Protalex, a clinical-stage biopharmaceutical company, announced that following completion of its US-based, multicentre phase 1b randomised, multiple-dose, dose-escalation study of PRTX-100 (the 104 Study) in combination with methotrexate or leflunomide in adults with active rheumatoid arthritis (RA), the company has initiated enrollment of a phase I/II open-label, multiple, fixed-dose study (the 105 Study) that is open only to 104 Study patients who indicated their desire for additional treatment. Protalex’s lead drug PRTX-100 is a highly purified form of Staphylococcal Protein A.

The PRTX-100-105 Study is an open-label, single group study with up to 12 former participants from the 104 Study who will receive a fixed dose of PRTX-100 over a 6-month period at a single site in the US. The primary study endpoint of the 105 Study is the safety and tolerability of a fixed dose of PRTX-100 administered over an extended period. The secondary endpoints include immunogenicity, effects on measures of RA disease activity, evaluation of anti-PRTX-100 antibody presence, and feasibility of joint evaluations with ultrasound and biomarkers as disease markers.

William E. Gannon, Jr, MD., Protalex’s chief medical officer, explained the 105 Study’s rationale, “Although the majority of RA patients achieve an improvement of their RA with older disease modifying agents such as methotrexate and leflunomide, all of these agents provoke adverse events. Commonly used biological agents, including TNF inhibitors like Humira, Enbrel and/or Remicade, increase the risk of serious infections. Our ongoing development programme is focussed on determining whether PRTX-100 modifies the disease course of RA with an improved safety profile and a dosing regimen comparable to current therapies.”

“In addition, on average the patients in the 104 Study had RA for 13 years. Many of these patients had discontinued treatment with one or more of the TNF inhibitors. In the 104 Study, some patients experienced relief using PRTX-100 and asked their physician if they could continue to be treated with PRTX-100. Based on their request, as conveyed by the Principal Investigator of the 104 Study, the Company agreed to conduct the 105 Study in the belief that continued treatment may benefit these patients and provide longer term safety information about PRTX-100,” adds Dr. Gannon.