A negative regulatory review from the UK's Medicines and Healthcare Products Regulatory Agency has effectively halted the most advanced clinical milestone for tivoxavir marboxil, the lead influenza asset of Pennsylvania-based Traws Pharma, Inc. (Nasdaq: TRAW). The company reported that a planned Phase IIa human influenza challenge study has been deferred following the MHRA's unfavorable assessment, a setback that also invalidates the milestone-based warrant structure tied to MHRA approval in the company's April 2026 USD 60 million private placement financing. The MHRA decision, combined with an existing FDA clinical hold on Traws's US IND for tivoxavir marboxil — disclosed in February 2026 and linked to concerns over the mutagenicity data package — means the compound now faces regulatory obstacles in both its primary clinical jurisdictions.
No clinical efficacy data from the planned challenge study exist, as the study was deferred before enrollment. The scientific case for tivoxavir marboxil rests on preclinical findings: the company reported that a single dose demonstrated potent efficacy in three animal models of highly pathogenic avian influenza, and Phase I data in healthy volunteers showed plasma drug levels sustained above the EC₉₀ for more than 23 days following a single dose, a pharmacokinetic profile that underpinned the once-monthly prophylaxis strategy. A tablet formulation evaluated in early 2026 demonstrated a 30% increase in exposure versus the prototype, with modelling suggesting 28-day coverage. The MHRA's specific objections have not been publicly detailed, but Traws has indicated that mutagenic potential was a concern — the same issue cited by the FDA — and that backup candidates under development are described as devoid of mutagenic potential.
The influenza antiviral market is dominated by Roche's Tamiflu (oseltamivir) and Shionogi's Xofluza (baloxavir marboxil), the latter of which shares the same cap-dependent endonuclease mechanism as tivoxavir marboxil. Baloxavir is approved across multiple markets as a single-dose treatment, meaning Traws would need to demonstrate meaningful differentiation — most plausibly through the long-duration pharmacokinetics enabling prophylactic use — to carve out a position. With a cash runway extending to Q1 2027, Traws has stated it is advancing backup compounds designed to preserve tivoxavir marboxil's pharmacokinetic and antiviral profile while addressing the mutagenicity concerns that triggered both regulatory holds. The next meaningful milestone would be identification and advancement of a backup candidate into IND-enabling studies, though no timeline has been disclosed.
This article was generated with AI assistance and reviewed and edited by the AllSci editorial team Explore more at AllSci News: https://allsci.com/news/
Spot something wrong? Report an issue with this article