A Phase 1 trial in Healthy Adults and Adults with Factor V Leiden or Prothrombin G20210A Mutation

• Research type

  Research Study

• Full title

  A Phase 1, Randomised, Double-Blind, Placebo-Controlled Single Ascending Dose Study to Evaluate the Safety, Tolerability, Pharmacokinetics, and Pharmacodynamics of CITY-FXI, a FXI Targeting siRNA, Administered Subcutaneously in Healthy Adults and Adults with Factor V Leiden or Prothrombin G20210A Mutation

• IRAS ID

  1013145

• Contact name

  Gennadiy Koev

• Contact email

  gkoev@citytx.com

• Sponsor organisation

  City Therapeutics, Inc

• ISRCTN Number

  ISRCTN45090913

• Research summary

  We are conducting this study to learn more about an investigational drug called CITY-FXI. This is not yet approved for use by drug regulatory agencies and can only be given in clinical studies, the reason for this study. This clinical study will be the first time CITY-FXI will be given to humans.

  CITY-FXI is being developed to help prevent the occurrence of thromboembolic diseases (formation of harmful blood clots). A blood clot is when blood becomes thick and sticky and forms a lump that can block blood flow. These blood clots can sometimes be life-threatening, for example, when formed in the legs (known as deep vein thrombosis) or lungs (known as pulmonary embolism).

  Current medicines for thromboembolic diseases are effective but may increase the risk of serious bleeding, so there is a need for safer medicines that prevent clots without causing excess bleeding.
  CITY-FXI is an investigational drug that uses a type of molecule called small interfering ribonucleic acid (siRNA). It is designed to reduce the amount of a specific protein called Factor XI (FXI). FXI is a type of protein which helps the blood to clot. It is mainly made in the liver and plays a role in stopping bleeding during an injury.

  While FXI helps stabilise and strengthen blood clots, it is not necessary for the very first stages of clotting as the process of clot formation starts with platelets (types of cell elements that help to stop bleeding). This is important because by lowering FXI, CITY-FXI could help prevent harmful blood clots with a lower bleeding risk than with currently available drugs. It is not yet known whether CITY-FXI will have this effect.
  We are conducting this study in up to 128 male and female participants, aged between 18 and 45 years.

• REC name

  London - London Bridge Research Ethics Committee

• REC reference

  25/LO/0803

• Date of REC Opinion

  23 Dec 2025

• REC opinion

  Further Information Favourable Opinion