Background Chemotherapy remains the standard of care for numerous cancer indications; however, in addition to having poor overall tolerability, a negative effect of such regimens is the extracellular release of adenosine triphosphate, which is rapidly converted to immunosuppressive adenosine by the enzymes CD39 and CD73. Extracellular adenosine drives immunosuppression by activating the A_2aR and A_2bR adenosine receptors on immune cells, thereby inhibiting their activity and enabling tumor growth and survival. We have previously shown that etrumadenant (etruma), a dual A_2aR/A_2bR antagonist, prevents adenosine-mediated immunosuppression in vitro and combines with immunogenic chemotherapy to enable greater control of mouse syngeneic tumors. In our current work, we sought to evaluate the ability of etruma to enhance the anti-tumor immune activity of priming doses of chemotherapy, compared to an extended chemotherapy regimen alone.

Methods Mice were inoculated with syngeneic cancer cells, 4T1 or AT3-OVA. Once tumors were established (50 or 100 mm³), mice were treated with doxorubicin (5 mg/kg, Q7D), alone or in combination with etruma (100 mg/kg BID). Gross anatomic, histological and flow cytometric analyses of CD8+ T cells were performed on tumor or lung tissue.

Results We have previously shown in AT3-OVA tumors that etruma combines with doxorubicin (dox) to provide greater tumor control and CD8+ T cell infiltration compared to dox alone. Building upon these data, we combined etruma with 2 or 4 doses of dox and found that addition of etruma significantly reduced tumor burden and increased survival in both dox dosing regimens. Etruma combined with 2 dox doses showed similar tumor control as 4 doses of dox alone (2 dose dox: 601 ± 79 mm³; 2 dose combo: 232 ± 25 mm³; 4 dose dox: 263 ± 26 mm³). Similar results were observed in 4T1 tumor-bearing mice, where etruma in combination with dox suppressed lung metastases after 2 doses of dox with no further improvement observed with a third dose of chemotherapy (lung mets per mouse: 3 dose dox: 41 ± 5; 2 dose combo: 16 ± 4; 3 dose combo: 12 ± 2). These data suggest that etruma sustains the immune response driven by the initial doses of chemotherapy leading to enhanced tumor control.

Conclusions Altogether, these data show that the combined treatment of chemotherapy with etruma leads to increased tumor control in multiple preclinical models and suggest that etruma combined with a reduced course of chemotherapy may have comparable activity as an extended chemotherapy dosing regimen.