.

“We spoke with mgmt., who expects a potential rapid resolution of the partial clinical hold on two of the affected Ph I/II trials in AML, while the FDA seems predominantly focused on the ongoing pre-transplant conditioning study where the rate of hepatotoxicity is already high with standard of care chemotherapy alone,” noted Leerink’s Michael Schmidt Tuesday morning.

“Seattle Genetics is working diligently with the FDA to determine whether there is any association between hepatotoxicity and treatment with SGN-CD33A, to promptly identify appropriate protocol amendments for patient safety and to enable continuation of these trials,” the company said in a statement.

Their Phase III trial for older AML patients and a Phase I/II trial in myelodysplastic syndrome are continuing.

Seattle Genetics has been attracting some positive attention for this program from analysts looking for the biotech to expand its portfolio beyond Adcetris. The biotech launched its late-stage study in May after posting positive Phase I data from a combination study at ASH.

Data demonstrated that 15 of 23 (65 percent) evaluable patients achieved CR/CRi. At a median follow-up of 7.7 months, median survival had not yet been reached, and 72 percent of patients remained alive and on study.

Their Phase III combines a CD33-targeting antibody expressed in leukemic blasts in AML patients with Vidaza or Dacogen.

There have been more than a dozen full and partial clinical holds imposed by the FDA this year, ranging from short pauses at Adaptimmune to a near instant lift by the FDA followed by a disastrous new voluntary hold for Juno’s lead CAR-T. There’s no way to gauge how long a hold may last, as Zafgen found out for itself as it struggled to get out from under a regulatory block earlier in the year.


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