Protalex Inc. announced that data highlighting results from Cohorts 1 through 5 of its U.S.-based multicenter Phase 1b randomized, multiple-dose, dose-escalation study of PRTX-100 in combination with methotrexate or leflunomide in adults with active rheumatoid arthritis (RA; the PRTX-100-104 Study) were presented at the American College of Rheumatology (ACR) and the Association for Rheumatology Health Professionals Annual Meeting 2014, underway in Boston. The company reported final data from Cohorts 1 through 4 and an interim analysis of pooled data from Cohort 5 of the 104 Study. Cohort 5 included 20 patients with 4 swollen joints and 5 tender joints despite ongoing treatment with methotrexate or leflunomide.

The primary study endpoint of the104 study was safety and tolerability. The secondary endpoints included immunogenicity and effects on measures of RA disease activity. For patients in all five cohorts of the 104 Study, PRTX-100 appears safe and well tolerated in all individuals, including those who develop anti-drug antibodies (ADAs).

In Cohort 5, patients were randomized to 420 g PRTX-100 (12 patients), 240 g PRTX-100 (3 patients) or placebo (5 patients). Patients received five weekly doses of PRTX-100 followed by four monthly maintenance doses at weeks 8, 12, 16 and 20. The addition of four monthly maintenance doses after the five weekly doses did not increase the rate or type of adverse events (AEs), even in those patients who developed ADAs.

Additionally, there was no apparent correlation between the development of ADAs and effects on measures of RA disease activity. In a post-hoc analysis of Cohorts 1 through 4, patient samples were evaluated using the Vectra DA (Crescendo Bioscience Inc.) multi-biomarker test. Comparison of patients with Vectra DA scores above and below 30 at the time of enrollment showed that patients with Vectra DA scores) 30 were more likely to have reduced disease activity on Day 57.

This suggests that the Vectra DA biomarker test may enable identification of individuals who could benefit most from the use of PRTX-100 for the treatment of RA. The Vectra DA is a multi-biomarker test intended to assess RA disease activity by measuring the concentrations of 12 serum proteins, converted into the Vectra DA score via a proprietary algorithm.