SynOx Therapeutics has raised €37 million ($44 million) to advance a drug licensed from Roche. The series A tees SynOx up to build on signs the anti-CSF1R monoclonal antibody improves outcomes in patients with tenosynovial giant cell tumors (TGCTs).
Roche began three phase 1 clinical trials of emactuzumab, also known as RG7155 and RO5509554, from 2011 to 2016 but pulled out of a fourth planned study in 2018 and dropped the candidate from its pipeline. Celleron Therapeutics seized on the opportunity created by Roche’s decision in August, securing the global rights to the drug and outlining plans to develop it for use in TGCT patients.
Now, Celleron has spun out the asset to create SynOx, a biotech focused squarely on emactuzumab. SynOx has persuaded a clutch of leading European VCs to fund the work, securing €37 million in a round co-led by HealthCap and Medicxi with assists from Forbion and Gimv.
The syndicate signed up to support SynOx on the strength of data on 63 TGCT patients. Roche tested emactuzumab in multiple solid tumor types in the phase 1 trial, but it is the TGCT subpopulation that caught the eye.
A 2015 paper reported an 86% objective response rate (ORR) in the 28 TGCT patients then evaluable. Earlier this month, researchers published a larger data set with longer follow-up, revealing a 71% ORR that largely persisted over the follow-up period. Two years after enrollment, the ORR was 64%.
The authors of the paper compared the efficacy favorably to the results of other TGCT studies. Tyrosine kinase inhibitors Gleevec and Tasigna had ORRs below 20% in small clinical trials. Five Prime Therapeutics’ cabiralizumab and Daiichi Sankyo’s Turalio fared better, but neither has demonstrated the high, durable responses associated with emactuzumab.
There are shortcomings of the data from the emactuzumab trial, which suffered from a high number of discontinuations during the follow-up period, but the available evidence suggests the molecule is among the more promising TGCT prospects. Currently, TGCT is mainly treated surgically, but the form studied in the emactuzumab arm is harder to resect and prone to recurrences.
The emactuzumab trial contains evidence the drug can be used in retreatment. One patient had a partial response and stopped treatment for two years. The lesion grew back over that period, but the resumption of treatment triggered another partial response. TGCT is typically nonmalignant but can cause joint damage that is detrimental to quality of life.