Chimerix’s first approved drug had several high-profile setbacks and ended up with a much narrower regulatory nod than initially hoped. Now the company is selling rights to that drug to Emergent BioSolutions as a way of raising cash as it looks ahead to a key late-stage trial for its lead asset, a drug that treats a rare type of cancer.

Tembexa, the drug that Emergent is getting, was approved last June as a treatment for smallpox infection. Under a partnership with Biomedical Advanced Research and Development Authority (BARDA), Chimerix developed the antiviral as a medical countermeasure to protect against smallpox used as a biological weapon. For that application, the drug’s customer base is essentially a single customer—BARDA. So far, Durham, North Carolina-based Chimerix has yet to record sales of the approved drug to the agency.

According to terms of the deal announced Monday, Emergent has agreed to pay Chimerix $225 million when the deal closes, plus up to $100 million more in up to four $25 million milestone payments. Each of those milestone payments is tied to BARDA exercising procurement options on Tembexa. Chimerix said that it is in negotiations with BARDA on a procurement contract and will continue to lead that process until complete.

Had things worked out differently, Tembexa might have found wider use as a broad-spectrum antiviral. The drug, known for most of its history under the name brincidofovir, was hoped to offer advantages over an injectable Gilead Sciences antiviral, cidofovir. In addition to its pill formulation that is easier for patients to take, Chimerix had hoped brincidofovir would be safer than the Gilead drug, which is associated with kidney damage. The first indication Chimerix targeted was treating cytomegalovirus infections in transplant patients.

In 2009, during the early days of brincidofovir’s clinical development, Chimerix also began making the drug available under the FDA’s compassionate use program, which allows access to experimental therapies for patients who have no therapeutic options. As the antiviral progressed in clinical trials, Chimerix closed its compassionate use program to focus on pivotal tests of the drug that could support an application seeking FDA approval. But in 2014, Chimerix found itself in the midst of a national debate about the “right to try” experimental drugs. A Virginia boy, Josh Hardy, was suffering from adenovirus infection following cancer treatment and a bone marrow transplant. His physicians recommended treatment with brincidofovir under compassionate use. The debate about access to the still experimental drug played out prominently in national news and social media. The company’s CEO even received death threats.

Chimerix found a way to provide the drug to Hardy, but not under compassionate use. The company worked with the FDA to design an open-label clinical trial testing brincidofovir in adenovirus. Hardy was the only patient. He reportedly responded to the treatment and was able to return home.

Brincidofovir did not fare well in late-stage clinical development. In 2015, the drug failed a Phase 3 study in cytomegalovirus infection, which led the company to stop two additional late-stage studies for the drug. What was left of the drug was the BARDA-funded smallpox program. That research continued, but brincidofovir’s Phase 3 failure in cytomegalovirus infection essentially marked the beginning of the end of Chimerix as an antiviral drug developer.

In 2019, Chimerix outlicensed global rights to brincidofovir to SymBio Pharmaceuticals for development in all human indications, except for orthopoxviruses, such as smallpox. Tokyo-based SymBio paid $5 million up front and could pay up to $180 million more if the drug achieves regulatory and commercial milestones. The deal put Chimerix in line for royalties from sales if SymBio commercializes the drug. According to the deal terms with Emergent, Chimerix is eligible to receive up to $12.5 million in regulatory milestones stemming from SymBio’s work with the drug.

Chimerix and Emergent said the Tembexa transaction could close within the current quarter. When it does, it will be a needed cash infusion. In its report of first quarter 2022 financial results, Chimerix said it had $53.4 million in capital to fund its operations. The biotech’s lead program, ONC201, is being readied to advance to pivotal testing in H3-K27M-mutant glioma, a rare type of brain tumor that develops in children. This cancer cannot be treated with chemotherapy and is difficult to remove by surgery. Chimerix said in its quarterly report that it expects to begin the ONC201 clinical trial later this year. To conserve cash and focus its resources on its lead drug candidate, Chimerix terminated work on DSTAT, a program that had reached Phase 3 testing in acute myeloid leukemia. In a statement, CEO Mike Sherman said that the decision followed an internal pipeline review.

“This narrower focus of development resources will ensure we optimize our execution in bringing ONC201 to patients as quickly as possible,” he said.

Photo by Flickr user Paul Joseph via a Creative Commons license