iTeos Therapeutics Regains Worldwide Rights to Clinical-Stage IDO1 Inhibitor

January 4, 2018

Further evaluation of IDO1 inhibitor with clinically manageable safety profile to commence following review of Phase 1 clinical data and trial design


Gosselies, Belgium – January 4, 2018 – iTeos Therapeutics SA, a biotechnology company developing novel cancer immunotherapies, today announced that it has regained exclusive worldwide rights from Pfizer to develop and commercialise EOS200271, a highly selective, clinical-stage IDO1 inhibitor. 


Pfizer initiated a Phase 1 clinical study for EOS200271 (NCT02764151) as a single agent in patients with malignant gliomas (brain cancer), an area of significant unmet need, based on brain penetration of the compound. Interim data from 17 patients confirmed the safety and brain penetration of EOS200271 at doses ranging up to 500 mg BID, the maximum dose tested by Pfizer in the study. Efficacy was not observed and maximum tolerated dose was not reached in this dose range. iTeos is currently reviewing the full data set and plans to continue the development of EOS200271 in oncology indications, which have demonstrated an important role of IDO1 in immunosuppression.


Michel Detheux, Ph.D., Chief Executive Officer of iTeos Therapeutics, commented: “IDO1 inhibitors are one of the most promising immuno-oncology drugs currently in development. This asset is one of four IDO1 inhibitors in clinical development worldwide and EOS200271 is the only IDO1 inhibitor with excellent brain penetration. We believe that the return of this unique asset gives iTeos the exciting opportunity to continue to evaluate EOS200271’s potential in different indications and combinations.”


About EOS200271

EOS200271 is a synthetic, small molecule inhibitor of indoleamine 2,3-dioxygenase (IDO1), an immunosuppressive enzyme that is induced in a wide range of cancers. Inhibiting IDO1 in the tumor micro-environment suppresses a powerful immunosuppressive mechanism that is predicted to promote immune-mediated tumor elimination. EOS200271 has demonstrated anti-tumour activity in multiple preclinical tumour models in combination with immune checkpoint inhibitors. EOS200271 was originally licensed from iTeos to Pfizer in December 2014.


About IDO1

Indoleamine 2,3-dioxygenase (IDO1) is an enzyme that catalyze the transformation of the amino acid tryptophan in kynurenine. IDO1 has been implicated in immune modulation through its ability to limit T cell function and engage mechanisms of immune tolerance, and as such preventing tumor rejection. Emerging evidence suggests that IDO1 is induced during tumor development or after immune checkpoint treatment in multiple tumor types, helping malignant cells escape eradication by the immune system. 


About iTeos Therapeutics SA

iTeos is focused on expanding the benefits of immunotherapy for cancer patients by developing a proprietary pipeline targeting IDO1, A2A, TIGIT immune checkpoint and non-immunogenic (“cold”) tumours. iTeos’ competitive edge is in the combination of expertise in drug discovery, translational tumour immunology and early clinical trial design. The company uses a unique platform to identify rational combinations of immunotherapies and novel targets. Based in Gosselies, Belgium, iTeos is a spin-off from the Ludwig Cancer Research (LICR) and de Duve Institute (UCL). The company is supported in part by the Walloon Region of Belgium and the FEDER (European Fund for Economic and Regional Development). For more information, please visit


For further information, please contact:

Michel Detheux, CEO
iTeos Therapeutics
+32 71 919 933


Sarah McCabe
Stern Investor Relations, Inc.
+ 1 212 362-1200


Amber Fennell, Mathew Neal, Hendrik Thys, Suki Virji
Consilium Strategic Communications
+44 203 709 5700