NBTXR3 Activated By Radiotherapy Generates an Anti-Tumor Immune Response

Summary

Purpose/Objective(s): Hafnium oxide nanoparticles (NBTXR3) activated by radiotherapy (RT) increase radiation dose deposit within cancer cells compared to RT alone. Currently 7 clinical trials are underway to evaluate NBTXR3+RT. To date, no dose limiting toxicities (DLTs) have been observed. Given that RT can prime an anti-tumor immune response we hypothesized that this response could be enhanced by NBTXR3+RT in both animals and humans.

Materials/Methods: Immunocompetent mice were injected in both flanks with CT26 cells. An intratumoral injection of NBTXR3 (or vehicle) was performed in right flank tumors, followed by RT (3x4Gy). Tumor growth was followed, and animals sacrificed when tumors reached 800mm3. Alternatively, tumors were collected 3 days after last RT fraction and immune cell infiltrates analyzed by immunohistochemistry (IHC). Pts with locally advanced soft tissue sarcoma (STS) [NCT02379845] received either NBTXR3+RT or RT alone. Pre- and post-treatment tumor tissues (biopsy and tumor resection respectively) from pts were analyzed by IHC and Digital Pathology for immune biomarkers (>16 pts per arm).

Results: Animal studies demonstrated that NBTXR3+RT can induce an immune response which was not observed with RT alone. IHC analyses showed that significantly more CD8+ cells were present in NBTXR3+RT treated and untreated tumors, compared to tumors from mice treated with RT alone. Similarly, increased CD8+ T cell infiltration pre- vs post-treatment was observed in tumor tissues from STS pts treated with NBTXR3+RT. An increase in biomarkers, including CD8 and PD1, following NBTXR3 +RT was also observed by IHC in tumor samples from STS pts compared to RT alone.

Conclusion: These results demonstrate that NBTXR3+RT induces a specific adaptive immune profile in both mice and STS pts. As such, it may convert immunologically “cold” tumors into “hot” tumors, opening the potential for combination with immunotherapeutic agents. We have therefore sought to investigate the safety and systemic effect of NBTXR3 activated by stereotactic ablative radiotherapy (SABR) in combination with anti-PD-1 antibody in pts with locoregionally recurrent or metastatic (to lung or liver) head and neck squamous cell carcinoma (HNSCC), as well as in metastatic non-small cell lung cancer (NSCLC) and liver metastasis patients [NCT03589339].