PRTX-100 (Bevifimod): A Comprehensive Retrospective Analysis of a Staphylococcal Protein A-Based Immunomodulator for Autoimmune Disease

Executive Summary

PRTX-100, also known by the International Nonproprietary Name (INN) Bevifimod, is an investigational biologic therapeutic agent developed for the treatment of autoimmune diseases.[1] It is a highly-purified, native form of Staphylococcal Protein A (SpA), a 47 kDa protein derived from the A676 strain of the bacterium Staphylococcus aureus.[3] Contrary to its classification as a small molecule in some databases, PRTX-100 is a protein biologic intended for intravenous administration.[4]

The therapeutic rationale for PRTX-100 was based on a novel, dual-pathway immunomodulatory mechanism designed to restore immune system balance rather than induce broad immunosuppression.[5] The mechanism targeted both the adaptive and innate immune systems. First, by binding to the VH3-family of immunoglobulins, PRTX-100 was intended to selectively modulate the activity of B-cells responsible for producing pathogenic autoantibodies, a key driver in many autoimmune conditions.[2] Second, by forming immune complexes with IgG, it aimed to induce a suppressor phenotype in macrophages, thereby inhibiting the phagocytosis of antibody-coated cells, a mechanism directly relevant to the pathology of Immune Thrombocytopenia (ITP).[8]

The clinical development program, sponsored by Protalex, Inc., focused primarily on two indications: Rheumatoid Arthritis (RA) and ITP.[5] The program encompassed at least eight human clinical studies, including multiple Phase 1 and Phase 1/2 trials, which established a generally acceptable safety and tolerability profile at the low microgram-per-kilogram doses administered.[7] Despite this, the program was ultimately unsuccessful and has been discontinued.[12]