Theriva Biologics, Inc. announced the presentation of blinded safety and pharmacokinetic (PK) data from the ongoing Phase 1b/2a randomized, double-blinded, placebo-controlled clinical trial of SYN-004 (ribaxamase) in allogeneic hematopoietic cell transplant (HCT) recipients for the prevention of acute graft-versus-host-disease (aGVHD). These data will be featured in a poster presentation at the 2023 Tandem Meetings: Transplantation & Cellular Therapy Meetings of ASTCT and CIBMTR, being held in Orlando, Florida from February 15-19, 2023. Cohort 1 of the study enrolled 19 patients who received at least 1 dose of study drug (SYN-004 or Placebo randomized 2:1).

Twelve of these patients completed two doses of IV MER to be evaluable towards the study endpoints. While the study is on-going and remains blinded, key findings showcased in the poster presentation (#LBA6) titled “Interim Analysis of SYN-004 Phase 1b/2a Trial in Hematopoietic Cell Transplant (HCT) Recipients” include: Adverse events (AEs) and serious adverse events (SAEs) observed in Cohort 1 were typical of those observed in allo-HCT patients and no AEs or SAEs were determined to be related to study drug treatment by the investigators. Consistent with previous studies of SYN-004 in healthy volunteers, SYN-004 was not observed in blood samples from the majority of the evaluable patients.

Meropenem pharmacokinetics were as expected for this patient population. The ongoing randomized, double-blinded, placebo-controlled Phase 1b/2a clinical trial is being conducted at Washington University School of Medicine in St. Louis.

The trial is designed to evaluate the safety, tolerability, and potential absorption of oral SYN-004 (150 mg q.i.d. for a maximum of 28 days) into the systemic circulation of allogeneic HCT recipients who receive an IV antibiotic to treat fever. To mitigate risk, Cohort 1 of the study administered meropenem as the study-assigned antibiotic. Meropenem is a carbapenem antibiotic that is not metabolized by SYN-004.

Patients in Cohorts 2 and 3 will be administered piperacillin/tazobactam and cefepime respectively, each of which can be metabolized by SYN-004. The trial is also designed to evaluate potential protective effects of SYN-004 on the gut microbiome as well as generate preliminary information on potential therapeutic benefits and patient outcomes of SYN-004 in allogeneic HCT recipients. The trial is expected to enroll up to 36 participants with three sequential cohorts, each evaluating a different study-assigned IV beta-lactam antibiotic.

Safety and pharmacokinetic data for each cohort will be reviewed by an independent Data and Safety Monitoring Committee that will make a recommendation on whether to proceed to the next IV beta-lactam antibiotic. SYN-004 (ribaxamase) is an oral prophylactic therapy designed to degrade certain IV beta-lactam antibiotics within the GI tract and maintain the natural balance of the gut microbiome for the prevention of Clostridioides difficile infection (CDI), overgrowth of pathogenic organisms, the emergence of antimicrobial resistance (AMR) and acute graft-versus-host-disease (aGVHD) in allogeneic hematopoietic cell transplant (HCT) recipients. Allogeneic HCT recipients routinely receive long courses of IV beta-lactam antibiotics to treat infection following conditioning therapy.

Antibiotic-mediated damage of the gut microbiome in allogeneic HCT recipients may lead to adverse outcomes including CDI, VRE colonization and potentially fatal bacteremia and aGVHD. A previously completed placebo-controlled Phase 2b clinical trial of 412 patients demonstrated SYN-004 protected the gut microbiome from antibiotic-mediated dysbiosis. Patients who received SYN-004 also demonstrated significantly better maintenance and recovery of the gut microbiome as well as lower incidences of new colonization by opportunistic and potentially pathogenic microorganisms such as VRE.