Chronic Fatigue Syndrome/Myalgic Encephalomyelitis (CFS/ME): Characteristics of Responders to Rintatolimod
David R Strayer1
Bruce C Stouch2
Staci R Stevens3
Charles W Lapp5
Daniel L Peterson6
William A Carter1
William M Mitchell7*
1Hemispherx Biopharma, Inc., Philadelphia, Pennsylvania, United States of America
2BCS Statistical Solutions LLC, Philadelphia, Pennsylvania, United States of America
3Workwell Foundation, Ripon, California, United States of America
4Fatigue Consultation Clinic, Salt Lake City, Utah, United States of America
5Hunter-Hopkins Center, Charlotte, North Carolina, United States of America
6Sierra Internal Medicine Associates, Incline Village, Nevada, United States of America
7Vanderbilt University School of Medicine, Nashville, Tennessee, United States of America
*Corresponding author: William M. Mitchell, Department of Pathology, Microbiology & Immunology, Vanderbilt University, Nashville, TN 37205, USA, Tel: 615-322-3238;
Background: Chronic fatigue syndrome/myalgic encephalomyelitis (CFS/ME) is a debilitating disease of unknown pathogenesis consisting of a variety of flu-like symptoms including severe fatigue. Initial analysis of the use of rintatolimod (Poly I: Poly C12U), a selective TLR3 agonist, in a Phase III, double-blind, randomized, placebo-controlled trial of CFS/ME demonstrated statistical significance (p<0.05) in the reduction of fatigue as measured by exercise tolerance (ET) as the primary endpoint using a modified Bruce protocol with reduced physical exertion in patients with severe CFS/ME as defined by a Karnofsky performance score (KPS) of 40-60.
Methods and Findings: In order to better identify responders to rintatolimod, primary and secondary endpoints have been reexamined post hoc as a function of a pre-specified study baseline ET duration >9 minutes. Analysis of improvement in exercise performance at the ≥ 25% and ≥ 50% levels using ET at 40 weeks compared to baseline was performed for the intent-to-treat (ITT) population (n=208) using the pre-specified baseline exercise stratum (baseline ET duration >9 minutes). For this subset of patients (n=126), 33% (n=20), and 12% (n=8) of rintatolimod vs. placebo patients, respectively, improved ET duration by ≥ 25% (p=0.004) while 23% (n=14) compared to 4.5% (n=3) of rintatolimod vs. placebo patients, respectively improved ET duration by ≥ 50% (p=0.003). This corresponds to increases of ≥ 186 and ≥ 373 seconds for patients receiving rintatolimod, respectively, at ≥ 25% and ≥ 50% improvement responses. A frequency distribution analysis of ≥ 25% improvement, <25% change, and ≥ 25% deterioration in ET from baseline at 40 weeks for the baseline >9 minutes cohort showed net improvement to be 18.3% for the rintatolimod cohort vs. 4.6% deterioration for placebo (p=0.015). A continuous responder analysis using 5% increments from ≥ 25% to ≥ 50% provided a robust clinical enhancement in ET effect in the rintatolimod cohorts as compared to placebo. The KPS and Vitality (SF-36 subscale) quality of life secondary endpoints demonstrated similar clinically significant improvements for the rintatolimod cohort as a function of the same ET dichotomization. Rintatolimod was generally well-tolerated in this CFS/ME population.
Conclusions: Using a modified Bruce ET protocol with reduced physical exertion allowed clear identification of patient responders to rintatolimod with severe CFS/ME syndrome. Rintatolimod produced significant enhancement in ET and quality of life indicators in patients able to complete >9 minutes in a modified Bruce ET test. Rintatolimod also reduced deterioration in ET compared to placebo in patients with the poorest initial ET. Exercise endurance >9 minutes in a Bruce protocol modified for patients with CFS/ME provides a method to identify patients most likely to respond to rintatolimod.