122P - Intracellular adenosine drives profound lymphocyte suppression and can be reversed with EOS-984: A potent ENT1 antagonist

Background

The benefit of immune checkpoint blockade (ICB) in cancer therapy is limited to select patient subsets. ICB resistance factors include accumulation of immunosuppressive adenosine. Pharmacological inhibition of adenosine generation and signaling is under clinical investigation. Here we report a novel mechanism where adenosine suppresses anti-cancer immunity via intracellular transport.

Methods

Intratumoral adenosine levels in human tumors was quantified via quantitative mass spectrometry imaging (QMSI). T cell uptake of adenosine was assessed through radiolabeled uptake. In vitro T cell function was assessed by flow cytometry, metabolic flux analysis and liquid chromatography-mass spectrometry. Functional consequences of adenosine on T cell function were assessed in vitro via activation of memory and tumor-infiltrating T cells (TILs) and in vivo by assessing tumor growth in syngeneic mouse tumors and pharmacologic inhibition in humanized mice.

Results

QMSI revealed the accumulation of adenosine concentrations up to 300 μM in human tumors. Activated human T cells increased expression of equilibrative nucleoside transporter 1 (ENT1), resulting in adenosine uptake, inhibition of pyrimidine nucleotide production and suppressed proliferation. This was associated with diminished effector function and mitochondrial respiration. ENT1 deletion improved tumor control in syngeneic models including KPC, a poorly immunogenic pancreatic cancer model, increasing CD8+ TIL proliferation and cytokine production. ENT1-KO mice rejected MC38 tumor growth and remained resistant upon rechallenge. To target ENT1 therapeutically, we designed EOS-984, a novel and potent ENT1 antagonist currently under evaluation in advanced solid tumor patients. EOS-984 blocked intracellular adenosine transport, rescuing proliferation and function of T cells stimulated in the presence of adenosine in vitro. In a humanized mouse model of anti-PD-1-resistant TNBC (MDA-MB-231), EOS-984 controlled tumor growth synergistically with nivolumab.

Conclusions

In conclusion, intracellular adenosine metabolism is a novel mechanism of T cell immunosuppression, amenable to ENT1 inhibition to enhance anti-cancer immune responses.

Legal entity responsible for the study

iTeos Therapeutics.

Funding

iTeos Therapeutics.

Disclosure

E. Houthuys, T. Sanders, M. Brouwer, A. Hermant, L. Chaible, J. Deglasse, A. Pabois, W. Cathou, A. Smets, M. Deligny, J. Marchante, Q. Dubray, M. Letellier, C. Martinoli, R. Marillier, O. De Henau, Y. McGrath: Financial Interests, Personal, Full or part-time Employment: iTeos Therapeutics; Financial Interests, Personal, Stocks/Shares: iTeos Therapeutics. M. Vander Heiden: Financial Interests, Personal, Advisory Board: iTeos Therapeutics. All other authors have declared no conflicts of interest.