In January, it paid £9.2mln for 6.83mln Arrowhead shares. In a recent deal, it offloaded 2.036mln shares for £5.6mln, booking the gain in the process.
Proceeds will be used to fund Silence’s working capital requirements.
Chief executive Ali Mortazavi said: "Our balance sheet has been strengthened by the addition of £5.6mln in cash received from the partial sale of this stake in Arrowhead.
“As a biotech company focused on both our platform and our developing pipeline, we believe that this cash receipt will enable us to maintain our focus as we advance products towards the clinic.”