Rubius Therapeutics is discontinuing its Phase 1b trial investigating RTX-134, a potential cell therapy for people with phenylketonuria (PKU).
The decision comes as the company shifts its focus to the development of cell therapies for cancer and autoimmune diseases, according to a press release.
The trial (NCT04110496) was launched last November at the Children’s Hospital Colorado, with the first patient dosed early this year.
PKU is characterized by no activity of the enzyme phenylalanine hydroxylase, leading to the toxic build-up of the amino acid phenylalanine (amino acids are the building blocks of proteins).
Treatment with RTX-134 involves collecting red blood cells from healthy volunteers, which are then genetically engineering to produce phenylalanine ammonia lyase. This enzyme reduces the build-up of phenylalanine by metabolizing it into trans-cinnamic acid.
Trial participants were to be given a single intravenous infusion (directly into the bloodstream) of RTX-134, followed by 28 days of monitoring after the last detection of RTX-134 in the blood.
However, Rubius was unable to interpret data collected from the first dosed patient. This was due to the low dosage of RTX-134 and the sensitivity of the laboratory test used to detect circulating cells.
Besides shifting its focus to other therapeutic areas, the company’s decision to terminate the trial was also the result of unanticipated delays to the RTX-134 program and the high costs of producing a high-dose treatment that would need to be taken chronically.
Cell therapies produced by Rubius are created by a process called RED PLATFORM, a technique to engineer red blood cells into a new class of therapies that the company refers to as Red Cell Therapeutics.
Two other cell therapies generated by this platform, RTX-240 and RTX-321, have shown promising results in pre-clinical studies. The treatments are aimed at combating solid tumors and acute myeloid leukemia (RTX-240), and HPV-positive cancers (RTX-321).
Rubius was recently cleared by the U.S. Food and Drug Administration to start clinical trials of RTX-240. A similar application for RTX-321 is expected to be filed later this year.
“Over the past two years, we have generated exciting oncology pre-clinical data,” said Pablo Cagnoni, MD, president and CEO of Rubius. “By focusing on the development of our oncology and autoimmune pipeline, we believe we will have the greatest opportunity to bring life-saving therapies to patients.”
The company said it does not rule out the possibility of revisiting RTX-134 in the future. Enhancements to the RED PLATFORM technology, more efficient manufacturing, and added funding may enable Rubius to resume development of RTX-134.