NBTXR3 Activated By Radiotherapy In Cisplatin-Ineligible Patients With Locally Advanced HNSCC: A Phase I Trial

Summary

Purpose/Objective(s): Concurrent chemoradiation (CRT) with high dose cisplatin or cetuximab in case of contra-indication to cisplatin is the standard of care non-surgical approach for patients (pts) with locally advanced head and neck squamous cell carcinoma (LA HNSCC). Older age is a contra-indication to cisplatin and survival in older pts might not improve with cetuximab. The development of new treatment options for elderly pts with LA HNSCC is therefore urgently needed. NBTXR3, hafnium oxide nanoparticles that enhance the efficacy of radiotherapy (RT) by locally increasing the deposited dose, may benefit this patient population. In this phase I clinical trial we aimed to evaluate the feasibility and safety of intratumoral (IT) NBTXR3 injection prior to RT in elderly pts with LA HNSCC.

Materials/Methods: Patients with stage III-IV LA HNSCC of the oropharynx or oral cavity ineligible for platinum-based CRT received a single IT injection of NBTXR3 into a selected primary tumor followed by intensity modulated RT (IMRT; 70 Gy/35 fractions/7 weeks) [NCT01946867]. The study used a 3+3 dose escalation design to test NBTXR3 dose levels of 5, 10, 15, and 22% of baseline tumor volume, followed by a dose expansion at the Recommended Phase 2 Dose (RP2D). Primary endpoints included RP2D determination, and early dose limiting toxicities (DLT). NBTXR3 intratumoral bioavailability and anti-tumor activity (RECIST 1.1) were also evaluated.

Results: Enrollment at all dose levels has been completed: 5% (3 pts), 10% (3 pts), 15% (5 pts), and 22% (8 pts). There were no observed early DLT or SAE related to NBTXR3 or injection. Median follow-up from NBTXR3 administration is currently 7.6 months. One Grade 1 AE related to NBTXR3 at the 22% dose level and 4 Grade 1-2 AEs related to the injection at the 15% and 22% dose levels were observed. IMRT-related toxicity was as expected. NBTXR3 was well dispersed throughout the tumor and not in surrounding healthy tissues, as assessed by CT-scan. The RP2D was determined to be 22%. Preliminary efficacy was evaluated in pts who received the intended dose of NBTXR3 and RT. Among 13 evaluable pts at doses ≥10%, 9 pts (69%) achieved a complete response (2 unconfirmed) of the injected tumor and 5 pts (38%) achieved an overall complete response. Preliminary safety and efficacy data of the dose expansion cohort at the RP2D will also be presented.

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