Overcoming Resistance to Anti-PD-1 With Tumor Agnostic NBTXR3

Summary

Purpose/Objective(s): Immune checkpoint inhibitors (ICI) can improve outcomes in patients who respond to treatment, however most patients exhibit resistance. Overcoming this resistance is the main challenge in immune-oncology and recent studies suggest radiotherapy (RT) may improve ICI response rates. NBTXR3, composed of functionalized hafnium oxide nanoparticles, is injected intratumorally and activated by RT. NBTXR3 increases RT energy deposit inside tumor cells and subsequent tumor cell death, without adding toxicity to healthy tissues. Here we present evidence that NBTXR3 activated by RT primes the immune system, producing an anti-tumor immune response, including activation of the cGAS-STING pathway, that overcomes anti-PD-1 resistance both in murine models and patients.

/Methods: Abscopal assays were conducted in immunocompetent mice. Anti-PD-1 sensitive or resistant lung tumor cell lines were injected in both flanks. Intratumoral injection of NBTXR3 (or vehicle) followed by RT was performed in right flank (primary) tumors only. Some mice also received anti-PD-1 injections. Tumor growth was monitored, and tumor immune cell infiltrates analyzed by immunohistochemistry (IHC). Separately, in the phase II/III randomized Act.in.Sarc [NCT02379845] trial patients with locally advanced soft tissue sarcoma (STS) received either NBTXR3+RT or RT alone followed by tumor resection. Pre- and post-treatment tumor samples from patients in both groups were analyzed by IHC and Digital Pathology for immune biomarkers. The safety and efficacy of NBTXR3 plus stereotactic body radiotherapy (SBRT) in combination with anti-PD-1 is being evaluated in three cohorts of patients with advanced cancers in the Phase I 1100 [NCT03589339] trial.

Results: Pre-clinical studies demonstrated that NBTXR3+RT induces an immune response not observed with RT alone and enhances systemic control. IHC showed significant increase of CD8+ T-cell infiltrates in both NBTXR3+RT treated and untreated tumors compared to RT alone. Increased CD8+ T-cell and decreased FOXP3+ Treg density (pre- vs post-treatment) was also observed in tumors from STS patients treated with NBTXR3+RT. Furthermore, NBTXR3+RT in combination with anti-PD-1 improved local and systemic control in mice bearing anti-PD-1 resistant lung tumors, produced long-term memory, and reduced spontaneous lung metastases. Preliminary efficacy data from the 1100 trial showed tumor regression in 8/9 patients. Of note, tumor regression was observed in 6/7 patients who had progressed on prior anti-PD-1.

Conclusion: The clinical efficacy of NBTXR3+RT has been demonstrated as a single agent in STS. Here we demonstrate that it overcomes resistance to anti-PD-1 treatment mechanisms in mice and led to tumor regression in patients having progressed on anti-PD-1 therapy. These results highlight the potential of NBTXR3+RT to positively impact the immuno-oncology field.