Safety and toxicity of Iopofosine I 131 (CLR 131) with external beam radiation therapy in recurrent or metastatic head and neck cancer: results of a phase 1 single-centre, open-label, single-arm, dose escalation and dose expansion study.

BACKGROUND

Re-irradiation of recurrent head and neck cancer (HNC) is often limited by tumour adherence to critical structures and/or radiation tolerance of critical normal tissues. Iopofosine I 131 (CLR 131) is a targeted small molecular phospholipid ether (PLE) drug conjugate that delivers iodine-131 selectively to tumour cells. We conducted a phase 1, single-centre, open-label study to determine whether CLR 131 given with reduced dose of external beam radiation therapy (EBRT) would be tolerable and feasible.

METHODS

All participants received previous curative intent treatment with radiotherapy as primary or adjuvant treatment. Eligible participants demonstrated uptake of CLR 131 as indicated via single photon emission CT/CT (SPECT/CT) imaging following CLR 131 test dose. Participants received two therapeutic doses of CLR 131 (days 1 and 8) with SPECT/CT imaging performed to quantitate the biodistribution of CLR 131. Participants subsequently received EBRT to achieve the designated radiation dose (60-70 Gy). The primary endpoint was safety. This trial was registered with ClinicalTrials.gov, NCT04105543, and enrolment and follow-up are complete.

FINDINGS

Twelve participants completed treatment with CLR 131 and EBRT. Eight participants experienced grade 4 non-DLT haematologic toxicities (2 anaemia, 8 leukopenia, 5 thrombocytopenia) at least probably attributed to CLR 131, consistent with the expected toxicity profile. Haematologic toxicities occurred during weeks 6-8 from the first dose of CLR 131 and resolved within three weeks without sequelae. There were no treatment-related grade 3-4 non-haematologic toxicities.

INTERPRETATION

CLR 131 in combination with EBRT did not confer any safety concerns, and was tolerable in participants with recurrent/metastatic HNC. Myelosuppression was consistent with the known toxicity profile of CLR 131.

FUNDING

National Institutes of HealthP50 DE026787, National Cancer InstituteP30 CA014520, National Institutes of Health1UL1TR002373, Cellectar, NCT04105543.