Biossil Labs has built a business on buying discarded drug programs and reviving them with AI. On November 2 it added a gut-protection franchise, acquiring Theriva Biologics’ antibiotic-degrading enzyme portfolio for a modest upfront and a large stack of contingent payments.
The package covers SYN-004 (ribaxamase), its modifications and reformulations including SYN-007, plus certain assets tied to SYN-006 (carbapenemase). Theriva received $350K at closing and could collect up to $3M in regulatory milestones, low single-digit royalties capped at $250M, and up to $88M if cumulative worldwide sales thresholds are met. Biossil takes on all future development and commercialization costs.
What the enzymes do
Ribaxamase is an oral prophylactic designed to break down intravenous beta-lactam antibiotics that leak into the gastrointestinal tract, protecting the gut microbiome. Preserving that balance matters because disruption opens the door to Clostridioides difficile infection, overgrowth of resistant organisms, and the emergence of antimicrobial resistance. SYN-007 is a reformulation built for coadministration with oral beta-lactams.
A Phase 1b/2a trial at Washington University is testing the approach for preventing acute graft-versus-host disease and opportunistic infections in allogeneic transplant recipients receiving antibiotics, a population where gut damage can be catastrophic.
The buy-and-revive thesis gets another test
Theriva spent years and substantial capital on the program before deciding its future lay elsewhere, with chief executive Steven Shallcross pointing the company toward VCN-01. Biossil, based in Toronto and valued at $1B after an OpenAI-led round in September, argues that a different owner with a cheaper development model can finish what a small public biotech could not.
Alexander Mosa, Biossil’s chief scientific officer, called gut dysbiosis and resistant colonization in vulnerable patients an important unmet need. Cheap entry plus milestone-heavy structure keeps the downside small. Whether the upside is real depends on a transplant trial that has yet to read out.
