Summary

Background: Functionalized hafnium oxide nanoparticles (NBTXR3) have been developed as selective radioenhancers, which may represent a breakthrough approach for the local treatment of solid tumors. This is a unique approach where crystalline nanomaterials with high electron density when exposed to radiotherapy, can allow penetrate into the cell and make feasible the absorption/deposition of a high energy dose within the tumor cell. A phase I/II trial was implemented in patients with locally advanced STS.

Methods: Patientsreceived a single intratumor (IT) injection of NBTXR3, volume escalated, followed by 50Gy RTx. Primary endpoints include feasibility of the IT implantation and safety. Secondary endpoints focus on efficacy such as pathological and RECIST response, IT residency of NBTXR3 over all the RTx period and operability. Results: Enrollment was completed for volume 1, 2, and 3 (15 pts). Feasibility of the IT injection was confirmed. The treatment was safe with no SAE, no early DLT and allowed the pts for completion of the planned RTx schedule. No grade 3-4 toxicity occurred, main grade 1-2 toxicities related to NBTXR3 were injection pain/reaction (4 pts), pyrexia (2 pts), abdominal pain (1 pt), pruritus (1 pt) and paresthesia (1 pt). Results demonstrated that a single injection of NBTXR3 provides adequate bioavailability of NBTXR3 IT over five weeks of radiotherapy. No leakage of NBTXR3 to the adjoining healthy tissues was observed. Further, NBTXR3 persistence was established by CT scan before surgery.

Conclusions: Injection of NBTXR3 was well tolerated. All pts received the planned radiotherapy (50 Gy/25 fractions/ 5 weeks) followed by wide surgical resection of the sarcoma. NBTXR3 with RTx showed a very good safety profile. Encouraging signs of antitumor activity were observed in different sarcoma subtypes, such as undifferentiated sarcoma, rhabdomyosarcoma, and synovial sarcoma, which constitutes a promising feature for this subset of pts whose primary tumor is locally advanced and has an important risk of relapse. Clinical trial information: NCT01433068.