SynOx takes rare tumour treatment to phase 3 with $75m Series B

The UK/Irish company SynOx Therapeutics plans to run a phase 3 trial of a potentially best-in-class antibody therapy for the rare disease Tenosynovial Giant Cell Tumour (TGCT) with the help of a $75 million financing round.

The Series B round was led by the new investor Bioqube Ventures along with existing investors Forbion and HealthCap. The cash will be used to bankroll a phase 3 trial of SynOx’s TGCT treatment emactuzumab to the point of obtaining clinical and chemistry, manufacturing and controls (CMC) data.

The phase 3 trial, dubbed TANGENT, is due to launch this month and aims to enrol around 128 patients with TGCT. The company will compare infusions of emactuzumab with a placebo over 10 weeks and a subsequent follow-up period, with an end date set to 2027​.

“As a highly effective, next-generation therapy with a short treatment cycle, rapid onset and long duration of response, we believe that emactuzumab is differentiated from other agents in development and will provide a much needed and valuable option for patients suffering from this grievous disease,” said SynOx CEO Ray Barlow in a public statement​.

Treating TGCT​

Patients with TGCT have growths in joints and tendons including in the knee, hip and ankle, leading to pain, stiffness and disability. Patients can receive surgery to remove the growths and there is one treatment approved for TGCTs in the US called pexidartinib, developed by Daiichi Sankyo. However, more than 50% of patients see a recurrence in the disease by three years post-surgery, Barlow told this publication.

“Given that there is no cure, patients suffer from recurrence after surgery, and that TGCT is a disease throughout life, there is a large pool of patients with the disease,” Barlow said. The underreported condition occurs throughout the world in all ethnic groups and its market is estimated to be at least $850 million in the US, he said.

Pexidartinib blocks a cytokine called CSF-1 and is designed to prevent immune cells called macrophages from proliferating and causing the tumours. Nonetheless, the treatment has its own issues such as liver toxicity, said the CEO, adding that patients that stop taking the drug can also see a recurrence in their disease.

SynOx’s antibody emactuzumab was originally developed by Roche as a CSF-1 blocker and has shown promise as a treatment for TGCT in phase 1b and phase 1/2 studies. The treatment is delivered as an intravenous infusion every two weeks and is designed to shrink the tumors more effectively than other treatments in development. The treatment regime is completed within just 10 weeks compared to a typical 18 months, has a tolerable safety profile and works for longer, with early work suggesting an effect for more than 800 days, said Barlow.

“Patients drop off chronic oral therapy,” he said, adding that five short infusions “lead to advantages in patient compliance and adherence.”

TGCT is also gaining interest from pharmaceutical companies, Barlow said, citing Merck KGaA’s $605 million licensing deal with Chinese firm Abbisko Therapeutics in 2023 for China-based rights to an oral treatment candidate for TGCT called pimicotinib.

“This shows that sophisticated large pharma companies view this market as attractive and growing,” he said.