Bayer Begins Phase I Trial of GIRK4 Inhibitor for Atrial Fibrillation

Bayer Begins Phase I Trial of GIRK4 Inhibitor for Atrial Fibrillation

By, Admin 23 May 2025

Leverkusen, Germany — Bayer has announced the initiation of a Phase I clinical trial for BAY 3670549, an investigational highly selective G-protein-coupled inwardly rectifying potassium channel 4 (GIRK4) inhibitor. The compound has the potential to help control the electrical activity of heart cells in patients with atrial fibrillation (AFib).
A New Approach to Cardioversion

BAY 3670549 offers a novel approach for rapid cardioversion to normal sinus rhythm in AFib patients, aiming to:

  • Eliminate the need for sedation, anaesthesia, or electrical shock
  • Enable immediate, non-invasive treatment
  • Significantly reduce hospital stays

The first-in-human dose escalation study is a randomized, double-blind, placebo-controlled trial designed to assess:

  • Safety
  • Tolerability
  • Pharmacokinetics
  • Pharmacodynamics

The Unmet Need in AFib Treatment

AFib is the most common cardiac arrhythmia, affecting over 60 million people worldwide. It is a major risk factor for:

  • Stroke

  • Heart failure

Current treatments like electrical cardioversion (ECV), though effective, are resource-intensive and require sedation or anaesthesia. Alternatively, anti-arrhythmic drugs (AADs) are associated with:

  • Limited short-term efficacy

  • Contraindications (e.g., structural heart disease)
  • Safety risks, including abnormal heart rhythms and sudden death
  • Need for close monitoring

Scientific Rationale Behind GIRK4 Inhibition

GIRK4 channels regulate heart cell electrical activity by controlling potassium ion (K⁺) flow in response to acetylcholine (ACh). This process plays a key role in the atrial effective refractory period (AERP).

  • Increased GIRK4 activity shortens AERP

  • Shortened AERP leads to faster atrial recovery
  • This contributes to the onset and persistence of AFib

By selectively inhibiting GIRK4, BAY 3670549 may restore more regular electrical signaling in the atria, reducing AFib episodes.
A Growing Global Health Burden

AFib is characterized by rapid, disorganized electrical signals in the atria, causing:

  • Irregular contractions

  • Incomplete emptying of blood
  • Clot formation, potentially leading to stroke

Key statistics:

  • People with AFib are 5 times more likely to suffer a stroke
  • AFib-related strokes have a 50% one-year mortality rate
  • Projected rise in AFib cases:
  • 15.9 million in the U.S. by 2050
  • 17.9 million in Europe by 2060

Strategic Research Partnership

BAY 3670549 originates from Bayer’s strategic alliance with the Broad Institute. This partnership aligns with Bayer’s goal of delivering first-line pharmacological therapies that are fast-acting, effective, and well tolerated.

Executive Perspective

Initiating clinical development of our investigational GIRK4 inhibitor marks an important milestone of our ambition to transform atrial fibrillation treatment,” said Andrea Haegebarth, Ph.D., Global Head of Research and Early Development for Cardiovascular, Renal, and Immunology at Bayer. “We look forward to advancing the program to benefit a broad patient population in need of novel and better medicines.

Bayer’s Vision in Cardiovascular Medicine

Bayer is a global leader in cardiology with a strong pipeline of innovative treatments. The company’s strategy is to:

  • Address unmet needs in cardiovascular disease

  • Advance a precision cardiology approach
  • Unlock long-term growth in the cardiovascular market

Bayer’s current portfolio includes several advanced products and compounds in various stages of development.
About Bayer

Bayer is a global enterprise with core competencies in health care and nutrition. Its mission, “Health for all, Hunger for none,” guides efforts to meet the challenges of a growing and aging global population.

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