PRTX-100 (Staphylococcal Protein A)

I had been part in testing immunoadsorption with Staphylococcal Protein A, as only two patients (and both taking TNF-inhibitors at the same time!) showed response, I'm not too confident in PRTX-100.

E. Bernton et al. presented a pilot study at the 2012 EULAR meeting: "The primary disease activity response endpoint was the number of patients with a DAS28-CRP _3.2 at Week 6" - and this endpoint was "met by 3/29 PRTX-100 and 0/8 placebo patients". Promising, indeed [sarcasm OFF//]!

C. Wiesenhutter and colleagues presented [AB0343]: “TREATMENT OF RHEUMATOID ARTHRITIS PATIENTS WITH PARENTERAL STAPHYLOCOCCAL PROTEIN A (PRTX-100): AN OPEN-LABEL SINGLE-SITE EXTENSION TRIAL”. Conclusions: “Treatment with PRTX-100 in nine patients for the second time and two patients for the first time demonstrated an acceptable safety profile.” So it’s N=11! “At study day 196, 1 month after final infusion, all 11 patients demonstrated a reduction of DAS28CRP.” If we would look at 11 control patients with active RA and give the background therapy allowed by the study protocol, most probably these patients would also demonstrate "a reduction of DAS28CRP".

I had already been skeptic four years ago, and now I don’t see any real advance. So I don’t think that PRTX-100 will come as a drug against rheumatic diseases like rheumatoid arthritis.

Links:

http://rheumatologe.blogspot.de/2012/12/prtx-100-staphylococcal-protein-a.html

C. Wiesenhutter and colleagues presented [AB0343]: DOI: 10.1136/annrheumdis-2016-eular.2540

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14.11.2016:
No abstract published at the ACR 2016 Annual Meeting.

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PRTX-100 (Staphylococcal Protein A)

E. Bernton et al. presented: "A Phase 1, Randomized, Double-Blind, Placebo-Controlled Multiple-Dose Study of Intravenous Staphylococcal Protein A in Patients with Active Rheumatoid Arthritis On Methotrexate: Safety, Pharmacokinetics and Efficacy" (Abstract No. 833). "Results of this pilot study support further clinical trials of PRTX-100 at doses of 1.5 _g/kg and higher." "The primary disease activity response endpoint was the number of patients with a DAS28-CRP _3.2 at Week 6" - and this endpoint was "met by 3/29 PRTX-100 and 0/8 placebo patients". "PRTX-100 elicited anti-drug antibodies (ADAs) in the majority of patients but the incidence or titer of ADAs was not dose-dependent."

As I had been part in testing immunoadsorption, I'm not too confident in PRTX-100. Anti-drug antibodies in the majority of patients and a small effect on 10% of the patients make it hard to believe that we'll see a working drug added to existing drugs. But maybe it's still too early for skepticism.