ABOUT PRTX-100
PRTX-100 is a highly-purified form of Staphylococcal Protein A that binds directly to monocytes and a subset of B-cells that are involved in the development and progression of various autoimmune diseases.
These binding interactions enable the compound to modulate the function of these cells and restore the balance of the immune system. A Phase I clinical trial in healthy volunteers was completed in May 2006.
PRTX-100 aims to restore normal immune system function by binding directly to the surface of monocytes (white blood cells responsible for phagocytosis [ingestion] of foreign substances in the body) and a subset of B-cells that are potentially involved in the development and progression of certain autoimmune diseases, allow PRTX-100 to modulate the function of these cells and restore balance to the immune system.
Preclinical studies completed by Protalex indicate that extremely low doses of PRTX-100 have efficacy equal to or better than the approved biologic etanercept (Enbrel®), a currently available treatment for rheumatoid arthritis, but with little or no side effects. Data from these studies was presented by Protalex at the Fifth International Conference on Autoimmunity on December 1, 2006 in Sorrento, Italy. All 36 healthy volunteers who enrolled in the study completed the trial.
Protalex (PRTX-100) Approach – Selective Inhibition of B-Cell Activation
Mechanism of Action
PRTX-100, a highly-purified form of Staphylococcal Protein A (SpA or Protein A) naturally secreted by Staphylococcus aureus, strain A676 (S. aureus A676) into the medium, is a single polypeptide chain with 2 types of Immunoglobulin (Ig) binding activities.
Protein A binds avidly to B-cells expressing Vн3-encoded Ig. Protein A is believed to lead to clinical benefit in rheumatoid arthritis patients, based on the data gathered over several years from patients treated with an approved therapeutic device called the Prosorba® Column. This device, approved by the FDA in 1987, is a plastic cylinder that contains a sand-like substance (an inert silica matrix) coated with Protein A and is used in rheumatoid arthritis patients who have failed previous DMARD therapy, as well as in idiopathic thrombocytopenic purpura patients who have platelet counts of less than 100,000/mm. During the use of this device, small amounts of Protein A are released into the patient’s circulation as an incidental effect. It is now believed that the therapeutic efficacy of this treatment in patients with DMARD-refractory rheumatoid arthritis, as well as in those with idiopathic thrombocytopenic purpura, is the direct result of the inadvertent administration of small amounts of Protein A. Thus, Protalex believes that the therapeutic benefit of Protein A observed in the Prosorba® Column treatment over the last two decades substantiates the basis of potential application of PRTX-100 in idiopathic thrombocytopenic purpura, rheumatoid arthritis, and other autoimmune diseases.
B-cells are a type of white blood cell that, when activated, multiply and produce antibodies. Antibody production is triggered by antigens. In the case of idiopathic thrombocytopenic purpura, some B-cells produce auto-antibodies that bind antigens to platelets, which eventually leads to platelet destruction, resulting in low platelet count (Thrombocytopenia). The anti-platelet antibodies isolated from idiopathic thrombocytopenic purpura patients show an extraordinarily high usage of the VH3-30 heavy-chain gene, precisely the B-cell lineage that is the target of PRTX-100.
PRTX-100 aims to restore normal immune system function by selectively modulating only the B-cells that are producing pathogenic auto-antibodies, which play a role in the induction and maintenance of autoimmune diseases. PRTX-100 achieves this specificity due to its ability to bind to immunoglobulins that are of a specific lineage, namely VH3, which is also the lineage that is most prevalent in the auto-antibodies that are present in numerous autoimmune diseases.
On the monocyte level, PRTX-100 binds directly to the surface of 100% of monocytes (immune cells active in the development and progression of various autoimmune diseases) and has been shown to modulate cell surface proteins that are involved in the progression of autoimmune diseases (experiments are being conducted to test this hypothesis.) There exists a known interaction between the C3B receptor (CD46) and the cross-linking of the Fc receptor. This interaction gives negative regulatory signals specifically down-regulating IL-2, a very potent immune cytokine. In addition, PRTX-100 also regulates the CD16/FcγRIII receptor, which plays an important role in the clearance of platelets from idiopathic thrombocytopenic purpura patients. PRTX-100 also inhibits antibody formation, potentially making it an effective anti-B-cell therapy in rheumatoid arthritis.
When tested in vitro and in animal models, the binding of Protein A to B-cells altered a variety of activation events, which, in the absence of co-stimulatory signals, lead to anergy, apoptosis, and/or selective modulation of alloreactive B-cells. Unlike Rituxan®, which eliminates all B-cells with a CD20 receptor, i.e. normal B-cells and B-cells responsible for production of pathogenic antibodies, PRTX-100 in vitro studies showed a high binding affinity to only 30%-45% of human B-cells. When a patient is treated with Rituxan®, it could take up to a year for the patient to replace those healthy B-cells and have his/her immune system and helpful antibody production back in working order. Biologics, such as etanercept (Enbrel®), Remicade®, Humira®, and others in development, also have the same immunosuppressant limitation. On the other hand, PRTX-100 aims to restore normal immune system function by selectively inhibiting the activation of the B-cells responsible for production of pathogenic antibodies without compromising the immune system.
