Prothena Corp. (PRTA) to Discuss Phase 2 Development Strategy in Psoriatic Arthritis for PRX003

September 29, 2016 4:07 PM EDT
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Prothena Corporation plc (Nasdaq: PRTA), a late-stage clinical biotechnology company focused on the discovery, development and commercialization of novel protein immunotherapies, will host a conference call and webcast today at 4:30 PM Eastern Time to discuss its Phase 2 clinical development strategy in psoriatic arthritis for PRX003, an antibody that targets the cellular adhesion molecule CD146, which is expressed on the surface of Th17 cells.

“We are excited to highlight development plans for PRX003, an antibody designed to block pro-inflammatory Th17 cells from infiltrating into tissue and releasing multiple cytokines that contribute to inflammatory disease pathology,” stated Gene Kinney, PhD, Prothena’s Chief Operating Officer. “Based on the biology of psoriatic arthritis and the novel proposed mechanism of PRX003, we believe this approach has the potential to offer an improved therapeutic option for patients suffering from this disease.”

Pro-inflammatory Th17 Cells and PRX003 Potential Mechanisms of Action

Pro-inflammatory Th17 cells release multiple cytokines that contribute to inflammatory disease pathology, including IL-17, TNF-α, IL-6, IFNγ, IL-22, and CCL20 (Liuzzo, et. al., European Heart Journal, 2013; Mohan et. al., American Journal of Pathology, July 2012).

PRX003 was designed to target CD146, a cell adhesion molecule also known as melanoma cell adhesion molecule (MCAM), which is expressed on the surface of Th17 cells. CD146 facilitates Th17 cell migration from circulation into tissue, a necessary step required to initiate and/or perpetuate an inflammatory disease process. Prothena discovered that laminin α4 is the endothelial binding partner for CD146, and this binding is necessary to facilitate the migration of Th17 cells from circulation into tissue.

PRX003 is designed to occupy CD146, leading to downregulation which sequesters pro-inflammatory Th17 cells in the bloodstream, preventing their migration into tissue. PRX003 may also induce the demargination of Th17 cells that are already adherent to blood vessels or tissue.

Planned PRX003 Phase 2 Development Strategy

Prothena plans to advance a Phase 2 clinical study of PRX003 for the treatment of psoriatic arthritis, a Th17-mediated disease where multiple cytokines contribute to pathology.

Psoriatic arthritis is a potentially debilitating disease characterized by pain, stiffness and swelling in the joints and surrounding ligaments and tendons. According to the National Psoriais Foundation, as many as 45 percent of patients with psoriatic arthritis are dissatisfied with their current treatment (Armstrong AW, et. al., JAMA, 2013). There is an unmet need for more effective and tolerable therapies in this patient population.

In patients with psoriatic arthritis, there are significantly more CD146 expressing T cells at the site of inflammation than in the peripheral blood, suggesting a role for CD146 – expressed on the surface of Th17 cells – in the migration of pathogenic cells into joints (Raychaudhuri, et. al., poster presentation at 2105 ACR/ARHP Annual Meeting, abstract #982). Due to its proposed upstream mechanism of action, PRX003 is expected to block the release of multiple Th17 related cytokines that are known to contribute to psoriatic arthritis pathology including IL-17, TNF-α, IL-6, IFNγ, IL-22, and CCL20.

Prothena is conducting a Phase 1b double-blind, placebo controlled, multiple ascending dose, proof-of-biology study in approximately 56 patients with psoriasis. This study is evaluating safety, tolerability, pharmacokinetics, immunogenicity, and pharmacodynamics, and will also evaluate the Psoriasis Area and Severity Index (PASI) following treatment with PRX003 as a means to assess proof-of-biology.

Should the interim analysis of the ongoing Phase 1b multiple ascending dose proof-of-biology study in patients with psoriasis meet certain pre-specified criteria, Prothena will begin preparation for a Phase 2 study in patients with psoriatic arthritis. The interim analysis is expected by mid-2017.

Conference Call and Webcast Details

Prothena will host a webcast today at 4:30 PM Eastern Time to discuss its plans for Phase 2 development of PRX003. To access the conference call via dial-in, please dial (877) 887-5215 (U.S. toll free) or (315) 625-3069 (international) five minutes prior to the start time and refer to conference ID number 83102616. A replay of the webcast and call will be available for at least 90 days via dial-in at (855) 859-2056 (U.S. toll free) or (404) 537-3406 (international), Conference ID Number 83102616.

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