Chimerix shares crash as antiviral flops and deaths spike in first PhIII challenge

Chimerix CMO W. Garrett Nichols

High hopes for Chimerix's antiviral turned into a bad case of data shock Monday morning after the biotech revealed that brincidofovir had failed its first Phase III study. The stock ($CMRX) instantly plunged, erasing 79% of its value by midmorning as investors absorbed the news of the setback and the company halted enrollment in two other late-stage transplant trials.

Chimerix is best known for its refusal to provide the experimental antiviral to a dying boy whose parents had demanded it on a compassionate-use basis. Faced with an onslaught of viral rage driven in part by 24/7 cable coverage and a sustained social media outburst, Chimerix opted to start a new clinical trial, making him the first patient in the study. The boy rallied, the CEO was replaced and expectations skyrocketed--until today.

Investigators were testing the antiviral's ability to prevent cases of cytomegalovirus (CMV) infection through the first 24 weeks after hematopoietic cell transplantation. But the researchers say that during the final 10 weeks, when they were off treatment, cases of CMV shot up and exceeded the control arm. Deaths in the antiviral arm also exceeded the mortality rate in the control arm.

The biotech says that an early analysis suggested that a surge in graft-versus-host disease (GVHD) and the resulting use of corticosteroids drove the spike in deaths and infections. The full set of data is being held back for release at a scientific session.

Hoping to maintain some level of confidence, the company asserted that there's good reason to believe that their main development program will work against adenovirus and smallpox and in other populations, but Chimerix also halted new enrollment in kidney transplant patients as they assessed the failure.

Brincidofovir is a lipid-conjugated version of cidofovir specifically designed to amp up the antiviral impact with a pill while sparing kidneys from a toxic threat. Its ability to get into cells more effectively than cidofovir has vastly improved its punch against all 5 DNA viral infections. In a small open-label pilot study driven by the case of young Josh Hardy, the antiviral was successful in dramatically reducing the rate of adenovirus infections. But that study may ultimately raise fresh doubts about the value of running small, impromptu studies without a control arm.

"The population of allogeneic stem cell transplant recipients is heterogeneous and complex; we will be evaluating the sub-groups of patients within SUPPRESS, such as T-cell depleted transplant recipients who have a lower risk of GVHD, to better understand these results and inform our next steps," says Chief Medical Officer Dr. W. Garrett Nichols. "We are reaching out to investigators and other experts to help us assess the complete data set to understand what may have caused the results of the SUPPRESS trial to differ substantially from those seen in the Phase II study. Additionally, we are in communication with the U.S. Food and Drug Administration and other regulatory bodies, and will share any updates on the brincidofovir clinical program when we can."

- here's the release