Silence Therapeutics plc announced positive results from the ongoing SANRECO Phase 1 repeat dose study of divesiran (SLN124), a siRNA (short interfering RNA) targeting TMPRSS6, in patients with polycythemia vera (PV). The 34-week, open-label Phase 1 study is evaluating divesiran (3 mg/kg, 6 mg/kg and 9 mg/kg) administered subcutaneously every 6 weeks for four doses, with a 16-week follow-up period following the date of the last administered dose in up to 24 PV patients. Key inclusion criteria include a PV diagnosis and a history of requiring at least three phlebotomies in the last six months or five in the last year prior to screening.

Patients are allowed to be on stable doses of cytoreductive agents. Given the exploratory nature of this Phase 1 study, both well-controlled patients - defined as those with hematocrit (HCT) levels at 45% or less ? as well as those with HCT levels greater than 45% at baseline on current standard of care treatment were enrolled.

The data being presented on June 27, 2024 are based on a data cut-off date of March 29, 2024, and include analysis of 16 patients over a time range of approximately 4 to 34 weeks of study involvement. Of the 16 patients, 8 patients are considered well-controlled and 8 patients have HCT levels over 45% at baseline. To date, divesiran has been observed to be well tolerated with no major safety issues.

None of the 8 patients entering the trial with well-controlled HCT levels required a phlebotomy during the divesiran treatment period, which was defined in the study as the period up to 6 weeks after the last dose. All patients in the well-controlled group maintained adequate control of HCT levels as per treatment guidelines. Of the 8 patients entering the trial with HCT levels above 45%, 2 patients each required one phlebotomy.

The baseline HCTs of these 2 patients were 56% and 53%. None of the 6 other patients in this group required a phlebotomy. Notably, none of the 13 patients entering the trial with HCT levels of 50% or below ?

8 well-controlled patients and 5 patients with HCT levels of 46-50% - have required a phlebotomy to date. In all dose groups, there was a sustained reduction in hematocrit during the treatment period and favorable effects on indices of iron metabolism. Hepcidin levels increased and were sustained within physiological levels in all dose groups, demonstrating target engagement.

As of June 27, 2024, Silence has enrolled 21 patients in the SANRECO study and the Company anticipates closing enrollment at the end of this month. Full results are expected to be presented at a scientific meeting later this year. Divesiran has received FDA Fast Track designation and FDA Orphan Drug Designation for PV.