Novel Radioenhancer NBTXR3 Activated by Radiotherapy in Cisplatin-Ineligible Locally Advanced HNSCC Patients: Final Results of a Phase I Trial

PURPOSE/OBJECTIVE(S)

New approaches are needed for frail or elderly patients with locally advanced head and neck squamous cell carcinoma (LA HNSCC) who are unfit to receive cisplatin with concurrent radiotherapy (RT). NBTXR3 is a first-in-class radioenhancer, composed of functionalized hafnium oxide nanoparticles, administered by a single intratumoral (IT) injection and activated by RT. NBTXR3 locally amplifies the anti-tumoral response of RT without adding toxicity to surrounding healthy tissue as shown in a randomized trial in soft tissue sarcoma. This two-part study: dose-escalation followed by the dose-expansion part reported here, evaluated the safety and preliminary efficacy for NBTXR3 activated by RT in elderly or frail patients ineligible to cisplatin.

MATERIALS/METHODS

This trial enrolled patients who had previously untreated AJCC 8th Stage III-IVA or T3, T4 SCC of the oral cavity or oropharynx (OPC) ineligible to cisplatin. Eligible patients received a single IT injection of NBTXR3 at the recommended dose (22% of the baseline tumor volume) followed by RT (IMRT 70 Gy in 35 fractions). The primary objectives of the dose expansion part were to test the recommended dose, to confirm its safety, and obtain preliminary evidence of efficacy. The secondary objectives included the evaluation of progression-free survival (PFS) and overall survival (OS).

RESULTS

Fifty-sixpatients in the dose expansion part were treated from April 2019-January 2022; 44 patients were evaluable for objective tumor response. In the all-treated population, median age was 71.9 years. 64.3% had age-adjusted Charlson Comorbidity Index scores ≥4, 55.4% had OPC (45.2% HPV+) and 80% had T3-4. Median injected volume of NBTXR3 was 13.6 [0.5-57.1] mL. Grade ≥ 3 adverse events reported as potentially related to NBTXR3 or to injection procedure were 1.2% and 0.4% of all AEs reported, respectively. In the evaluable population, the best objective response rate of the NBTXR3 injected lesion was 81.8% with a complete response rate of 63.6%. The best overall response rate (injected and non-injected lesions) was 79.5%. Final analyses on PFS and OS with long-term follow-up will be presented.

CONCLUSION

NBTXR3 IT injection followed by activation with RT was confirmed to be feasible and well tolerated in elderly or frail patients with LA HNSSC and significant comorbidities. The high rate of best overall response suggests that NBTXR3+RT is effective in this elderly population ineligible to cisplatin with a high unmet medical need. These results support our ongoing phase III study comparing NBTXR3/RT ± cetuximab vs. RT ± cetuximab in platinum-based chemotherapy ineligible elderly patients with LA-HNSCC: NANORAY 312 (NCIT04892173).

Assessment of the Spatial Bio-Distribution of NBTXR3 for Locally Advanced or Borderline-Resectable Pancreatic Ductal Adenocarcinoma (LAPC or BRPC) Patients Undergoing Radiation Therapy

PURPOSE/OBJECTIVE(S)

NBTXR3 is a novel radioenhancer composed of functionalized hafnium oxide nanoparticles that are injected directly into the tumor. An ongoing phase I trial is assessing the application of NBTXR3 in the treatment of locally-advanced or borderline-resectable pancreatic ductal adenocarcinoma, with the primary goal of determining the recommended NBTXR3 dose for a subsequent phase II trial. Using patients from the ongoing phase I trial, we evaluated the spatial bio-distribution of NBTXR3 in the pancreas as function of time and assessed if there is migration of the compound during radiation therapy.

MATERIALS/METHODS

Adult patients with LAPC or BRPC were enrolled. Analysis of 8 patients who underwent CT simulation at least 24 hours after receiving the NBTXR3 intratumoral injection in the pancreatic lesion under general anesthesia guided by an endoscopic ultrasound was conducted. Patients were simulated with and without iodinated intravenous contrast under breath hold, with 3mm CT slice thickness and 50-60cm FoV. A contrast-enhanced CT series was chosen for RT planning purposes. All patients were planned for a 15-fraction IMRT course using 6-MV beam energy, with 45Gy and 37.5Gy dose levels (using a simultaneous integrated boost technique) to gross primary tumor and microscopic disease/regional nodes, respectively. Daily image guidance included either cone-beam CT (CBCT, n = 1) or CT-on-Rails (CTOR, n = 7) and were fused to the planning CT images using Velocity, ver. 3.0.1. The NBTXR3 volume was determined by thresholding the images to 165 HU and 300 HU for CTOR and CBCT images, respectively. Bones, stents, and artifacts were manually removed from the NBTXR3 volume. The volumes for the NBTXR3 and the NBTXR3 overlapping with the GTV for each patient were individually fit to a linear model in R, ver. 4.1.3.

RESULTS

One patient from the CTOR cohort was excluded from analysis due to the small volume of NBTXR3 (0.02 cm3) compared to the rest of the cohort (0.716 - 6.917 cm3). The total volume of NBTXR3 in the CBCT images could not be analyzed due the substantial image artifacts, only the volume overlapping the GTV was calculated. There were no statistically significant changes (p > 0.1 Adj-R2 = 0.99) in the raw volume of NBTXR3 for the duration of the treatment in all CTOR patients. For the NBTXR3 volume overlapping with the GTV, five cases did not present with a volume change during the treatment (p > 0.1 Adj-R2 = 0.99), while one CTOR case had a reduction in volume of about 1.5%/day (p = 0.7), and the CBCT case had a reduction of 3%/day (p < 0.001).

CONCLUSION

The raw volume of NBTXR3 injected in the pancreas did not significantly change over the duration of the three weeks of treatment. We also did not observe significant changes in the NBTXR3 volume overlapping the GTV in most cases. The stability of NBTXR3 was demonstrated during RT.