A Phase 1 Study to Assess STP938 as a Monotherapy in Adults With High Risk Essential Thrombocythaemia

Overview

The goal of this clinical trial is to learn if the drug STP938 works to treat adults with high risk essential thrombocythaemia (ET) who are resistant to, or intolerant of, hydroxycarbamide (also known as hydroxyurea) therapy. The trial will also learn about the safety of STP938. The main questions the trial aims to answer are: * Does STP938 control platelet counts * Does STP938 control platelet counts without inducing unwanted side effects Participants will: * Take STP938 every day for up to 12 months. * Visit the clinic once every week for the first month, then every 2 weeks for checkups and tests. * Complete a questionnaire about symptoms once a month.

The aim of the study is to assess a new drug called STP938 for the treatment of essential thrombocythaemia (ET). The study with assess how effective STP938 in treating ET, and also assess any side effects of taking the drug. The study will enrol individuals with high risk ET who require treatment to lower their platelet count. Individuals enrolling on the study will have already tried treatment with hydroxycarbamide (also known as hydroxyurea) but are in need of a different treatment as hydroxycarbamide either did not control the platelet count or produced unwanted side effects. STP938 is a new class of drug that inhibits the enzyme cytidine triphosphate synthase 1 (CTPS1). Inhibition of CTPS1 is a novel way of lowering the platelet count. This study is a phase 1b, open-label, multicentre trial. Participants will receive STP938 capsules every day, in cycles of 28 days, for approximately 12 months. Participants may continue to receive study drug for a longer period, so long as it is controlling the platelet count and not causing side effects. During the study, participants will visit the study site about 26 times (2 times per cycle) over an estimated 12 months. Once the treatment is complete, safety follow-up visit(s) will occur to make sure the participant is not experiencing any adverse effects. The following study procedures will be performed: (a) physical examinations (b) ECGs (c) blood tests, (d) urine tests (e) CT/MRI scans (f) bone marrow biopsies (g) drug administration (h) study drug blood level tests and (i) gene testing.