Shares in Poseida Therapeutics toppled as much as 38% on Monday after the company disclosed in a US Securities and Exchange Commission filing that a Phase I trial for P-PSMA-101 in metastatic, castrate-resistant prostate cancer has been placed on clinical hold by the FDA. According to Poseida, the decision follows the death of a patient in the study who had been treated with the investigational autologous CAR-T-cell therapy in late July.
The patient in question, who had previously failed treatment with multiple anti-cancer agents, died of hepatic failure 19 days post-treatment with P-PSMA-101, after developing symptoms consistent with macrophage activation syndrome (MAS), "a serious and potentially fatal overactivation of the immune system which has been associated with CAR-T therapies, but can have other causes such as infection and autoimmune disease," Poseida said.
Prior to that, through the first seven days after treatment with P-PSMA-101, the patient had normal laboratory results and showed no clinical symptoms indicating an adverse event. Poseida said the patient missed both his day 10 and day 14 follow up visits, but during this time developed symptoms that subsequently led to hospitalisation and he died of hepatic failure at day 19. The patient also developed blurred vision that was diagnosed as uveitis.
"To date, there have been no other serious adverse events of decreased vision, uveitis, MAS, or hepatic failure reported in study P-PSMA-101-001," the company said in the regulatory filing, adding "there has also been no cytokine release syndrome or neurotoxicity reported."
Poseida is now assessing the patient death and evaluating its next steps, including suggesting possible protocol changes. The company said it is awaiting a formal response from the FDA and also preparing recommendations designed to allow resumption of the trial.
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