RT-activated hafnium oxide nanoparticles in cisplatin-ineligible locally advanced HNSCC patients

Summary

Purpose/Objective: Elderly and frail patients (pts) with head and neck squamous cell carcinoma (HSNCC) remain a challenging population to manage due to the lack of evidence-based recommendations. Despite representing approximately 20% of the HNSCC population no consensus exists on the optimal treatment for these pts with locally advanced (LA) disease, vulnerable to current standard of care treatment-induced toxicities. New approaches are thus needed to improve clinical outcomes without adding toxicity. NBTXR3 hafnium oxide nanoparticles injected intratumorally may represent such an option. Otherwise inert, this first-in-class radioenhancer augments the radiotherapy (RT) dose within tumor cells when activated by RT, increasing tumor cell death compared to RT alone. The results presented here demonstrate the feasibility and safety of NBTXR3 activated by RT in elderly patients, a population with few therapeutic options.

Material/Methods: Patients with Stage III-IV LA HNSCC of the oropharynx or oral cavity ineligible for platinum-based chemoradiation received a single intratumoral injection of NBTXR3 and intensity modulated radiation therapy (IMRT; 70 Gy/35 fractions/7 weeks). This is a 3+3 design dose escalation study to test NBTXR3 dose levels equivalent to 5, 10, 15, and 22% of baseline theoretical tumor volume, followed by a dose expansion. Primary endpoints include Recommended Phase 2 Dose (RP2D) determination and early dose limiting toxicities (DLT). NBTXR3 presence in surrounding healthy tissues and anti-tumor activity (RECIST 1.1) were also evaluated.

Results: Enrollment was completed at all dose levels: 5% (3 pts), 10% (3 pts), 15% (5 pts), and 22% (8 pts). No early DLT or SAE related to NBTXR3 or injection were observed. One G1 AE (asthenia; 22%) related to NBTXR3 and four AEs (G2 oral pain, G1 tumor hemorrhage, asthenia, and injection site hemorrhage) related to injection were observed. RT-related toxicity was as expected with IMRT. The RP2D was determined to be 22% by the DSMB. CT-scan assessment demonstrated localization of NBTXR3 intratumorally without presence in surrounding healthy tissues. At a median follow-up of 231 days, 9/13 (2 unconfirmed) evaluable pts receiving doses ≥10%, achieved a complete response of the treated tumors. The final dose escalation safety and efficacy results will be presented herein.

Conclusion: NBTXR3 was well tolerated at all tested doses and demonstrated preliminary anti-tumor activity. The dose expansion part at the RP2D is ongoing. These results highlight the potential of NBTXR3 as a novel treatment option for elderly pts with LA HNSCC and address an unmet medical need.