UK to Begin Siga’s Monkeypox Drug Trials as Soon as Next Week

Clinical trials for Siga Technologies Inc.’s monkeypox treatment will start as early as next week in the UK as the outbreak continues to grow, the company’s chief scientific officer told Bloomberg Law.

The UK studies will mark the first of a dozen clinical trial sites to launch around the world under the latest outbreak, Dennis E. Hruby, Siga’s executive vice president and chief scientific officer, said in an interview Tuesday.

US studies run by the National Institutes of Health are set to follow mid-September, and Canada isn’t far behind, he added. The trials could potentially ease some access issues to the drug faced in the US, Hruby said.

There will likely be some interim analysis along the way that will guide regulators about whether they want to continue with the trials or stop if there are sufficient data to evaluate the safety and efficacy of the vaccine.

Hruby said “we should see some data in this fall,” while noting that the timing of the data depends on how the pandemic rolls out.

Tpoxx is an antiviral that the US Food and Drug Administration approved in 2018 to treat smallpox, which is part of the same family of viruses. But that approval was largely based on animal data, which the agency allows when it’s unethical and impossible to conduct human studies without an outbreak.

The NIH had planned some studies in the Democratic Republic of Congo but that was with a different strain of the virus than the one causing the current outbreak. Hruby said Siga’s been working with Oxford University for two years on initiating a trial in the Central African Republic prior to the current monkeypox outbreak.

“Unfortunately, we have the outbreak. But for us, it also provides an opportunity to get that data to be able to get a full label approval for monkeypox,” Siga CEO Phillip Gomez said.

Historically Siga sells its Tpoxx to countries such as the US and Canada to stockpile in case of a smallpox outbreak.

“When there’s an outbreak like this, it is very important that the product is stockpiled and can be deployed rapidly. It then provides the natural follow up that we all expect, which is we want to collect real-world data to make sure we verify the very rigorous animal studies,” Gomez said.

As of Aug. 15, there are more than 36,500 cases of monkeypox in 92 locations globally. The US leads the world in cases with 11,890 reported by the Centers for Disease Control and Prevention.

Active vs. Placebo

The UK trial aims to enroll 500 volunteers, a target doubled by US researchers. Both trials will include placebo and active arms, but patients who progress to serious disease will be taken off the placebo arm.

US studies also will enroll children, but they will all get Tpoxx and won’t be placed in the placebo arm, Hruby said.

Tpoxx is only available in the US under an expanded access protocol, which requires a clinician to request access from federal authorities. There have been complaints about the paperwork involved, despite work by the FDA and CDC to reduce red tape.

“If you enroll in the clinical trial, you can probably get the drug much more quickly, Hruby said."Of course, you run the risk of getting placebo instead.”

There’s a longstanding history of doing these types of trials in parallel with expanded access for products such as Tpoxx, which had an initial approval and whose manufacturers are looking to expand the label, Gomez said.

“Our colleagues in the UK, Europe, Canada, and US have thought carefully about the ethics,” he said. “That’s why if someone progressed to severe disease, they would be converted over to active drug.”

A spokesperson for the National Institute of Allergy and Infectious Diseases in the NIH confirmed that it’s planning to start clinical trials next month through an existing clinical trials network in the AIDS Clinical Group. The agency couldn’t confirm the enrollment targets or whether kids would be part of the study yet, but details will be forthcoming.

Pediatric, Preventive Versions in Works

Siga is also developing a pediatric version of Tpoxx that would be formulated as a powder, and a physician or pharmacist would reconstitute it into a liquid. The company is also looking to expand the approval so the drug could be used as a post-exposure preventive.

Currently the US is using Jynneos, Bavarian Nordic A/S’s vaccine, to protect people after a potential exposure. But patients with a diagnosed infection aren’t eligible for the vaccine, Mary Foote, chief medical officer of the New York City Department of Health and Mental Hygiene said during a recent Infectious Diseases Society of America call.

“In the case of an outbreak—whether it’s monkeypox or, God forbid, smallpox—post exposure prophylaxis might in fact, be the most important use of the drug,” Hruby said.

“You’re not going to know who’s been exposed, who’s not been exposed, or how long you’ve been incubating the virus. If you were to treat with Tpoxx, you’ll stop progression of the disease and no one’s going to get ill, then you can vaccinate simultaneously. And they can generate long term immunity,” he said. Clinical trials will test that hypothesis.

—With assistance from Madison Muller